Yocto Project Mega-Manual

Scott Rifenbark

Scotty's Documentation Services, INC

Permission is granted to copy, distribute and/or modify this document under the terms of the Creative Commons Attribution-Share Alike 2.0 UK: England & Wales as published by Creative Commons.

Manual Notes

  • This version of the Yocto Project Mega-Manual is for the 2.5 release of the Yocto Project. To be sure you have the latest version of the manual for this release, go to the Yocto Project documentation page and select the manual from that site. Manuals from the site are more up-to-date than manuals derived from the Yocto Project released TAR files.

  • If you located this manual through a web search, the version of the manual might not be the one you want (e.g. the search might have returned a manual much older than the Yocto Project version with which you are working). You can see all Yocto Project major releases by visiting the Releases page. If you need a version of this manual for a different Yocto Project release, visit the Yocto Project documentation page and select the manual set by using the "ACTIVE RELEASES DOCUMENTATION" or "DOCUMENTS ARCHIVE" pull-down menus.

  • To report any inaccuracies or problems with this manual, send an email to the Yocto Project discussion group at yocto@yoctoproject.com or log into the freenode #yocto channel.

Revision History
Revision 1.8April 2015
Released with the Yocto Project 1.8 Release.
Revision 2.0October 2015
Released with the Yocto Project 2.0 Release.
Revision 2.1April 2016
Released with the Yocto Project 2.1 Release.
Revision 2.2October 2016
Released with the Yocto Project 2.2 Release.
Revision 2.3May 2017
Released with the Yocto Project 2.3 Release.
Revision 2.4October 2017
Released with the Yocto Project 2.4 Release.
Revision 2.5May 2018
Released with the Yocto Project 2.5 Release.

Abstract

The Yocto Project Mega-Manual is a concatenation of the published Yocto Project HTML manuals for the given release. The manual exists to help users efficiently search for strings across the entire Yocto Project documentation set.

Yocto Project Quick Build

Permission is granted to copy, distribute and/or modify this document under the terms of the Creative Commons Attribution-Share Alike 2.0 UK: England & Wales as published by Creative Commons.

Abstract


1. Welcome!

Welcome! This short document steps you through the process for a typical image build using the Yocto Project. The document also introduces how to configure a build for specific hardware. You will use Yocto Project to build a reference embedded OS called Poky.

Note

The examples in this paper assume you are using a native Linux system running a recent Ubuntu Linux distribution. If the machine you want to use Yocto Project on to build an image is not a native Linux system, you can still perform these steps by using CROss PlatformS (CROPS) and setting up a Poky container. See the Setting Up to Use CROss PlatformS (CROPS)" section in the Yocto Project Development Tasks Manual for more information.

If you want more conceptual or background information on the Yocto Project, see the Yocto project Overview and Concepts Manual.

2. Compatible Linux Distribution

Make sure your build host meets the following requirements:

  • 50 Gbytes of free disk space

  • Runs a supported Linux distribution (i.e. recent releases of Fedora, openSUSE, CentOS, Debian, or Ubuntu). For a list of Linux distributions that support the Yocto Project, see the "Supported Linux Distributions" section in the Yocto Project Reference Manual.

    • Git 1.8.3.1 or greater

    • tar 1.27 or greater

    • Python 3.4.0 or greater.

    If your build host does not meet any of these three listed version requirements, you can take steps to prepare the system so that you can still use the Yocto Project. See the "Required Git, tar, and Python Versions" section in the Yocto Project Reference Manual for information.

3. Build Host Packages

You must install essential host packages on your build host. The following command installs the host packages based on an Ubuntu distribution:

Note

For host package requirements on all supported Linux distributions, see the "Required Packages for the Host Development System" section in the Yocto Project Reference Manual.

     $ sudo apt-get install gawk wget git-core diffstat unzip texinfo gcc-multilib \
     build-essential chrpath socat cpio python python3 python3-pip python3-pexpect \
     xz-utils debianutils iputils-ping libsdl1.2-dev xterm
            

4. Use Git to Clone Poky

Once you complete the setup instructions for your machine, you need to get a copy of the Poky repository on your build host. Use the following commands to clone the Poky repository and then checkout the yocto-2.5 release:

     $ git clone git://git.yoctoproject.org/poky
     Cloning into 'poky'...
     remote: Counting objects: 361782, done.
     remote: Compressing objects: 100% (87100/87100), done.
     remote: Total 361782 (delta 268619), reused 361439 (delta 268277)
     Receiving objects: 100% (361782/361782), 131.94 MiB | 6.88 MiB/s, done.
     Resolving deltas: 100% (268619/268619), done.
     Checking connectivity... done.
     $ git checkout tags/yocto-2.5 -b my-yocto-2.5
            

The previous Git checkout command creates a local branch named my-yocto-2.5. The files available to you in that branch exactly match the repository's files in the "sumo" development branch at the time of the Yocto Project 2.5 release.

For more options and information about accessing Yocto Project related repositories, see the "Locating Yocto Project Source Files" section in the Yocto Project Development Tasks Manual.

5. Building Your Image

Use the following steps to build your image. The build process creates an entire Linux distribution, including the toolchain, from source.

Note

  • If you are working behind a firewall and your build host is not set up for proxies, you could encounter problems with the build process when fetching source code (e.g. fetcher failures or Git failures).

  • If you do not know your proxy settings, consult your local network infrastructure resources and get that information. A good starting point could also be to check your web browser settings. Finally, you can find more information on the "Working Behind a Network Proxy" page of the Yocto Project Wiki.

  1. Initialize the Build Environment: Run the oe-init-build-env environment setup script to define Yocto Project's build environment on your build host.

         $ source oe-init-build-env
                        

    Among other things, the script creates the Build Directory, which is build in this case and is located in the Source Directory. After the script runs, your current working directory is set to the Build Directory. Later, when the build completes, the Build Directory contains all the files created during the build.

  2. Examine Your Local Configuration File: When you set up the build environment, a local configuration file named local.conf becomes available in a conf subdirectory of the Build Directory. For this example, the defaults are set to build for a qemux86 target, which is suitable for emulation. The package manager used is set to the RPM package manager.

    Tip

    You can significantly speed up your build and guard against fetcher failures by using mirrors. To use mirrors, add these lines to your local.conf file in the Build directory:
         SSTATE_MIRRORS = "\
         file://.* http://sstate.yoctoproject.org/dev/PATH;downloadfilename=PATH \n \
         file://.* http://sstate.yoctoproject.org/2.4/PATH;downloadfilename=PATH \n \
         file://.* http://sstate.yoctoproject.org/2.5/PATH;downloadfilename=PATH \n \
         "
                            
    The previous examples showed how to add sstate paths for Yocto Project 2.4, 2.5, and a development area. For a complete index of sstate locations, see http://sstate.yoctoproject.org/.

  3. Start the Build: Continue with the following command to build an OS image for the target, which is core-image-sato in this example:

         $ bitbake core-image-sato
                        

    For information on using the bitbake command, see the "BitBake" section in the Yocto Project Overview and Concepts Manual, or see the "BitBake Command" section in the BitBake User Manual.

  4. Simulate Your Image Using QEMU: Once this particular image is built, you can start QEMU, which is a Quick EMUlator that ships with the Yocto Project:

         $ runqemu qemux86
                        

    If you want to learn more about running QEMU, see the "Using the Quick EMUlator (QEMU)" chapter in the Yocto Project Development Tasks Manual.

  5. Exit QEMU: Exit QEMU by either clicking on the shutdown icon or by typing Ctrl-C in the QEMU transcript window from which you evoked QEMU.

6. Customizing Your Build for Specific Hardware

So far, all you have done is quickly built an image suitable for emulation only. This section shows you how to customize your build for specific hardware by adding a hardware layer into the Yocto Project development environment.

In general, layers are repositories that contain related sets of instructions and configurations that tell the Yocto Project what to do. Isolating related metadata into functionally specific layers facilitates modular development and makes it easier to reuse the layer metadata.

Note

By convention, layer names start with the string "meta-".

Follow these steps to add a hardware layer:

  1. Find a Layer: Lots of hardware layers exist. The Yocto Project Source Repositories has many hardware layers. This example adds the meta-altera hardware layer.

  2. Clone the Layer Use Git to make a local copy of the layer on your machine. You can put the copy in the top level of the copy of the Poky repository created earlier:

         $ cd ~/poky
         $ git clone https://github.com/kraj/meta-altera.git
         Cloning into 'meta-altera'...
         remote: Counting objects: 25170, done.
         remote: Compressing objects: 100% (350/350), done.
         remote: Total 25170 (delta 645), reused 719 (delta 538), pack-reused 24219
         Receiving objects: 100% (25170/25170), 41.02 MiB | 1.64 MiB/s, done.
         Resolving deltas: 100% (13385/13385), done.
         Checking connectivity... done.
                        

    The hardware layer now exists with other layers inside the Poky reference repository on your build host as meta-altera and contains all the metadata needed to support hardware from Altera, which is owned by Intel.

  3. Change the Configuration to Build for a Specific Machine: The MACHINE variable in the local.conf file specifies the machine for the build. For this example, set the MACHINE variable to "cyclone5". These configurations are used: https://github.com/kraj/meta-altera/blob/master/conf/machine/cyclone5.conf.

    Note

    See the "Examine Your Local Configuration File" step earlier for more information on configuring the build.

  4. Add Your Layer to the Layer Configuration File: Before you can use a layer during a build, you must add it to your bblayers.conf file, which is found in the Build Directory's conf directory.

    Use the bitbake-layers add-layer command to add the layer to the configuration file:

         $ cd ~/poky/build
         $ bitbake-layers add-layer ../meta-altera
         NOTE: Starting bitbake server...
         Parsing recipes: 100% |##################################################################| Time: 0:00:32
         Parsing of 918 .bb files complete (0 cached, 918 parsed). 1401 targets, 123 skipped, 0 masked, 0 errors.
                        

    You can find more information on adding layers in the "Adding a Layer Using the bitbake-layers Script" section.

Completing these steps has added the meta-altera layer to your Yocto Project development environment and configured it to build for the "cyclone5" machine.

Note

The previous steps are for demonstration purposes only. If you were to attempt to build an image for the "cyclone5" build, you should read the Altera README.

7. Creating Your Own General Layer

Maybe you have an application or specific set of behaviors you need to isolate. You can create your own general layer using the bitbake-layers create-layer command. The tool automates layer creation by setting up a subdirectory with a layer.conf configuration file, a recipes-example subdirectory that contains an example.bb recipe, a licensing file, and a README.

The following commands run the tool to create a layer named meta-mylayer in the poky directory:

     $ cd ~/poky
     $ bitbake-layers create-layer meta-mylayer
     NOTE: Starting bitbake server...
     Add your new layer with 'bitbake-layers add-layer meta-mylayer'
            

For more information on layers and how to create them, see the "Creating a General Layer Using the bitbake-layers Script" section in the Yocto Project Development Tasks Manual.

8. Where To Go Next

Now that you have experienced using the Yocto Project, you might be asking yourself "What now?" The Yocto Project has many sources of information including the website, wiki pages, and user manuals:

  • Website: The Yocto Project Website provides background information, the latest builds, breaking news, full development documentation, and access to a rich Yocto Project Development Community into which you can tap.

  • Developer Screencast: The Getting Started with the Yocto Project - New Developer Screencast Tutorial provides a 30-minute video created for users unfamiliar with the Yocto Project but familiar with Linux build hosts. While this screencast is somewhat dated, the introductory and fundamental concepts are useful for the beginner.

  • Yocto Project Overview and Concepts Manual: The Yocto project Overview and Concepts Manual is a great place to start to learn about the Yocto Project. This manual introduces you to the Yocto Project and its development environment. The manual also provides conceptual information for various aspects of the Yocto Project.

  • Yocto Project Wiki: The Yocto Project Wiki provides additional information on where to go next when ramping up with the Yocto Project, release information, project planning, and QA information.

  • Yocto Project Mailing Lists: Related mailing lists provide a forum for discussion, patch submission and announcements. Several mailing lists exist and are grouped according to areas of concern. See the "Mailing lists" section in the Yocto Project Reference Manual for a complete list of Yocto Project mailing lists.

  • Comprehensive List of Links and Other Documentation: The "Links and Related Documentation" section in the Yocto Project Reference Manual provides a comprehensive list of all related links and other user documentation.

Chapter 1. The Yocto Project Overview and Concepts Manual

1.1. Welcome

Welcome to the Yocto Project Overview and Concepts Manual! This manual introduces the Yocto Project by providing concepts, software overviews, best-known-methods (BKMs), and any other high-level introductory information suitable for a new Yocto Project user.

The following list describes what you can get from this manual:

  • Introducing the Yocto Project: This chapter provides an introduction to the Yocto Project. You will learn about features and challenges of the Yocto Project, the layer model, components and tools, development methods, the Poky reference distribution, the OpenEmbedded build system workflow, and some basic Yocto terms.

  • The Yocto Project Development Environment: This chapter helps you get started understanding the Yocto Project development environment. You will learn about open source, development hosts, Yocto Project source repositories, workflows using Git and the Yocto Project, a Git primer, and information about licensing.

  • Yocto Project Concepts: This chapter presents various concepts regarding the Yocto Project. You can find conceptual information about components, development, cross-toolchains, and so forth.

This manual does not give you the following:

  • Step-by-step Instructions for Development Tasks: Instructional procedures reside in other manuals within the Yocto Project documentation set. For example, the Yocto Project Development Tasks Manual provides examples on how to perform various development tasks. As another example, the Yocto Project Application Development and the Extensible Software Development Kit (eSDK) manual contains detailed instructions on how to install an SDK, which is used to develop applications for target hardware.

  • Reference Material: This type of material resides in an appropriate reference manual. For example, system variables are documented in the Yocto Project Reference Manual. As another example, the Yocto Project Board Support Package (BSP) Developer's Guide contains reference information on BSPs.

  • Detailed Public Information Not Specific to the Yocto Project: For example, exhaustive information on how to use the Source Control Manager Git is better covered with Internet searches and official Git Documentation than through the Yocto Project documentation.

1.2. Other Information

Because this manual presents information for many different topics, supplemental information is recommended for full comprehension. For additional introductory information on the Yocto Project, see the Yocto Project Website. If you want to build an image with no knowledge of Yocto Project as a way of quickly testing it out, see the Yocto Project Quick Build document. For a comprehensive list of links and other documentation, see the "Links and Related Documentation" section in the Yocto Project Reference Manual.

Chapter 2. Introducing the Yocto Project

2.1. What is the Yocto Project?

The Yocto Project is an open source collaboration project that helps developers create custom Linux-based systems that are designed for embedded products regardless of the product's hardware architecture. Yocto Project provides a flexible toolset and a development environment that allows embedded device developers across the world to collaborate through shared technologies, software stacks, configurations, and best practices used to create these tailored Linux images.

Thousands of developers worldwide have discovered that Yocto Project provides advantages in both systems and applications development, archival and management benefits, and customizations used for speed, footprint, and memory utilization. The project is a standard when it comes to delivering embedded software stacks. The project allows software customizations and build interchange for multiple hardware platforms as well as software stacks that can be maintained and scaled.

For further introductory information on the Yocto Project, you might be interested in this article by Drew Moseley and in this short introductory video.

The remainder of this section overviews advantages and challenges tied to the Yocto Project.

2.1.1. Features

The following list describes features and advantages of the Yocto Project:

  • Widely Adopted Across the Industry: Semiconductor, operating system, software, and service vendors exist whose products and services adopt and support the Yocto Project. For a look at the Yocto Project community and the companies involved with the Yocto Project, see the "COMMUNITY" and "ECOSYSTEM" tabs on the Yocto Project home page.

  • Architecture Agnostic: Yocto Project supports Intel, ARM, MIPS, AMD, PPC and other architectures. Most ODMs, OSVs, and chip vendors create and supply BSPs that support their hardware. If you have custom silicon, you can create a BSP that supports that architecture.

    Aside from lots of architecture support, the Yocto Project fully supports a wide range of device emulation through the Quick EMUlator (QEMU).

  • Images and Code Transfer Easily: Yocto Project output can easily move between architectures without moving to new development environments. Additionally, if you have used the Yocto Project to create an image or application and you find yourself not able to support it, commercial Linux vendors such as Wind River, Mentor Graphics, Timesys, and ENEA could take it and provide ongoing support. These vendors have offerings that are built using the Yocto Project.

  • Flexibility: Corporations use the Yocto Project many different ways. One example is to create an internal Linux distribution as a code base the corporation can use across multiple product groups. Through customization and layering, a project group can leverage the base Linux distribution to create a distribution that works for their product needs.

  • Ideal for Constrained Embedded and IoT devices: Unlike a full Linux distribution, you can use the Yocto Project to create exactly what you need for embedded devices. You only add the feature support or packages that you absolutely need for the device. For devices that have display hardware, you can use available system components such as X11, GTK+, Qt, Clutter, and SDL (among others) to create a rich user experience. For devices that do not have a display or where you want to use alternative UI frameworks, you can choose to not install these components.

  • Comprehensive Toolchain Capabilities: Toolchains for supported architectures satisfy most use cases. However, if your hardware supports features that are not part of a standard toolchain, you can easily customize that toolchain through specification of platform-specific tuning parameters. And, should you need to use a third-party toolchain, mechanisms built into the Yocto Project allow for that.

  • Mechanism Rules Over Policy: Focusing on mechanism rather than policy ensures that you are free to set policies based on the needs of your design instead of adopting decisions enforced by some system software provider.

  • Uses a Layer Model: The Yocto Project layer infrastructure groups related functionality into separate bundles. You can incrementally add these grouped functionalities to your project as needed. Using layers to isolate and group functionality reduces project complexity and redundancy, allows you to easily extend the system, make customizations, and keep functionality organized.

  • Supports Partial Builds: You can build and rebuild individual packages as needed. Yocto Project accomplishes this through its shared-state cache (sstate) scheme. Being able to build and debug components individually eases project development.

  • Releases According to a Strict Schedule: Major releases occur on a six-month cycle predictably in October and April. The most recent two releases support point releases to address common vulnerabilities and exposures. This predictability is crucial for projects based on the Yocto Project and allows development teams to plan activities.

  • Rich Ecosystem of Individuals and Organizations: For open source projects, the value of community is very important. Support forums, expertise, and active developers who continue to push the Yocto Project forward are readily available.

  • Binary Reproducibility: The Yocto Project allows you to be very specific about dependencies and achieves very high percentages of binary reproducibility (e.g. 99.8% for core-image-minimal). When distributions are not specific about which packages are pulled in and in what order to support dependencies, other build systems can arbitrarily include packages.

  • License Manifest: The Yocto Project provides a license manifest for review by people who need to track the use of open source licenses (e.g.legal teams).

2.1.2. Challenges

The following list presents challenges you might encounter when developing using the Yocto Project:

  • Steep Learning Curve: The Yocto Project has a steep learning curve and has many different ways to accomplish similar tasks. It can be difficult to choose how to proceed when varying methods exist by which to accomplish a given task.

  • Understanding What Changes You Need to Make For Your Design Requires Some Research: Beyond the simple tutorial stage, understanding what changes need to be made for your particular design can require a significant amount of research and investigation. For information that helps you transition from trying out the Yocto Project to using it for your project, see the "What I wish I'd Known" and "Transitioning to a Custom Environment for Systems Development" documents on the Yocto Project website.

  • Project Workflow Could Be Confusing: The Yocto Project workflow could be confusing if you are used to traditional desktop and server software development. In a desktop development environment, mechanisms exist to easily pull and install new packages, which are typically pre-compiled binaries from servers accessible over the Internet. Using the Yocto Project, you must modify your configuration and rebuild to add additional packages.

  • Working in a Cross-Build Environment Can Feel Unfamiliar: When developing code to run on a target, compilation, execution, and testing done on the actual target can be faster than running a BitBake build on a development host and then deploying binaries to the target for test. While the Yocto Project does support development tools on the target, the additional step of integrating your changes back into the Yocto Project build environment would be required. Yocto Project supports an intermediate approach that involves making changes on the development system within the BitBake environment and then deploying only the updated packages to the target.

    The Yocto Project OpenEmbedded build system produces packages in standard formats (i.e. RPM, DEB, IPK, and TAR). You can deploy these packages into the running system on the target by using utilities on the target such as rpm or ipk.

  • Initial Build Times Can be Significant: Long initial build times are unfortunately unavoidable due to the large number of packages initially built from scratch for a fully functioning Linux system. Once that initial build is completed, however, the shared-state (sstate) cache mechanism Yocto Project uses keeps the system from rebuilding packages that have not been "touched" since the last build. The sstate mechanism significantly reduces times for successive builds.

2.2. The Yocto Project Layer Model

The Yocto Project's "Layer Model" is a development model for embedded and IoT Linux creation that distinguishes the Yocto Project from other simple build systems. The Layer Model simultaneously supports collaboration and customization. Layers are repositories that contain related sets of instructions that tell the OpenEmbedded build system what to do. You can collaborate, share, and reuse layers.

Layers can contain changes to previous instructions or settings at any time. This powerful override capability is what allows you to customize previously supplied collaborative or community layers to suit your product requirements.

You use different layers to logically separate information in your build. As an example, you could have BSP, GUI, distro configuration, middleware, or application layers. Putting your entire build into one layer limits and complicates future customization and reuse. Isolating information into layers, on the other hand, helps simplify future customizations and reuse. You might find it tempting to keep everything in one layer when working on a single project. However, the more modular your Metadata, the easier it is to cope with future changes.

Notes

  • Use Board Support Package (BSP) layers from silicon vendors when possible.

  • Familiarize yourself with the Yocto Project curated layer index or the OpenEmbedded layer index. The latter contains more layers but they are less universally validated.

  • Layers support the inclusion of technologies, hardware components, and software components. The Yocto Project Compatible designation provides a minimum level of standardization that contributes to a strong ecosystem. "YP Compatible" is applied to appropriate products and software components such as BSPs, other OE-compatible layers, and related open-source projects, allowing the producer to use Yocto Project badges and branding assets.

To illustrate how layers are used to keep things modular, consider machine customizations. These types of customizations typically reside in a special layer, rather than a general layer, called a BSP Layer. Furthermore, the machine customizations should be isolated from recipes and Metadata that support a new GUI environment, for example. This situation gives you a couple of layers: one for the machine configurations, and one for the GUI environment. It is important to understand, however, that the BSP layer can still make machine-specific additions to recipes within the GUI environment layer without polluting the GUI layer itself with those machine-specific changes. You can accomplish this through a recipe that is a BitBake append (.bbappend) file, which is described later in this section.

Note

For general information on BSP layer structure, see the Yocto Project Board Support Packages (BSP) Developer's Guide.

The Source Directory contains both general layers and BSP layers right out of the box. You can easily identify layers that ship with a Yocto Project release in the Source Directory by their names. Layers typically have names that begin with the string meta-.

Note

It is not a requirement that a layer name begin with the prefix meta-, but it is a commonly accepted standard in the Yocto Project community.

For example, if you were to examine the tree view of the poky repository, you will see several layers: meta, meta-skeleton, meta-selftest, meta-poky, and meta-yocto-bsp. Each of these repositories represents a distinct layer.

For procedures on how to create layers, see the "Understanding and Creating Layers" section in the Yocto Project Development Tasks Manual.

2.3. Components and Tools

The Yocto Project employs a collection of components and tools used by the project itself, by project developers, and by those using the Yocto Project. These components and tools are open source projects and metadata that are separate from the reference distribution (Poky) and the OpenEmbedded build system. Most of the components and tools are downloaded separately.

This section provides brief overviews of the components and tools associated with the Yocto Project.

2.3.1. Development Tools

The following list consists of tools that help you develop images and applications using the Yocto Project:

  • CROPS: CROPS is an open source, cross-platform development framework that leverages Docker Containers. CROPS provides an easily managed, extensible environment that allows you to build binaries for a variety of architectures on Windows, Linux and Mac OS X hosts.

  • devtool: This command-line tool is available as part of the extensible SDK (eSDK) and is its cornerstone. You can use devtool to help build, test, and package software within the eSDK. You can use the tool to optionally integrate what you build into an image built by the OpenEmbedded build system.

    The devtool command employs a number of sub-commands that allow you to add, modify, and upgrade recipes. As with the OpenEmbedded build system, “recipes” represent software packages within devtool. When you use devtool add, a recipe is automatically created. When you use devtool modify, the specified existing recipe is used in order to determine where to get the source code and how to patch it. In both cases, an environment is set up so that when you build the recipe a source tree that is under your control is used in order to allow you to make changes to the source as desired. By default, both new recipes and the source go into a “workspace” directory under the eSDK. The devtool upgrade command updates an existing recipe so that you can build it for an updated set of source files.

    You can read about the devtool workflow in the Yocto Project Application Development and Extensible Software Development Kit (eSDK) Manual in the "Using devtool in Your SDK Workflow'" section.

  • Extensible Software Development Kit (eSDK): The eSDK provides a cross-development toolchain and libraries tailored to the contents of a specific image. The eSDK makes it easy to add new applications and libraries to an image, modify the source for an existing component, test changes on the target hardware, and integrate into the rest of the OpenEmbedded build system. The eSDK gives you a toolchain experience supplemented with the powerful set of devtool commands tailored for the Yocto Project environment.

    For information on the eSDK, see the Yocto Project Application Development and the Extensible Software Development Kit (eSDK) Manual.

  • Eclipse™ IDE Plug-in: This plug-in enables you to use the popular Eclipse Integrated Development Environment (IDE), which allows for development using the Yocto Project all within the Eclipse IDE. You can work within Eclipse to cross-compile, deploy, and execute your output into a QEMU emulation session as well as onto actual target hardware.

    The environment also supports performance enhancing tools that allow you to perform remote profiling, tracing, collection of power data, collection of latency data, and collection of performance data.

    Once you enable the plug-in, standard Eclipse functions automatically use the cross-toolchain and target system libraries. You can build applications using any of these libraries.

    For more information on the Eclipse plug-in, see the "Working Within Eclipse" section in the Yocto Project Application Development and the Extensible Software Development Kit (eSDK) manual.

  • Toaster: Toaster is a web interface to the Yocto Project OpenEmbedded build system. Toaster allows you to configure, run, and view information about builds. For information on Toaster, see the Toaster User Manual.

2.3.2. Production Tools

The following list consists of tools that help production related activities using the Yocto Project:

  • Auto Upgrade Helper: This utility when used in conjunction with the OpenEmbedded build system (BitBake and OE-Core) automatically generates upgrades for recipes that are based on new versions of the recipes published upstream.

  • Recipe Reporting System: The Recipe Reporting System tracks recipe versions available for Yocto Project. The main purpose of the system is to help you manage the recipes you maintain and to offer a dynamic overview of the project. The Recipe Reporting System is built on top of the OpenEmbedded Layer Index, which is a website that indexes OpenEmbedded-Core layers.

  • Patchwork: Patchwork is a fork of a project originally started by OzLabs. The project is a web-based tracking system designed to streamline the process of bringing contributions into a project. The Yocto Project uses Patchwork as an organizational tool to handle patches, which number in the thousands for every release.

  • AutoBuilder: AutoBuilder is a project that automates build tests and quality assurance (QA). By using the public AutoBuilder, anyone can determine the status of the current "master" branch of Poky.

    Note

    AutoBuilder is based on buildbot.

    A goal of the Yocto Project is to lead the open source industry with a project that automates testing and QA procedures. In doing so, the project encourages a development community that publishes QA and test plans, publicly demonstrates QA and test plans, and encourages development of tools that automate and test and QA procedures for the benefit of the development community.

    You can learn more about the AutoBuilder used by the Yocto Project here.

  • Cross-Prelink: Prelinking is the process of pre-computing the load addresses and link tables generated by the dynamic linker as compared to doing this at runtime. Doing this ahead of time results in performance improvements when the application is launched and reduced memory usage for libraries shared by many applications.

    Historically, cross-prelink is a variant of prelink, which was conceived by Jakub Jelínek a number of years ago. Both prelink and cross-prelink are maintained in the same repository albeit on separate branches. By providing an emulated runtime dynamic linker (i.e. glibc-derived ld.so emulation), the cross-prelink project extends the prelink software’s ability to prelink a sysroot environment. Additionally, the cross-prelink software enables the ability to work in sysroot style environments.

    The dynamic linker determines standard load address calculations based on a variety of factors such as mapping addresses, library usage, and library function conflicts. The prelink tool uses this information, from the dynamic linker, to determine unique load addresses for executable and linkable format (ELF) binaries that are shared libraries and dynamically linked. The prelink tool modifies these ELF binaries with the pre-computed information. The result is faster loading and often lower memory consumption because more of the library code can be re-used from shared Copy-On-Write (COW) pages.

    The original upstream prelink project only supports running prelink on the end target device due to the reliance on the target device’s dynamic linker. This restriction causes issues when developing a cross-compiled system. The cross-prelink adds a synthesized dynamic loader that runs on the host, thus permitting cross-prelinking without ever having to run on a read-write target filesystem.

  • Pseudo: Pseudo is the Yocto Project implementation of fakeroot, which is used to run commands in an environment that seemingly has root privileges.

    During a build, it can be necessary to perform operations that require system administrator privileges. For example, file ownership or permissions might need definition. Pseudo is a tool that you can either use directly or through the environment variable LD_PRELOAD. Either method allows these operations to succeed as if system administrator privileges exist even when they do not.

    You can read more about Pseudo in the "Fakeroot and Pseudo" section.

2.3.3. Open-Embedded Build System Components

The following list consists of components associated with the OpenEmbedded build system:

  • BitBake: BitBake is a core component of the Yocto Project and is used by the OpenEmbedded build system to build images. While BitBake is key to the build system, BitBake is maintained separately from the Yocto Project.

    BitBake is a generic task execution engine that allows shell and Python tasks to be run efficiently and in parallel while working within complex inter-task dependency constraints. In short, BitBake is a build engine that works through recipes written in a specific format in order to perform sets of tasks.

    You can learn more about BitBake in the BitBake User Manual.

  • OpenEmbedded-Core: OpenEmbedded-Core (OE-Core) is a common layer of metadata (i.e. recipes, classes, and associated files) used by OpenEmbedded-derived systems, which includes the Yocto Project. The Yocto Project and the OpenEmbedded Project both maintain the OpenEmbedded-Core. You can find the OE-Core metadata in the Yocto Project Source Repositories.

    Historically, the Yocto Project integrated the OE-Core metadata throughout the Yocto Project source repository reference system (Poky). After Yocto Project Version 1.0, the Yocto Project and OpenEmbedded agreed to work together and share a common core set of metadata (OE-Core), which contained much of the functionality previously found in Poky. This collaboration achieved a long-standing OpenEmbedded objective for having a more tightly controlled and quality-assured core. The results also fit well with the Yocto Project objective of achieving a smaller number of fully featured tools as compared to many different ones.

    Sharing a core set of metadata results in Poky as an integration layer on top of OE-Core. You can see that in this figure. The Yocto Project combines various components such as BitBake, OE-Core, script “glue”, and documentation for its build system.

2.3.4. Reference Distribution (Poky)

Poky is the Yocto Project reference distribution. It contains the Open-Embedded build system (BitBake and OE-Core) as well as a set of metadata to get you started building your own distribution. See the figure in "What is the Yocto Project?" section for an illustration that shows Poky and its relationship with other parts of the Yocto Project.

To use the Yocto Project tools and components, you can download (clone) Poky and use it to bootstrap your own distribution.

Note

Poky does not contain binary files. It is a working example of how to build your own custom Linux distribution from source.

You can read more about Poky in the "Reference Embedded Distribution (Poky)" section.

2.3.5. Packages for Finished Targets

The following lists components associated with packages for finished targets:

  • Matchbox: Matchbox is an Open Source, base environment for the X Window System running on non-desktop, embedded platforms such as handhelds, set-top boxes, kiosks, and anything else for which screen space, input mechanisms, or system resources are limited.

    Matchbox consists of a number of interchangeable and optional applications that you can tailor to a specific, non-desktop platform to enhance usability in constrained environments.

    You can find the Matchbox source in the Yocto Project Source Repositories.

  • Opkg Open PacKaGe management (opkg) is a lightweight package management system based on the itsy package (ipkg) management system. Opkg is written in C and resembles Advanced Package Tool (APT) and Debian Package (dpkg) in operation.

    Opkg is intended for use on embedded Linux devices and is used in this capacity in the OpenEmbedded and OpenWrt projects, as well as the Yocto Project.

    Note

    As best it can, opkg maintains backwards compatibility with ipkg and conforms to a subset of Debian’s policy manual regarding control files.

2.3.6. Archived Components

The Build Appliance is a virtual machine image that enables you to build and boot a custom embedded Linux image with the Yocto Project using a non-Linux development system.

Historically, the Build Appliance was the second of three methods by which you could use the Yocto Project on a system that was not native to Linux.

  1. Hob: Hob, which is now deprecated and is no longer available since the 2.1 release of the Yocto Project provided a rudimentary, GUI-based interface to the Yocto Project. Toaster has fully replaced Hob.

  2. Build Appliance: Post Hob, the Build Appliance became available. It was never recommended that you use the Build Appliance as a day-to-day production development environment with the Yocto Project. Build Appliance was useful as a way to try out development in the Yocto Project environment.

  3. CROPS: The final and best solution available now for developing using the Yocto Project on a system not native to Linux is with CROPS.

2.4. Development Methods

The Yocto Project development environment usually involves a Build Host and target hardware. You use the Build Host to build images and develop applications, while you use the target hardware to test deployed software.

This section provides an introduction to the choices or development methods you have when setting up your Build Host. Depending on the your particular workflow preference and the type of operating system your Build Host runs, several choices exist that allow you to use the Yocto Project.

Note

For additional detail about the Yocto Project development environment, see the "The Yocto Project Development Environment" chapter.

  • Native Linux Host: By far the best option for a Build Host. A system running Linux as its native operating system allows you to develop software by directly using the BitBake tool. You can accomplish all aspects of development from a familiar shell of a supported Linux distribution.

    For information on how to set up a Build Host on a system running Linux as its native operating system, see the "Setting Up a Native Linux Host" section in the Yocto Project Development Tasks Manual.

  • CROss PlatformS (CROPS): Typically, you use CROPS, which leverages Docker Containers, to set up a Build Host that is not running Linux (e.g. Microsoft® Windows™ or macOS®).

    Note

    You can, however, use CROPS on a Linux-based system.

    CROPS is an open source, cross-platform development framework that provides an easily managed, extensible environment for building binaries targeted for a variety of architectures on Windows, macOS, or Linux hosts. Once the Build Host is set up using CROPS, you can prepare a shell environment to mimic that of a shell being used on a system natively running Linux.

    For information on how to set up a Build Host with CROPS, see the "Setting Up to Use CROss PlatformS (CROPS)" section in the Yocto Project Development Tasks Manual.

  • Toaster: Regardless of what your Build Host is running, you can use Toaster to develop software using the Yocto Project. Toaster is a web interface to the Yocto Project's Open-Embedded build system. The interface enables you to configure and run your builds. Information about builds is collected and stored in a database. You can use Toaster to configure and start builds on multiple remote build servers.

    For information about and how to use Toaster, see the Toaster User Manual.

  • Eclipse™ IDE: If your Build Host supports and runs the popular Eclipse IDE, you can install the Yocto Project Eclipse plug-in and use the Yocto Project to develop software. The plug-in integrates the Yocto Project functionality into Eclipse development practices.

    For information about how to install and use the Yocto Project Eclipse plug-in, see the "Developing Applications Using Eclipse" chapter in the Yocto Project Application Development and the Extensible Software Development Kit (eSDK) Manual.

2.5. Reference Embedded Distribution (Poky)

"Poky", which is pronounced Pock-ee, is the name of the Yocto Project's reference distribution or Reference OS Kit. Poky contains the OpenEmbedded Build System (BitBake and OpenEmbedded-Core) as well as a set of metadata to get you started building your own distro. In other words, Poky is a base specification of the functionality needed for a typical embedded system as well as the components from the Yocto Project that allow you to build a distribution into a usable binary image.

Poky is a combined repository of BitBake, OpenEmbedded-Core (which is found in meta), meta-poky, meta-yocto-bsp, and documentation provided all together and known to work well together. You can view these items that make up the Poky repository in the Source Repositories.

Note

If you are interested in all the contents of the poky Git repository, see the "Top-Level Core Components" section in the Yocto Project Reference Manual.

The following figure illustrates what generally comprises Poky:

  • BitBake is a task executor and scheduler that is the heart of the OpenEmbedded build system.

  • meta-poky, which is Poky-specific metadata.

  • meta-yocto-bsp, which are Yocto Project-specific Board Support Packages (BSPs).

  • OpenEmbedded-Core (OE-Core) metadata, which includes shared configurations, global variable definitions, shared classes, packaging, and recipes. Classes define the encapsulation and inheritance of build logic. Recipes are the logical units of software and images to be built.

  • Documentation, which contains the Yocto Project source files used to make the set of user manuals.

Note

While Poky is a "complete" distribution specification and is tested and put through QA, you cannot use it as a product "out of the box" in its current form.

To use the Yocto Project tools, you can use Git to clone (download) the Poky repository then use your local copy of the reference distribution to bootstrap your own distribution.

Note

Poky does not contain binary files. It is a working example of how to build your own custom Linux distribution from source.

Poky has a regular, well established, six-month release cycle under its own version. Major releases occur at the same time major releases (point releases) occur for the Yocto Project, which are typically in the Spring and Fall. For more information on the Yocto Project release schedule and cadence, see the "Yocto Project Releases and the Stable Release Process" chapter in the Yocto Project Reference Manual.

Much has been said about Poky being a "default configuration." A default configuration provides a starting image footprint. You can use Poky out of the box to create an image ranging from a shell-accessible minimal image all the way up to a Linux Standard Base-compliant image that uses a GNOME Mobile and Embedded (GMAE) based reference user interface called Sato.

One of the most powerful properties of Poky is that every aspect of a build is controlled by the metadata. You can use metadata to augment these base image types by adding metadata layers that extend functionality. These layers can provide, for example, an additional software stack for an image type, add a board support package (BSP) for additional hardware, or even create a new image type.

Metadata is loosely grouped into configuration files or package recipes. A recipe is a collection of non-executable metadata used by BitBake to set variables or define additional build-time tasks. A recipe contains fields such as the recipe description, the recipe version, the license of the package and the upstream source repository. A recipe might also indicate that the build process uses autotools, make, distutils or any other build process, in which case the basic functionality can be defined by the classes it inherits from the OE-Core layer's class definitions in ./meta/classes. Within a recipe you can also define additional tasks as well as task prerequisites. Recipe syntax through BitBake also supports both _prepend and _append operators as a method of extending task functionality. These operators inject code into the beginning or end of a task. For information on these BitBake operators, see the "Appending and Prepending (Override Style Syntax)" section in the BitBake User's Manual.

2.6. The OpenEmbedded Build System Workflow

The OpenEmbedded build system uses a "workflow" to accomplish image and SDK generation. The following figure overviews that workflow:

Following is a brief summary of the "workflow":

  1. Developers specify architecture, policies, patches and configuration details.

  2. The build system fetches and downloads the source code from the specified location. The build system supports standard methods such as tarballs or source code repositories systems such as Git.

  3. Once source code is downloaded, the build system extracts the sources into a local work area where patches are applied and common steps for configuring and compiling the software are run.

  4. The build system then installs the software into a temporary staging area where the binary package format you select (DEB, RPM, or IPK) is used to roll up the software.

  5. Different QA and sanity checks run throughout entire build process.

  6. After the binaries are created, the build system generates a binary package feed that is used to create the final root file image.

  7. The build system generates the file system image and a customized Extensible SDK (eSDSK) for application development in parallel.

For a very detailed look at this workflow, see the "OpenEmbedded Build System Concepts" section.

2.7. Some Basic Terms

It helps to understand some basic fundamental terms when learning the Yocto Project. Although a list of terms exists in the "Yocto Project Terms" section of the Yocto Project Reference Manual, this section provides the definitions of some terms helpful for getting started:

  • Configuration Files: Files that hold global definitions of variables, user-defined variables, and hardware configuration information. These files tell the Open-Embedded build system what to build and what to put into the image to support a particular platform.

  • Extensible Software Development Kit (eSDK): A custom SDK for application developers. This eSDK allows developers to incorporate their library and programming changes back into the image to make their code available to other application developers. For information on the eSDK, see the Yocto Project Application Development and the Extensible Software Development Kit (eSDK) manual.

  • Layer: A collection of related recipes. Layers allow you to consolidate related metadata to customize your build. Layers also isolate information used when building for multiple architectures. Layers are hierarchical in their ability to override previous specifications. You can include any number of available layers from the Yocto Project and customize the build by adding your layers after them. You can search the Layer Index for layers used within Yocto Project.

    For more detailed information on layers, see the "Understanding and Creating Layers" section in the Yocto Project Development Tasks Manual. For a discussion specifically on BSP Layers, see the "BSP Layers" section in the Yocto Project Board Support Packages (BSP) Developer's Guide.

  • Metadata: A key element of the Yocto Project is the Metadata that is used to construct a Linux distribution and is contained in the files that the OpenEmbedded build system parses when building an image. In general, Metadata includes recipes, configuration files, and other information that refers to the build instructions themselves, as well as the data used to control what things get built and the effects of the build. Metadata also includes commands and data used to indicate what versions of software are used, from where they are obtained, and changes or additions to the software itself (patches or auxiliary files) that are used to fix bugs or customize the software for use in a particular situation. OpenEmbedded-Core is an important set of validated metadata.

  • OpenEmbedded Build System: The terms "BitBake" and "build system" are sometimes used for the OpenEmbedded Build System.

    BitBake is a task scheduler and execution engine that parses instructions (i.e. recipes) and configuration data. After a parsing phase, BitBake creates a dependency tree to order the compilation, schedules the compilation of the included code, and finally executes the building of the specified custom Linux image (distribution). BitBake is similar to the make tool.

    During a build process, the build system tracks dependencies and performs a native or cross-compilation of the package. As a first step in a cross-build setup, the framework attempts to create a cross-compiler toolchain (i.e. Extensible SDK) suited for the target platform.

  • OpenEmbedded-Core (OE-Core): OE-Core is metadata comprised of foundation recipes, classes, and associated files that are meant to be common among many different OpenEmbedded-derived systems, including the Yocto Project. OE-Core is a curated subset of an original repository developed by the OpenEmbedded community that has been pared down into a smaller, core set of continuously validated recipes. The result is a tightly controlled and quality-assured core set of recipes.

    You can see the Metadata in the meta directory of the Yocto Project Source Repositories.

  • Packages: In the context of the Yocto Project, this term refers to a recipe's packaged output produced by BitBake (i.e. a "baked recipe"). A package is generally the compiled binaries produced from the recipe's sources. You "bake" something by running it through BitBake.

    It is worth noting that the term "package" can, in general, have subtle meanings. For example, the packages referred to in the "Required Packages for the Host Development System" section in the Yocto Project Reference Manual are compiled binaries that, when installed, add functionality to your Linux distribution.

    Another point worth noting is that historically within the Yocto Project, recipes were referred to as packages - thus, the existence of several BitBake variables that are seemingly mis-named, (e.g. PR, PV, and PE).

  • Poky: Poky is a reference embedded distribution and a reference test configuration. Poky provides the following:

    • A base-level functional distro used to illustrate how to customize a distribution.

    • A means by which to test the Yocto Project components (i.e. Poky is used to validate the Yocto Project).

    • A vehicle through which you can download the Yocto Project.

    Poky is not a product level distro. Rather, it is a good starting point for customization.

    Note

    Poky is an integration layer on top of OE-Core.

  • Recipe: The most common form of metadata. A recipe contains a list of settings and tasks (i.e. instructions) for building packages that are then used to build the binary image. A recipe describes where you get source code and which patches to apply. Recipes describe dependencies for libraries or for other recipes as well as configuration and compilation options. Related recipes are consolidated into a layer.

Chapter 3. The Yocto Project Development Environment

This chapter takes a look at the Yocto Project development environment. The chapter provides Yocto Project Development environment concepts that help you understand how work is accomplished in an open source environment, which is very different as compared to work accomplished in a closed, proprietary environment.

Specifically, this chapter addresses open source philosophy, source repositories, workflows, Git, and licensing.

3.1. Open Source Philosophy

Open source philosophy is characterized by software development directed by peer production and collaboration through an active community of developers. Contrast this to the more standard centralized development models used by commercial software companies where a finite set of developers produces a product for sale using a defined set of procedures that ultimately result in an end product whose architecture and source material are closed to the public.

Open source projects conceptually have differing concurrent agendas, approaches, and production. These facets of the development process can come from anyone in the public (community) who has a stake in the software project. The open source environment contains new copyright, licensing, domain, and consumer issues that differ from the more traditional development environment. In an open source environment, the end product, source material, and documentation are all available to the public at no cost.

A benchmark example of an open source project is the Linux kernel, which was initially conceived and created by Finnish computer science student Linus Torvalds in 1991. Conversely, a good example of a non-open source project is the Windows® family of operating systems developed by Microsoft® Corporation.

Wikipedia has a good historical description of the Open Source Philosophy here. You can also find helpful information on how to participate in the Linux Community here.

3.2. The Development Host

A development host or build host is key to using the Yocto Project. Because the goal of the Yocto Project is to develop images or applications that run on embedded hardware, development of those images and applications generally takes place on a system not intended to run the software - the development host.

You need to set up a development host in order to use it with the Yocto Project. Most find that it is best to have a native Linux machine function as the development host. However, it is possible to use a system that does not run Linux as its operating system as your development host. When you have a Mac or Windows-based system, you can set it up as the development host by using CROPS, which leverages Docker Containers. Once you take the steps to set up a CROPS machine, you effectively have access to a shell environment that is similar to what you see when using a Linux-based development host. For the steps needed to set up a system using CROPS, see the "Setting Up to Use CROss PlatformS (CROPS)" section in the Yocto Project Development Tasks Manual.

If your development host is going to be a system that runs a Linux distribution, steps still exist that you must take to prepare the system for use with the Yocto Project. You need to be sure that the Linux distribution on the system is one that supports the Yocto Project. You also need to be sure that the correct set of host packages are installed that allow development using the Yocto Project. For the steps needed to set up a development host that runs Linux, see the "Setting Up a Native Linux Host" section in the Yocto Project Development Tasks Manual.

Once your development host is set up to use the Yocto Project, several methods exist for you to do work in the Yocto Project environment:

  • Command Lines, BitBake, and Shells: Traditional development in the Yocto Project involves using the OpenEmbedded build system, which uses BitBake, in a command-line environment from a shell on your development host. You can accomplish this from a host that is a native Linux machine or from a host that has been set up with CROPS. Either way, you create, modify, and build images and applications all within a shell-based environment using components and tools available through your Linux distribution and the Yocto Project.

    For a general flow of the build procedures, see the "Building a Simple Image" section in the Yocto Project Development Tasks Manual.

  • Board Support Package (BSP) Development: Development of BSPs involves using the Yocto Project to create and test layers that allow easy development of images and applications targeted for specific hardware. To development BSPs, you need to take some additional steps beyond what was described in setting up a development host.

    The Yocto Project Board Support Package (BSP) Developer's Guide provides BSP-related development information. For specifics on development host preparation, see the "Preparing Your Build Host to Work With BSP Layers" section in the Yocto Project Board Support Package (BSP) Developer's Guide.

  • Kernel Development: If you are going to be developing kernels using the Yocto Project you likely will be using devtool. A workflow using devtool makes kernel development quicker by reducing iteration cycle times.

    The Yocto Project Linux Kernel Development Manual provides kernel-related development information. For specifics on development host preparation, see the "Preparing the Build Host to Work on the Kernel" section in the Yocto Project Linux Kernel Development Manual.

  • Using the Eclipse™ IDE: One of two Yocto Project development methods that involves an interface that effectively puts the Yocto Project into the background is the popular Eclipse IDE. This method of development is advantageous if you are already familiar with working within Eclipse. Development is supported through a plugin that you install onto your development host.

    For steps that show you how to set up your development host to use the Eclipse Yocto Project plugin, see the "Developing Applications Using Eclipse" Chapter in the Yocto Project Application Development and the Extensible Software Development Kit (eSDK) manual.

  • Using Toaster: The other Yocto Project development method that involves an interface that effectively puts the Yocto Project into the background is Toaster. Toaster provides an interface to the OpenEmbedded build system. The interface enables you to configure and run your builds. Information about builds is collected and stored in a database. You can use Toaster to configure and start builds on multiple remote build servers.

    For steps that show you how to set up your development host to use Toaster and on how to use Toaster in general, see the Toaster User Manual.

3.3. Yocto Project Source Repositories

The Yocto Project team maintains complete source repositories for all Yocto Project files at http://git.yoctoproject.org. This web-based source code browser is organized into categories by function such as IDE Plugins, Matchbox, Poky, Yocto Linux Kernel, and so forth. From the interface, you can click on any particular item in the "Name" column and see the URL at the bottom of the page that you need to clone a Git repository for that particular item. Having a local Git repository of the Source Directory, which is usually named "poky", allows you to make changes, contribute to the history, and ultimately enhance the Yocto Project's tools, Board Support Packages, and so forth.

For any supported release of Yocto Project, you can also go to the Yocto Project Website and select the "DOWNLOADS" item from the "SOFTWARE" menu and get a released tarball of the poky repository, any supported BSP tarball, or Yocto Project tools. Unpacking these tarballs gives you a snapshot of the released files.

Notes

  • The recommended method for setting up the Yocto Project Source Directory and the files for supported BSPs (e.g., meta-intel) is to use Git to create a local copy of the upstream repositories.

  • Be sure to always work in matching branches for both the selected BSP repository and the Source Directory (i.e. poky) repository. For example, if you have checked out the "master" branch of poky and you are going to use meta-intel, be sure to checkout the "master" branch of meta-intel.

In summary, here is where you can get the project files needed for development:

  • Source Repositories: This area contains IDE Plugins, Matchbox, Poky, Poky Support, Tools, Yocto Linux Kernel, and Yocto Metadata Layers. You can create local copies of Git repositories for each of these areas.

    For steps on how to view and access these upstream Git repositories, see the "Accessing Source Repositories" Section in the Yocto Project Development Tasks Manual.

  • Index of /releases: This is an index of releases such as the Eclipse™ Yocto Plug-in, miscellaneous support, Poky, Pseudo, installers for cross-development toolchains, and all released versions of Yocto Project in the form of images or tarballs. Downloading and extracting these files does not produce a local copy of the Git repository but rather a snapshot of a particular release or image.

    For steps on how to view and access these files, see the "Accessing Index of Releases" section in the Yocto Project Development Tasks Manual.

  • "DOWNLOADS" page for the Yocto Project Website:

    The Yocto Project website includes a "DOWNLOADS" page accessible through the "SOFTWARE" menu that allows you to download any Yocto Project release, tool, and Board Support Package (BSP) in tarball form. The tarballs are similar to those found in the Index of /releases: area.

    For steps on how to use the "DOWNLOADS" page, see the "Using the Downloads Page" section in the Yocto Project Development Tasks Manual.

3.4. Git Workflows and the Yocto Project

Developing using the Yocto Project likely requires the use of Git. Git is a free, open source distributed version control system used as part of many collaborative design environments. This section provides workflow concepts using the Yocto Project and Git. In particular, the information covers basic practices that describe roles and actions in a collaborative development environment.

Note

If you are familiar with this type of development environment, you might not want to read this section.

The Yocto Project files are maintained using Git in "branches" whose Git histories track every change and whose structures provide branches for all diverging functionality. Although there is no need to use Git, many open source projects do so.

For the Yocto Project, a key individual called the "maintainer" is responsible for the integrity of the "master" branch of a given Git repository. The "master" branch is the “upstream” repository from which final or most recent builds of a project occur. The maintainer is responsible for accepting changes from other developers and for organizing the underlying branch structure to reflect release strategies and so forth.

Note

For information on finding out who is responsible for (maintains) a particular area of code in the Yocto Project, see the "Submitting a Change to the Yocto Project" section of the Yocto Project Development Tasks Manual.

The Yocto Project poky Git repository also has an upstream contribution Git repository named poky-contrib. You can see all the branches in this repository using the web interface of the Source Repositories organized within the "Poky Support" area. These branches hold changes (commits) to the project that have been submitted or committed by the Yocto Project development team and by community members who contribute to the project. The maintainer determines if the changes are qualified to be moved from the "contrib" branches into the "master" branch of the Git repository.

Developers (including contributing community members) create and maintain cloned repositories of upstream branches. The cloned repositories are local to their development platforms and are used to develop changes. When a developer is satisfied with a particular feature or change, they "push" the change to the appropriate "contrib" repository.

Developers are responsible for keeping their local repository up-to-date with whatever upstream branch they are working against. They are also responsible for straightening out any conflicts that might arise within files that are being worked on simultaneously by more than one person. All this work is done locally on the development host before anything is pushed to a "contrib" area and examined at the maintainer’s level.

A somewhat formal method exists by which developers commit changes and push them into the "contrib" area and subsequently request that the maintainer include them into an upstream branch. This process is called “submitting a patch” or "submitting a change." For information on submitting patches and changes, see the "Submitting a Change to the Yocto Project" section in the Yocto Project Development Tasks Manual.

In summary, a single point of entry exists for changes into a "master" or development branch of the Git repository, which is controlled by the project’s maintainer. And, a set of developers exist who independently develop, test, and submit changes to "contrib" areas for the maintainer to examine. The maintainer then chooses which changes are going to become a permanent part of the project.

While each development environment is unique, there are some best practices or methods that help development run smoothly. The following list describes some of these practices. For more information about Git workflows, see the workflow topics in the Git Community Book.

  • Make Small Changes: It is best to keep the changes you commit small as compared to bundling many disparate changes into a single commit. This practice not only keeps things manageable but also allows the maintainer to more easily include or refuse changes.

  • Make Complete Changes: It is also good practice to leave the repository in a state that allows you to still successfully build your project. In other words, do not commit half of a feature, then add the other half as a separate, later commit. Each commit should take you from one buildable project state to another buildable state.

  • Use Branches Liberally: It is very easy to create, use, and delete local branches in your working Git repository on the development host. You can name these branches anything you like. It is helpful to give them names associated with the particular feature or change on which you are working. Once you are done with a feature or change and have merged it into your local master branch, simply discard the temporary branch.

  • Merge Changes: The git merge command allows you to take the changes from one branch and fold them into another branch. This process is especially helpful when more than a single developer might be working on different parts of the same feature. Merging changes also automatically identifies any collisions or "conflicts" that might happen as a result of the same lines of code being altered by two different developers.

  • Manage Branches: Because branches are easy to use, you should use a system where branches indicate varying levels of code readiness. For example, you can have a "work" branch to develop in, a "test" branch where the code or change is tested, a "stage" branch where changes are ready to be committed, and so forth. As your project develops, you can merge code across the branches to reflect ever-increasing stable states of the development.

  • Use Push and Pull: The push-pull workflow is based on the concept of developers "pushing" local commits to a remote repository, which is usually a contribution repository. This workflow is also based on developers "pulling" known states of the project down into their local development repositories. The workflow easily allows you to pull changes submitted by other developers from the upstream repository into your work area ensuring that you have the most recent software on which to develop. The Yocto Project has two scripts named create-pull-request and send-pull-request that ship with the release to facilitate this workflow. You can find these scripts in the scripts folder of the Source Directory. For information on how to use these scripts, see the "Using Scripts to Push a Change Upstream and Request a Pull" section in the Yocto Project Development Tasks Manual.

  • Patch Workflow: This workflow allows you to notify the maintainer through an email that you have a change (or patch) you would like considered for the "master" branch of the Git repository. To send this type of change, you format the patch and then send the email using the Git commands git format-patch and git send-email. For information on how to use these scripts, see the "Submitting a Change to the Yocto Project" section in the Yocto Project Development Tasks Manual.

3.5. Git

The Yocto Project makes extensive use of Git, which is a free, open source distributed version control system. Git supports distributed development, non-linear development, and can handle large projects. It is best that you have some fundamental understanding of how Git tracks projects and how to work with Git if you are going to use the Yocto Project for development. This section provides a quick overview of how Git works and provides you with a summary of some essential Git commands.

Notes

3.5.1. Repositories, Tags, and Branches

As mentioned briefly in the previous section and also in the "Git Workflows and the Yocto Project" section, the Yocto Project maintains source repositories at http://git.yoctoproject.org. If you look at this web-interface of the repositories, each item is a separate Git repository.

Git repositories use branching techniques that track content change (not files) within a project (e.g. a new feature or updated documentation). Creating a tree-like structure based on project divergence allows for excellent historical information over the life of a project. This methodology also allows for an environment from which you can do lots of local experimentation on projects as you develop changes or new features.

A Git repository represents all development efforts for a given project. For example, the Git repository poky contains all changes and developments for that repository over the course of its entire life. That means that all changes that make up all releases are captured. The repository maintains a complete history of changes.

You can create a local copy of any repository by "cloning" it with the git clone command. When you clone a Git repository, you end up with an identical copy of the repository on your development system. Once you have a local copy of a repository, you can take steps to develop locally. For examples on how to clone Git repositories, see the "Locating Yocto Project Source Files" section in the Yocto Project Development Tasks Manual.

It is important to understand that Git tracks content change and not files. Git uses "branches" to organize different development efforts. For example, the poky repository has several branches that include the current "sumo" branch, the "master" branch, and many branches for past Yocto Project releases. You can see all the branches by going to http://git.yoctoproject.org/cgit.cgi/poky/ and clicking on the [...] link beneath the "Branch" heading.

Each of these branches represents a specific area of development. The "master" branch represents the current or most recent development. All other branches represent offshoots of the "master" branch.

When you create a local copy of a Git repository, the copy has the same set of branches as the original. This means you can use Git to create a local working area (also called a branch) that tracks a specific development branch from the upstream source Git repository. in other words, you can define your local Git environment to work on any development branch in the repository. To help illustrate, consider the following example Git commands:

     $ cd ~
     $ git clone git://git.yoctoproject.org/poky
     $ cd poky
     $ git checkout -b sumo origin/sumo
            

In the previous example after moving to the home directory, the git clone command creates a local copy of the upstream poky Git repository. By default, Git checks out the "master" branch for your work. After changing the working directory to the new local repository (i.e. poky), the git checkout command creates and checks out a local branch named "sumo", which tracks the upstream "origin/sumo" branch. Changes you make while in this branch would ultimately affect the upstream "sumo" branch of the poky repository.

It is important to understand that when you create and checkout a local working branch based on a branch name, your local environment matches the "tip" of that particular development branch at the time you created your local branch, which could be different from the files in the "master" branch of the upstream repository. In other words, creating and checking out a local branch based on the "sumo" branch name is not the same as checking out the "master" branch in the repository. Keep reading to see how you create a local snapshot of a Yocto Project Release.

Git uses "tags" to mark specific changes in a repository branch structure. Typically, a tag is used to mark a special point such as the final change (or commit) before a project is released. You can see the tags used with the poky Git repository by going to http://git.yoctoproject.org/cgit.cgi/poky/ and clicking on the [...] link beneath the "Tag" heading.

Some key tags for the poky repository are jethro-14.0.3, morty-16.0.1, pyro-17.0.0, and sumo-20.0.0. These tags represent Yocto Project releases.

When you create a local copy of the Git repository, you also have access to all the tags in the upstream repository. Similar to branches, you can create and checkout a local working Git branch based on a tag name. When you do this, you get a snapshot of the Git repository that reflects the state of the files when the change was made associated with that tag. The most common use is to checkout a working branch that matches a specific Yocto Project release. Here is an example:

     $ cd ~
     $ git clone git://git.yoctoproject.org/poky
     $ cd poky
     $ git fetch --tags
     $ git checkout tags/rocko-18.0.0 -b my_rocko-18.0.0
            

In this example, the name of the top-level directory of your local Yocto Project repository is poky. After moving to the poky directory, the git fetch command makes all the upstream tags available locally in your repository. Finally, the git checkout command creates and checks out a branch named "my-rocko-18.0.0" that is based on the upstream branch whose "HEAD" matches the commit in the repository associated with the "rocko-18.0.0" tag. The files in your repository now exactly match that particular Yocto Project release as it is tagged in the upstream Git repository. It is important to understand that when you create and checkout a local working branch based on a tag, your environment matches a specific point in time and not the entire development branch (i.e. from the "tip" of the branch backwards).

3.5.2. Basic Commands

Git has an extensive set of commands that lets you manage changes and perform collaboration over the life of a project. Conveniently though, you can manage with a small set of basic operations and workflows once you understand the basic philosophy behind Git. You do not have to be an expert in Git to be functional. A good place to look for instruction on a minimal set of Git commands is here.

The following list of Git commands briefly describes some basic Git operations as a way to get started. As with any set of commands, this list (in most cases) simply shows the base command and omits the many arguments it supports. See the Git documentation for complete descriptions and strategies on how to use these commands:

  • git init: Initializes an empty Git repository. You cannot use Git commands unless you have a .git repository.

  • git clone: Creates a local clone of a Git repository that is on equal footing with a fellow developer’s Git repository or an upstream repository.

  • git add: Locally stages updated file contents to the index that Git uses to track changes. You must stage all files that have changed before you can commit them.

  • git commit: Creates a local "commit" that documents the changes you made. Only changes that have been staged can be committed. Commits are used for historical purposes, for determining if a maintainer of a project will allow the change, and for ultimately pushing the change from your local Git repository into the project’s upstream repository.

  • git status: Reports any modified files that possibly need to be staged and gives you a status of where you stand regarding local commits as compared to the upstream repository.

  • git checkout branch-name: Changes your local working branch and in this form assumes the local branch already exists. This command is analogous to "cd".

  • git checkout –b working-branch upstream-branch: Creates and checks out a working branch on your local machine. The local branch tracks the upstream branch. You can use your local branch to isolate your work. It is a good idea to use local branches when adding specific features or changes. Using isolated branches facilitates easy removal of changes if they do not work out.

  • git branch: Displays the existing local branches associated with your local repository. The branch that you have currently checked out is noted with an asterisk character.

  • git branch -D branch-name: Deletes an existing local branch. You need to be in a local branch other than the one you are deleting in order to delete branch-name.

  • git pull --rebase: Retrieves information from an upstream Git repository and places it in your local Git repository. You use this command to make sure you are synchronized with the repository from which you are basing changes (.e.g. the "master" branch). The "--rebase" option ensures that any local commits you have in your branch are preserved at the top of your local branch.

  • git push repo-name local-branch:upstream-branch: Sends all your committed local changes to the upstream Git repository that your local repository is tracking (e.g. a contribution repository). The maintainer of the project draws from these repositories to merge changes (commits) into the appropriate branch of project's upstream repository.

  • git merge: Combines or adds changes from one local branch of your repository with another branch. When you create a local Git repository, the default branch is named "master". A typical workflow is to create a temporary branch that is based off "master" that you would use for isolated work. You would make your changes in that isolated branch, stage and commit them locally, switch to the "master" branch, and then use the git merge command to apply the changes from your isolated branch into the currently checked out branch (e.g. "master"). After the merge is complete and if you are done with working in that isolated branch, you can safely delete the isolated branch.

  • git cherry-pick commits: Choose and apply specific commits from one branch into another branch. There are times when you might not be able to merge all the changes in one branch with another but need to pick out certain ones.

  • gitk: Provides a GUI view of the branches and changes in your local Git repository. This command is a good way to graphically see where things have diverged in your local repository.

    Note

    You need to install the gitk package on your development system to use this command.

  • git log: Reports a history of your commits to the repository. This report lists all commits regardless of whether you have pushed them upstream or not.

  • git diff: Displays line-by-line differences between a local working file and the same file as understood by Git. This command is useful to see what you have changed in any given file.

3.6. Licensing

Because open source projects are open to the public, they have different licensing structures in place. License evolution for both Open Source and Free Software has an interesting history. If you are interested in this history, you can find basic information here:

In general, the Yocto Project is broadly licensed under the Massachusetts Institute of Technology (MIT) License. MIT licensing permits the reuse of software within proprietary software as long as the license is distributed with that software. MIT is also compatible with the GNU General Public License (GPL). Patches to the Yocto Project follow the upstream licensing scheme. You can find information on the MIT license here. You can find information on the GNU GPL here.

When you build an image using the Yocto Project, the build process uses a known list of licenses to ensure compliance. You can find this list in the Source Directory at meta/files/common-licenses. Once the build completes, the list of all licenses found and used during that build are kept in the Build Directory at tmp/deploy/licenses.

If a module requires a license that is not in the base list, the build process generates a warning during the build. These tools make it easier for a developer to be certain of the licenses with which their shipped products must comply. However, even with these tools it is still up to the developer to resolve potential licensing issues.

The base list of licenses used by the build process is a combination of the Software Package Data Exchange (SPDX) list and the Open Source Initiative (OSI) projects. SPDX Group is a working group of the Linux Foundation that maintains a specification for a standard format for communicating the components, licenses, and copyrights associated with a software package. OSI is a corporation dedicated to the Open Source Definition and the effort for reviewing and approving licenses that conform to the Open Source Definition (OSD).

You can find a list of the combined SPDX and OSI licenses that the Yocto Project uses in the meta/files/common-licenses directory in your Source Directory.

For information that can help you maintain compliance with various open source licensing during the lifecycle of a product created using the Yocto Project, see the "Maintaining Open Source License Compliance During Your Product's Lifecycle" section in the Yocto Project Development Tasks Manual.

Chapter 4. Yocto Project Concepts

This chapter provides explanations for Yocto Project concepts that go beyond the surface of "how-to" information and reference (or look-up) material. Concepts such as components, the OpenEmbedded build system workflow, cross-development toolchains, shared state cache, and so forth are explained.

4.1. Yocto Project Components

The BitBake task executor together with various types of configuration files form the OpenEmbedded-Core. This section overviews these components by describing their use and how they interact.

BitBake handles the parsing and execution of the data files. The data itself is of various types:

  • Recipes: Provides details about particular pieces of software.

  • Class Data: Abstracts common build information (e.g. how to build a Linux kernel).

  • Configuration Data: Defines machine-specific settings, policy decisions, and so forth. Configuration data acts as the glue to bind everything together.

BitBake knows how to combine multiple data sources together and refers to each data source as a layer. For information on layers, see the "Understanding and Creating Layers" section of the Yocto Project Development Tasks Manual.

Following are some brief details on these core components. For additional information on how these components interact during a build, see the "OpenEmbedded Build System Concepts" section.

4.1.1. BitBake

BitBake is the tool at the heart of the OpenEmbedded build system and is responsible for parsing the Metadata, generating a list of tasks from it, and then executing those tasks.

This section briefly introduces BitBake. If you want more information on BitBake, see the BitBake User Manual.

To see a list of the options BitBake supports, use either of the following commands:

     $ bitbake -h
     $ bitbake --help
                

The most common usage for BitBake is bitbake packagename, where packagename is the name of the package you want to build (referred to as the "target"). The target often equates to the first part of a recipe's filename (e.g. "foo" for a recipe named foo_1.3.0-r0.bb). So, to process the matchbox-desktop_1.2.3.bb recipe file, you might type the following:

     $ bitbake matchbox-desktop
                

Several different versions of matchbox-desktop might exist. BitBake chooses the one selected by the distribution configuration. You can get more details about how BitBake chooses between different target versions and providers in the "Preferences" section of the BitBake User Manual.

BitBake also tries to execute any dependent tasks first. So for example, before building matchbox-desktop, BitBake would build a cross compiler and glibc if they had not already been built.

A useful BitBake option to consider is the -k or --continue option. This option instructs BitBake to try and continue processing the job as long as possible even after encountering an error. When an error occurs, the target that failed and those that depend on it cannot be remade. However, when you use this option other dependencies can still be processed.

4.1.2. Recipes

Files that have the .bb suffix are "recipes" files. In general, a recipe contains information about a single piece of software. This information includes the location from which to download the unaltered source, any source patches to be applied to that source (if needed), which special configuration options to apply, how to compile the source files, and how to package the compiled output.

The term "package" is sometimes used to refer to recipes. However, since the word "package" is used for the packaged output from the OpenEmbedded build system (i.e. .ipk or .deb files), this document avoids using the term "package" when referring to recipes.

4.1.3. Classes

Class files (.bbclass) contain information that is useful to share between recipes files. An example is the autotools class, which contains common settings for any application that Autotools uses. The "Classes" chapter in the Yocto Project Reference Manual provides details about classes and how to use them.

4.1.4. Configurations

The configuration files (.conf) define various configuration variables that govern the OpenEmbedded build process. These files fall into several areas that define machine configuration options, distribution configuration options, compiler tuning options, general common configuration options, and user configuration options in conf/local.conf, which is found in the Build Directory.

4.2. Layers

Layers are repositories that contain related metadata (i.e. sets of instructions) that tell the OpenEmbedded build system how to build a target. Yocto Project's layer model facilitates collaboration, sharing, customization, and reuse within the Yocto Project development environment. Layers logically separate information for your project. For example, you can use a layer to hold all the configurations for a particular piece of hardware. Isolating hardware-specific configurations allows you to share other metadata by using a different layer where that metadata might be common across several pieces of hardware.

Many layers exist that work in the Yocto Project development environment. The Yocto Project Curated Layer Index and OpenEmbedded Layer Index both contain layers from which you can use or leverage.

By convention, layers in the Yocto Project follow a specific form. Conforming to a known structure allows BitBake to make assumptions during builds on where to find types of metadata. You can find procedures and learn about tools (i.e. bitbake-layers) for creating layers suitable for the Yocto Project in the "Understanding and Creating Layers" section of the Yocto Project Development Tasks Manual.

4.3. OpenEmbedded Build System Concepts

This section takes a more detailed look inside the build process used by the OpenEmbedded build system, which is the build system specific to the Yocto Project. At the heart of the build system is BitBake, the task executor.

The following diagram represents the high-level workflow of a build. The remainder of this section expands on the fundamental input, output, process, and metadata logical blocks that make up the workflow.

In general, the build's workflow consists of several functional areas:

  • User Configuration: metadata you can use to control the build process.

  • Metadata Layers: Various layers that provide software, machine, and distro metadata.

  • Source Files: Upstream releases, local projects, and SCMs.

  • Build System: Processes under the control of BitBake. This block expands on how BitBake fetches source, applies patches, completes compilation, analyzes output for package generation, creates and tests packages, generates images, and generates cross-development tools.

  • Package Feeds: Directories containing output packages (RPM, DEB or IPK), which are subsequently used in the construction of an image or Software Development Kit (SDK), produced by the build system. These feeds can also be copied and shared using a web server or other means to facilitate extending or updating existing images on devices at runtime if runtime package management is enabled.

  • Images: Images produced by the workflow.

  • Application Development SDK: Cross-development tools that are produced along with an image or separately with BitBake.

4.3.1. User Configuration

User configuration helps define the build. Through user configuration, you can tell BitBake the target architecture for which you are building the image, where to store downloaded source, and other build properties.

The following figure shows an expanded representation of the "User Configuration" box of the general workflow figure:

BitBake needs some basic configuration files in order to complete a build. These files are *.conf files. The minimally necessary ones reside as example files in the build/conf directory of the Source Directory. For simplicity, this section refers to the Source Directory as the "Poky Directory."

When you clone the Poky Git repository or you download and unpack a Yocto Project release, you can set up the Source Directory to be named anything you want. For this discussion, the cloned repository uses the default name poky.

Note

The Poky repository is primarily an aggregation of existing repositories. It is not a canonical upstream source.

The meta-poky layer inside Poky contains a conf directory that has example configuration files. These example files are used as a basis for creating actual configuration files when you source oe-init-build-env, which is the build environment script.

Sourcing the build environment script creates a Build Directory if one does not already exist. BitBake uses the Build Directory for all its work during builds. The Build Directory has a conf directory that contains default versions of your local.conf and bblayers.conf configuration files. These default configuration files are created only if versions do not already exist in the Build Directory at the time you source the build environment setup script.

Because the Poky repository is fundamentally an aggregation of existing repositories, some users might be familiar with running the oe-init-build-env script in the context of separate OpenEmbedded-Core and BitBake repositories rather than a single Poky repository. This discussion assumes the script is executed from within a cloned or unpacked version of Poky.

Depending on where the script is sourced, different sub-scripts are called to set up the Build Directory (Yocto or OpenEmbedded). Specifically, the script scripts/oe-setup-builddir inside the poky directory sets up the Build Directory and seeds the directory (if necessary) with configuration files appropriate for the Yocto Project development environment.

Note

The scripts/oe-setup-builddir script uses the $TEMPLATECONF variable to determine which sample configuration files to locate.

The local.conf file provides many basic variables that define a build environment. Here is a list of a few. To see the default configurations in a local.conf file created by the build environment script, see the local.conf.sample in the meta-poky layer:

  • Target Machine Selection: Controlled by the MACHINE variable.

  • Download Directory: Controlled by the DL_DIR variable.

  • Shared State Directory: Controlled by the SSTATE_DIR variable.

  • Build Output: Controlled by the TMPDIR variable.

  • Distribution Policy: Controlled by the DISTRO variable.

  • Packaging Format: Controlled by the PACKAGE_CLASSES variable.

  • SDK Target Architecture: Controlled by the SDKMACHINE variable.

  • Extra Image Packages: Controlled by the EXTRA_IMAGE_FEATURES variable.

Note

Configurations set in the conf/local.conf file can also be set in the conf/site.conf and conf/auto.conf configuration files.

The bblayers.conf file tells BitBake what layers you want considered during the build. By default, the layers listed in this file include layers minimally needed by the build system. However, you must manually add any custom layers you have created. You can find more information on working with the bblayers.conf file in the "Enabling Your Layer" section in the Yocto Project Development Tasks Manual.

The files site.conf and auto.conf are not created by the environment initialization script. If you want the site.conf file, you need to create that yourself. The auto.conf file is typically created by an autobuilder:

  • site.conf: You can use the conf/site.conf configuration file to configure multiple build directories. For example, suppose you had several build environments and they shared some common features. You can set these default build properties here. A good example is perhaps the packaging format to use through the PACKAGE_CLASSES variable.

    One useful scenario for using the conf/site.conf file is to extend your BBPATH variable to include the path to a conf/site.conf. Then, when BitBake looks for Metadata using BBPATH, it finds the conf/site.conf file and applies your common configurations found in the file. To override configurations in a particular build directory, alter the similar configurations within that build directory's conf/local.conf file.

  • auto.conf: The file is usually created and written to by an autobuilder. The settings put into the file are typically the same as you would find in the conf/local.conf or the conf/site.conf files.

You can edit all configuration files to further define any particular build environment. This process is represented by the "User Configuration Edits" box in the figure.

When you launch your build with the bitbake target command, BitBake sorts out the configurations to ultimately define your build environment. It is important to understand that the OpenEmbedded build system reads the configuration files in a specific order: site.conf, auto.conf, and local.conf. And, the build system applies the normal assignment statement rules as described in the "Syntax and Operators" chapter of the BitBake User Manual. Because the files are parsed in a specific order, variable assignments for the same variable could be affected. For example, if the auto.conf file and the local.conf set variable1 to different values, because the build system parses local.conf after auto.conf, variable1 is assigned the value from the local.conf file.

4.3.2. Metadata, Machine Configuration, and Policy Configuration

The previous section described the user configurations that define BitBake's global behavior. This section takes a closer look at the layers the build system uses to further control the build. These layers provide Metadata for the software, machine, and policies.

In general, three types of layer input exists. You can see them below the "User Configuration" box in the general workflow figure:

  • Metadata (.bb + Patches): Software layers containing user-supplied recipe files, patches, and append files. A good example of a software layer might be the meta-qt5 layer from the OpenEmbedded Layer Index. This layer is for version 5.0 of the popular Qt cross-platform application development framework for desktop, embedded and mobile.

  • Machine BSP Configuration: Board Support Package (BSP) layers (i.e. "BSP Layer" in the following figure) providing machine-specific configurations. This type of information is specific to a particular target architecture. A good example of a BSP layer from the Poky Reference Distribution is the meta-yocto-bsp layer.

  • Policy Configuration: Distribution Layers (i.e. "Distro Layer" in the following figure) providing top-level or general policies for the images or SDKs being built for a particular distribution. For example, in the Poky Reference Distribution the distro layer is the meta-poky layer. Within the distro layer is a conf/distro directory that contains distro configuration files (e.g. poky.conf that contain many policy configurations for the Poky distribution.

The following figure shows an expanded representation of these three layers from the general workflow figure:

In general, all layers have a similar structure. They all contain a licensing file (e.g. COPYING.MIT) if the layer is to be distributed, a README file as good practice and especially if the layer is to be distributed, a configuration directory, and recipe directories. You can learn about the general structure for layers used with the Yocto Project in the "Creating Your Own Layer" section in the Yocto Project Development Tasks Manual. For a general discussion on layers and the many layers from which you can draw, see the "Layers" and "The Yocto Project Layer Model" sections both earlier in this manual.

If you explored the previous links, you discovered some areas where many layers that work with the Yocto Project exist. The Source Repositories also shows layers categorized under "Yocto Metadata Layers."

Note

Layers exist in the Yocto Project Source Repositories that cannot be found in the OpenEmbedded Layer Index. These layers are either deprecated or experimental in nature.

BitBake uses the conf/bblayers.conf file, which is part of the user configuration, to find what layers it should be using as part of the build.

4.3.2.1. Distro Layer

The distribution layer provides policy configurations for your distribution. Best practices dictate that you isolate these types of configurations into their own layer. Settings you provide in conf/distro/distro.conf override similar settings that BitBake finds in your conf/local.conf file in the Build Directory.

The following list provides some explanation and references for what you typically find in the distribution layer:

  • classes: Class files (.bbclass) hold common functionality that can be shared among recipes in the distribution. When your recipes inherit a class, they take on the settings and functions for that class. You can read more about class files in the "Classes" chapter of the Yocto Reference Manual.

  • conf: This area holds configuration files for the layer (conf/layer.conf), the distribution (conf/distro/distro.conf), and any distribution-wide include files.

  • recipes-*: Recipes and append files that affect common functionality across the distribution. This area could include recipes and append files to add distribution-specific configuration, initialization scripts, custom image recipes, and so forth. Examples of recipes-* directories are recipes-core and recipes-extra. Hierarchy and contents within a recipes-* directory can vary. Generally, these directories contain recipe files (*.bb), recipe append files (*.bbappend), directories that are distro-specific for configuration files, and so forth.

4.3.2.2. BSP Layer

The BSP Layer provides machine configurations that target specific hardware. Everything in this layer is specific to the machine for which you are building the image or the SDK. A common structure or form is defined for BSP layers. You can learn more about this structure in the Yocto Project Board Support Package (BSP) Developer's Guide.

Note

In order for a BSP layer to be considered compliant with the Yocto Project, it must meet some structural requirements.

The BSP Layer's configuration directory contains configuration files for the machine (conf/machine/machine.conf) and, of course, the layer (conf/layer.conf).

The remainder of the layer is dedicated to specific recipes by function: recipes-bsp, recipes-core, recipes-graphics, recipes-kernel, and so forth. Metadata can exist for multiple formfactors, graphics support systems, and so forth.

Note

While the figure shows several recipes-* directories, not all these directories appear in all BSP layers.

4.3.2.3. Software Layer

The software layer provides the Metadata for additional software packages used during the build. This layer does not include Metadata that is specific to the distribution or the machine, which are found in their respective layers.

This layer contains any recipes, append files, and patches, that your project needs.

4.3.3. Sources

In order for the OpenEmbedded build system to create an image or any target, it must be able to access source files. The general workflow figure represents source files using the "Upstream Project Releases", "Local Projects", and "SCMs (optional)" boxes. The figure represents mirrors, which also play a role in locating source files, with the "Source Materials" box.

The method by which source files are ultimately organized is a function of the project. For example, for released software, projects tend to use tarballs or other archived files that can capture the state of a release guaranteeing that it is statically represented. On the other hand, for a project that is more dynamic or experimental in nature, a project might keep source files in a repository controlled by a Source Control Manager (SCM) such as Git. Pulling source from a repository allows you to control the point in the repository (the revision) from which you want to build software. Finally, a combination of the two might exist, which would give the consumer a choice when deciding where to get source files.

BitBake uses the SRC_URI variable to point to source files regardless of their location. Each recipe must have a SRC_URI variable that points to the source.

Another area that plays a significant role in where source files come from is pointed to by the DL_DIR variable. This area is a cache that can hold previously downloaded source. You can also instruct the OpenEmbedded build system to create tarballs from Git repositories, which is not the default behavior, and store them in the DL_DIR by using the BB_GENERATE_MIRROR_TARBALLS variable.

Judicious use of a DL_DIR directory can save the build system a trip across the Internet when looking for files. A good method for using a download directory is to have DL_DIR point to an area outside of your Build Directory. Doing so allows you to safely delete the Build Directory if needed without fear of removing any downloaded source file.

The remainder of this section provides a deeper look into the source files and the mirrors. Here is a more detailed look at the source file area of the general workflow figure:

4.3.3.1. Upstream Project Releases

Upstream project releases exist anywhere in the form of an archived file (e.g. tarball or zip file). These files correspond to individual recipes. For example, the figure uses specific releases each for BusyBox, Qt, and Dbus. An archive file can be for any released product that can be built using a recipe.

4.3.3.2. Local Projects

Local projects are custom bits of software the user provides. These bits reside somewhere local to a project - perhaps a directory into which the user checks in items (e.g. a local directory containing a development source tree used by the group).

The canonical method through which to include a local project is to use the externalsrc class to include that local project. You use either the local.conf or a recipe's append file to override or set the recipe to point to the local directory on your disk to pull in the whole source tree.

4.3.3.3. Source Control Managers (Optional)

Another place the build system can get source files from is through an SCM such as Git or Subversion. In this case, a repository is cloned or checked out. The do_fetch task inside BitBake uses the SRC_URI variable and the argument's prefix to determine the correct fetcher module.

Note

For information on how to have the OpenEmbedded build system generate tarballs for Git repositories and place them in the DL_DIR directory, see the BB_GENERATE_MIRROR_TARBALLS variable.

When fetching a repository, BitBake uses the SRCREV variable to determine the specific revision from which to build.

4.3.3.4. Source Mirror(s)

Two kinds of mirrors exist: pre-mirrors and regular mirrors. The PREMIRRORS and MIRRORS variables point to these, respectively. BitBake checks pre-mirrors before looking upstream for any source files. Pre-mirrors are appropriate when you have a shared directory that is not a directory defined by the DL_DIR variable. A Pre-mirror typically points to a shared directory that is local to your organization.

Regular mirrors can be any site across the Internet that is used as an alternative location for source code should the primary site not be functioning for some reason or another.

4.3.4. Package Feeds

When the OpenEmbedded build system generates an image or an SDK, it gets the packages from a package feed area located in the Build Directory. The general workflow figure shows this package feeds area in the upper-right corner.

This section looks a little closer into the package feeds area used by the build system. Here is a more detailed look at the area:

Package feeds are an intermediary step in the build process. The OpenEmbedded build system provides classes to generate different package types, and you specify which classes to enable through the PACKAGE_CLASSES variable. Before placing the packages into package feeds, the build process validates them with generated output quality assurance checks through the insane class.

The package feed area resides in the Build Directory. The directory the build system uses to temporarily store packages is determined by a combination of variables and the particular package manager in use. See the "Package Feeds" box in the illustration and note the information to the right of that area. In particular, the following defines where package files are kept:

  • DEPLOY_DIR: Defined as tmp/deploy in the Build Directory.

  • DEPLOY_DIR_*: Depending on the package manager used, the package type sub-folder. Given RPM, IPK, or DEB packaging and tarball creation, the DEPLOY_DIR_RPM, DEPLOY_DIR_IPK, DEPLOY_DIR_DEB, or DEPLOY_DIR_TAR, variables are used, respectively.

  • PACKAGE_ARCH: Defines architecture-specific sub-folders. For example, packages could exist for the i586 or qemux86 architectures.

BitBake uses the do_package_write_* tasks to generate packages and place them into the package holding area (e.g. do_package_write_ipk for IPK packages). See the "do_package_write_deb", "do_package_write_ipk", "do_package_write_rpm", and "do_package_write_tar" sections in the Yocto Project Reference Manual for additional information. As an example, consider a scenario where an IPK packaging manager is being used and package architecture support for both i586 and qemux86 exist. Packages for the i586 architecture are placed in build/tmp/deploy/ipk/i586, while packages for the qemux86 architecture are placed in build/tmp/deploy/ipk/qemux86.

4.3.5. BitBake

The OpenEmbedded build system uses BitBake to produce images and Software Development Kits (SDKs). You can see from the general workflow figure, the BitBake area consists of several functional areas. This section takes a closer look at each of those areas.

Note

Separate documentation exists for the BitBake tool. See the BitBake User Manual for reference material on BitBake.

4.3.5.1. Source Fetching

The first stages of building a recipe are to fetch and unpack the source code:

The do_fetch and do_unpack tasks fetch the source files and unpack them into the Build Directory.

Note

For every local file (e.g. file://) that is part of a recipe's SRC_URI statement, the OpenEmbedded build system takes a checksum of the file for the recipe and inserts the checksum into the signature for the do_fetch task. If any local file has been modified, the do_fetch task and all tasks that depend on it are re-executed.

By default, everything is accomplished in the Build Directory, which has a defined structure. For additional general information on the Build Directory, see the "build/" section in the Yocto Project Reference Manual.

Each recipe has an area in the Build Directory where the unpacked source code resides. The S variable points to this area for a recipe's unpacked source code. The name of that directory for any given recipe is defined from several different variables. The preceding figure and the following list describe the Build Directory's hierarchy:

  • TMPDIR: The base directory where the OpenEmbedded build system performs all its work during the build. The default base directory is the tmp directory.

  • PACKAGE_ARCH: The architecture of the built package or packages. Depending on the eventual destination of the package or packages (i.e. machine architecture, build host, SDK, or specific machine), PACKAGE_ARCH varies. See the variable's description for details.

  • TARGET_OS: The operating system of the target device. A typical value would be "linux" (e.g. "qemux86-poky-linux").

  • PN: The name of the recipe used to build the package. This variable can have multiple meanings. However, when used in the context of input files, PN represents the the name of the recipe.

  • WORKDIR: The location where the OpenEmbedded build system builds a recipe (i.e. does the work to create the package).

    • PV: The version of the recipe used to build the package.

    • PR: The revision of the recipe used to build the package.

  • S: Contains the unpacked source files for a given recipe.

    • BPN: The name of the recipe used to build the package. The BPN variable is a version of the PN variable but with common prefixes and suffixes removed.

    • PV: The version of the recipe used to build the package.

Note

In the previous figure, notice that two sample hierarchies exist: one based on package architecture (i.e. PACKAGE_ARCH) and one based on a machine (i.e. MACHINE). The underlying structures are identical. The differentiator being what the OpenEmbedded build system is using as a build target (e.g. general architecture, a build host, an SDK, or a specific machine).

4.3.5.2. Patching

Once source code is fetched and unpacked, BitBake locates patch files and applies them to the source files:

The do_patch task uses a recipe's SRC_URI statements and the FILESPATH variable to locate applicable patch files.

Default processing for patch files assumes the files have either *.patch or *.diff file types. You can use SRC_URI parameters to change the way the build system recognizes patch files. See the do_patch task for more information.

BitBake finds and applies multiple patches for a single recipe in the order in which it locates the patches. The FILESPATH variable defines the default set of directories that the build system uses to search for patch files. Once found, patches are applied to the recipe's source files, which are located in the S directory.

For more information on how the source directories are created, see the "Source Fetching" section. For more information on how to create patches and how the build system processes patches, see the "Patching Code" section in the Yocto Project Development Tasks Manual. You can also see the "Use devtool modify to Modify the Source of an Existing Component" section in the Yocto Project Application Development and the Extensible Software Development Kit (SDK) manual and the "Using Traditional Kernel Development to Patch the Kernel" section in the Yocto Project Linux Kernel Development Manual.

4.3.5.3. Configuration, Compilation, and Staging

After source code is patched, BitBake executes tasks that configure and compile the source code. Once compilation occurs, the files are copied to a holding area (staged) in preparation for packaging:

This step in the build process consists of the following tasks:

  • do_prepare_recipe_sysroot: This task sets up the two sysroots in ${WORKDIR} (i.e. recipe-sysroot and recipe-sysroot-native) so that during the packaging phase the sysroots can contain the contents of the do_populate_sysroot tasks of the recipes on which the recipe containing the tasks depends. A sysroot exists for both the target and for the native binaries, which run on the host system.

  • do_configure: This task configures the source by enabling and disabling any build-time and configuration options for the software being built. Configurations can come from the recipe itself as well as from an inherited class. Additionally, the software itself might configure itself depending on the target for which it is being built.

    The configurations handled by the do_configure task are specific to configurations for the source code being built by the recipe.

    If you are using the autotools class, you can add additional configuration options by using the EXTRA_OECONF or PACKAGECONFIG_CONFARGS variables. For information on how this variable works within that class, see the autotools class here.

  • do_compile: Once a configuration task has been satisfied, BitBake compiles the source using the do_compile task. Compilation occurs in the directory pointed to by the B variable. Realize that the B directory is, by default, the same as the S directory.

  • do_install: After compilation completes, BitBake executes the do_install task. This task copies files from the B directory and places them in a holding area pointed to by the D variable. Packaging occurs later using files from this holding directory.

4.3.5.4. Package Splitting

After source code is configured, compiled, and staged, the build system analyzes the results and splits the output into packages:

The do_package and do_packagedata tasks combine to analyze the files found in the D directory and split them into subsets based on available packages and files. Analysis involves the following as well as other items: splitting out debugging symbols, looking at shared library dependencies between packages, and looking at package relationships.

The do_packagedata task creates package metadata based on the analysis such that the build system can generate the final packages. The do_populate_sysroot task stages (copies) a subset of the files installed by the do_install task into the appropriate sysroot. Working, staged, and intermediate results of the analysis and package splitting process use several areas:

  • PKGD: The destination directory (i.e. package) for packages before they are split into individual packages.

  • PKGDESTWORK: A temporary work area (i.e. pkgdata) used by the do_package task to save package metadata.

  • PKGDEST: The parent directory (i.e. packages-split) for packages after they have been split.

  • PKGDATA_DIR: A shared, global-state directory that holds packaging metadata generated during the packaging process. The packaging process copies metadata from PKGDESTWORK to the PKGDATA_DIR area where it becomes globally available.

  • STAGING_DIR_HOST: The path for the sysroot for the system on which a component is built to run (i.e. recipe-sysroot).

  • STAGING_DIR_NATIVE: The path for the sysroot used when building components for the build host (i.e. recipe-sysroot-native).

  • STAGING_DIR_TARGET: The path for the sysroot used when a component that is built to execute on a system and it generates code for yet another machine (e.g. cross-canadian recipes).

The FILES variable defines the files that go into each package in PACKAGES. If you want details on how this is accomplished, you can look at package.bbclass.

Depending on the type of packages being created (RPM, DEB, or IPK), the do_package_write_* task creates the actual packages and places them in the Package Feed area, which is ${TMPDIR}/deploy. You can see the "Package Feeds" section for more detail on that part of the build process.

Note

Support for creating feeds directly from the deploy/* directories does not exist. Creating such feeds usually requires some kind of feed maintenance mechanism that would upload the new packages into an official package feed (e.g. the Ångström distribution). This functionality is highly distribution-specific and thus is not provided out of the box.

4.3.5.5. Image Generation

Once packages are split and stored in the Package Feeds area, the build system uses BitBake to generate the root filesystem image:

The image generation process consists of several stages and depends on several tasks and variables. The do_rootfs task creates the root filesystem (file and directory structure) for an image. This task uses several key variables to help create the list of packages to actually install:

  • IMAGE_INSTALL: Lists out the base set of packages from which to install from the Package Feeds area.

  • PACKAGE_EXCLUDE: Specifies packages that should not be installed into the image.

  • IMAGE_FEATURES: Specifies features to include in the image. Most of these features map to additional packages for installation.

  • PACKAGE_CLASSES: Specifies the package backend (e.g. RPM, DEB, or IPK) to use and consequently helps determine where to locate packages within the Package Feeds area.

  • IMAGE_LINGUAS: Determines the language(s) for which additional language support packages are installed.

  • PACKAGE_INSTALL: The final list of packages passed to the package manager for installation into the image.

With IMAGE_ROOTFS pointing to the location of the filesystem under construction and the PACKAGE_INSTALL variable providing the final list of packages to install, the root file system is created.

Package installation is under control of the package manager (e.g. dnf/rpm, opkg, or apt/dpkg) regardless of whether or not package management is enabled for the target. At the end of the process, if package management is not enabled for the target, the package manager's data files are deleted from the root filesystem. As part of the final stage of package installation, post installation scripts that are part of the packages are run. Any scripts that fail to run on the build host are run on the target when the target system is first booted. If you are using a read-only root filesystem, all the post installation scripts must succeed on the build host during the package installation phase since the root filesystem on the target is read-only.

The final stages of the do_rootfs task handle post processing. Post processing includes creation of a manifest file and optimizations.

The manifest file (.manifest) resides in the same directory as the root filesystem image. This file lists out, line-by-line, the installed packages. The manifest file is useful for the testimage class, for example, to determine whether or not to run specific tests. See the IMAGE_MANIFEST variable for additional information.

Optimizing processes that are run across the image include mklibs, prelink, and any other post-processing commands as defined by the ROOTFS_POSTPROCESS_COMMAND variable. The mklibs process optimizes the size of the libraries, while the prelink process optimizes the dynamic linking of shared libraries to reduce start up time of executables.

After the root filesystem is built, processing begins on the image through the do_image task. The build system runs any pre-processing commands as defined by the IMAGE_PREPROCESS_COMMAND variable. This variable specifies a list of functions to call before the build system creates the final image output files.

The build system dynamically creates do_image_* tasks as needed, based on the image types specified in the IMAGE_FSTYPES variable. The process turns everything into an image file or a set of image files and can compress the root filesystem image to reduce the overall size of the image. The formats used for the root filesystem depend on the IMAGE_FSTYPES variable. Compression depends on whether the formats support compression.

As an example, a dynamically created task when creating a particular image type would take the following form:

     do_image_type
                    

So, if the type as specified by the IMAGE_FSTYPES were ext4, the dynamically generated task would be as follows:

     do_image_ext4
                    

The final task involved in image creation is the do_image_complete task. This task completes the image by applying any image post processing as defined through the IMAGE_POSTPROCESS_COMMAND variable. The variable specifies a list of functions to call once the build system has created the final image output files.

Note

The entire image generation process is run under Pseudo. Running under Pseudo ensures that the files in the root filesystem have correct ownership.

4.3.5.6. SDK Generation

The OpenEmbedded build system uses BitBake to generate the Software Development Kit (SDK) installer scripts for both the standard SDK and the extensible SDK (eSDK):

Note

For more information on the cross-development toolchain generation, see the "Cross-Development Toolchain Generation" section. For information on advantages gained when building a cross-development toolchain using the do_populate_sdk task, see the "Building an SDK Installer" section in the Yocto Project Application Development and the Extensible Software Development Kit (eSDK) manual.

Like image generation, the SDK script process consists of several stages and depends on many variables. The do_populate_sdk and do_populate_sdk_ext tasks use these key variables to help create the list of packages to actually install. For information on the variables listed in the figure, see the "Application Development SDK" section.

The do_populate_sdk task helps create the standard SDK and handles two parts: a target part and a host part. The target part is the part built for the target hardware and includes libraries and headers. The host part is the part of the SDK that runs on the SDKMACHINE.

The do_populate_sdk_ext task helps create the extensible SDK and handles host and target parts differently than its counter part does for the standard SDK. For the extensible SDK, the task encapsulates the build system, which includes everything needed (host and target) for the SDK.

Regardless of the type of SDK being constructed, the tasks perform some cleanup after which a cross-development environment setup script and any needed configuration files are created. The final output is the Cross-development toolchain installation script (.sh file), which includes the environment setup script.

4.3.5.7. Stamp Files and the Rerunning of Tasks

For each task that completes successfully, BitBake writes a stamp file into the STAMPS_DIR directory. The beginning of the stamp file's filename is determined by the STAMP variable, and the end of the name consists of the task's name and current input checksum.

Note

This naming scheme assumes that BB_SIGNATURE_HANDLER is "OEBasicHash", which is almost always the case in current OpenEmbedded.

To determine if a task needs to be rerun, BitBake checks if a stamp file with a matching input checksum exists for the task. If such a stamp file exists, the task's output is assumed to exist and still be valid. If the file does not exist, the task is rerun.

Note

The stamp mechanism is more general than the shared state (sstate) cache mechanism described in the "Setscene Tasks and Shared State" section. BitBake avoids rerunning any task that has a valid stamp file, not just tasks that can be accelerated through the sstate cache.

However, you should realize that stamp files only serve as a marker that some work has been done and that these files do not record task output. The actual task output would usually be somewhere in TMPDIR (e.g. in some recipe's WORKDIR.) What the sstate cache mechanism adds is a way to cache task output that can then be shared between build machines.

Since STAMPS_DIR is usually a subdirectory of TMPDIR, removing TMPDIR will also remove STAMPS_DIR, which means tasks will properly be rerun to repopulate TMPDIR.

If you want some task to always be considered "out of date", you can mark it with the nostamp varflag. If some other task depends on such a task, then that task will also always be considered out of date, which might not be what you want.

For details on how to view information about a task's signature, see the "Viewing Task Variable Dependencies" section in the Yocto Project Development Tasks Manual.

4.3.5.8. Setscene Tasks and Shared State

The description of tasks so far assumes that BitBake needs to build everything and no available prebuilt objects exist. BitBake does support skipping tasks if prebuilt objects are available. These objects are usually made available in the form of a shared state (sstate) cache.

Note

For information on variables affecting sstate, see the SSTATE_DIR and SSTATE_MIRRORS variables.

The idea of a setscene task (i.e do_taskname_setscene) is a version of the task where instead of building something, BitBake can skip to the end result and simply place a set of files into specific locations as needed. In some cases, it makes sense to have a setscene task variant (e.g. generating package files in the do_package_write_* task). In other cases, it does not make sense (e.g. a do_patch task or a do_unpack task) since the work involved would be equal to or greater than the underlying task.

In the build system, the common tasks that have setscene variants are do_package, do_package_write_*, do_deploy, do_packagedata, and do_populate_sysroot. Notice that these tasks represent most of the tasks whose output is an end result.

The build system has knowledge of the relationship between these tasks and other preceding tasks. For example, if BitBake runs do_populate_sysroot_setscene for something, it does not make sense to run any of the do_fetch, do_unpack, do_patch, do_configure, do_compile, and do_install tasks. However, if do_package needs to be run, BitBake needs to run those other tasks.

It becomes more complicated if everything can come from an sstate cache because some objects are simply not required at all. For example, you do not need a compiler or native tools, such as quilt, if nothing exists to compile or patch. If the do_package_write_* packages are available from sstate, BitBake does not need the do_package task data.

To handle all these complexities, BitBake runs in two phases. The first is the "setscene" stage. During this stage, BitBake first checks the sstate cache for any targets it is planning to build. BitBake does a fast check to see if the object exists rather than a complete download. If nothing exists, the second phase, which is the setscene stage, completes and the main build proceeds.

If objects are found in the sstate cache, the build system works backwards from the end targets specified by the user. For example, if an image is being built, the build system first looks for the packages needed for that image and the tools needed to construct an image. If those are available, the compiler is not needed. Thus, the compiler is not even downloaded. If something was found to be unavailable, or the download or setscene task fails, the build system then tries to install dependencies, such as the compiler, from the cache.

The availability of objects in the sstate cache is handled by the function specified by the BB_HASHCHECK_FUNCTION variable and returns a list of available objects. The function specified by the BB_SETSCENE_DEPVALID variable is the function that determines whether a given dependency needs to be followed, and whether for any given relationship the function needs to be passed. The function returns a True or False value.

4.3.6. Images

The images produced by the build system are compressed forms of the root filesystem and are ready to boot on a target device. You can see from the general workflow figure that BitBake output, in part, consists of images. This section takes a closer look at this output:

Note

For a list of example images that the Yocto Project provides, see the "Images" chapter in the Yocto Project Reference Manual.

The build process writes images out to the Build Directory inside the tmp/deploy/images/machine/ folder as shown in the figure. This folder contains any files expected to be loaded on the target device. The DEPLOY_DIR variable points to the deploy directory, while the DEPLOY_DIR_IMAGE variable points to the appropriate directory containing images for the current configuration.

  • kernel-image: A kernel binary file. The KERNEL_IMAGETYPE variable determines the naming scheme for the kernel image file. Depending on this variable, the file could begin with a variety of naming strings. The deploy/images/machine directory can contain multiple image files for the machine.

  • root-filesystem-image: Root filesystems for the target device (e.g. *.ext3 or *.bz2 files). The IMAGE_FSTYPES variable determines the root filesystem image type. The deploy/images/machine directory can contain multiple root filesystems for the machine.

  • kernel-modules: Tarballs that contain all the modules built for the kernel. Kernel module tarballs exist for legacy purposes and can be suppressed by setting the MODULE_TARBALL_DEPLOY variable to "0". The deploy/images/machine directory can contain multiple kernel module tarballs for the machine.

  • bootloaders: If applicable to the target machine, bootloaders supporting the image. The deploy/images/machine directory can contain multiple bootloaders for the machine.

  • symlinks: The deploy/images/machine folder contains a symbolic link that points to the most recently built file for each machine. These links might be useful for external scripts that need to obtain the latest version of each file.

4.3.7. Application Development SDK

In the general workflow figure, the output labeled "Application Development SDK" represents an SDK. The SDK generation process differs depending on whether you build an extensible SDK (e.g. bitbake -c populate_sdk_ext imagename) or a standard SDK (e.g. bitbake -c populate_sdk imagename). This section takes a closer look at this output:

The specific form of this output is a set of files that includes a self-extracting SDK installer (*.sh), host and target manifest files, and files used for SDK testing. When the SDK installer file is run, it installs the SDK. The SDK consists of a cross-development toolchain, a set of libraries and headers, and an SDK environment setup script. Running this installer essentially sets up your cross-development environment. You can think of the cross-toolchain as the "host" part because it runs on the SDK machine. You can think of the libraries and headers as the "target" part because they are built for the target hardware. The environment setup script is added so that you can initialize the environment before using the tools.

Notes

  • The Yocto Project supports several methods by which you can set up this cross-development environment. These methods include downloading pre-built SDK installers or building and installing your own SDK installer.

  • For background information on cross-development toolchains in the Yocto Project development environment, see the "Cross-Development Toolchain Generation" section.

  • For information on setting up a cross-development environment, see the Yocto Project Application Development and the Extensible Software Development Kit (eSDK) manual.

All the output files for an SDK are written to the deploy/sdk folder inside the Build Directory as shown in the previous figure. Depending on the type of SDK, several variables exist that help configure these files. The following list shows the variables associated with an extensible SDK:

  • DEPLOY_DIR: Points to the deploy directory.

  • SDK_EXT_TYPE: Controls whether or not shared state artifacts are copied into the extensible SDK. By default, all required shared state artifacts are copied into the SDK.

  • SDK_INCLUDE_PKGDATA: Specifies whether or not packagedata is included in the extensible SDK for all recipes in the "world" target.

  • SDK_INCLUDE_TOOLCHAIN: Specifies whether or not the toolchain is included when building the extensible SDK.

  • SDK_LOCAL_CONF_WHITELIST: A list of variables allowed through from the build system configuration into the extensible SDK configuration.

  • SDK_LOCAL_CONF_BLACKLIST: A list of variables not allowed through from the build system configuration into the extensible SDK configuration.

  • SDK_INHERIT_BLACKLIST: A list of classes to remove from the INHERIT value globally within the extensible SDK configuration.

This next list, shows the variables associated with a standard SDK:

  • DEPLOY_DIR: Points to the deploy directory.

  • SDKMACHINE: Specifies the architecture of the machine on which the cross-development tools are run to create packages for the target hardware.

  • SDKIMAGE_FEATURES: Lists the features to include in the "target" part of the SDK.

  • TOOLCHAIN_HOST_TASK: Lists packages that make up the host part of the SDK (i.e. the part that runs on the SDKMACHINE). When you use bitbake -c populate_sdk imagename to create the SDK, a set of default packages apply. This variable allows you to add more packages.

  • TOOLCHAIN_TARGET_TASK: Lists packages that make up the target part of the SDK (i.e. the part built for the target hardware).

  • SDKPATH: Defines the default SDK installation path offered by the installation script.

  • SDK_HOST_MANIFEST: Lists all the installed packages that make up the host part of the SDK. This variable also plays a minor role for extensible SDK development as well. However, it is mainly used for the standard SDK.

  • SDK_TARGET_MANIFEST: Lists all the installed packages that make up the target part of the SDK. This variable also plays a minor role for extensible SDK development as well. However, it is mainly used for the standard SDK.

4.4. Cross-Development Toolchain Generation

The Yocto Project does most of the work for you when it comes to creating cross-development toolchains. This section provides some technical background on how cross-development toolchains are created and used. For more information on toolchains, you can also see the Yocto Project Application Development and the Extensible Software Development Kit (eSDK) manual.

In the Yocto Project development environment, cross-development toolchains are used to build images and applications that run on the target hardware. With just a few commands, the OpenEmbedded build system creates these necessary toolchains for you.

The following figure shows a high-level build environment regarding toolchain construction and use.

Most of the work occurs on the Build Host. This is the machine used to build images and generally work within the the Yocto Project environment. When you run BitBake to create an image, the OpenEmbedded build system uses the host gcc compiler to bootstrap a cross-compiler named gcc-cross. The gcc-cross compiler is what BitBake uses to compile source files when creating the target image. You can think of gcc-cross simply as an automatically generated cross-compiler that is used internally within BitBake only.

Note

The extensible SDK does not use gcc-cross-canadian since this SDK ships a copy of the OpenEmbedded build system and the sysroot within it contains gcc-cross.

The chain of events that occurs when gcc-cross is bootstrapped is as follows:

     gcc -> binutils-cross -> gcc-cross-initial -> linux-libc-headers -> glibc-initial -> glibc -> gcc-cross -> gcc-runtime
            

  • gcc: The build host's GNU Compiler Collection (GCC).

  • binutils-cross: The bare minimum binary utilities needed in order to run the gcc-cross-initial phase of the bootstrap operation.

  • gcc-cross-initial: An early stage of the bootstrap process for creating the cross-compiler. This stage builds enough of the gcc-cross, the C library, and other pieces needed to finish building the final cross-compiler in later stages. This tool is a "native" package (i.e. it is designed to run on the build host).

  • linux-libc-headers: Headers needed for the cross-compiler.

  • glibc-initial: An initial version of the Embedded GNU C Library (GLIBC) needed to bootstrap glibc.

  • glibc: The GNU C Library.

  • gcc-cross: The final stage of the bootstrap process for the cross-compiler. This stage results in the actual cross-compiler that BitBake uses when it builds an image for a targeted device.

    Note

    If you are replacing this cross compiler toolchain with a custom version, you must replace gcc-cross.

    This tool is also a "native" package (i.e. it is designed to run on the build host).

  • gcc-runtime: Runtime libraries resulting from the toolchain bootstrapping process. This tool produces a binary that consists of the runtime libraries need for the targeted device.

You can use the OpenEmbedded build system to build an installer for the relocatable SDK used to develop applications. When you run the installer, it installs the toolchain, which contains the development tools (e.g., gcc-cross-canadian, binutils-cross-canadian, and other nativesdk-* tools), which are tools native to the SDK (i.e. native to SDK_ARCH), you need to cross-compile and test your software. The figure shows the commands you use to easily build out this toolchain. This cross-development toolchain is built to execute on the SDKMACHINE, which might or might not be the same machine as the Build Host.

Note

If your target architecture is supported by the Yocto Project, you can take advantage of pre-built images that ship with the Yocto Project and already contain cross-development toolchain installers.

Here is the bootstrap process for the relocatable toolchain:

     gcc -> binutils-crosssdk -> gcc-crosssdk-initial -> linux-libc-headers ->
        glibc-initial -> nativesdk-glibc -> gcc-crosssdk -> gcc-cross-canadian
            

  • gcc: The build host's GNU Compiler Collection (GCC).

  • binutils-crosssdk: The bare minimum binary utilities needed in order to run the gcc-crosssdk-initial phase of the bootstrap operation.

  • gcc-crosssdk-initial: An early stage of the bootstrap process for creating the cross-compiler. This stage builds enough of the gcc-crosssdk and supporting pieces so that the final stage of the bootstrap process can produce the finished cross-compiler. This tool is a "native" binary that runs on the build host.

  • linux-libc-headers: Headers needed for the cross-compiler.

  • glibc-initial: An initial version of the Embedded GLIBC needed to bootstrap nativesdk-glibc.

  • nativesdk-glibc: The Embedded GLIBC needed to bootstrap the gcc-crosssdk.

  • gcc-crosssdk: The final stage of the bootstrap process for the relocatable cross-compiler. The gcc-crosssdk is a transitory compiler and never leaves the build host. Its purpose is to help in the bootstrap process to create the eventual gcc-cross-canadian compiler, which is relocatable. This tool is also a "native" package (i.e. it is designed to run on the build host).

  • gcc-cross-canadian: The final relocatable cross-compiler. When run on the SDKMACHINE, this tool produces executable code that runs on the target device. Only one cross-canadian compiler is produced per architecture since they can be targeted at different processor optimizations using configurations passed to the compiler through the compile commands. This circumvents the need for multiple compilers and thus reduces the size of the toolchains.

Note

For information on advantages gained when building a cross-development toolchain installer, see the "Building an SDK Installer" appendix in the Yocto Project Application Development and the Extensible Software Development Kit (eSDK) manual.

4.5. Shared State Cache

By design, the OpenEmbedded build system builds everything from scratch unless BitBake can determine that parts do not need to be rebuilt. Fundamentally, building from scratch is attractive as it means all parts are built fresh and no possibility of stale data exists that can cause problems. When developers hit problems, they typically default back to building from scratch so they have a know state from the start.

Building an image from scratch is both an advantage and a disadvantage to the process. As mentioned in the previous paragraph, building from scratch ensures that everything is current and starts from a known state. However, building from scratch also takes much longer as it generally means rebuilding things that do not necessarily need to be rebuilt.

The Yocto Project implements shared state code that supports incremental builds. The implementation of the shared state code answers the following questions that were fundamental roadblocks within the OpenEmbedded incremental build support system:

  • What pieces of the system have changed and what pieces have not changed?

  • How are changed pieces of software removed and replaced?

  • How are pre-built components that do not need to be rebuilt from scratch used when they are available?

For the first question, the build system detects changes in the "inputs" to a given task by creating a checksum (or signature) of the task's inputs. If the checksum changes, the system assumes the inputs have changed and the task needs to be rerun. For the second question, the shared state (sstate) code tracks which tasks add which output to the build process. This means the output from a given task can be removed, upgraded or otherwise manipulated. The third question is partly addressed by the solution for the second question assuming the build system can fetch the sstate objects from remote locations and install them if they are deemed to be valid.

Notes

The rest of this section goes into detail about the overall incremental build architecture, the checksums (signatures), and shared state.

4.5.1. Overall Architecture

When determining what parts of the system need to be built, BitBake works on a per-task basis rather than a per-recipe basis. You might wonder why using a per-task basis is preferred over a per-recipe basis. To help explain, consider having the IPK packaging backend enabled and then switching to DEB. In this case, the do_install and do_package task outputs are still valid. However, with a per-recipe approach, the build would not include the .deb files. Consequently, you would have to invalidate the whole build and rerun it. Rerunning everything is not the best solution. Also, in this case, the core must be "taught" much about specific tasks. This methodology does not scale well and does not allow users to easily add new tasks in layers or as external recipes without touching the packaged-staging core.

4.5.2. Checksums (Signatures)

The shared state code uses a checksum, which is a unique signature of a task's inputs, to determine if a task needs to be run again. Because it is a change in a task's inputs that triggers a rerun, the process needs to detect all the inputs to a given task. For shell tasks, this turns out to be fairly easy because the build process generates a "run" shell script for each task and it is possible to create a checksum that gives you a good idea of when the task's data changes.

To complicate the problem, there are things that should not be included in the checksum. First, there is the actual specific build path of a given task - the WORKDIR. It does not matter if the work directory changes because it should not affect the output for target packages. Also, the build process has the objective of making native or cross packages relocatable.

Note

Both native and cross packages run on the build host. However, cross packages generate output for the target architecture.

The checksum therefore needs to exclude WORKDIR. The simplistic approach for excluding the work directory is to set WORKDIR to some fixed value and create the checksum for the "run" script.

Another problem results from the "run" scripts containing functions that might or might not get called. The incremental build solution contains code that figures out dependencies between shell functions. This code is used to prune the "run" scripts down to the minimum set, thereby alleviating this problem and making the "run" scripts much more readable as a bonus.

So far, solutions for shell scripts exist. What about Python tasks? The same approach applies even though these tasks are more difficult. The process needs to figure out what variables a Python function accesses and what functions it calls. Again, the incremental build solution contains code that first figures out the variable and function dependencies, and then creates a checksum for the data used as the input to the task.

Like the WORKDIR case, situations exist where dependencies should be ignored. For these situations, you can instruct the build process to ignore a dependency by using a line like the following:

     PACKAGE_ARCHS[vardepsexclude] = "MACHINE"
                

This example ensures that the PACKAGE_ARCHS variable does not depend on the value of MACHINE, even if it does reference it.

Equally, there are cases where you need to add dependencies BitBake is not able to find. You can accomplish this by using a line like the following:

      PACKAGE_ARCHS[vardeps] = "MACHINE"
                

This example explicitly adds the MACHINE variable as a dependency for PACKAGE_ARCHS.

As an example, consider a case with in-line Python where BitBake is not able to figure out dependencies. When running in debug mode (i.e. using -DDD), BitBake produces output when it discovers something for which it cannot figure out dependencies. The Yocto Project team has currently not managed to cover those dependencies in detail and is aware of the need to fix this situation.

Thus far, this section has limited discussion to the direct inputs into a task. Information based on direct inputs is referred to as the "basehash" in the code. However, the question of a task's indirect inputs still exits - items already built and present in the Build Directory. The checksum (or signature) for a particular task needs to add the hashes of all the tasks on which the particular task depends. Choosing which dependencies to add is a policy decision. However, the effect is to generate a master checksum that combines the basehash and the hashes of the task's dependencies.

At the code level, a variety of ways exist by which both the basehash and the dependent task hashes can be influenced. Within the BitBake configuration file, you can give BitBake some extra information to help it construct the basehash. The following statement effectively results in a list of global variable dependency excludes (i.e. variables never included in any checksum):

     BB_HASHBASE_WHITELIST ?= "TMPDIR FILE PATH PWD BB_TASKHASH BBPATH DL_DIR \
         SSTATE_DIR THISDIR FILESEXTRAPATHS FILE_DIRNAME HOME LOGNAME SHELL TERM \
         USER FILESPATH STAGING_DIR_HOST STAGING_DIR_TARGET COREBASE PRSERV_HOST \
         PRSERV_DUMPDIR PRSERV_DUMPFILE PRSERV_LOCKDOWN PARALLEL_MAKE \
         CCACHE_DIR EXTERNAL_TOOLCHAIN CCACHE CCACHE_DISABLE LICENSE_PATH SDKPKGSUFFIX"
                

The previous example excludes WORKDIR since that variable is actually constructed as a path within TMPDIR, which is on the whitelist.

The rules for deciding which hashes of dependent tasks to include through dependency chains are more complex and are generally accomplished with a Python function. The code in meta/lib/oe/sstatesig.py shows two examples of this and also illustrates how you can insert your own policy into the system if so desired. This file defines the two basic signature generators OE-Core uses: "OEBasic" and "OEBasicHash". By default, a dummy "noop" signature handler is enabled in BitBake. This means that behavior is unchanged from previous versions. OE-Core uses the "OEBasicHash" signature handler by default through this setting in the bitbake.conf file:

     BB_SIGNATURE_HANDLER ?= "OEBasicHash"
                

The "OEBasicHash" BB_SIGNATURE_HANDLER is the same as the "OEBasic" version but adds the task hash to the stamp files. This results in any metadata change that changes the task hash, automatically causing the task to be run again. This removes the need to bump PR values, and changes to metadata automatically ripple across the build.

It is also worth noting that the end result of these signature generators is to make some dependency and hash information available to the build. This information includes:

  • BB_BASEHASH_task-taskname: The base hashes for each task in the recipe.

  • BB_BASEHASH_filename:taskname: The base hashes for each dependent task.

  • BBHASHDEPS_filename:taskname: The task dependencies for each task.

  • BB_TASKHASH: The hash of the currently running task.

4.5.3. Shared State

Checksums and dependencies, as discussed in the previous section, solve half the problem of supporting a shared state. The other half of the problem is being able to use checksum information during the build and being able to reuse or rebuild specific components.

The sstate class is a relatively generic implementation of how to "capture" a snapshot of a given task. The idea is that the build process does not care about the source of a task's output. Output could be freshly built or it could be downloaded and unpacked from somewhere. In other words, the build process does not need to worry about its origin.

Two types of output exist. One type is just about creating a directory in WORKDIR. A good example is the output of either do_install or do_package. The other type of output occurs when a set of data is merged into a shared directory tree such as the sysroot.

The Yocto Project team has tried to keep the details of the implementation hidden in sstate class. From a user's perspective, adding shared state wrapping to a task is as simple as this do_deploy example taken from the deploy class:

     DEPLOYDIR = "${WORKDIR}/deploy-${PN}"
     SSTATETASKS += "do_deploy"
     do_deploy[sstate-inputdirs] = "${DEPLOYDIR}"
     do_deploy[sstate-outputdirs] = "${DEPLOY_DIR_IMAGE}"

     python do_deploy_setscene () {
         sstate_setscene(d)
     }
     addtask do_deploy_setscene
     do_deploy[dirs] = "${DEPLOYDIR} ${B}"
     do_deploy[stamp-extra-info] = "${MACHINE_ARCH}"
                

The following list explains the previous example:

  • Adding "do_deploy" to SSTATETASKS adds some required sstate-related processing, which is implemented in the sstate class, to before and after the do_deploy task.

  • The do_deploy[sstate-inputdirs] = "${DEPLOYDIR}" declares that do_deploy places its output in ${DEPLOYDIR} when run normally (i.e. when not using the sstate cache). This output becomes the input to the shared state cache.

  • The do_deploy[sstate-outputdirs] = "${DEPLOY_DIR_IMAGE}" line causes the contents of the shared state cache to be copied to ${DEPLOY_DIR_IMAGE}.

    Note

    If do_deploy is not already in the shared state cache or if its input checksum (signature) has changed from when the output was cached, the task runs to populate the shared state cache, after which the contents of the shared state cache is copied to ${DEPLOY_DIR_IMAGE}. If do_deploy is in the shared state cache and its signature indicates that the cached output is still valid (i.e. if no relevant task inputs have changed), then the contents of the shared state cache copies directly to ${DEPLOY_DIR_IMAGE} by the do_deploy_setscene task instead, skipping the do_deploy task.

  • The following task definition is glue logic needed to make the previous settings effective:

         python do_deploy_setscene () {
             sstate_setscene(d)
         }
         addtask do_deploy_setscene
                            

    sstate_setscene() takes the flags above as input and accelerates the do_deploy task through the shared state cache if possible. If the task was accelerated, sstate_setscene() returns True. Otherwise, it returns False, and the normal do_deploy task runs. For more information, see the "setscene" section in the BitBake User Manual.

  • The do_deploy[dirs] = "${DEPLOYDIR} ${B}" line creates ${DEPLOYDIR} and ${B} before the do_deploy task runs, and also sets the current working directory of do_deploy to ${B}. For more information, see the "Variable Flags" section in the BitBake User Manual.

    Note

    In cases where sstate-inputdirs and sstate-outputdirs would be the same, you can use sstate-plaindirs. For example, to preserve the ${PKGD} and ${PKGDEST} output from the do_package task, use the following:
         do_package[sstate-plaindirs] = "${PKGD} ${PKGDEST}"
                                

  • The do_deploy[stamp-extra-info] = "${MACHINE_ARCH}" line appends extra metadata to the stamp file. In this case, the metadata makes the task specific to a machine's architecture. See "The Task List" section in the BitBake User Manual for more information on the stamp-extra-info flag.

  • sstate-inputdirs and sstate-outputdirs can also be used with multiple directories. For example, the following declares PKGDESTWORK and SHLIBWORK as shared state input directories, which populates the shared state cache, and PKGDATA_DIR and SHLIBSDIR as the corresponding shared state output directories:

         do_package[sstate-inputdirs] = "${PKGDESTWORK} ${SHLIBSWORKDIR}"
         do_package[sstate-outputdirs] = "${PKGDATA_DIR} ${SHLIBSDIR}"
                            

  • These methods also include the ability to take a lockfile when manipulating shared state directory structures, for cases where file additions or removals are sensitive:

         do_package[sstate-lockfile] = "${PACKAGELOCK}"
                            

Behind the scenes, the shared state code works by looking in SSTATE_DIR and SSTATE_MIRRORS for shared state files. Here is an example:

     SSTATE_MIRRORS ?= "\
     file://.* http://someserver.tld/share/sstate/PATH;downloadfilename=PATH \n \
     file://.* file:///some/local/dir/sstate/PATH"
                

Note

The shared state directory (SSTATE_DIR) is organized into two-character subdirectories, where the subdirectory names are based on the first two characters of the hash. If the shared state directory structure for a mirror has the same structure as SSTATE_DIR, you must specify "PATH" as part of the URI to enable the build system to map to the appropriate subdirectory.

The shared state package validity can be detected just by looking at the filename since the filename contains the task checksum (or signature) as described earlier in this section. If a valid shared state package is found, the build process downloads it and uses it to accelerate the task.

The build processes use the *_setscene tasks for the task acceleration phase. BitBake goes through this phase before the main execution code and tries to accelerate any tasks for which it can find shared state packages. If a shared state package for a task is available, the shared state package is used. This means the task and any tasks on which it is dependent are not executed.

As a real world example, the aim is when building an IPK-based image, only the do_package_write_ipk tasks would have their shared state packages fetched and extracted. Since the sysroot is not used, it would never get extracted. This is another reason why a task-based approach is preferred over a recipe-based approach, which would have to install the output from every task.

4.6. Automatically Added Runtime Dependencies

The OpenEmbedded build system automatically adds common types of runtime dependencies between packages, which means that you do not need to explicitly declare the packages using RDEPENDS. Three automatic mechanisms exist (shlibdeps, pcdeps, and depchains) that handle shared libraries, package configuration (pkg-config) modules, and -dev and -dbg packages, respectively. For other types of runtime dependencies, you must manually declare the dependencies.

  • shlibdeps: During the do_package task of each recipe, all shared libraries installed by the recipe are located. For each shared library, the package that contains the shared library is registered as providing the shared library. More specifically, the package is registered as providing the soname of the library. The resulting shared-library-to-package mapping is saved globally in PKGDATA_DIR by the do_packagedata task.

    Simultaneously, all executables and shared libraries installed by the recipe are inspected to see what shared libraries they link against. For each shared library dependency that is found, PKGDATA_DIR is queried to see if some package (likely from a different recipe) contains the shared library. If such a package is found, a runtime dependency is added from the package that depends on the shared library to the package that contains the library.

    The automatically added runtime dependency also includes a version restriction. This version restriction specifies that at least the current version of the package that provides the shared library must be used, as if "package (>= version)" had been added to RDEPENDS. This forces an upgrade of the package containing the shared library when installing the package that depends on the library, if needed.

    If you want to avoid a package being registered as providing a particular shared library (e.g. because the library is for internal use only), then add the library to PRIVATE_LIBS inside the package's recipe.

  • pcdeps: During the do_package task of each recipe, all pkg-config modules (*.pc files) installed by the recipe are located. For each module, the package that contains the module is registered as providing the module. The resulting module-to-package mapping is saved globally in PKGDATA_DIR by the do_packagedata task.

    Simultaneously, all pkg-config modules installed by the recipe are inspected to see what other pkg-config modules they depend on. A module is seen as depending on another module if it contains a "Requires:" line that specifies the other module. For each module dependency, PKGDATA_DIR is queried to see if some package contains the module. If such a package is found, a runtime dependency is added from the package that depends on the module to the package that contains the module.

    Note

    The pcdeps mechanism most often infers dependencies between -dev packages.

  • depchains: If a package foo depends on a package bar, then foo-dev and foo-dbg are also made to depend on bar-dev and bar-dbg, respectively. Taking the -dev packages as an example, the bar-dev package might provide headers and shared library symlinks needed by foo-dev, which shows the need for a dependency between the packages.

    The dependencies added by depchains are in the form of RRECOMMENDS.

    Note

    By default, foo-dev also has an RDEPENDS-style dependency on foo, because the default value of RDEPENDS_${PN}-dev (set in bitbake.conf) includes "${PN}".

    To ensure that the dependency chain is never broken, -dev and -dbg packages are always generated by default, even if the packages turn out to be empty. See the ALLOW_EMPTY variable for more information.

The do_package task depends on the do_packagedata task of each recipe in DEPENDS through use of a [deptask] declaration, which guarantees that the required shared-library/module-to-package mapping information will be available when needed as long as DEPENDS has been correctly set.

4.7. Fakeroot and Pseudo

Some tasks are easier to implement when allowed to perform certain operations that are normally reserved for the root user (e.g. do_install, do_package_write*, do_rootfs, and do_image*). For example, the do_install task benefits from being able to set the UID and GID of installed files to arbitrary values.

One approach to allowing tasks to perform root-only operations would be to require BitBake to run as root. However, this method is cumbersome and has security issues. The approach that is actually used is to run tasks that benefit from root privileges in a "fake" root environment. Within this environment, the task and its child processes believe that they are running as the root user, and see an internally consistent view of the filesystem. As long as generating the final output (e.g. a package or an image) does not require root privileges, the fact that some earlier steps ran in a fake root environment does not cause problems.

The capability to run tasks in a fake root environment is known as "fakeroot", which is derived from the BitBake keyword/variable flag that requests a fake root environment for a task.

In the OpenEmbedded build system, the program that implements fakeroot is known as Pseudo. Pseudo overrides system calls by using the environment variable LD_PRELOAD, which results in the illusion of running as root. To keep track of "fake" file ownership and permissions resulting from operations that require root permissions, Pseudo uses an SQLite 3 database. This database is stored in ${WORKDIR}/pseudo/files.db for individual recipes. Storing the database in a file as opposed to in memory gives persistence between tasks and builds, which is not accomplished using fakeroot.

Caution

If you add your own task that manipulates the same files or directories as a fakeroot task, then that task also needs to run under fakeroot. Otherwise, the task cannot run root-only operations, and cannot see the fake file ownership and permissions set by the other task. You need to also add a dependency on virtual/fakeroot-native:do_populate_sysroot, giving the following:
       fakeroot do_mytask () {
           ...
       }
       do_mytask[depends] += "virtual/fakeroot-native:do_populate_sysroot"
                

For more information, see the FAKEROOT* variables in the BitBake User Manual. You can also reference the "Pseudo" and "Why Not Fakeroot?" articles for background information on Pseudo.

Chapter 5. The Yocto Project Development Tasks Manual

5.1. Welcome

Welcome to the Yocto Project Development Tasks Manual! This manual provides relevant procedures necessary for developing in the Yocto Project environment (i.e. developing embedded Linux images and user-space applications that run on targeted devices). The manual groups related procedures into higher-level sections. Procedures can consist of high-level steps or low-level steps depending on the topic.

The following list describes what you can get from this manual:

  • Procedures that help you get going with the Yocto Project. For example, procedures that show you how to set up a build host and work with the Yocto Project source repositories.

  • Procedures that show you how to submit changes to the Yocto Project. Changes can be improvements, new features, or bug fixes.

  • Procedures related to "everyday" tasks you perform while developing images and applications using the Yocto Project. For example, procedures to create a layer, customize an image, write a new recipe, and so forth.

This manual will not give you the following:

  • Redundant Step-by-step Instructions: For example, the Yocto Project Application Development and the Extensible Software Development Kit (eSDK) manual contains detailed instructions on how to install an SDK, which is used to develop applications for target hardware.

  • Reference or Conceptual Material: This type of material resides in an appropriate reference manual. For example, system variables are documented in the Yocto Project Reference Manual.

  • Detailed Public Information Not Specific to the Yocto Project: For example, exhaustive information on how to use the Source Control Manager Git is better covered with Internet searches and official Git Documentation than through the Yocto Project documentation.

5.2. Other Information

Because this manual presents information for many different topics, supplemental information is recommended for full comprehension. For introductory information on the Yocto Project, see the Yocto Project Website. If you want to build an image with no knowledge of Yocto Project as a way of quickly testing it out, see the Yocto Project Quick Build document.

For a comprehensive list of links and other documentation, see the "Links and Related Documentation" section in the Yocto Project Reference Manual.

Chapter 6. Setting Up to Use the Yocto Project

This chapter provides procedures related to getting set up to use the Yocto Project. You can learn about creating a team environment that develops using the Yocto Project, how to set up a build host, how to locate Yocto Project source repositories, and how to create local Git repositories.

6.1. Creating a Team Development Environment

It might not be immediately clear how you can use the Yocto Project in a team development environment, or scale it for a large team of developers. One of the strengths of the Yocto Project is that it is extremely flexible. Thus, you can adapt it to many different use cases and scenarios. However, these characteristics can cause a struggle if you are trying to create a working setup that scales across a large team.

To help you understand how to set up this type of environment, this section presents a procedure that gives you the information to learn how to get the results you want. The procedure is high-level and presents some of the project's most successful experiences, practices, solutions, and available technologies that work well. Keep in mind, the procedure here is a starting point. You can build off it and customize it to fit any particular working environment and set of practices.

  1. Determine Who is Going to be Developing: You need to understand who is going to be doing anything related to the Yocto Project and what their roles would be. Making this determination is essential to completing the steps two and three, which are to get your equipment together and set up your development environment's hardware topology.

    The following roles exist:

    • Application Development: These types of developers do application level work on top of an existing software stack.

    • Core System Development: These types of developers work on the contents of the operating system image itself.

    • Build Engineer: This type of developer manages Autobuilders and releases. Not all environments need a Build Engineer.

    • Test Engineer: This type of developer creates and manages automated tests needed to ensure all application and core system development meets desired quality standards.

  2. Gather the Hardware: Based on the size and make-up of the team, get the hardware together. Any development, build, or test engineer should be using a system that is running a supported Linux distribution. Systems, in general, should be high performance (e.g. dual, six-core Xeons with 24 Gbytes of RAM and plenty of disk space). You can help ensure efficiency by having any machines used for testing or that run Autobuilders be as high performance as possible.

  3. Understand the Hardware Topology of the Environment: Once you understand the hardware involved and the make-up of the team, you can understand the hardware topology of the development environment. You can get a visual idea of the machines and their roles across the development environment.

  4. Use Git as Your Source Control Manager (SCM): Keeping your Metadata and any software you are developing under the control of an SCM system that is compatible with the OpenEmbedded build system is advisable. Of the SCMs BitBake supports, the Yocto Project team strongly recommends using Git. Git is a distributed system that is easy to backup, allows you to work remotely, and then connects back to the infrastructure.

    Note

    For information about BitBake, see the BitBake User Manual.

    It is relatively easy to set up Git services and create infrastructure like http://git.yoctoproject.org, which is based on server software called gitolite with cgit being used to generate the web interface that lets you view the repositories. The gitolite software identifies users using SSH keys and allows branch-based access controls to repositories that you can control as little or as much as necessary.

    Note

    The setup of these services is beyond the scope of this manual. However, sites such as these exist that describe how to perform setup:

  5. Set up the Application Development Machines: As mentioned earlier, application developers are creating applications on top of existing software stacks. Following are some best practices for setting up machines that do application development:

    • Use a pre-built toolchain that contains the software stack itself. Then, develop the application code on top of the stack. This method works well for small numbers of relatively isolated applications.

    • When possible, use the Yocto Project plug-in for the Eclipse™ IDE and SDK development practices. For more information, see the "Yocto Project Application Development and the Extensible Software Development Kit (eSDK)" manual.

    • Keep your cross-development toolchains updated. You can do this through provisioning either as new toolchain downloads or as updates through a package update mechanism using opkg to provide updates to an existing toolchain. The exact mechanics of how and when to do this are a question for local policy.

    • Use multiple toolchains installed locally into different locations to allow development across versions.

  6. Set up the Core Development Machines: As mentioned earlier, these types of developers work on the contents of the operating system itself. Following are some best practices for setting up machines used for developing images:

    • Have the Yocto Project build system itself available on the developer workstations so developers can run their own builds and directly rebuild the software stack.

    • Keep the core system unchanged as much as possible and do your work in layers on top of the core system. Doing so gives you a greater level of portability when upgrading to new versions of the core system or Board Support Packages (BSPs).

    • Share layers amongst the developers of a particular project and contain the policy configuration that defines the project.

  7. Set up an Autobuilder: Autobuilders are often the core of the development environment. It is here that changes from individual developers are brought together and centrally tested and subsequent decisions about releases can be made. Autobuilders also allow for "continuous integration" style testing of software components and regression identification and tracking.

    See "Yocto Project Autobuilder" for more information and links to buildbot. The Yocto Project team has found this implementation works well in this role. A public example of this is the Yocto Project Autobuilders, which we use to test the overall health of the project.

    The features of this system are:

    • Highlights when commits break the build.

    • Populates an sstate cache from which developers can pull rather than requiring local builds.

    • Allows commit hook triggers, which trigger builds when commits are made.

    • Allows triggering of automated image booting and testing under the QuickEMUlator (QEMU).

    • Supports incremental build testing and from-scratch builds.

    • Shares output that allows developer testing and historical regression investigation.

    • Creates output that can be used for releases.

    • Allows scheduling of builds so that resources can be used efficiently.

  8. Set up Test Machines: Use a small number of shared, high performance systems for testing purposes. Developers can use these systems for wider, more extensive testing while they continue to develop locally using their primary development system.

  9. Document Policies and Change Flow: The Yocto Project itself uses a hierarchical structure and a pull model. Scripts exist to create and send pull requests (i.e. create-pull-request and send-pull-request). This model is in line with other open source projects where maintainers are responsible for specific areas of the project and a single maintainer handles the final "top-of-tree" merges.

    Note

    You can also use a more collective push model. The gitolite software supports both the push and pull models quite easily.

    As with any development environment, it is important to document the policy used as well as any main project guidelines so they are understood by everyone. It is also a good idea to have well structured commit messages, which are usually a part of a project's guidelines. Good commit messages are essential when looking back in time and trying to understand why changes were made.

    If you discover that changes are needed to the core layer of the project, it is worth sharing those with the community as soon as possible. Chances are if you have discovered the need for changes, someone else in the community needs them also.

  10. Development Environment Summary: Aside from the previous steps, some best practices exist within the Yocto Project development environment. Consider the following:

    • Use Git as the source control system.

    • Maintain your Metadata in layers that make sense for your situation. See the "Understanding and Creating Layers" section for more information on layers.

    • Separate the project's Metadata and code by using separate Git repositories. See the "Yocto Project Source Repositories" section for information on these repositories. See the "Locating Yocto Project Source Files" section for information on how to set up local Git repositories for related upstream Yocto Project Git repositories.

    • Set up the directory for the shared state cache (SSTATE_DIR) where it makes sense. For example, set up the sstate cache on a system used by developers in the same organization and share the same source directories on their machines.

    • Set up an Autobuilder and have it populate the sstate cache and source directories.

    • The Yocto Project community encourages you to send patches to the project to fix bugs or add features. If you do submit patches, follow the project commit guidelines for writing good commit messages. See the "Submitting a Change to the Yocto Project" section.

    • Send changes to the core sooner than later as others are likely to run into the same issues. For some guidance on mailing lists to use, see the list in the "Submitting a Change to the Yocto Project" section. For a description of the available mailing lists, see the "Mailing Lists" section in the Yocto Project Reference Manual.

6.2. Preparing the Build Host

This section provides procedures to set up your development host to use the Yocto Project. You can use the Yocto Project on a native Linux development host or you can use CROPS, which leverages Docker Containers, to prepare any Linux, Mac, or Windows development host.

Once your development host is set up to use the Yocto Project, further steps are necessary depending on what you want to accomplish. See the following references for information on how to prepare for Board Support Package (BSP) development, kernel development, and development using the Eclipse™ IDE:

6.2.1. Setting Up a Native Linux Host

Follow these steps to prepare a native Linux machine as your Yocto Project development host:

  1. Use a Supported Linux Distribution: You should have a reasonably current Linux-based host system. You will have the best results with a recent release of Fedora, openSUSE, Debian, Ubuntu, or CentOS as these releases are frequently tested against the Yocto Project and officially supported. For a list of the distributions under validation and their status, see the "Supported Linux Distributions" section in the Yocto Project Reference Manual and the wiki page at Distribution Support.

  2. Have Enough Free Memory: You should have at least 50 Gbytes of free disk space for building images.

  3. Meet Minimal Version Requirements: The OpenEmbedded build system should be able to run on any modern distribution that has the following versions for Git, tar, and Python.

    • Git 1.8.3.1 or greater

    • tar 1.27 or greater

    • Python 3.4.0 or greater.

    If your build host does not meet any of these three listed version requirements, you can take steps to prepare the system so that you can still use the Yocto Project. See the "Required Git, tar, and Python Versions" section in the Yocto Project Reference Manual for information.

  4. Install Development Host Packages: Required development host packages vary depending on your build machine and what you want to do with the Yocto Project. Collectively, the number of required packages is large if you want to be able to cover all cases.

    For lists of required packages for all scenarios, see the "Required Packages for the Host Development System" section in the Yocto Project Reference Manual.

Once you have completed the previous steps, you are ready to continue using a given development path on your native Linux machine. If you are going to use BitBake, see the "Cloning the poky Repository" section. If you are going to use the Extensible SDK, see the "Using the Extensible SDK" Chapter in the Yocto Project Application Development and the Extensible Software Development Kit (eSDK) manual. If you want to work on the kernel, see the Yocto Project Linux Kernel Development Manual. If you are going to use Toaster, see the "Setting Up and Using Toaster" section in the Toaster User Manual.

6.2.2. Setting Up to Use CROss PlatformS (CROPS)

With CROPS, which leverages Docker Containers, you can create a Yocto Project development environment that is operating system agnostic. You can set up a container in which you can develop using the Yocto Project on a Windows, Mac, or Linux machine.

Follow these general steps to prepare a Windows, Mac, or Linux machine as your Yocto Project development host:

  1. Go to the Docker Installation Site: Docker is a software container platform that you need to install on the host development machine. To start the installation process, see the Docker Installation site.

  2. Choose Your Docker Edition: Docker comes in several editions. For the Yocto Project, the stable community edition (i.e. "Docker CE Stable") is adequate. You can learn more about the Docker editions from the site.

  3. Go to the Install Site for Your Platform: Click the link for the Docker edition associated with your development host machine's native software. For example, if your machine is running Microsoft Windows Version 10 and you want the Docker CE Stable edition, click that link under "Supported Platforms".

  4. Understand What You Need: The install page has pre-requisites your machine must meet. Be sure you read through this page and make sure your machine meets the requirements to run Docker. If your machine does not meet the requirements, the page has instructions to handle exceptions. For example, to run Docker on Windows 10, you must have the pro version of the operating system. If you have the home version, you need to install the Docker Toolbox.

    Another example is that a Windows machine needs to have Microsoft Hyper-V. If you have a legacy version of the the Microsoft operating system or for any other reason you do not have Microsoft Hyper-V, you would have to enter the BIOS and enable virtualization.

  5. Install the Software: Once you have understood all the pre-requisites, you can download and install the appropriate software. Follow the instructions for your specific machine and the type of the software you need to install.

  6. Optionally Orient Yourself With Docker: If you are unfamiliar with Docker and the container concept, you can learn more here - https://docs.docker.com/get-started/. You should be able to launch Docker or the Docker Toolbox and have a terminal shell on your development host.

  7. Set Up the Containers to Use the Yocto Project: Go to https://github.com/crops/docker-win-mac-docs/wiki and follow the directions for your particular development host (i.e. Linux, Mac, or Windows).

    Once you complete the setup instructions for your machine, you have the Poky, Extensible SDK, and Toaster containers available. You can click those links from the page and learn more about using each of those containers.

Once you have a container set up, everything is in place to develop just as if you were running on a native Linux machine. If you are going to use the Poky container, see the "Cloning the poky Repository" section. If you are going to use the Extensible SDK container, see the "Using the Extensible SDK" Chapter in the Yocto Project Application Development and the Extensible Software Development Kit (eSDK) manual. If you are going to use the Toaster container, see the "Setting Up and Using Toaster" section in the Toaster User Manual.

6.3. Locating Yocto Project Source Files

This section contains procedures related to locating Yocto Project files. You establish and use these local files to work on projects.

Notes

  • For concepts and introductory information about Git as it is used in the Yocto Project, see the "Git" section in the Yocto Project Overview and Concepts Manual.

  • For concepts on Yocto Project source repositories, see the "Yocto Project Source Repositories" section in the Yocto Project Overview and Concepts Manual."

6.3.1. Accessing Source Repositories

Working from a copy of the upstream Yocto Project Source Repositories is the preferred method for obtaining and using a Yocto Project release. You can view the Yocto Project Source Repositories at http://git.yoctoproject.org. In particular, you can find the poky repository at http://git.yoctoproject.org/cgit/cgit.cgi/poky/.

Use the following procedure to locate the latest upstream copy of the poky Git repository:

  1. Access Repositories: Open a browser and go to http://git.yoctoproject.org to access the GUI-based interface into the Yocto Project source repositories.

  2. Select the Repository: Click on the repository in which you are interested (i.e. poky).

  3. Find the URL Used to Clone the Repository: At the bottom of the page, note the URL used to clone that repository (e.g. http://git.yoctoproject.org/poky).

    Note

    For information on cloning a repository, see the "Cloning the poky Repository" section.

6.3.2. Accessing Index of Releases

Yocto Project maintains an Index of Releases area that contains related files that contribute to the Yocto Project. Rather than Git repositories, these files are tarballs that represent snapshots in time of a given component.

Tip

The recommended method for accessing Yocto Project components is to use Git to clone the upstream repository and work from within that locally cloned repository. The procedure in this section exists should you desire a tarball snapshot of any given component.

  1. Access the Index of Releases: Open a browser and go to http://downloads.yoctoproject.org/releases to access the Index of Releases. The list represents released components (e.g. eclipse-plugin, sato, and so on).

    Note

    The yocto directory contains the full array of released Poky tarballs. The poky directory in the Index of Releases was historically used for very early releases and exists now only for retroactive completeness.

  2. Select a Component: Click on any released component in which you are interested (e.g. yocto).

  3. Find the Tarball: Drill down to find the associated tarball. For example, click on yocto-2.5 to view files associated with the Yocto Project 2.5 release (e.g. poky-sumo-20.0.0.tar.bz2, which is the released Poky tarball).

  4. Download the Tarball: Click the tarball to download and save a snapshot of the given component.

6.3.3. Using the Downloads Page

The Yocto Project Website uses a "DOWNLOADS" page from which you can locate and download tarballs of any Yocto Project release. Rather than Git repositories, these files represent snapshot tarballs.

Tip

The recommended method for accessing Yocto Project components is to use Git to clone a repository and work from within that local repository. The procedure in this section exists should you desire a tarball snapshot of any given component.

  1. Go to the Yocto Project Website: Open The Yocto Project Website in your browser.

  2. Get to the Downloads Area: Select the "DOWNLOADS" item from the pull-down "SOFTWARE" tab menu.

  3. Select a Yocto Project Release: Use the menu next to "RELEASE" to display and choose a Yocto Project release (e.g. sumo, rocko, pyro, and so forth. For a "map" of Yocto Project releases to version numbers, see the Releases wiki page.

  4. Download Tools or Board Support Packages (BSPs): From the "DOWNLOADS" page, you can download tools or BSPs as well. Just scroll down the page and look for what you need.

6.3.4. Accessing Nightly Builds

Yocto Project maintains an area for nightly builds that contains tarball releases at https://autobuilder.yocto.io//pub/nightly/. These builds include Yocto Project releases, SDK installation scripts, and experimental builds.

Should you ever want to access a nightly build of a particular Yocto Project component, use the following procedure:

  1. Access the Nightly Builds: Open a browser and go to https://autobuilder.yocto.io//pub/nightly/ to access the Nightly Builds.

  2. Select a Build: Click on any build by date in which you are interested.

  3. Find the Tarball: Drill down to find the associated tarball.

  4. Download the Tarball: Click the tarball to download and save a snapshot of the given component.

6.4. Cloning and Checking Out Branches

To use the Yocto Project, you need a release of the Yocto Project locally installed on your development system. The locally installed set of files is referred to as the Source Directory in the Yocto Project documentation.

You create your Source Directory by using Git to clone a local copy of the upstream poky repository.

Tip

The preferred method of getting the Yocto Project Source Directory set up is to clone the repository.

Working from a copy of the upstream repository allows you to contribute back into the Yocto Project or simply work with the latest software on a development branch. Because Git maintains and creates an upstream repository with a complete history of changes and you are working with a local clone of that repository, you have access to all the Yocto Project development branches and tag names used in the upstream repository.

6.4.1. Cloning the poky Repository

Follow these steps to create a local version of the upstream poky Git repository.

  1. Set Your Directory: Be in the directory where you want to create your local copy of poky.

  2. Clone the Repository: The following command clones the repository and uses the default name "poky" for your local repository:

         $ git clone git://git.yoctoproject.org/poky
         Cloning into 'poky'...
         remote: Counting objects: 367178, done.
         remote: Compressing objects: 100% (88161/88161), done.
         remote: Total 367178 (delta 272761), reused 366942 (delta 272525)
         Receiving objects: 100% (367178/367178), 133.26 MiB | 6.40 MiB/s, done.
         Resolving deltas: 100% (272761/272761), done.
         Checking connectivity... done.
                        

    Unless you specify a specific development branch or tag name, Git clones the "master" branch, which results in a snapshot of the latest development changes for "master". For information on how to check out a specific development branch or on how to check out a local branch based on a tag name, see the "Checking Out By Branch in Poky" and Checking Out By Tag in Poky" sections, respectively.

    Once the repository is created, you can change to that directory and check its status. Here, the single "master" branch exists on your system and by default, it is checked out:

         $ cd ~/poky
         $ git status
         On branch master
         Your branch is up-to-date with 'origin/master'.
         nothing to commit, working directory clean
         $ git branch
         * master
                        

    Your local repository of poky is identical to the upstream poky repository at the time from which it was cloned.

6.4.2. Checking Out by Branch in Poky

When you clone the upstream poky repository, you have access to all its development branches. Each development branch in a repository is unique as it forks off the "master" branch. To see and use the files of a particular development branch locally, you need to know the branch name and then specifically check out that development branch.

Note

Checking out an active development branch by branch name gives you a snapshot of that particular branch at the time you check it out. Further development on top of the branch that occurs after check it out can occur.

  1. Switch to the Poky Directory: If you have a local poky Git repository, switch to that directory. If you do not have the local copy of poky, see the "Cloning the poky Repository" section.

  2. Determine Existing Branch Names:

         $ git branch -a
         * master
           remotes/origin/1.1_M1
           remotes/origin/1.1_M2
           remotes/origin/1.1_M3
           remotes/origin/1.1_M4
           remotes/origin/1.2_M1
           remotes/origin/1.2_M2
           remotes/origin/1.2_M3
               .
               .
               .
           remotes/origin/master-next
           remotes/origin/master-next2
           remotes/origin/morty
           remotes/origin/pinky
           remotes/origin/purple
           remotes/origin/pyro
           remotes/origin/rocko
                        

  3. Checkout the Branch: Checkout the development branch in which you want to work. For example, to access the files for the Yocto Project 2.5 Release (Sumo), use the following command:

         $ git checkout -b sumo origin/sumo
         Branch sumo set up to track remote branch sumo from origin.
         Switched to a new branch 'sumo'
                        

    The previous command checks out the "sumo" development branch and reports that the branch is tracking the upstream "origin/sumo" branch.

    The following command displays the branches that are now part of your local poky repository. The asterisk character indicates the branch that is currently checked out for work:

         $ git branch
           master
         * sumo
                        

6.4.3. Checking Out by Tag in Poky

Similar to branches, the upstream repository uses tags to mark specific commits associated with significant points in a development branch (i.e. a release point or stage of a release). You might want to set up a local branch based on one of those points in the repository. The process is similar to checking out by branch name except you use tag names.

Note

Checking out a branch based on a tag gives you a stable set of files not affected by development on the branch above the tag.

  1. Switch to the Poky Directory: If you have a local poky Git repository, switch to that directory. If you do not have the local copy of poky, see the "Cloning the poky Repository" section.

  2. Fetch the Tag Names: To checkout the branch based on a tag name, you need to fetch the upstream tags into your local repository:

         $ git fetch --tags
         $
                        

  3. List the Tag Names: You can list the tag names now:

         $ git tag
         1.1_M1.final
         1.1_M1.rc1
         1.1_M1.rc2
         1.1_M2.final
         1.1_M2.rc1
            .
            .
            .
         yocto-2.2
         yocto-2.2.1
         yocto-2.3
         yocto-2.3.1
         yocto-2.4
         yocto_1.5_M5.rc8
                        

  4. Checkout the Branch:

         $ git checkout tags/yocto-2.5 -b my_yocto_2.5
         Switched to a new branch 'my_yocto_2.5'
         $ git branch
           master
         * my_yocto_2.5
                        

    The previous command creates and checks out a local branch named "my_yocto_2.5", which is based on the commit in the upstream poky repository that has the same tag. In this example, the files you have available locally as a result of the checkout command are a snapshot of the "sumo" development branch at the point where Yocto Project 2.5 was released.

Chapter 7. Common Tasks

7.1. Understanding and Creating Layers
7.1.1. Creating Your Own Layer
7.1.2. Following Best Practices When Creating Layers
7.1.3. Making Sure Your Layer is Compatible With Yocto Project
7.1.4. Enabling Your Layer
7.1.5. Using .bbappend Files in Your Layer
7.1.6. Prioritizing Your Layer
7.1.7. Managing Layers
7.1.8. Creating a General Layer Using the bitbake-layers Script
7.1.9. Adding a Layer Using the bitbake-layers Script
7.2. Customizing Images
7.2.1. Customizing Images Using local.conf
7.2.2. Customizing Images Using Custom IMAGE_FEATURES and EXTRA_IMAGE_FEATURES
7.2.3. Customizing Images Using Custom .bb Files
7.2.4. Customizing Images Using Custom Package Groups
7.2.5. Customizing an Image Hostname
7.3. Writing a New Recipe
7.3.1. Overview
7.3.2. Locate or Automatically Create a Base Recipe
7.3.3. Storing and Naming the Recipe
7.3.4. Running a Build on the Recipe
7.3.5. Fetching Code
7.3.6. Unpacking Code
7.3.7. Patching Code
7.3.8. Licensing
7.3.9. Dependencies
7.3.10. Configuring the Recipe
7.3.11. Using Headers to Interface with Devices
7.3.12. Compilation
7.3.13. Installing
7.3.14. Enabling System Services
7.3.15. Packaging
7.3.16. Sharing Files Between Recipes
7.3.17. Using Virtual Providers
7.3.18. Properly Versioning Pre-Release Recipes
7.3.19. Post-Installation Scripts
7.3.20. Testing
7.3.21. Examples
7.3.22. Following Recipe Style Guidelines
7.3.23. Recipe Syntax
7.4. Adding a New Machine
7.4.1. Adding the Machine Configuration File
7.4.2. Adding a Kernel for the Machine
7.4.3. Adding a Formfactor Configuration File
7.5. Upgrading Recipes
7.5.1. Using the Auto Upgrade Helper (AUH)
7.5.2. Using devtool upgrade
7.5.3. Manually Upgrading a Recipe
7.6. Finding Temporary Source Code
7.7. Using Quilt in Your Workflow
7.8. Using a Development Shell
7.9. Using a Development Python Shell
7.10. Building
7.10.1. Building a Simple Image
7.10.2. Building Targets with Multiple Configurations
7.10.3. Building an Initial RAM Filesystem (initramfs) Image
7.10.4. Building a Tiny System
7.10.5. Building Images for More than One Machine
7.10.6. Building Software from an External Source
7.11. Speeding Up a Build
7.12. Working With Libraries
7.12.1. Including Static Library Files
7.12.2. Combining Multiple Versions of Library Files into One Image
7.12.3. Installing Multiple Versions of the Same Library
7.13. Using x32 psABI
7.14. Enabling GObject Introspection Support
7.14.1. Enabling the Generation of Introspection Data
7.14.2. Disabling the Generation of Introspection Data
7.14.3. Testing that Introspection Works in an Image
7.14.4. Known Issues
7.15. Optionally Using an External Toolchain
7.16. Creating Partitioned Images Using Wic
7.16.1. Background
7.16.2. Requirements
7.16.3. Getting Help
7.16.4. Operational Modes
7.16.5. Using an Existing Kickstart File
7.16.6. Using the Wic Plug-Ins Interface
7.16.7. Examples
7.17. Flashing Images Using bmaptool
7.18. Making Images More Secure
7.18.1. General Considerations
7.18.2. Security Flags
7.18.3. Considerations Specific to the OpenEmbedded Build System
7.18.4. Tools for Hardening Your Image
7.19. Creating Your Own Distribution
7.20. Creating a Custom Template Configuration Directory
7.21. Conserving Disk Space During Builds
7.22. Working with Packages
7.22.1. Excluding Packages from an Image
7.22.2. Incrementing a Package Version
7.22.3. Handling Optional Module Packaging
7.22.4. Using Runtime Package Management
7.22.5. Generating and Using Signed Packages
7.22.6. Testing Packages With ptest
7.23. Efficiently Fetching Source Files During a Build
7.23.1. Setting up Effective Mirrors
7.23.2. Getting Source Files and Suppressing the Build
7.24. Selecting an Initialization Manager
7.24.1. Using systemd Exclusively
7.24.2. Using systemd for the Main Image and Using SysVinit for the Rescue Image
7.25. Selecting a Device Manager
7.25.1. Using Persistent and Pre-Populated/dev
7.25.2. Using devtmpfs and a Device Manager
7.26. Using an External SCM
7.27. Creating a Read-Only Root Filesystem
7.27.1. Creating the Root Filesystem
7.27.2. Post-Installation Scripts
7.27.3. Areas With Write Access
7.28. Maintaining Build Output Quality
7.28.1. Enabling and Disabling Build History
7.28.2. Understanding What the Build History Contains
7.29. Performing Automated Runtime Testing
7.29.1. Enabling Tests
7.29.2. Running Tests
7.29.3. Exporting Tests
7.29.4. Writing New Tests
7.29.5. Installing Packages in the DUT Without the Package Manager
7.30. Debugging Tools and Techniques
7.30.1. Viewing Logs from Failed Tasks
7.30.2. Viewing Variable Values
7.30.3. Viewing Package Information with oe-pkgdata-util
7.30.4. Viewing Dependencies Between Recipes and Tasks
7.30.5. Viewing Task Variable Dependencies
7.30.6. Viewing Metadata Used to Create the Input Signature of a Shared State Task
7.30.7. Invalidating Shared State to Force a Task to Run
7.30.8. Running Specific Tasks
7.30.9. General BitBake Problems
7.30.10. Building with No Dependencies
7.30.11. Recipe Logging Mechanisms
7.30.12. Debugging Parallel Make Races
7.30.13. Debugging With the GNU Project Debugger (GDB) Remotely
7.30.14. Debugging with the GNU Project Debugger (GDB) on the Target
7.30.15. Other Debugging Tips
7.31. Making Changes to the Yocto Project
7.31.1. Submitting a Defect Against the Yocto Project
7.31.2. Submitting a Change to the Yocto Project
7.32. Working With Licenses
7.32.1. Tracking License Changes
7.32.2. Enabling Commercially Licensed Recipes
7.32.3. Maintaining Open Source License Compliance During Your Product's Lifecycle
7.33. Using the Error Reporting Tool
7.33.1. Enabling and Using the Tool
7.33.2. Disabling the Tool
7.33.3. Setting Up Your Own Error Reporting Server
7.34. Using Wayland and Weston
7.34.1. Enabling Wayland in an Image
7.34.2. Running Weston

This chapter describes fundamental procedures such as creating layers, adding new software packages, extending or customizing images, porting work to new hardware (adding a new machine), and so forth. You will find that the procedures documented here occur often in the development cycle using the Yocto Project.

7.1. Understanding and Creating Layers

The OpenEmbedded build system supports organizing Metadata into multiple layers. Layers allow you to isolate different types of customizations from each other. For introductory information on the Yocto Project Layer Model, see the "The Yocto Project Layer Model" section in the Yocto Project Overview and Concepts Manual.

7.1.1. Creating Your Own Layer

It is very easy to create your own layers to use with the OpenEmbedded build system. The Yocto Project ships with tools that speed up creating layers. This section describes the steps you perform by hand to create layers so that you can better understand them. For information about the layer-creation tools, see the "Creating a New BSP Layer Using the bitbake-layers Script" section in the Yocto Project Board Support Package (BSP) Developer's Guide and the "Creating a General Layer Using the bitbake-layers Script" section further down in this manual.

Follow these general steps to create your layer without using tools:

  1. Check Existing Layers: Before creating a new layer, you should be sure someone has not already created a layer containing the Metadata you need. You can see the OpenEmbedded Metadata Index for a list of layers from the OpenEmbedded community that can be used in the Yocto Project. You could find a layer that is identical or close to what you need.

  2. Create a Directory: Create the directory for your layer. When you create the layer, be sure to create the directory in an area not associated with the Yocto Project Source Directory (e.g. the cloned poky repository).

    While not strictly required, prepend the name of the directory with the string "meta-". For example:

         meta-mylayer
         meta-GUI_xyz
         meta-mymachine
                            

    With rare exceptions, a layer's name follows this form:

         meta-root_name
                            

    Following this layer naming convention can save you trouble later when tools, components, or variables "assume" your layer name begins with "meta-". A notable example is in configuration files as shown in the following step where layer names without the "meta-" string are appended to several variables used in the configuration.

  3. Create a Layer Configuration File: Inside your new layer folder, you need to create a conf/layer.conf file. It is easiest to take an existing layer configuration file and copy that to your layer's conf directory and then modify the file as needed.

    The meta-yocto-bsp/conf/layer.conf file in the Yocto Project Source Repositories demonstrates the required syntax. For your layer, you need to replace "yoctobsp" with a unique identifier for your layer (e.g. "machinexyz" for a layer named "meta-machinexyz"):

         # We have a conf and classes directory, add to BBPATH
         BBPATH .= ":${LAYERDIR}"
    
         # We have recipes-* directories, add to BBFILES
         BBFILES += "${LAYERDIR}/recipes-*/*/*.bb \
                     ${LAYERDIR}/recipes-*/*/*.bbappend"
    
         BBFILE_COLLECTIONS += "yoctobsp"
         BBFILE_PATTERN_yoctobsp = "^${LAYERDIR}/"
         BBFILE_PRIORITY_yoctobsp = "5"
         LAYERVERSION_yoctobsp = "4"
         LAYERSERIES_COMPAT_yoctobsp = "sumo"
                            

    Following is an explanation of the layer configuration file:

    • BBPATH: Adds the layer's root directory to BitBake's search path. Through the use of the BBPATH variable, BitBake locates class files (.bbclass), configuration files, and files that are included with include and require statements. For these cases, BitBake uses the first file that matches the name found in BBPATH. This is similar to the way the PATH variable is used for binaries. It is recommended, therefore, that you use unique class and configuration filenames in your custom layer.

    • BBFILES: Defines the location for all recipes in the layer.

    • BBFILE_COLLECTIONS: Establishes the current layer through a unique identifier that is used throughout the OpenEmbedded build system to refer to the layer. In this example, the identifier "yoctobsp" is the representation for the container layer named "meta-yocto-bsp".

    • BBFILE_PATTERN: Expands immediately during parsing to provide the directory of the layer.

    • BBFILE_PRIORITY: Establishes a priority to use for recipes in the layer when the OpenEmbedded build finds recipes of the same name in different layers.

    • LAYERVERSION: Establishes a version number for the layer. You can use this version number to specify this exact version of the layer as a dependency when using the LAYERDEPENDS variable.

    • LAYERSERIES_COMPAT: Lists the Yocto Project releases for which the current version is compatible. This variable is a good way to indicate how up-to-date your particular layer is.

  4. Add Content: Depending on the type of layer, add the content. If the layer adds support for a machine, add the machine configuration in a conf/machine/ file within the layer. If the layer adds distro policy, add the distro configuration in a conf/distro/ file within the layer. If the layer introduces new recipes, put the recipes you need in recipes-* subdirectories within the layer.

    Note

    For an explanation of layer hierarchy that is compliant with the Yocto Project, see the "Example Filesystem Layout" section in the Yocto Project Board Support Package (BSP) Developer's Guide.

  5. Optionally Test for Compatibility: If you want permission to use the Yocto Project Compatibility logo with your layer or application that uses your layer, perform the steps to apply for compatibility. See the "Making Sure Your Layer is Compatible With Yocto Project" section for more information.

7.1.2. Following Best Practices When Creating Layers

To create layers that are easier to maintain and that will not impact builds for other machines, you should consider the information in the following list:

  • Avoid "Overlaying" Entire Recipes from Other Layers in Your Configuration: In other words, do not copy an entire recipe into your layer and then modify it. Rather, use an append file (.bbappend) to override only those parts of the original recipe you need to modify.

  • Avoid Duplicating Include Files: Use append files (.bbappend) for each recipe that uses an include file. Or, if you are introducing a new recipe that requires the included file, use the path relative to the original layer directory to refer to the file. For example, use require recipes-core/package/file.inc instead of require file.inc. If you're finding you have to overlay the include file, it could indicate a deficiency in the include file in the layer to which it originally belongs. If this is the case, you should try to address that deficiency instead of overlaying the include file. For example, you could address this by getting the maintainer of the include file to add a variable or variables to make it easy to override the parts needing to be overridden.

  • Structure Your Layers: Proper use of overrides within append files and placement of machine-specific files within your layer can ensure that a build is not using the wrong Metadata and negatively impacting a build for a different machine. Following are some examples:

    • Modify Variables to Support a Different Machine: Suppose you have a layer named meta-one that adds support for building machine "one". To do so, you use an append file named base-files.bbappend and create a dependency on "foo" by altering the DEPENDS variable:

           DEPENDS = "foo"
                                      

      The dependency is created during any build that includes the layer meta-one. However, you might not want this dependency for all machines. For example, suppose you are building for machine "two" but your bblayers.conf file has the meta-one layer included. During the build, the base-files for machine "two" will also have the dependency on foo.

      To make sure your changes apply only when building machine "one", use a machine override with the DEPENDS statement:

           DEPENDS_one = "foo"
                                      

      You should follow the same strategy when using _append and _prepend operations:

           DEPENDS_append_one = " foo"
           DEPENDS_prepend_one = "foo "
                                      

      As an actual example, here's a line from the recipe for gnutls, which adds dependencies on "argp-standalone" when building with the musl C library:

           DEPENDS_append_libc-musl = " argp-standalone"
                                      

      Note

      Avoiding "+=" and "=+" and using machine-specific _append and _prepend operations is recommended as well.

    • Place Machine-Specific Files in Machine-Specific Locations: When you have a base recipe, such as base-files.bb, that contains a SRC_URI statement to a file, you can use an append file to cause the build to use your own version of the file. For example, an append file in your layer at meta-one/recipes-core/base-files/base-files.bbappend could extend FILESPATH using FILESEXTRAPATHS as follows:

           FILESEXTRAPATHS_prepend := "${THISDIR}/${BPN}:"
                                      

      The build for machine "one" will pick up your machine-specific file as long as you have the file in meta-one/recipes-core/base-files/base-files/. However, if you are building for a different machine and the bblayers.conf file includes the meta-one layer and the location of your machine-specific file is the first location where that file is found according to FILESPATH, builds for all machines will also use that machine-specific file.

      You can make sure that a machine-specific file is used for a particular machine by putting the file in a subdirectory specific to the machine. For example, rather than placing the file in meta-one/recipes-core/base-files/base-files/ as shown above, put it in meta-one/recipes-core/base-files/base-files/one/. Not only does this make sure the file is used only when building for machine "one", but the build process locates the file more quickly.

      In summary, you need to place all files referenced from SRC_URI in a machine-specific subdirectory within the layer in order to restrict those files to machine-specific builds.

  • Perform Steps to Apply for Yocto Project Compatibility: If you want permission to use the Yocto Project Compatibility logo with your layer or application that uses your layer, perform the steps to apply for compatibility. See the "Making Sure Your Layer is Compatible With Yocto Project" section for more information.

  • Follow the Layer Naming Convention: Store custom layers in a Git repository that use the meta-layer_name format.

  • Group Your Layers Locally: Clone your repository alongside other cloned meta directories from the Source Directory.

7.1.3. Making Sure Your Layer is Compatible With Yocto Project

When you create a layer used with the Yocto Project, it is advantageous to make sure that the layer interacts well with existing Yocto Project layers (i.e. the layer is compatible with the Yocto Project). Ensuring compatibility makes the layer easy to be consumed by others in the Yocto Project community and could allow you permission to use the Yocto Project Compatible Logo.

Note

Only Yocto Project member organizations are permitted to use the Yocto Project Compatible Logo. The logo is not available for general use. For information on how to become a Yocto Project member organization, see the Yocto Project Website.

The Yocto Project Compatibility Program consists of a layer application process that requests permission to use the Yocto Project Compatibility Logo for your layer and application. The process consists of two parts:

  1. Successfully passing a script (yocto-check-layer) that when run against your layer, tests it against constraints based on experiences of how layers have worked in the real world and where pitfalls have been found. Getting a "PASS" result from the script is required for successful compatibility registration.

  2. Completion of an application acceptance form, which you can find at https://www.yoctoproject.org/webform/yocto-project-compatible-registration.

To be granted permission to use the logo, you need to satisfy the following:

  • Be able to check the box indicating that you got a "PASS" when running the script against your layer.

  • Answer "Yes" to the questions on the form or have an acceptable explanation for any questions answered "No".

  • Be a Yocto Project Member Organization.

The remainder of this section presents information on the registration form and on the yocto-check-layer script.

7.1.3.1. Yocto Project Compatible Program Application

Use the form to apply for your layer's approval. Upon successful application, you can use the Yocto Project Compatibility Logo with your layer and the application that uses your layer.

To access the form, use this link: https://www.yoctoproject.org/webform/yocto-project-compatible-registration. Follow the instructions on the form to complete your application.

The application consists of the following sections:

  • Contact Information: Provide your contact information as the fields require. Along with your information, provide the released versions of the Yocto Project for which your layer is compatible.

  • Acceptance Criteria: Provide "Yes" or "No" answers for each of the items in the checklist. Space exists at the bottom of the form for any explanations for items for which you answered "No".

  • Recommendations: Provide answers for the questions regarding Linux kernel use and build success.

7.1.3.2. yocto-check-layer Script

The yocto-check-layer script provides you a way to assess how compatible your layer is with the Yocto Project. You should run this script prior to using the form to apply for compatibility as described in the previous section. You need to achieve a "PASS" result in order to have your application form successfully processed.

The script divides tests into three areas: COMMON, BSP, and DISTRO. For example, given a distribution layer (DISTRO), the layer must pass both the COMMON and DISTRO related tests. Furthermore, if your layer is a BSP layer, the layer must pass the COMMON and BSP set of tests.

To execute the script, enter the following commands from your build directory:

     $ source oe-init-build-env
     $ yocto-check-layer your_layer_directory
                    

Be sure to provide the actual directory for your layer as part of the command.

Entering the command causes the script to determine the type of layer and then to execute a set of specific tests against the layer. The following list overviews the test:

  • common.test_readme: Tests if a README file exists in the layer and the file is not empty.

  • common.test_parse: Tests to make sure that BitBake can parse the files without error (i.e. bitbake -p).

  • common.test_show_environment: Tests that the global or per-recipe environment is in order without errors (i.e. bitbake -e).

  • common.test_signatures: Tests to be sure that BSP and DISTRO layers do not come with recipes that change signatures.

  • bsp.test_bsp_defines_machines: Tests if a BSP layer has machine configurations.

  • bsp.test_bsp_no_set_machine: Tests to ensure a BSP layer does not set the machine when the layer is added.

  • distro.test_distro_defines_distros: Tests if a DISTRO layer has distro configurations.

  • distro.test_distro_no_set_distro: Tests to ensure a DISTRO layer does not set the distribution when the layer is added.

7.1.4. Enabling Your Layer

Before the OpenEmbedded build system can use your new layer, you need to enable it. To enable your layer, simply add your layer's path to the BBLAYERS variable in your conf/bblayers.conf file, which is found in the Build Directory. The following example shows how to enable a layer named meta-mylayer:

     # POKY_BBLAYERS_CONF_VERSION is increased each time build/conf/bblayers.conf
     # changes incompatibly
     POKY_BBLAYERS_CONF_VERSION = "2"

     BBPATH = "${TOPDIR}"
     BBFILES ?= ""

     BBLAYERS ?= " \
       /home/user/poky/meta \
       /home/user/poky/meta-poky \
       /home/user/poky/meta-yocto-bsp \
       /home/user/poky/meta-mylayer \
       "
                

BitBake parses each conf/layer.conf file from the top down as specified in the BBLAYERS variable within the conf/bblayers.conf file. During the processing of each conf/layer.conf file, BitBake adds the recipes, classes and configurations contained within the particular layer to the source directory.

7.1.5. Using .bbappend Files in Your Layer

A recipe that appends Metadata to another recipe is called a BitBake append file. A BitBake append file uses the .bbappend file type suffix, while the corresponding recipe to which Metadata is being appended uses the .bb file type suffix.

You can use a .bbappend file in your layer to make additions or changes to the content of another layer's recipe without having to copy the other layer's recipe into your layer. Your .bbappend file resides in your layer, while the main .bb recipe file to which you are appending Metadata resides in a different layer.

Being able to append information to an existing recipe not only avoids duplication, but also automatically applies recipe changes from a different layer into your layer. If you were copying recipes, you would have to manually merge changes as they occur.

When you create an append file, you must use the same root name as the corresponding recipe file. For example, the append file someapp_2.5.bbappend must apply to someapp_2.5.bb. This means the original recipe and append file names are version number-specific. If the corresponding recipe is renamed to update to a newer version, you must also rename and possibly update the corresponding .bbappend as well. During the build process, BitBake displays an error on starting if it detects a .bbappend file that does not have a corresponding recipe with a matching name. See the BB_DANGLINGAPPENDS_WARNONLY variable for information on how to handle this error.

As an example, consider the main formfactor recipe and a corresponding formfactor append file both from the Source Directory. Here is the main formfactor recipe, which is named formfactor_0.0.bb and located in the "meta" layer at meta/recipes-bsp/formfactor:

     SUMMARY = "Device formfactor information"
     SECTION = "base"
     LICENSE = "MIT"
     LIC_FILES_CHKSUM = "file://${COREBASE}/meta/COPYING.MIT;md5=3da9cfbcb788c80a0384361b4de20420"
     PR = "r45"

     SRC_URI = "file://config file://machconfig"
     S = "${WORKDIR}"

     PACKAGE_ARCH = "${MACHINE_ARCH}"
     INHIBIT_DEFAULT_DEPS = "1"

     do_install() {
	     # Install file only if it has contents
             install -d ${D}${sysconfdir}/formfactor/
             install -m 0644 ${S}/config ${D}${sysconfdir}/formfactor/
	     if [ -s "${S}/machconfig" ]; then
	             install -m 0644 ${S}/machconfig ${D}${sysconfdir}/formfactor/
	     fi
     }                

In the main recipe, note the SRC_URI variable, which tells the OpenEmbedded build system where to find files during the build.

Following is the append file, which is named formfactor_0.0.bbappend and is from the Raspberry Pi BSP Layer named meta-raspberrypi. The file is in the layer at recipes-bsp/formfactor:

     FILESEXTRAPATHS_prepend := "${THISDIR}/${PN}:"
                

By default, the build system uses the FILESPATH variable to locate files. This append file extends the locations by setting the FILESEXTRAPATHS variable. Setting this variable in the .bbappend file is the most reliable and recommended method for adding directories to the search path used by the build system to find files.

The statement in this example extends the directories to include ${THISDIR}/${PN}, which resolves to a directory named formfactor in the same directory in which the append file resides (i.e. meta-raspberrypi/recipes-bsp/formfactor. This implies that you must have the supporting directory structure set up that will contain any files or patches you will be including from the layer.

Using the immediate expansion assignment operator := is important because of the reference to THISDIR. The trailing colon character is important as it ensures that items in the list remain colon-separated.

Note

BitBake automatically defines the THISDIR variable. You should never set this variable yourself. Using "_prepend" as part of the FILESEXTRAPATHS ensures your path will be searched prior to other paths in the final list.

Also, not all append files add extra files. Many append files simply exist to add build options (e.g. systemd). For these cases, your append file would not even use the FILESEXTRAPATHS statement.

7.1.6. Prioritizing Your Layer

Each layer is assigned a priority value. Priority values control which layer takes precedence if there are recipe files with the same name in multiple layers. For these cases, the recipe file from the layer with a higher priority number takes precedence. Priority values also affect the order in which multiple .bbappend files for the same recipe are applied. You can either specify the priority manually, or allow the build system to calculate it based on the layer's dependencies.

To specify the layer's priority manually, use the BBFILE_PRIORITY variable and append the layer's root name:

     BBFILE_PRIORITY_mylayer = "1"
                

Note

It is possible for a recipe with a lower version number PV in a layer that has a higher priority to take precedence.

Also, the layer priority does not currently affect the precedence order of .conf or .bbclass files. Future versions of BitBake might address this.

7.1.7. Managing Layers

You can use the BitBake layer management tool bitbake-layers to provide a view into the structure of recipes across a multi-layer project. Being able to generate output that reports on configured layers with their paths and priorities and on .bbappend files and their applicable recipes can help to reveal potential problems.

For help on the BitBake layer management tool, use the following command:

     $ bitbake-layers --help
     NOTE: Starting bitbake server...
     usage: bitbake-layers [-d] [-q] [-F] [--color COLOR] [-h] <subcommand> ...

     BitBake layers utility

     optional arguments:
       -d, --debug           Enable debug output
       -q, --quiet           Print only errors
       -F, --force           Force add without recipe parse verification
       --color COLOR         Colorize output (where COLOR is auto, always, never)
       -h, --help            show this help message and exit

     subcommands:
       <subcommand>
         show-layers         show current configured layers.
         show-overlayed      list overlayed recipes (where the same recipe exists
                             in another layer)
         show-recipes        list available recipes, showing the layer they are
                             provided by
         show-appends        list bbappend files and recipe files they apply to
         show-cross-depends  Show dependencies between recipes that cross layer
                             boundaries.
         add-layer           Add one or more layers to bblayers.conf.
         remove-layer        Remove one or more layers from bblayers.conf.
         flatten             flatten layer configuration into a separate output
                             directory.
         layerindex-fetch    Fetches a layer from a layer index along with its
                             dependent layers, and adds them to conf/bblayers.conf.
         layerindex-show-depends
                             Find layer dependencies from layer index.
         create-layer        Create a basic layer

     Use bitbake-layers <subcommand> --help to get help on a specific command
                

The following list describes the available commands:

  • help: Displays general help or help on a specified command.

  • show-layers: Shows the current configured layers.

  • show-overlayed: Lists overlayed recipes. A recipe is overlayed when a recipe with the same name exists in another layer that has a higher layer priority.

  • show-recipes: Lists available recipes and the layers that provide them.

  • show-appends: Lists .bbappend files and the recipe files to which they apply.

  • show-cross-depends: Lists dependency relationships between recipes that cross layer boundaries.

  • add-layer: Adds a layer to bblayers.conf.

  • remove-layer: Removes a layer from bblayers.conf

  • flatten: Flattens the layer configuration into a separate output directory. Flattening your layer configuration builds a "flattened" directory that contains the contents of all layers, with any overlayed recipes removed and any .bbappend files appended to the corresponding recipes. You might have to perform some manual cleanup of the flattened layer as follows:

    • Non-recipe files (such as patches) are overwritten. The flatten command shows a warning for these files.

    • Anything beyond the normal layer setup has been added to the layer.conf file. Only the lowest priority layer's layer.conf is used.

    • Overridden and appended items from .bbappend files need to be cleaned up. The contents of each .bbappend end up in the flattened recipe. However, if there are appended or changed variable values, you need to tidy these up yourself. Consider the following example. Here, the bitbake-layers command adds the line #### bbappended ... so that you know where the following lines originate:

           ...
           DESCRIPTION = "A useful utility"
           ...
           EXTRA_OECONF = "--enable-something"
           ...
      
           #### bbappended from meta-anotherlayer ####
      
           DESCRIPTION = "Customized utility"
           EXTRA_OECONF += "--enable-somethingelse"
                                      

      Ideally, you would tidy up these utilities as follows:

           ...
           DESCRIPTION = "Customized utility"
           ...
           EXTRA_OECONF = "--enable-something --enable-somethingelse"
           ...
                                      

  • layerindex-fetch: Fetches a layer from a layer index, along with its dependent layers, and adds the layers to the conf/bblayers.conf file.

  • layerindex-show-depends: Finds layer dependencies from the layer index.

  • create-layer: Creates a basic layer.

7.1.8. Creating a General Layer Using the bitbake-layers Script

The bitbake-layers script with the create-layer subcommand simplifies creating a new general layer.

Notes

  • For information on BSP layers, see the "BSP Layers" section in the Yocto Project Board Specific (BSP) Developer's Guide.

  • In order to use a layer with the OpenEmbedded build system, you need to add the layer to your bblayers.conf configuration file. See the "Adding a Layer Using the bitbake-layers Script" section for more information.

The default mode of the script's operation with this subcommand is to create a layer with the following:

  • A layer priority of 6.

  • A conf subdirectory that contains a layer.conf file.

  • A recipes-example subdirectory that contains a further subdirectory named example, which contains an example.bb recipe file.

  • A COPYING.MIT, which is the license statement for the layer. The script assumes you want to use the MIT license, which is typical for most layers, for the contents of the layer itself.

  • A README file, which is a file describing the contents of your new layer.

In its simplest form, you can use the following command form to create a layer. The command creates a layer whose name corresponds to your_layer_name in the current directory:

     $ bitbake-layers create-layer your_layer_name
                

As an example, the following command creates a layer named meta-scottrif in your home directory:

     $ cd /usr/home
     $ bitbake-layers create-layer meta-scottrif
     NOTE: Starting bitbake server...
     Add your new layer with 'bitbake-layers add-layer meta-scottrif'
                

If you want to set the priority of the layer to other than the default value of "6", you can either use the ‐‐priority option or you can edit the BBFILE_PRIORITY value in the conf/layer.conf after the script creates it. Furthermore, if you want to give the example recipe file some name other than the default, you can use the ‐‐example-recipe-name option.

The easiest way to see how the bitbake-layers create-layer command works is to experiment with the script. You can also read the usage information by entering the following:

     $ bitbake-layers create-layer --help
     NOTE: Starting bitbake server...
     usage: bitbake-layers create-layer [-h] [--priority PRIORITY]
                                        [--example-recipe-name EXAMPLERECIPE]
                                        layerdir

     Create a basic layer

     positional arguments:
       layerdir              Layer directory to create

     optional arguments:
       -h, --help            show this help message and exit
       --priority PRIORITY, -p PRIORITY
                             Layer directory to create
       --example-recipe-name EXAMPLERECIPE, -e EXAMPLERECIPE
                             Filename of the example recipe
                

7.1.9. Adding a Layer Using the bitbake-layers Script

Once you create your general layer, you must add it to your bblayers.conf file. Adding the layer to this configuration file makes the OpenEmbedded build system aware of your layer so that it can search it for metadata.

Add your layer by using the bitbake-layers add-layer command:

     $ bitbake-layers add-layer your_layer_name
                

Here is an example that adds a layer named meta-scottrif to the configuration file. Following the command that adds the layer is another bitbake-layers command that shows the layers that are in your bblayers.conf file:

     $ bitbake-layers add-layer meta-scottrif
     NOTE: Starting bitbake server...
     Parsing recipes: 100% |##########################################################| Time: 0:00:49
     Parsing of 1441 .bb files complete (0 cached, 1441 parsed). 2055 targets, 56 skipped, 0 masked, 0 errors.
     $ bitbake-layers show-layers
     NOTE: Starting bitbake server...
     layer                 path                                      priority
     ==========================================================================
     meta                  /home/scottrif/poky/meta                  5
     meta-poky             /home/scottrif/poky/meta-poky             5
     meta-yocto-bsp        /home/scottrif/poky/meta-yocto-bsp        5
     workspace             /home/scottrif/poky/build/workspace       99
     meta-scottrif         /home/scottrif/poky/build/meta-scottrif   6
                

Adding the layer to this file enables the build system to locate the layer during the build.

Note

During a build, the OpenEmbedded build system looks in the layers from the top of the list down to the bottom in that order.

7.2. Customizing Images

You can customize images to satisfy particular requirements. This section describes several methods and provides guidelines for each.

7.2.1. Customizing Images Using local.conf

Probably the easiest way to customize an image is to add a package by way of the local.conf configuration file. Because it is limited to local use, this method generally only allows you to add packages and is not as flexible as creating your own customized image. When you add packages using local variables this way, you need to realize that these variable changes are in effect for every build and consequently affect all images, which might not be what you require.

To add a package to your image using the local configuration file, use the IMAGE_INSTALL variable with the _append operator:

     IMAGE_INSTALL_append = " strace"
                

Use of the syntax is important - specifically, the space between the quote and the package name, which is strace in this example. This space is required since the _append operator does not add the space.

Furthermore, you must use _append instead of the += operator if you want to avoid ordering issues. The reason for this is because doing so unconditionally appends to the variable and avoids ordering problems due to the variable being set in image recipes and .bbclass files with operators like ?=. Using _append ensures the operation takes affect.

As shown in its simplest use, IMAGE_INSTALL_append affects all images. It is possible to extend the syntax so that the variable applies to a specific image only. Here is an example:

     IMAGE_INSTALL_append_pn-core-image-minimal = " strace"
                

This example adds strace to the core-image-minimal image only.

You can add packages using a similar approach through the CORE_IMAGE_EXTRA_INSTALL variable. If you use this variable, only core-image-* images are affected.

7.2.2. Customizing Images Using Custom IMAGE_FEATURES and EXTRA_IMAGE_FEATURES

Another method for customizing your image is to enable or disable high-level image features by using the IMAGE_FEATURES and EXTRA_IMAGE_FEATURES variables. Although the functions for both variables are nearly equivalent, best practices dictate using IMAGE_FEATURES from within a recipe and using EXTRA_IMAGE_FEATURES from within your local.conf file, which is found in the Build Directory.

To understand how these features work, the best reference is meta/classes/core-image.bbclass. This class lists out the available IMAGE_FEATURES of which most map to package groups while some, such as debug-tweaks and read-only-rootfs, resolve as general configuration settings.

In summary, the file looks at the contents of the IMAGE_FEATURES variable and then maps or configures the feature accordingly. Based on this information, the build system automatically adds the appropriate packages or configurations to the IMAGE_INSTALL variable. Effectively, you are enabling extra features by extending the class or creating a custom class for use with specialized image .bb files.

Use the EXTRA_IMAGE_FEATURES variable from within your local configuration file. Using a separate area from which to enable features with this variable helps you avoid overwriting the features in the image recipe that are enabled with IMAGE_FEATURES. The value of EXTRA_IMAGE_FEATURES is added to IMAGE_FEATURES within meta/conf/bitbake.conf.

To illustrate how you can use these variables to modify your image, consider an example that selects the SSH server. The Yocto Project ships with two SSH servers you can use with your images: Dropbear and OpenSSH. Dropbear is a minimal SSH server appropriate for resource-constrained environments, while OpenSSH is a well-known standard SSH server implementation. By default, the core-image-sato image is configured to use Dropbear. The core-image-full-cmdline and core-image-lsb images both include OpenSSH. The core-image-minimal image does not contain an SSH server.

You can customize your image and change these defaults. Edit the IMAGE_FEATURES variable in your recipe or use the EXTRA_IMAGE_FEATURES in your local.conf file so that it configures the image you are working with to include ssh-server-dropbear or ssh-server-openssh.

Note

See the "Images" section in the Yocto Project Reference Manual for a complete list of image features that ship with the Yocto Project.

7.2.3. Customizing Images Using Custom .bb Files

You can also customize an image by creating a custom recipe that defines additional software as part of the image. The following example shows the form for the two lines you need:

     IMAGE_INSTALL = "packagegroup-core-x11-base package1 package2"

     inherit core-image
                

Defining the software using a custom recipe gives you total control over the contents of the image. It is important to use the correct names of packages in the IMAGE_INSTALL variable. You must use the OpenEmbedded notation and not the Debian notation for the names (e.g. glibc-dev instead of libc6-dev).

The other method for creating a custom image is to base it on an existing image. For example, if you want to create an image based on core-image-sato but add the additional package strace to the image, copy the meta/recipes-sato/images/core-image-sato.bb to a new .bb and add the following line to the end of the copy:

     IMAGE_INSTALL += "strace"
                

7.2.4. Customizing Images Using Custom Package Groups

For complex custom images, the best approach for customizing an image is to create a custom package group recipe that is used to build the image or images. A good example of a package group recipe is meta/recipes-core/packagegroups/packagegroup-base.bb.

If you examine that recipe, you see that the PACKAGES variable lists the package group packages to produce. The inherit packagegroup statement sets appropriate default values and automatically adds -dev, -dbg, and -ptest complementary packages for each package specified in the PACKAGES statement.

Note

The inherit packages should be located near the top of the recipe, certainly before the PACKAGES statement.

For each package you specify in PACKAGES, you can use RDEPENDS and RRECOMMENDS entries to provide a list of packages the parent task package should contain. You can see examples of these further down in the packagegroup-base.bb recipe.

Here is a short, fabricated example showing the same basic pieces:

     DESCRIPTION = "My Custom Package Groups"

     inherit packagegroup

     PACKAGES = "\
         packagegroup-custom-apps \
         packagegroup-custom-tools \
         "

     RDEPENDS_packagegroup-custom-apps = "\
         dropbear \
         portmap \
         psplash"

     RDEPENDS_packagegroup-custom-tools = "\
         oprofile \
         oprofileui-server \
         lttng-tools"

     RRECOMMENDS_packagegroup-custom-tools = "\
         kernel-module-oprofile"
                

In the previous example, two package group packages are created with their dependencies and their recommended package dependencies listed: packagegroup-custom-apps, and packagegroup-custom-tools. To build an image using these package group packages, you need to add packagegroup-custom-apps and/or packagegroup-custom-tools to IMAGE_INSTALL. For other forms of image dependencies see the other areas of this section.

7.2.5. Customizing an Image Hostname

By default, the configured hostname (i.e. /etc/hostname) in an image is the same as the machine name. For example, if MACHINE equals "qemux86", the configured hostname written to /etc/hostname is "qemux86".

You can customize this name by altering the value of the "hostname" variable in the base-files recipe using either an append file or a configuration file. Use the following in an append file:

     hostname="myhostname"
                

Use the following in a configuration file:

     hostname_pn-base-files = "myhostname"
                

Changing the default value of the variable "hostname" can be useful in certain situations. For example, suppose you need to do extensive testing on an image and you would like to easily identify the image under test from existing images with typical default hostnames. In this situation, you could change the default hostname to "testme", which results in all the images using the name "testme". Once testing is complete and you do not need to rebuild the image for test any longer, you can easily reset the default hostname.

Another point of interest is that if you unset the variable, the image will have no default hostname in the filesystem. Here is an example that unsets the variable in a configuration file:

     hostname_pn-base-files = ""
                

Having no default hostname in the filesystem is suitable for environments that use dynamic hostnames such as virtual machines.

7.3. Writing a New Recipe

Recipes (.bb files) are fundamental components in the Yocto Project environment. Each software component built by the OpenEmbedded build system requires a recipe to define the component. This section describes how to create, write, and test a new recipe.

Note

For information on variables that are useful for recipes and for information about recipe naming issues, see the "Required" section of the Yocto Project Reference Manual.

7.3.1. Overview

The following figure shows the basic process for creating a new recipe. The remainder of the section provides details for the steps.

7.3.2. Locate or Automatically Create a Base Recipe

You can always write a recipe from scratch. However, three choices exist that can help you quickly get a start on a new recipe:

  • devtool add: A command that assists in creating a recipe and an environment conducive to development.

  • recipetool create: A command provided by the Yocto Project that automates creation of a base recipe based on the source files.

  • Existing Recipes: Location and modification of an existing recipe that is similar in function to the recipe you need.

Note

For information on recipe syntax, see the "Recipe Syntax" section.

7.3.2.1. Creating the Base Recipe Using devtool add

The devtool add command uses the same logic for auto-creating the recipe as recipetool create, which is listed below. Additionally, however, devtool add sets up an environment that makes it easy for you to patch the source and to make changes to the recipe as is often necessary when adding a recipe to build a new piece of software to be included in a build.

You can find a complete description of the devtool add command in the "A Closer Look at devtool add" section in the Yocto Project Application Development and the Extensible Software Development Kit (eSDK) manual.

7.3.2.2. Creating the Base Recipe Using recipetool create

recipetool create automates creation of a base recipe given a set of source code files. As long as you can extract or point to the source files, the tool will construct a recipe and automatically configure all pre-build information into the recipe. For example, suppose you have an application that builds using Autotools. Creating the base recipe using recipetool results in a recipe that has the pre-build dependencies, license requirements, and checksums configured.

To run the tool, you just need to be in your Build Directory and have sourced the build environment setup script (i.e. oe-init-build-env). To get help on the tool, use the following command:

     $ recipetool -h
     NOTE: Starting bitbake server...
     usage: recipetool [-d] [-q] [--color COLOR] [-h] <subcommand> ...

     OpenEmbedded recipe tool

     options:
       -d, --debug     Enable debug output
       -q, --quiet     Print only errors
       --color COLOR   Colorize output (where COLOR is auto, always, never)
       -h, --help      show this help message and exit

     subcommands:
       create          Create a new recipe
       newappend       Create a bbappend for the specified target in the specified
                       layer
       setvar          Set a variable within a recipe
       appendfile      Create/update a bbappend to replace a target file
       appendsrcfiles  Create/update a bbappend to add or replace source files
       appendsrcfile   Create/update a bbappend to add or replace a source file
     Use recipetool <subcommand> --help to get help on a specific command
                    

Running recipetool create -o OUTFILE creates the base recipe and locates it properly in the layer that contains your source files. Following are some syntax examples:

Use this syntax to generate a recipe based on source. Once generated, the recipe resides in the existing source code layer:

     recipetool create -o OUTFILE source
                    

Use this syntax to generate a recipe using code that you extract from source. The extracted code is placed in its own layer defined by EXTERNALSRC.

     recipetool create -o OUTFILE -x EXTERNALSRC source
                    

Use this syntax to generate a recipe based on source. The options direct recipetool to generate debugging information. Once generated, the recipe resides in the existing source code layer:

     recipetool create -d -o OUTFILE source
                    

7.3.2.3. Locating and Using a Similar Recipe

Before writing a recipe from scratch, it is often useful to discover whether someone else has already written one that meets (or comes close to meeting) your needs. The Yocto Project and OpenEmbedded communities maintain many recipes that might be candidates for what you are doing. You can find a good central index of these recipes in the OpenEmbedded Layer Index.

Working from an existing recipe or a skeleton recipe is the best way to get started. Here are some points on both methods:

  • Locate and modify a recipe that is close to what you want to do: This method works when you are familiar with the current recipe space. The method does not work so well for those new to the Yocto Project or writing recipes.

    Some risks associated with this method are using a recipe that has areas totally unrelated to what you are trying to accomplish with your recipe, not recognizing areas of the recipe that you might have to add from scratch, and so forth. All these risks stem from unfamiliarity with the existing recipe space.

  • Use and modify the following skeleton recipe: If for some reason you do not want to use recipetool and you cannot find an existing recipe that is close to meeting your needs, you can use the following structure to provide the fundamental areas of a new recipe.

         DESCRIPTION = ""
         HOMEPAGE = ""
         LICENSE = ""
         SECTION = ""
         DEPENDS = ""
         LIC_FILES_CHKSUM = ""
    
         SRC_URI = ""
                                

7.3.3. Storing and Naming the Recipe

Once you have your base recipe, you should put it in your own layer and name it appropriately. Locating it correctly ensures that the OpenEmbedded build system can find it when you use BitBake to process the recipe.

  • Storing Your Recipe: The OpenEmbedded build system locates your recipe through the layer's conf/layer.conf file and the BBFILES variable. This variable sets up a path from which the build system can locate recipes. Here is the typical use:

         BBFILES += "${LAYERDIR}/recipes-*/*/*.bb \
                     ${LAYERDIR}/recipes-*/*/*.bbappend"
                        

    Consequently, you need to be sure you locate your new recipe inside your layer such that it can be found.

    You can find more information on how layers are structured in the "Understanding and Creating Layers" section.

  • Naming Your Recipe: When you name your recipe, you need to follow this naming convention:

         basename_version.bb
                        

    Use lower-cased characters and do not include the reserved suffixes -native, -cross, -initial, or -dev casually (i.e. do not use them as part of your recipe name unless the string applies). Here are some examples:

         cups_1.7.0.bb
         gawk_4.0.2.bb
         irssi_0.8.16-rc1.bb
                        

7.3.4. Running a Build on the Recipe

Creating a new recipe is usually an iterative process that requires using BitBake to process the recipe multiple times in order to progressively discover and add information to the recipe file.

Assuming you have sourced the build environment setup script (i.e. oe-init-build-env) and you are in the Build Directory, use BitBake to process your recipe. All you need to provide is the basename of the recipe as described in the previous section:

     $ bitbake basename
                

During the build, the OpenEmbedded build system creates a temporary work directory for each recipe (${WORKDIR}) where it keeps extracted source files, log files, intermediate compilation and packaging files, and so forth.

The path to the per-recipe temporary work directory depends on the context in which it is being built. The quickest way to find this path is to have BitBake return it by running the following:

     $ bitbake -e basename | grep ^WORKDIR=
                

As an example, assume a Source Directory top-level folder named poky, a default Build Directory at poky/build, and a qemux86-poky-linux machine target system. Furthermore, suppose your recipe is named foo_1.3.0.bb. In this case, the work directory the build system uses to build the package would be as follows:

     poky/build/tmp/work/qemux86-poky-linux/foo/1.3.0-r0
                

Inside this directory you can find sub-directories such as image, packages-split, and temp. After the build, you can examine these to determine how well the build went.

Note

You can find log files for each task in the recipe's temp directory (e.g. poky/build/tmp/work/qemux86-poky-linux/foo/1.3.0-r0/temp). Log files are named log.taskname (e.g. log.do_configure, log.do_fetch, and log.do_compile).

You can find more information about the build process in "The Yocto Project Development Environment" chapter of the Yocto Project Overview and Concepts Manual.

7.3.5. Fetching Code

The first thing your recipe must do is specify how to fetch the source files. Fetching is controlled mainly through the SRC_URI variable. Your recipe must have a SRC_URI variable that points to where the source is located. For a graphical representation of source locations, see the "Sources" section in the Yocto Project Overview and Concepts Manual.

The do_fetch task uses the prefix of each entry in the SRC_URI variable value to determine which fetcher to use to get your source files. It is the SRC_URI variable that triggers the fetcher. The do_patch task uses the variable after source is fetched to apply patches. The OpenEmbedded build system uses FILESOVERRIDES for scanning directory locations for local files in SRC_URI.

The SRC_URI variable in your recipe must define each unique location for your source files. It is good practice to not hard-code pathnames in an URL used in SRC_URI. Rather than hard-code these paths, use ${PV}, which causes the fetch process to use the version specified in the recipe filename. Specifying the version in this manner means that upgrading the recipe to a future version is as simple as renaming the recipe to match the new version.

Here is a simple example from the meta/recipes-devtools/cdrtools/cdrtools-native_3.01a20.bb recipe where the source comes from a single tarball. Notice the use of the PV variable:

     SRC_URI = "ftp://ftp.berlios.de/pub/cdrecord/alpha/cdrtools-${PV}.tar.bz2"
                

Files mentioned in SRC_URI whose names end in a typical archive extension (e.g. .tar, .tar.gz, .tar.bz2, .zip, and so forth), are automatically extracted during the do_unpack task. For another example that specifies these types of files, see the "Autotooled Package" section.

Another way of specifying source is from an SCM. For Git repositories, you must specify SRCREV and you should specify PV to include the revision with SRCPV. Here is an example from the recipe meta/recipes-kernel/blktrace/blktrace_git.bb:

     SRCREV = "d6918c8832793b4205ed3bfede78c2f915c23385"

     PR = "r6"
     PV = "1.0.5+git${SRCPV}"

     SRC_URI = "git://git.kernel.dk/blktrace.git \
                file://ldflags.patch"
                

If your SRC_URI statement includes URLs pointing to individual files fetched from a remote server other than a version control system, BitBake attempts to verify the files against checksums defined in your recipe to ensure they have not been tampered with or otherwise modified since the recipe was written. Two checksums are used: SRC_URI[md5sum] and SRC_URI[sha256sum].

If your SRC_URI variable points to more than a single URL (excluding SCM URLs), you need to provide the md5 and sha256 checksums for each URL. For these cases, you provide a name for each URL as part of the SRC_URI and then reference that name in the subsequent checksum statements. Here is an example:

     SRC_URI = "${DEBIAN_MIRROR}/main/a/apmd/apmd_3.2.2.orig.tar.gz;name=tarball \
                ${DEBIAN_MIRROR}/main/a/apmd/apmd_${PV}.diff.gz;name=patch"

     SRC_URI[tarball.md5sum] = "b1e6309e8331e0f4e6efd311c2d97fa8"
     SRC_URI[tarball.sha256sum] = "7f7d9f60b7766b852881d40b8ff91d8e39fccb0d1d913102a5c75a2dbb52332d"

     SRC_URI[patch.md5sum] = "57e1b689264ea80f78353519eece0c92"
     SRC_URI[patch.sha256sum] = "7905ff96be93d725544d0040e425c42f9c05580db3c272f11cff75b9aa89d430"
                

Proper values for md5 and sha256 checksums might be available with other signatures on the download page for the upstream source (e.g. md5, sha1, sha256, GPG, and so forth). Because the OpenEmbedded build system only deals with sha256sum and md5sum, you should verify all the signatures you find by hand.

If no SRC_URI checksums are specified when you attempt to build the recipe, or you provide an incorrect checksum, the build will produce an error for each missing or incorrect checksum. As part of the error message, the build system provides the checksum string corresponding to the fetched file. Once you have the correct checksums, you can copy and paste them into your recipe and then run the build again to continue.

Note

As mentioned, if the upstream source provides signatures for verifying the downloaded source code, you should verify those manually before setting the checksum values in the recipe and continuing with the build.

This final example is a bit more complicated and is from the meta/recipes-sato/rxvt-unicode/rxvt-unicode_9.20.bb recipe. The example's SRC_URI statement identifies multiple files as the source files for the recipe: a tarball, a patch file, a desktop file, and an icon.

     SRC_URI = "http://dist.schmorp.de/rxvt-unicode/Attic/rxvt-unicode-${PV}.tar.bz2 \
                file://xwc.patch \
                file://rxvt.desktop \
                file://rxvt.png"
                

When you specify local files using the file:// URI protocol, the build system fetches files from the local machine. The path is relative to the FILESPATH variable and searches specific directories in a certain order: ${BP}, ${BPN}, and files. The directories are assumed to be subdirectories of the directory in which the recipe or append file resides. For another example that specifies these types of files, see the "Single .c File Package (Hello World!)" section.

The previous example also specifies a patch file. Patch files are files whose names usually end in .patch or .diff but can end with compressed suffixes such as diff.gz and patch.bz2, for example. The build system automatically applies patches as described in the "Patching Code" section.

7.3.6. Unpacking Code

During the build, the do_unpack task unpacks the source with ${S} pointing to where it is unpacked.

If you are fetching your source files from an upstream source archived tarball and the tarball's internal structure matches the common convention of a top-level subdirectory named ${BPN}-${PV}, then you do not need to set S. However, if SRC_URI specifies to fetch source from an archive that does not use this convention, or from an SCM like Git or Subversion, your recipe needs to define S.

If processing your recipe using BitBake successfully unpacks the source files, you need to be sure that the directory pointed to by ${S} matches the structure of the source.

7.3.7. Patching Code

Sometimes it is necessary to patch code after it has been fetched. Any files mentioned in SRC_URI whose names end in .patch or .diff or compressed versions of these suffixes (e.g. diff.gz are treated as patches. The do_patch task automatically applies these patches.

The build system should be able to apply patches with the "-p1" option (i.e. one directory level in the path will be stripped off). If your patch needs to have more directory levels stripped off, specify the number of levels using the "striplevel" option in the SRC_URI entry for the patch. Alternatively, if your patch needs to be applied in a specific subdirectory that is not specified in the patch file, use the "patchdir" option in the entry.

As with all local files referenced in SRC_URI using file://, you should place patch files in a directory next to the recipe either named the same as the base name of the recipe (BP and BPN) or "files".

7.3.8. Licensing

Your recipe needs to have both the LICENSE and LIC_FILES_CHKSUM variables:

  • LICENSE: This variable specifies the license for the software. If you do not know the license under which the software you are building is distributed, you should go to the source code and look for that information. Typical files containing this information include COPYING, LICENSE, and README files. You could also find the information near the top of a source file. For example, given a piece of software licensed under the GNU General Public License version 2, you would set LICENSE as follows:

         LICENSE = "GPLv2"
                            

    The licenses you specify within LICENSE can have any name as long as you do not use spaces, since spaces are used as separators between license names. For standard licenses, use the names of the files in meta/files/common-licenses/ or the SPDXLICENSEMAP flag names defined in meta/conf/licenses.conf.

  • LIC_FILES_CHKSUM: The OpenEmbedded build system uses this variable to make sure the license text has not changed. If it has, the build produces an error and it affords you the chance to figure it out and correct the problem.

    You need to specify all applicable licensing files for the software. At the end of the configuration step, the build process will compare the checksums of the files to be sure the text has not changed. Any differences result in an error with the message containing the current checksum. For more explanation and examples of how to set the LIC_FILES_CHKSUM variable, see the "Tracking License Changes" section.

    To determine the correct checksum string, you can list the appropriate files in the LIC_FILES_CHKSUM variable with incorrect md5 strings, attempt to build the software, and then note the resulting error messages that will report the correct md5 strings. See the "Fetching Code" section for additional information.

    Here is an example that assumes the software has a COPYING file:

         LIC_FILES_CHKSUM = "file://COPYING;md5=xxx"
                            

    When you try to build the software, the build system will produce an error and give you the correct string that you can substitute into the recipe file for a subsequent build.

7.3.9. Dependencies

Most software packages have a short list of other packages that they require, which are called dependencies. These dependencies fall into two main categories: build-time dependencies, which are required when the software is built; and runtime dependencies, which are required to be installed on the target in order for the software to run.

Within a recipe, you specify build-time dependencies using the DEPENDS variable. Although nuances exist, items specified in DEPENDS should be names of other recipes. It is important that you specify all build-time dependencies explicitly. If you do not, due to the parallel nature of BitBake's execution, you can end up with a race condition where the dependency is present for one task of a recipe (e.g. do_configure) and then gone when the next task runs (e.g. do_compile).

Another consideration is that configure scripts might automatically check for optional dependencies and enable corresponding functionality if those dependencies are found. This behavior means that to ensure deterministic results and thus avoid more race conditions, you need to either explicitly specify these dependencies as well, or tell the configure script explicitly to disable the functionality. If you wish to make a recipe that is more generally useful (e.g. publish the recipe in a layer for others to use), instead of hard-disabling the functionality, you can use the PACKAGECONFIG variable to allow functionality and the corresponding dependencies to be enabled and disabled easily by other users of the recipe.

Similar to build-time dependencies, you specify runtime dependencies through a variable - RDEPENDS, which is package-specific. All variables that are package-specific need to have the name of the package added to the end as an override. Since the main package for a recipe has the same name as the recipe, and the recipe's name can be found through the ${PN} variable, then you specify the dependencies for the main package by setting RDEPENDS_${PN}. If the package were named ${PN}-tools, then you would set RDEPENDS_${PN}-tools, and so forth.

Some runtime dependencies will be set automatically at packaging time. These dependencies include any shared library dependencies (i.e. if a package "example" contains "libexample" and another package "mypackage" contains a binary that links to "libexample" then the OpenEmbedded build system will automatically add a runtime dependency to "mypackage" on "example"). See the "Automatically Added Runtime Dependencies" section in the Yocto Project Overview and Concepts Manual for further details.

7.3.10. Configuring the Recipe

Most software provides some means of setting build-time configuration options before compilation. Typically, setting these options is accomplished by running a configure script with some options, or by modifying a build configuration file.

Note

As of Yocto Project Release 1.7, some of the core recipes that package binary configuration scripts now disable the scripts due to the scripts previously requiring error-prone path substitution. The OpenEmbedded build system uses pkg-config now, which is much more robust. You can find a list of the *-config scripts that are disabled list in the "Binary Configuration Scripts Disabled" section in the Yocto Project Reference Manual.

A major part of build-time configuration is about checking for build-time dependencies and possibly enabling optional functionality as a result. You need to specify any build-time dependencies for the software you are building in your recipe's DEPENDS value, in terms of other recipes that satisfy those dependencies. You can often find build-time or runtime dependencies described in the software's documentation.

The following list provides configuration items of note based on how your software is built:

  • Autotools: If your source files have a configure.ac file, then your software is built using Autotools. If this is the case, you just need to worry about modifying the configuration.

    When using Autotools, your recipe needs to inherit the autotools class and your recipe does not have to contain a do_configure task. However, you might still want to make some adjustments. For example, you can set EXTRA_OECONF or PACKAGECONFIG_CONFARGS to pass any needed configure options that are specific to the recipe.

  • CMake: If your source files have a CMakeLists.txt file, then your software is built using CMake. If this is the case, you just need to worry about modifying the configuration.

    When you use CMake, your recipe needs to inherit the cmake class and your recipe does not have to contain a do_configure task. You can make some adjustments by setting EXTRA_OECMAKE to pass any needed configure options that are specific to the recipe.

  • Other: If your source files do not have a configure.ac or CMakeLists.txt file, then your software is built using some method other than Autotools or CMake. If this is the case, you normally need to provide a do_configure task in your recipe unless, of course, there is nothing to configure.

    Even if your software is not being built by Autotools or CMake, you still might not need to deal with any configuration issues. You need to determine if configuration is even a required step. You might need to modify a Makefile or some configuration file used for the build to specify necessary build options. Or, perhaps you might need to run a provided, custom configure script with the appropriate options.

    For the case involving a custom configure script, you would run ./configure --help and look for the options you need to set.

Once configuration succeeds, it is always good practice to look at the log.do_configure file to ensure that the appropriate options have been enabled and no additional build-time dependencies need to be added to DEPENDS. For example, if the configure script reports that it found something not mentioned in DEPENDS, or that it did not find something that it needed for some desired optional functionality, then you would need to add those to DEPENDS. Looking at the log might also reveal items being checked for, enabled, or both that you do not want, or items not being found that are in DEPENDS, in which case you would need to look at passing extra options to the configure script as needed. For reference information on configure options specific to the software you are building, you can consult the output of the ./configure --help command within ${S} or consult the software's upstream documentation.

7.3.11. Using Headers to Interface with Devices

If your recipe builds an application that needs to communicate with some device or needs an API into a custom kernel, you will need to provide appropriate header files. Under no circumstances should you ever modify the existing meta/recipes-kernel/linux-libc-headers/linux-libc-headers.inc file. These headers are used to build libc and must not be compromised with custom or machine-specific header information. If you customize libc through modified headers all other applications that use libc thus become affected.

Warning

Never copy and customize the libc header file (i.e. meta/recipes-kernel/linux-libc-headers/linux-libc-headers.inc).

The correct way to interface to a device or custom kernel is to use a separate package that provides the additional headers for the driver or other unique interfaces. When doing so, your application also becomes responsible for creating a dependency on that specific provider.

Consider the following:

  • Never modify linux-libc-headers.inc. Consider that file to be part of the libc system, and not something you use to access the kernel directly. You should access libc through specific libc calls.

  • Applications that must talk directly to devices should either provide necessary headers themselves, or establish a dependency on a special headers package that is specific to that driver.

For example, suppose you want to modify an existing header that adds I/O control or network support. If the modifications are used by a small number programs, providing a unique version of a header is easy and has little impact. When doing so, bear in mind the guidelines in the previous list.

Note

If for some reason your changes need to modify the behavior of the libc, and subsequently all other applications on the system, use a .bbappend to modify the linux-kernel-headers.inc file. However, take care to not make the changes machine specific.

Consider a case where your kernel is older and you need an older libc ABI. The headers installed by your recipe should still be a standard mainline kernel, not your own custom one.

When you use custom kernel headers you need to get them from STAGING_KERNEL_DIR, which is the directory with kernel headers that are required to build out-of-tree modules. Your recipe will also need the following:

     do_configure[depends] += "virtual/kernel:do_shared_workdir"
                

7.3.12. Compilation

During a build, the do_compile task happens after source is fetched, unpacked, and configured. If the recipe passes through do_compile successfully, nothing needs to be done.

However, if the compile step fails, you need to diagnose the failure. Here are some common issues that cause failures.

Note

For cases where improper paths are detected for configuration files or for when libraries/headers cannot be found, be sure you are using the more robust pkg-config. See the note in section "Configuring the Recipe" for additional information.

  • Parallel build failures: These failures manifest themselves as intermittent errors, or errors reporting that a file or directory that should be created by some other part of the build process could not be found. This type of failure can occur even if, upon inspection, the file or directory does exist after the build has failed, because that part of the build process happened in the wrong order.

    To fix the problem, you need to either satisfy the missing dependency in the Makefile or whatever script produced the Makefile, or (as a workaround) set PARALLEL_MAKE to an empty string:

         PARALLEL_MAKE = ""
                            

    For information on parallel Makefile issues, see the "Debugging Parallel Make Races" section.

  • Improper host path usage: This failure applies to recipes building for the target or nativesdk only. The failure occurs when the compilation process uses improper headers, libraries, or other files from the host system when cross-compiling for the target.

    To fix the problem, examine the log.do_compile file to identify the host paths being used (e.g. /usr/include, /usr/lib, and so forth) and then either add configure options, apply a patch, or do both.

  • Failure to find required libraries/headers: If a build-time dependency is missing because it has not been declared in DEPENDS, or because the dependency exists but the path used by the build process to find the file is incorrect and the configure step did not detect it, the compilation process could fail. For either of these failures, the compilation process notes that files could not be found. In these cases, you need to go back and add additional options to the configure script as well as possibly add additional build-time dependencies to DEPENDS.

    Occasionally, it is necessary to apply a patch to the source to ensure the correct paths are used. If you need to specify paths to find files staged into the sysroot from other recipes, use the variables that the OpenEmbedded build system provides (e.g. STAGING_BINDIR, STAGING_INCDIR, STAGING_DATADIR, and so forth).

7.3.13. Installing

During do_install, the task copies the built files along with their hierarchy to locations that would mirror their locations on the target device. The installation process copies files from the ${S}, ${B}, and ${WORKDIR} directories to the ${D} directory to create the structure as it should appear on the target system.

How your software is built affects what you must do to be sure your software is installed correctly. The following list describes what you must do for installation depending on the type of build system used by the software being built:

  • Autotools and CMake: If the software your recipe is building uses Autotools or CMake, the OpenEmbedded build system understands how to install the software. Consequently, you do not have to have a do_install task as part of your recipe. You just need to make sure the install portion of the build completes with no issues. However, if you wish to install additional files not already being installed by make install, you should do this using a do_install_append function using the install command as described in the "Manual" bulleted item later in this list.

  • Other (using make install): You need to define a do_install function in your recipe. The function should call oe_runmake install and will likely need to pass in the destination directory as well. How you pass that path is dependent on how the Makefile being run is written (e.g. DESTDIR=${D}, PREFIX=${D}, INSTALLROOT=${D}, and so forth).

    For an example recipe using make install, see the "Makefile-Based Package" section.

  • Manual: You need to define a do_install function in your recipe. The function must first use install -d to create the directories under ${D}. Once the directories exist, your function can use install to manually install the built software into the directories.

    You can find more information on install at http://www.gnu.org/software/coreutils/manual/html_node/install-invocation.html.

For the scenarios that do not use Autotools or CMake, you need to track the installation and diagnose and fix any issues until everything installs correctly. You need to look in the default location of ${D}, which is ${WORKDIR}/image, to be sure your files have been installed correctly.

Notes

  • During the installation process, you might need to modify some of the installed files to suit the target layout. For example, you might need to replace hard-coded paths in an initscript with values of variables provided by the build system, such as replacing /usr/bin/ with ${bindir}. If you do perform such modifications during do_install, be sure to modify the destination file after copying rather than before copying. Modifying after copying ensures that the build system can re-execute do_install if needed.

  • oe_runmake install, which can be run directly or can be run indirectly by the autotools and cmake classes, runs make install in parallel. Sometimes, a Makefile can have missing dependencies between targets that can result in race conditions. If you experience intermittent failures during do_install, you might be able to work around them by disabling parallel Makefile installs by adding the following to the recipe:

         PARALLEL_MAKEINST = ""
                            

    See PARALLEL_MAKEINST for additional information.

7.3.14. Enabling System Services

If you want to install a service, which is a process that usually starts on boot and runs in the background, then you must include some additional definitions in your recipe.

If you are adding services and the service initialization script or the service file itself is not installed, you must provide for that installation in your recipe using a do_install_append function. If your recipe already has a do_install function, update the function near its end rather than adding an additional do_install_append function.

When you create the installation for your services, you need to accomplish what is normally done by make install. In other words, make sure your installation arranges the output similar to how it is arranged on the target system.

The OpenEmbedded build system provides support for starting services two different ways:

  • SysVinit: SysVinit is a system and service manager that manages the init system used to control the very basic functions of your system. The init program is the first program started by the Linux kernel when the system boots. Init then controls the startup, running and shutdown of all other programs.

    To enable a service using SysVinit, your recipe needs to inherit the update-rc.d class. The class helps facilitate safely installing the package on the target.

    You will need to set the INITSCRIPT_PACKAGES, INITSCRIPT_NAME, and INITSCRIPT_PARAMS variables within your recipe.

  • systemd: System Management Daemon (systemd) was designed to replace SysVinit and to provide enhanced management of services. For more information on systemd, see the systemd homepage at http://freedesktop.org/wiki/Software/systemd/.

    To enable a service using systemd, your recipe needs to inherit the systemd class. See the systemd.bbclass file located in your Source Directory. section for more information.

7.3.15. Packaging

Successful packaging is a combination of automated processes performed by the OpenEmbedded build system and some specific steps you need to take. The following list describes the process:

  • Splitting Files: The do_package task splits the files produced by the recipe into logical components. Even software that produces a single binary might still have debug symbols, documentation, and other logical components that should be split out. The do_package task ensures that files are split up and packaged correctly.

  • Running QA Checks: The insane class adds a step to the package generation process so that output quality assurance checks are generated by the OpenEmbedded build system. This step performs a range of checks to be sure the build's output is free of common problems that show up during runtime. For information on these checks, see the insane class and the "QA Error and Warning Messages" chapter in the Yocto Project Reference Manual.

  • Hand-Checking Your Packages: After you build your software, you need to be sure your packages are correct. Examine the ${WORKDIR}/packages-split directory and make sure files are where you expect them to be. If you discover problems, you can set PACKAGES, FILES, do_install(_append), and so forth as needed.

  • Splitting an Application into Multiple Packages: If you need to split an application into several packages, see the "Splitting an Application into Multiple Packages" section for an example.

  • Installing a Post-Installation Script: For an example showing how to install a post-installation script, see the "Post-Installation Scripts" section.

  • Marking Package Architecture: Depending on what your recipe is building and how it is configured, it might be important to mark the packages produced as being specific to a particular machine, or to mark them as not being specific to a particular machine or architecture at all.

    By default, packages apply to any machine with the same architecture as the target machine. When a recipe produces packages that are machine-specific (e.g. the MACHINE value is passed into the configure script or a patch is applied only for a particular machine), you should mark them as such by adding the following to the recipe:

         PACKAGE_ARCH = "${MACHINE_ARCH}"
                            

    On the other hand, if the recipe produces packages that do not contain anything specific to the target machine or architecture at all (e.g. recipes that simply package script files or configuration files), you should use the allarch class to do this for you by adding this to your recipe:

         inherit allarch
                            

    Ensuring that the package architecture is correct is not critical while you are doing the first few builds of your recipe. However, it is important in order to ensure that your recipe rebuilds (or does not rebuild) appropriately in response to changes in configuration, and to ensure that you get the appropriate packages installed on the target machine, particularly if you run separate builds for more than one target machine.

7.3.16. Sharing Files Between Recipes

Recipes often need to use files provided by other recipes on the build host. For example, an application linking to a common library needs access to the library itself and its associated headers. The way this access is accomplished is by populating a sysroot with files. Each recipe has two sysroots in its work directory, one for target files (recipe-sysroot) and one for files that are native to the build host (recipe-sysroot-native).

Note

You could find the term "staging" used within the Yocto project regarding files populating sysroots (e.g. the STAGING_DIR variable).

Recipes should never populate the sysroot directly (i.e. write files into sysroot). Instead, files should be installed into standard locations during the do_install task within the ${D} directory. The reason for this limitation is that almost all files that populate the sysroot are cataloged in manifests in order to ensure the files can be removed later when a recipe is either modified or removed. Thus, the sysroot is able to remain free from stale files.

A subset of the files installed by the do_install task are used by the do_populate_sysroot task as defined by the the SYSROOT_DIRS variable to automatically populate the sysroot. It is possible to modify the list of directories that populate the sysroot. The following example shows how you could add the /opt directory to the list of directories within a recipe:

     SYSROOT_DIRS += "/opt"
                

For a more complete description of the do_populate_sysroot task and its associated functions, see the staging class.

7.3.17. Using Virtual Providers

Prior to a build, if you know that several different recipes provide the same functionality, you can use a virtual provider (i.e. virtual/*) as a placeholder for the actual provider. The actual provider is determined at build-time.

A common scenario where a virtual provider is used would be for the kernel recipe. Suppose you have three kernel recipes whose PN values map to kernel-big, kernel-mid, and kernel-small. Furthermore, each of these recipes in some way uses a PROVIDES statement that essentially identifies itself as being able to provide virtual/kernel. Here is one way through the kernel class:

     PROVIDES += "${@ "virtual/kernel" if (d.getVar("KERNEL_PACKAGE_NAME") == "kernel") else "" }"
                

Any recipe that inherits the kernel class is going to utilize a PROVIDES statement that identifies that recipe as being able to provide the virtual/kernel item.

Now comes the time to actually build an image and you need a kernel recipe, but which one? You can configure your build to call out the kernel recipe you want by using the PREFERRED_PROVIDER variable. As an example, consider the x86-base.inc include file, which is a machine (i.e. MACHINE) configuration file. This include file is the reason all x86-based machines use the linux-yocto kernel. Here are the relevant lines from the include file:

     PREFERRED_PROVIDER_virtual/kernel ??= "linux-yocto"
     PREFERRED_VERSION_linux-yocto ??= "4.15%"
                

When you use a virtual provider, you do not have to "hard code" a recipe name as a build dependency. You can use the DEPENDS variable to state the build is dependent on virtual/kernel for example:

     DEPENDS = "virtual/kernel"
                

During the build, the OpenEmbedded build system picks the correct recipe needed for the virtual/kernel dependency based on the PREFERRED_PROVIDER variable. If you want to use the small kernel mentioned at the beginning of this section, configure your build as follows:

     PREFERRED_PROVIDER_virtual/kernel ??= "kernel-small"
                

Note

Any recipe that PROVIDES a virtual/* item that is ultimately not selected through PREFERRED_PROVIDER does not get built. Preventing these recipes from building is usually the desired behavior since this mechanism's purpose is to select between mutually exclusive alternative providers.

The following lists specific examples of virtual providers:

  • virtual/kernel: Provides the name of the kernel recipe to use when building a kernel image.

  • virtual/bootloader: Provides the name of the bootloader to use when building an image.

  • virtual/mesa: Provides gbm.pc.

  • virtual/egl: Provides egl.pc and possibly wayland-egl.pc.

  • virtual/libgl: Provides gl.pc (i.e. libGL).

  • virtual/libgles1: Provides glesv1_cm.pc (i.e. libGLESv1_CM).

  • virtual/libgles2: Provides glesv2.pc (i.e. libGLESv2).

7.3.18. Properly Versioning Pre-Release Recipes

Sometimes the name of a recipe can lead to versioning problems when the recipe is upgraded to a final release. For example, consider the irssi_0.8.16-rc1.bb recipe file in the list of example recipes in the "Storing and Naming the Recipe" section. This recipe is at a release candidate stage (i.e. "rc1"). When the recipe is released, the recipe filename becomes irssi_0.8.16.bb. The version change from 0.8.16-rc1 to 0.8.16 is seen as a decrease by the build system and package managers, so the resulting packages will not correctly trigger an upgrade.

In order to ensure the versions compare properly, the recommended convention is to set PV within the recipe to "previous_version+current_version". You can use an additional variable so that you can use the current version elsewhere. Here is an example:

     REALPV = "0.8.16-rc1"
     PV = "0.8.15+${REALPV}"
                

7.3.19. Post-Installation Scripts

Post-installation scripts run immediately after installing a package on the target or during image creation when a package is included in an image. To add a post-installation script to a package, add a pkg_postinst_PACKAGENAME() function to the recipe file (.bb) and replace PACKAGENAME with the name of the package you want to attach to the postinst script. To apply the post-installation script to the main package for the recipe, which is usually what is required, specify ${PN} in place of PACKAGENAME.

A post-installation function has the following structure:

     pkg_postinst_PACKAGENAME() {
     # Commands to carry out
     }
                

The script defined in the post-installation function is called when the root filesystem is created. If the script succeeds, the package is marked as installed. If the script fails, the package is marked as unpacked and the script is executed when the image boots again.

Note

Any RPM post-installation script that runs on the target should return a 0 exit code. RPM does not allow non-zero exit codes for these scripts, and the RPM package manager will cause the package to fail installation on the target.

Sometimes it is necessary for the execution of a post-installation script to be delayed until the first boot. For example, the script might need to be executed on the device itself. To delay script execution until boot time, use the following structure in the post-installation script:

     pkg_postinst_PACKAGENAME() {
     if [ x"$D" = "x" ]; then
          # Actions to carry out on the device go here
     else
          exit 1
     fi
     }
                

The previous example delays execution until the image boots again because the environment variable D points to the directory containing the image when the root filesystem is created at build time but is unset when executed on the first boot.

If you have recipes that use pkg_postinst scripts and they require the use of non-standard native tools that have dependencies during rootfs construction, you need to use the PACKAGE_WRITE_DEPS variable in your recipe to list these tools. If you do not use this variable, the tools might be missing and execution of the post-installation script is deferred until first boot. Deferring the script to first boot is undesirable and for read-only rootfs impossible.

Note

Equivalent support for pre-install, pre-uninstall, and post-uninstall scripts exist by way of pkg_preinst, pkg_prerm, and pkg_postrm, respectively. These scrips work in exactly the same way as does pkg_postinst with the exception that they run at different times. Also, because of when they run, they are not applicable to being run at image creation time like pkg_postinst.

7.3.20. Testing

The final step for completing your recipe is to be sure that the software you built runs correctly. To accomplish runtime testing, add the build's output packages to your image and test them on the target.

For information on how to customize your image by adding specific packages, see the "Customizing Images" section.

7.3.21. Examples

To help summarize how to write a recipe, this section provides some examples given various scenarios:

  • Recipes that use local files

  • Using an Autotooled package

  • Using a Makefile-based package

  • Splitting an application into multiple packages

  • Adding binaries to an image

7.3.21.1. Single .c File Package (Hello World!)

Building an application from a single file that is stored locally (e.g. under files) requires a recipe that has the file listed in the SRC_URI variable. Additionally, you need to manually write the do_compile and do_install tasks. The S variable defines the directory containing the source code, which is set to WORKDIR in this case - the directory BitBake uses for the build.

     SUMMARY = "Simple helloworld application"
     SECTION = "examples"
     LICENSE = "MIT"
     LIC_FILES_CHKSUM = "file://${COMMON_LICENSE_DIR}/MIT;md5=0835ade698e0bcf8506ecda2f7b4f302"

     SRC_URI = "file://helloworld.c"

     S = "${WORKDIR}"

     do_compile() {
     	${CC} helloworld.c -o helloworld
     }

     do_install() {
     	install -d ${D}${bindir}
     	install -m 0755 helloworld ${D}${bindir}
     }
                    

By default, the helloworld, helloworld-dbg, and helloworld-dev packages are built. For information on how to customize the packaging process, see the "Splitting an Application into Multiple Packages" section.

7.3.21.2. Autotooled Package

Applications that use Autotools such as autoconf and automake require a recipe that has a source archive listed in SRC_URI and also inherit the autotools class, which contains the definitions of all the steps needed to build an Autotool-based application. The result of the build is automatically packaged. And, if the application uses NLS for localization, packages with local information are generated (one package per language). Following is one example: (hello_2.3.bb)

     SUMMARY = "GNU Helloworld application"
     SECTION = "examples"
     LICENSE = "GPLv2+"
     LIC_FILES_CHKSUM = "file://COPYING;md5=751419260aa954499f7abaabaa882bbe"

     SRC_URI = "${GNU_MIRROR}/hello/hello-${PV}.tar.gz"

     inherit autotools gettext
                     

The variable LIC_FILES_CHKSUM is used to track source license changes as described in the "Tracking License Changes" section in the Yocto Project Overview and Concepts Manual. You can quickly create Autotool-based recipes in a manner similar to the previous example.

7.3.21.3. Makefile-Based Package

Applications that use GNU make also require a recipe that has the source archive listed in SRC_URI. You do not need to add a do_compile step since by default BitBake starts the make command to compile the application. If you need additional make options, you should store them in the EXTRA_OEMAKE or PACKAGECONFIG_CONFARGS variables. BitBake passes these options into the GNU make invocation. Note that a do_install task is still required. Otherwise, BitBake runs an empty do_install task by default.

Some applications might require extra parameters to be passed to the compiler. For example, the application might need an additional header path. You can accomplish this by adding to the CFLAGS variable. The following example shows this:

     CFLAGS_prepend = "-I ${S}/include "
                    

In the following example, mtd-utils is a makefile-based package:

     SUMMARY = "Tools for managing memory technology devices"
     SECTION = "base"
     DEPENDS = "zlib lzo e2fsprogs util-linux"
     HOMEPAGE = "http://www.linux-mtd.infradead.org/"
     LICENSE = "GPLv2+"
     LIC_FILES_CHKSUM = "file://COPYING;md5=0636e73ff0215e8d672dc4c32c317bb3 \
                         file://include/common.h;beginline=1;endline=17;md5=ba05b07912a44ea2bf81ce409380049c"

     # Use the latest version at 26 Oct, 2013
     SRCREV = "9f107132a6a073cce37434ca9cda6917dd8d866b"
     SRC_URI = "git://git.infradead.org/mtd-utils.git \
                     file://add-exclusion-to-mkfs-jffs2-git-2.patch \
     "

     PV = "1.5.1+git${SRCPV}"

     S = "${WORKDIR}/git"

     EXTRA_OEMAKE = "'CC=${CC}' 'RANLIB=${RANLIB}' 'AR=${AR}' 'CFLAGS=${CFLAGS} -I${S}/include -DWITHOUT_XATTR' 'BUILDDIR=${S}'"

     do_install () {
             oe_runmake install DESTDIR=${D} SBINDIR=${sbindir} MANDIR=${mandir} INCLUDEDIR=${includedir}
     }

     PACKAGES =+ "mtd-utils-jffs2 mtd-utils-ubifs mtd-utils-misc"

     FILES_mtd-utils-jffs2 = "${sbindir}/mkfs.jffs2 ${sbindir}/jffs2dump ${sbindir}/jffs2reader ${sbindir}/sumtool"
     FILES_mtd-utils-ubifs = "${sbindir}/mkfs.ubifs ${sbindir}/ubi*"
     FILES_mtd-utils-misc = "${sbindir}/nftl* ${sbindir}/ftl* ${sbindir}/rfd* ${sbindir}/doc* ${sbindir}/serve_image ${sbindir}/recv_image"

     PARALLEL_MAKE = ""

     BBCLASSEXTEND = "native"
                    

7.3.21.4. Splitting an Application into Multiple Packages

You can use the variables PACKAGES and FILES to split an application into multiple packages.

Following is an example that uses the libxpm recipe. By default, this recipe generates a single package that contains the library along with a few binaries. You can modify the recipe to split the binaries into separate packages:

     require xorg-lib-common.inc

     SUMMARY = "Xpm: X Pixmap extension library"
     LICENSE = "BSD"
     LIC_FILES_CHKSUM = "file://COPYING;md5=51f4270b012ecd4ab1a164f5f4ed6cf7"
     DEPENDS += "libxext libsm libxt"
     PE = "1"

     XORG_PN = "libXpm"

     PACKAGES =+ "sxpm cxpm"
     FILES_cxpm = "${bindir}/cxpm"
     FILES_sxpm = "${bindir}/sxpm"
                    

In the previous example, we want to ship the sxpm and cxpm binaries in separate packages. Since bindir would be packaged into the main PN package by default, we prepend the PACKAGES variable so additional package names are added to the start of list. This results in the extra FILES_* variables then containing information that define which files and directories go into which packages. Files included by earlier packages are skipped by latter packages. Thus, the main PN package does not include the above listed files.

7.3.21.5. Packaging Externally Produced Binaries

Sometimes, you need to add pre-compiled binaries to an image. For example, suppose that binaries for proprietary code exist, which are created by a particular division of a company. Your part of the company needs to use those binaries as part of an image that you are building using the OpenEmbedded build system. Since you only have the binaries and not the source code, you cannot use a typical recipe that expects to fetch the source specified in SRC_URI and then compile it.

One method is to package the binaries and then install them as part of the image. Generally, it is not a good idea to package binaries since, among other things, it can hinder the ability to reproduce builds and could lead to compatibility problems with ABI in the future. However, sometimes you have no choice.

The easiest solution is to create a recipe that uses the bin_package class and to be sure that you are using default locations for build artifacts. In most cases, the bin_package class handles "skipping" the configure and compile steps as well as sets things up to grab packages from the appropriate area. In particular, this class sets noexec on both the do_configure and do_compile tasks, sets FILES_${PN} to "/" so that it picks up all files, and sets up a do_install task, which effectively copies all files from ${S} to ${D}. The bin_package class works well when the files extracted into ${S} are already laid out in the way they should be laid out on the target. For more information on these variables, see the FILES, PN, S, and D variables in the Yocto Project Reference Manual's variable glossary.

Notes

  • Using DEPENDS is a good idea even for components distributed in binary form, and is often necessary for shared libraries. For a shared library, listing the library dependencies in DEPENDS makes sure that the libraries are available in the staging sysroot when other recipes link against the library, which might be necessary for successful linking.

  • Using DEPENDS also allows runtime dependencies between packages to be added automatically. See the "Automatically Added Runtime Dependencies" section in the Yocto Project Overview and Concepts Manual for more information.

If you cannot use the bin_package class, you need to be sure you are doing the following:

  • Create a recipe where the do_configure and do_compile tasks do nothing: It is usually sufficient to just not define these tasks in the recipe, because the default implementations do nothing unless a Makefile is found in ${S}.

    If ${S} might contain a Makefile, or if you inherit some class that replaces do_configure and do_compile with custom versions, then you can use the [noexec] flag to turn the tasks into no-ops, as follows:

         do_configure[noexec] = "1"
         do_compile[noexec] = "1"
                                

    Unlike deleting the tasks, using the flag preserves the dependency chain from the do_fetch, do_unpack, and do_patch tasks to the do_install task.

  • Make sure your do_install task installs the binaries appropriately.

  • Ensure that you set up FILES (usually FILES_${PN}) to point to the files you have installed, which of course depends on where you have installed them and whether those files are in different locations than the defaults.

7.3.22. Following Recipe Style Guidelines

When writing recipes, it is good to conform to existing style guidelines. The OpenEmbedded Styleguide wiki page provides rough guidelines for preferred recipe style.

It is common for existing recipes to deviate a bit from this style. However, aiming for at least a consistent style is a good idea. Some practices, such as omitting spaces around = operators in assignments or ordering recipe components in an erratic way, are widely seen as poor style.

7.3.23. Recipe Syntax

Understanding recipe file syntax is important for writing recipes. The following list overviews the basic items that make up a BitBake recipe file. For more complete BitBake syntax descriptions, see the "Syntax and Operators" chapter of the BitBake User Manual.

  • Variable Assignments and Manipulations: Variable assignments allow a value to be assigned to a variable. The assignment can be static text or might include the contents of other variables. In addition to the assignment, appending and prepending operations are also supported.

    The following example shows some of the ways you can use variables in recipes:

         S = "${WORKDIR}/postfix-${PV}"
         CFLAGS += "-DNO_ASM"
         SRC_URI_append = " file://fixup.patch"
                            

  • Functions: Functions provide a series of actions to be performed. You usually use functions to override the default implementation of a task function or to complement a default function (i.e. append or prepend to an existing function). Standard functions use sh shell syntax, although access to OpenEmbedded variables and internal methods are also available.

    The following is an example function from the sed recipe:

         do_install () {
             autotools_do_install
             install -d ${D}${base_bindir}
             mv ${D}${bindir}/sed ${D}${base_bindir}/sed
             rmdir ${D}${bindir}/
         }
                            

    It is also possible to implement new functions that are called between existing tasks as long as the new functions are not replacing or complementing the default functions. You can implement functions in Python instead of shell. Both of these options are not seen in the majority of recipes.

  • Keywords: BitBake recipes use only a few keywords. You use keywords to include common functions (inherit), load parts of a recipe from other files (include and require) and export variables to the environment (export).

    The following example shows the use of some of these keywords:

         export POSTCONF = "${STAGING_BINDIR}/postconf"
         inherit autoconf
         require otherfile.inc
                            

  • Comments (#): Any lines that begin with the hash character (#) are treated as comment lines and are ignored:

         # This is a comment
                            

This next list summarizes the most important and most commonly used parts of the recipe syntax. For more information on these parts of the syntax, you can reference the Syntax and Operators chapter in the BitBake User Manual.

  • Line Continuation (\): Use the backward slash (\) character to split a statement over multiple lines. Place the slash character at the end of the line that is to be continued on the next line:

         VAR = "A really long \
                line"
                            

    Note

    You cannot have any characters including spaces or tabs after the slash character.

  • Using Variables (${VARNAME}): Use the ${VARNAME} syntax to access the contents of a variable:

         SRC_URI = "${SOURCEFORGE_MIRROR}/libpng/zlib-${PV}.tar.gz"
                            

    Note

    It is important to understand that the value of a variable expressed in this form does not get substituted automatically. The expansion of these expressions happens on-demand later (e.g. usually when a function that makes reference to the variable executes). This behavior ensures that the values are most appropriate for the context in which they are finally used. On the rare occasion that you do need the variable expression to be expanded immediately, you can use the := operator instead of = when you make the assignment, but this is not generally needed.

  • Quote All Assignments ("value"): Use double quotes around values in all variable assignments (e.g. "value"). Following is an example:

         VAR1 = "${OTHERVAR}"
         VAR2 = "The version is ${PV}"
                            

  • Conditional Assignment (?=): Conditional assignment is used to assign a value to a variable, but only when the variable is currently unset. Use the question mark followed by the equal sign (?=) to make a "soft" assignment used for conditional assignment. Typically, "soft" assignments are used in the local.conf file for variables that are allowed to come through from the external environment.

    Here is an example where VAR1 is set to "New value" if it is currently empty. However, if VAR1 has already been set, it remains unchanged:

         VAR1 ?= "New value"
                            

    In this next example, VAR1 is left with the value "Original value":

         VAR1 = "Original value"
         VAR1 ?= "New value"
                            

  • Appending (+=): Use the plus character followed by the equals sign (+=) to append values to existing variables.

    Note

    This operator adds a space between the existing content of the variable and the new content.

    Here is an example:

         SRC_URI += "file://fix-makefile.patch"
                            

  • Prepending (=+): Use the equals sign followed by the plus character (=+) to prepend values to existing variables.

    Note

    This operator adds a space between the new content and the existing content of the variable.

    Here is an example:

         VAR =+ "Starts"
                            

  • Appending (_append): Use the _append operator to append values to existing variables. This operator does not add any additional space. Also, the operator is applied after all the +=, and =+ operators have been applied and after all = assignments have occurred.

    The following example shows the space being explicitly added to the start to ensure the appended value is not merged with the existing value:

         SRC_URI_append = " file://fix-makefile.patch"
                            

    You can also use the _append operator with overrides, which results in the actions only being performed for the specified target or machine:

         SRC_URI_append_sh4 = " file://fix-makefile.patch"
                            

  • Prepending (_prepend): Use the _prepend operator to prepend values to existing variables. This operator does not add any additional space. Also, the operator is applied after all the +=, and =+ operators have been applied and after all = assignments have occurred.

    The following example shows the space being explicitly added to the end to ensure the prepended value is not merged with the existing value:

         CFLAGS_prepend = "-I${S}/myincludes "
                            

    You can also use the _prepend operator with overrides, which results in the actions only being performed for the specified target or machine:

         CFLAGS_prepend_sh4 = "-I${S}/myincludes "
                            

  • Overrides: You can use overrides to set a value conditionally, typically based on how the recipe is being built. For example, to set the KBRANCH variable's value to "standard/base" for any target MACHINE, except for qemuarm where it should be set to "standard/arm-versatile-926ejs", you would do the following:

         KBRANCH = "standard/base"
         KBRANCH_qemuarm  = "standard/arm-versatile-926ejs"
                            

    Overrides are also used to separate alternate values of a variable in other situations. For example, when setting variables such as FILES and RDEPENDS that are specific to individual packages produced by a recipe, you should always use an override that specifies the name of the package.

  • Indentation: Use spaces for indentation rather than than tabs. For shell functions, both currently work. However, it is a policy decision of the Yocto Project to use tabs in shell functions. Realize that some layers have a policy to use spaces for all indentation.

  • Using Python for Complex Operations: For more advanced processing, it is possible to use Python code during variable assignments (e.g. search and replacement on a variable).

    You indicate Python code using the ${@python_code} syntax for the variable assignment:

         SRC_URI = "ftp://ftp.info-zip.org/pub/infozip/src/zip${@d.getVar('PV',1).replace('.', '')}.tgz
                            

  • Shell Function Syntax: Write shell functions as if you were writing a shell script when you describe a list of actions to take. You should ensure that your script works with a generic sh and that it does not require any bash or other shell-specific functionality. The same considerations apply to various system utilities (e.g. sed, grep, awk, and so forth) that you might wish to use. If in doubt, you should check with multiple implementations - including those from BusyBox.

7.4. Adding a New Machine

Adding a new machine to the Yocto Project is a straightforward process. This section describes how to add machines that are similar to those that the Yocto Project already supports.

Note

Although well within the capabilities of the Yocto Project, adding a totally new architecture might require changes to gcc/glibc and to the site information, which is beyond the scope of this manual.

For a complete example that shows how to add a new machine, see the "Creating a New BSP Layer Using the bitbake-layers Script" section in the Yocto Project Board Support Package (BSP) Developer's Guide.

7.4.1. Adding the Machine Configuration File

To add a new machine, you need to add a new machine configuration file to the layer's conf/machine directory. This configuration file provides details about the device you are adding.

The OpenEmbedded build system uses the root name of the machine configuration file to reference the new machine. For example, given a machine configuration file named crownbay.conf, the build system recognizes the machine as "crownbay".

The most important variables you must set in your machine configuration file or include from a lower-level configuration file are as follows:

You might also need these variables:

You can find full details on these variables in the reference section. You can leverage existing machine .conf files from meta-yocto-bsp/conf/machine/.

7.4.2. Adding a Kernel for the Machine

The OpenEmbedded build system needs to be able to build a kernel for the machine. You need to either create a new kernel recipe for this machine, or extend an existing kernel recipe. You can find several kernel recipe examples in the Source Directory at meta/recipes-kernel/linux that you can use as references.

If you are creating a new kernel recipe, normal recipe-writing rules apply for setting up a SRC_URI. Thus, you need to specify any necessary patches and set S to point at the source code. You need to create a do_configure task that configures the unpacked kernel with a defconfig file. You can do this by using a make defconfig command or, more commonly, by copying in a suitable defconfig file and then running make oldconfig. By making use of inherit kernel and potentially some of the linux-*.inc files, most other functionality is centralized and the defaults of the class normally work well.

If you are extending an existing kernel recipe, it is usually a matter of adding a suitable defconfig file. The file needs to be added into a location similar to defconfig files used for other machines in a given kernel recipe. A possible way to do this is by listing the file in the SRC_URI and adding the machine to the expression in COMPATIBLE_MACHINE:

     COMPATIBLE_MACHINE = '(qemux86|qemumips)'
                

For more information on defconfig files, see the "Changing the Configuration" section in the Yocto Project Linux Kernel Development Manual.

7.4.3. Adding a Formfactor Configuration File

A formfactor configuration file provides information about the target hardware for which the image is being built and information that the build system cannot obtain from other sources such as the kernel. Some examples of information contained in a formfactor configuration file include framebuffer orientation, whether or not the system has a keyboard, the positioning of the keyboard in relation to the screen, and the screen resolution.

The build system uses reasonable defaults in most cases. However, if customization is necessary, you need to create a machconfig file in the meta/recipes-bsp/formfactor/files directory. This directory contains directories for specific machines such as qemuarm and qemux86. For information about the settings available and the defaults, see the meta/recipes-bsp/formfactor/files/config file found in the same area.

Following is an example for "qemuarm" machine:

     HAVE_TOUCHSCREEN=1
     HAVE_KEYBOARD=1

     DISPLAY_CAN_ROTATE=0
     DISPLAY_ORIENTATION=0
     #DISPLAY_WIDTH_PIXELS=640
     #DISPLAY_HEIGHT_PIXELS=480
     #DISPLAY_BPP=16
     DISPLAY_DPI=150
     DISPLAY_SUBPIXEL_ORDER=vrgb
                

7.5. Upgrading Recipes

Over time, upstream developers publish new versions for software built by layer recipes. It is recommended to keep recipes up-to-date with upstream version releases. You can use the Automated Upgrade Helper (AUH) to set up automatic version upgrades. Alternatively, you can use devtool upgrade to set up semi-automatic version upgrades. Finally, you can even manually upgrade a recipe by editing the recipe itself.

7.5.1. Using the Auto Upgrade Helper (AUH)

The AUH utility works in conjunction with the OpenEmbedded build system in order to automatically generate upgrades for recipes based on new versions being published upstream. Use AUH when you want to create a service that performs the upgrades automatically and optionally sends you an email with the results.

AUH allows you to update several recipes with a single use. You can also optionally perform build and integration tests using images with the results saved to your hard drive and emails of results optionally sent to recipe maintainers. Finally, AUH creates Git commits with appropriate commit messages in the layer's tree for the changes made to recipes.

Note

Conditions do exist when you should not use AUH to upgrade recipes and you should instead use either devtool upgrade or upgrade your recipes manually:
  • When AUH cannot complete the upgrade sequence. This situation usually results because custom patches carried by the recipe cannot be automatically rebased to the new version. In this case, devtool upgrade allows you to manually resolve conflicts.

  • When for any reason you want fuller control over the upgrade process. For example, when you want special arrangements for testing.

The following steps describe how to set up the AUH utility:

  1. Be Sure the Development Host is Set Up: You need to be sure that your development host is set up to use the Yocto Project. For information on how to set up your host, see the "Preparing the Build Host" section.

  2. Make Sure Git is Configured: The AUH utility requires Git to be configured because AUH uses Git to save upgrades. Thus, you must have Git user and email configured. The following command shows your configurations:

         $ git config --list
                            

    If you do not have the user and email configured, you can use the following commands to do so:

         $ git config --global user.name some_name
         $ git config --global user.email username@domain.com
                            

  3. Clone the AUH Repository: To use AUH, you must clone the repository onto your development host. The following command uses Git to create a local copy of the repository on your system:

         $ git clone git://git.yoctoproject.org/auto-upgrade-helper
         Cloning into 'auto-upgrade-helper'...
         remote: Counting objects: 768, done.
         remote: Compressing objects: 100% (300/300), done.
         remote: Total 768 (delta 499), reused 703 (delta 434)
         Receiving objects: 100% (768/768), 191.47 KiB | 98.00 KiB/s, done.
         Resolving deltas: 100% (499/499), done.
         Checking connectivity... done.
                            

    AUH is not part of the OpenEmbedded-Core (OE-Core) or Poky repositories.

  4. Create a Dedicated Build Directory: Run the oe-init-build-env script to create a fresh build directory that you use exclusively for running the AUH utility:

         $ cd ~/poky
         $ source oe-init-build-env your_AUH_build_directory
                            

    Re-using an existing build directory and its configurations is not recommended as existing settings could cause AUH to fail or behave undesirably.

  5. Make Configurations in Your Local Configuration File: Several settings need to exist in the local.conf file in the build directory you just created for AUH. Make these following configurations:

    • Enable "distrodata" as follows:

           INHERIT =+ "distrodata"
                                      

    • If you want to enable Build History, which is optional, you need the following lines in the conf/local.conf file:

           INHERIT =+ "buildhistory"
           BUILDHISTORY_COMMIT = "1"
                                      

      With this configuration and a successful upgrade, a build history "diff" file appears in the upgrade-helper/work/recipe/buildhistory-diff.txt file found in your build directory.

    • If you want to enable testing through the testimage class, which is optional, you need to have the following set in your conf/local.conf file:

           INHERIT += "testimage"
                                      

      Note

      If your distro does not enable by default ptest, which Poky does, you need the following in your local.conf file:
           DISTRO_FEATURES_append = " ptest"
                                          

  6. Optionally Start a vncserver: If you are running in a server without an X11 session, you need to start a vncserver:

         $ vncserver :1
         $ export DISPLAY=:1
                            

  7. Create and Edit an AUH Configuration File: You need to have the upgrade-helper/upgrade-helper.conf configuration file in your build directory. You can find a sample configuration file in the AUH source repository.

    Read through the sample file and make configurations as needed. For example, if you enabled build history in your local.conf as described earlier, you must enable it in upgrade-helper.conf.

    Also, if you are using the default maintainers.inc file supplied with Poky and located in meta-yocto and you do not set a "maintainers_whitelist" or "global_maintainer_override" in the upgrade-helper.conf configuration, and you specify "-e all" on the AUH command-line, the utility automatically sends out emails to all the default maintainers. Please avoid this.

This next set of examples describes how to use the AUH:

  • Upgrading a Specific Recipe: To upgrade a specific recipe, use the following form:

         $ upgrade-helper.py recipe_name
                            

    For example, this command upgrades the xmodmap recipe:

         $ upgrade-helper.py xmodmap
                            

  • Upgrading a Specific Recipe to a Particular Version: To upgrade a specific recipe to a particular version, use the following form:

         $ upgrade-helper.py recipe_name -t version
                            

    For example, this command upgrades the xmodmap recipe to version 1.2.3:

         $ upgrade-helper.py xmodmap -t 1.2.3
                            

  • Upgrading all Recipes to the Latest Versions and Suppressing Email Notifications: To upgrade all recipes to their most recent versions and suppress the email notifications, use the following command:

         $ upgrade-helper.py all
                            

  • Upgrading all Recipes to the Latest Versions and Send Email Notifications: To upgrade all recipes to their most recent versions and send email messages to maintainers for each attempted recipe as well as a status email, use the following command:

         $ upgrade-helper.py -e all
                            

Once you have run the AUH utility, you can find the results in the AUH build directory:

     ${BUILDDIR}/upgrade-helper/timestamp
                

The AUH utility also creates recipe update commits from successful upgrade attempts in the layer tree.

You can easily set up to run the AUH utility on a regular basis by using a cron job. See the weeklyjob.sh file distributed with the utility for an example.

7.5.2. Using devtool upgrade

As mentioned earlier, an alternative method for upgrading recipes to newer versions is to use devtool upgrade. You can read about devtool upgrade in general in the "Use devtool upgrade to Create a Version of the Recipe that Supports a Newer Version of the Software" section in the Yocto Project Application Development and the Extensible Software Development Kit (eSDK) Manual.

To see all the command-line options available with devtool upgrade, use the following help command:

     $ devtool upgrade -h
                

If you want to find out what version a recipe is currently at upstream without any attempt to upgrade your local version of the recipe, you can use the following command:

     $ devtool latest-version recipe_name
                

As mentioned in the previous section describing AUH, devtool upgrade works in a less-automated manner than AUH. Specifically, devtool upgrade only works on a single recipe that you name on the command line, cannot perform build and integration testing using images, and does not automatically generate commits for changes in the source tree. Despite all these "limitations", devtool upgrade updates the recipe file to the new upstream version and attempts to rebase custom patches contained by the recipe as needed.

Note

AUH uses much of devtool upgrade behind the scenes making AUH somewhat of a "wrapper" application for devtool upgrade.

A typical scenario involves having used Git to clone an upstream repository that you use during build operations. Because you are (or have) built the recipe in the past, the layer is likely added to your configuration already. If for some reason, the layer is not added, you could add it easily using the bitbake-layers script. For example, suppose you use the nano.bb recipe from the meta-oe layer in the meta-openembedded repository. For this example, assume that the layer has been cloned into following area:

     /home/scottrif/meta-openembedded
                

The following command from your Build Directory adds the layer to your build configuration (i.e. ${BUILDDIR}/conf/bblayers.conf):

     $ bitbake-layers add-layer /home/scottrif/meta-openembedded/meta-oe
     NOTE: Starting bitbake server...
     Parsing recipes: 100% |##########################################| Time: 0:00:55
     Parsing of 1431 .bb files complete (0 cached, 1431 parsed). 2040 targets, 56 skipped, 0 masked, 0 errors.
     Removing 12 recipes from the x86_64 sysroot: 100% |##############| Time: 0:00:00
     Removing 1 recipes from the x86_64_i586 sysroot: 100% |##########| Time: 0:00:00
     Removing 5 recipes from the i586 sysroot: 100% |#################| Time: 0:00:00
     Removing 5 recipes from the qemux86 sysroot: 100% |##############| Time: 0:00:00
                

For this example, assume that the nano.bb recipe that is upstream has a 2.9.3 version number. However, the version in the local repository is 2.7.4. The following command from your build directory automatically upgrades the recipe for you:

Note

Using the -V option is not necessary. Omitting the version number causes devtool upgrade to upgrade the recipe to the most recent version.

     $ devtool upgrade nano -V 2.9.3
     NOTE: Starting bitbake server...
     NOTE: Creating workspace layer in /home/scottrif/poky/build/workspace
     Parsing recipes: 100% |##########################################| Time: 0:00:46
     Parsing of 1431 .bb files complete (0 cached, 1431 parsed). 2040 targets, 56 skipped, 0 masked, 0 errors.
     NOTE: Extracting current version source...
     NOTE: Resolving any missing task queue dependencies
            .
            .
            .
     NOTE: Executing SetScene Tasks
     NOTE: Executing RunQueue Tasks
     NOTE: Tasks Summary: Attempted 74 tasks of which 72 didn't need to be rerun and all succeeded.
     Adding changed files: 100% |#####################################| Time: 0:00:00
     NOTE: Upgraded source extracted to /home/scottrif/poky/build/workspace/sources/nano
     NOTE: New recipe is /home/scottrif/poky/build/workspace/recipes/nano/nano_2.9.3.bb
                

Continuing with this example, you can use devtool build to build the newly upgraded recipe:

     $ devtool build nano
     NOTE: Starting bitbake server...
     Loading cache: 100% |################################################################################################| Time: 0:00:01
     Loaded 2040 entries from dependency cache.
     Parsing recipes: 100% |##############################################################################################| Time: 0:00:00
     Parsing of 1432 .bb files complete (1431 cached, 1 parsed). 2041 targets, 56 skipped, 0 masked, 0 errors.
     NOTE: Resolving any missing task queue dependencies
            .
            .
            .
     NOTE: Executing SetScene Tasks
     NOTE: Executing RunQueue Tasks
     NOTE: nano: compiling from external source tree /home/scottrif/poky/build/workspace/sources/nano
     NOTE: Tasks Summary: Attempted 520 tasks of which 304 didn't need to be rerun and all succeeded.
                

Within the devtool upgrade workflow, opportunity exists to deploy and test your rebuilt software. For this example, however, running devtool finish cleans up the workspace once the source in your workspace is clean. This usually means using Git to stage and submit commits for the changes generated by the upgrade process.

Once the tree is clean, you can clean things up in this example with the following command from the ${BUILDDIR}/workspace/sources/nano directory:

     $ devtool finish nano meta-oe
     NOTE: Starting bitbake server...
     Loading cache: 100% |################################################################################################| Time: 0:00:00
     Loaded 2040 entries from dependency cache.
     Parsing recipes: 100% |##############################################################################################| Time: 0:00:01
     Parsing of 1432 .bb files complete (1431 cached, 1 parsed). 2041 targets, 56 skipped, 0 masked, 0 errors.
     NOTE: Adding new patch 0001-nano.bb-Stuff-I-changed-when-upgrading-nano.bb.patch
     NOTE: Updating recipe nano_2.9.3.bb
     NOTE: Removing file /home/scottrif/meta-openembedded/meta-oe/recipes-support/nano/nano_2.7.4.bb
     NOTE: Moving recipe file to /home/scottrif/meta-openembedded/meta-oe/recipes-support/nano
     NOTE: Leaving source tree /home/scottrif/poky/build/workspace/sources/nano as-is; if you no longer need it then please delete it manually
                

Using the devtool finish command cleans up the workspace and creates a patch file based on your commits. The tool puts all patch files back into the source directory in a sub-directory named nano in this case.

7.5.3. Manually Upgrading a Recipe

If for some reason you choose not to upgrade recipes using the Auto Upgrade Helper (AUH) or by using devtool upgrade, you can manually edit the recipe files to upgrade the versions.

Caution

Manually updating multiple recipes scales poorly and involves many steps. The recommendation to upgrade recipe versions is through AUH or devtool upgrade, both of which automate some steps and provide guidance for others needed for the manual process.

To manually upgrade recipe versions, follow these general steps:

  1. Change the Version: Rename the recipe such that the version (i.e. the PV part of the recipe name) changes appropriately. If the version is not part of the recipe name, change the value as it is set for PV within the recipe itself.

  2. Update SRCREV if Needed: If the source code your recipe builds is fetched from Git or some other version control system, update SRCREV to point to the commit hash that matches the new version.

  3. Build the Software: Try to build the recipe using BitBake. Typical build failures include the following:

    • License statements were updated for the new version. For this case, you need to review any changes to the license and update the values of LICENSE and LIC_FILES_CHKSUM as needed.

      Note

      License changes are often inconsequential. For example, the license text's copyright year might have changed.

    • Custom patches carried by the older version of the recipe might fail to apply to the new version. For these cases, you need to review the failures. Patches might not be necessary for the new version of the software if the upgraded version has fixed those issues. If a patch is necessary and failing, you need to rebase it into the new version.

  4. Optionally Attempt to Build for Several Architectures: Once you successfully build the new software for a given architecture, you could test the build for other architectures by changing the MACHINE variable and rebuilding the software. This optional step is especially important if the recipe is to be released publicly.

  5. Check the Upstream Change Log or Release Notes: Checking both these reveals if new features exist that could break backwards-compatibility. If so, you need to take steps to mitigate or eliminate that situation.

  6. Optionally Create a Bootable Image and Test: If you want, you can test the new software by booting it onto actual hardware.

  7. Create a Commit with the Change in the Layer Repository: After all builds work and any testing is successful, you can create commits for any changes in the layer holding your upgraded recipe.

7.6. Finding Temporary Source Code

You might find it helpful during development to modify the temporary source code used by recipes to build packages. For example, suppose you are developing a patch and you need to experiment a bit to figure out your solution. After you have initially built the package, you can iteratively tweak the source code, which is located in the Build Directory, and then you can force a re-compile and quickly test your altered code. Once you settle on a solution, you can then preserve your changes in the form of patches.

During a build, the unpacked temporary source code used by recipes to build packages is available in the Build Directory as defined by the S variable. Below is the default value for the S variable as defined in the meta/conf/bitbake.conf configuration file in the Source Directory:

     S = "${WORKDIR}/${BP}"
            

You should be aware that many recipes override the S variable. For example, recipes that fetch their source from Git usually set S to ${WORKDIR}/git.

Note

The BP represents the base recipe name, which consists of the name and version:
     BP = "${BPN}-${PV}"
                

The path to the work directory for the recipe (WORKDIR) is defined as follows:

     ${TMPDIR}/work/${MULTIMACH_TARGET_SYS}/${PN}/${EXTENDPE}${PV}-${PR}
            

The actual directory depends on several things:

  • TMPDIR: The top-level build output directory.

  • MULTIMACH_TARGET_SYS: The target system identifier.

  • PN: The recipe name.

  • EXTENDPE: The epoch - (if PE is not specified, which is usually the case for most recipes, then EXTENDPE is blank).

  • PV: The recipe version.

  • PR: The recipe revision.

As an example, assume a Source Directory top-level folder named poky, a default Build Directory at poky/build, and a qemux86-poky-linux machine target system. Furthermore, suppose your recipe is named foo_1.3.0.bb. In this case, the work directory the build system uses to build the package would be as follows:

     poky/build/tmp/work/qemux86-poky-linux/foo/1.3.0-r0
            

7.7. Using Quilt in Your Workflow

Quilt is a powerful tool that allows you to capture source code changes without having a clean source tree. This section outlines the typical workflow you can use to modify source code, test changes, and then preserve the changes in the form of a patch all using Quilt.

Tip

With regard to preserving changes to source files, if you clean a recipe or have rm_work enabled, the devtool workflow as described in the Yocto Project Application Development and the Extensible Software Development Kit (eSDK) manual is a safer development flow than the flow that uses Quilt.

Follow these general steps:

  1. Find the Source Code: Temporary source code used by the OpenEmbedded build system is kept in the Build Directory. See the "Finding Temporary Source Code" section to learn how to locate the directory that has the temporary source code for a particular package.

  2. Change Your Working Directory: You need to be in the directory that has the temporary source code. That directory is defined by the S variable.

  3. Create a New Patch: Before modifying source code, you need to create a new patch. To create a new patch file, use quilt new as below:

         $ quilt new my_changes.patch
                        

  4. Notify Quilt and Add Files: After creating the patch, you need to notify Quilt about the files you plan to edit. You notify Quilt by adding the files to the patch you just created:

         $ quilt add file1.c file2.c file3.c
                        

  5. Edit the Files: Make your changes in the source code to the files you added to the patch.

  6. Test Your Changes: Once you have modified the source code, the easiest way to test your changes is by calling the do_compile task as shown in the following example:

         $ bitbake -c compile -f package
                        

    The -f or --force option forces the specified task to execute. If you find problems with your code, you can just keep editing and re-testing iteratively until things work as expected.

    Note

    All the modifications you make to the temporary source code disappear once you run the do_clean or do_cleanall tasks using BitBake (i.e. bitbake -c clean package and bitbake -c cleanall package). Modifications will also disappear if you use the rm_work feature as described in the "Conserving Disk Space During Builds" section.

  7. Generate the Patch: Once your changes work as expected, you need to use Quilt to generate the final patch that contains all your modifications.

         $ quilt refresh
                        

    At this point, the my_changes.patch file has all your edits made to the file1.c, file2.c, and file3.c files.

    You can find the resulting patch file in the patches/ subdirectory of the source (S) directory.

  8. Copy the Patch File: For simplicity, copy the patch file into a directory named files, which you can create in the same directory that holds the recipe (.bb) file or the append (.bbappend) file. Placing the patch here guarantees that the OpenEmbedded build system will find the patch. Next, add the patch into the SRC_URI of the recipe. Here is an example:

         SRC_URI += "file://my_changes.patch"
                        

7.8. Using a Development Shell

When debugging certain commands or even when just editing packages, devshell can be a useful tool. When you invoke devshell, all tasks up to and including do_patch are run for the specified target. Then, a new terminal is opened and you are placed in ${S}, the source directory. In the new terminal, all the OpenEmbedded build-related environment variables are still defined so you can use commands such as configure and make. The commands execute just as if the OpenEmbedded build system were executing them. Consequently, working this way can be helpful when debugging a build or preparing software to be used with the OpenEmbedded build system.

Following is an example that uses devshell on a target named matchbox-desktop:

     $ bitbake matchbox-desktop -c devshell
            

This command spawns a terminal with a shell prompt within the OpenEmbedded build environment. The OE_TERMINAL variable controls what type of shell is opened.

For spawned terminals, the following occurs:

  • The PATH variable includes the cross-toolchain.

  • The pkgconfig variables find the correct .pc files.

  • The configure command finds the Yocto Project site files as well as any other necessary files.

Within this environment, you can run configure or compile commands as if they were being run by the OpenEmbedded build system itself. As noted earlier, the working directory also automatically changes to the Source Directory (S).

To manually run a specific task using devshell, run the corresponding run.* script in the ${WORKDIR}/temp directory (e.g., run.do_configure.pid). If a task's script does not exist, which would be the case if the task was skipped by way of the sstate cache, you can create the task by first running it outside of the devshell:

     $ bitbake -c task
            

Notes

  • Execution of a task's run.* script and BitBake's execution of a task are identical. In other words, running the script re-runs the task just as it would be run using the bitbake -c command.

  • Any run.* file that does not have a .pid extension is a symbolic link (symlink) to the most recent version of that file.

Remember, that the devshell is a mechanism that allows you to get into the BitBake task execution environment. And as such, all commands must be called just as BitBake would call them. That means you need to provide the appropriate options for cross-compilation and so forth as applicable.

When you are finished using devshell, exit the shell or close the terminal window.

Notes

  • It is worth remembering that when using devshell you need to use the full compiler name such as arm-poky-linux-gnueabi-gcc instead of just using gcc. The same applies to other applications such as binutils, libtool and so forth. BitBake sets up environment variables such as CC to assist applications, such as make to find the correct tools.

  • It is also worth noting that devshell still works over X11 forwarding and similar situations.

7.9. Using a Development Python Shell

Similar to working within a development shell as described in the previous section, you can also spawn and work within an interactive Python development shell. When debugging certain commands or even when just editing packages, devpyshell can be a useful tool. When you invoke devpyshell, all tasks up to and including do_patch are run for the specified target. Then a new terminal is opened. Additionally, key Python objects and code are available in the same way they are to BitBake tasks, in particular, the data store 'd'. So, commands such as the following are useful when exploring the data store and running functions:

     pydevshell> d.getVar("STAGING_DIR", True)
     '/media/build1/poky/build/tmp/sysroots'
     pydevshell> d.getVar("STAGING_DIR", False)
     '${TMPDIR}/sysroots'
     pydevshell> d.setVar("FOO", "bar")
     pydevshell> d.getVar("FOO", True)
     'bar'
     pydevshell> d.delVar("FOO")
     pydevshell> d.getVar("FOO", True)
     pydevshell> bb.build.exec_func("do_unpack", d)
     pydevshell>
            

The commands execute just as if the OpenEmbedded build system were executing them. Consequently, working this way can be helpful when debugging a build or preparing software to be used with the OpenEmbedded build system.

Following is an example that uses devpyshell on a target named matchbox-desktop:

     $ bitbake matchbox-desktop -c devpyshell
            

This command spawns a terminal and places you in an interactive Python interpreter within the OpenEmbedded build environment. The OE_TERMINAL variable controls what type of shell is opened.

When you are finished using devpyshell, you can exit the shell either by using Ctrl+d or closing the terminal window.

7.10. Building

This section describes various build procedures. For example, the steps needed for a simple build, a target that uses multiple configurations, building an image for more than one machine, and so forth.

7.10.1. Building a Simple Image

In the development environment, you need to build an image whenever you change hardware support, add or change system libraries, or add or change services that have dependencies. Several methods exist that allow you to build an image within the Yocto Project. This section presents the basic steps you need to build a simple image using BitBake from a build host running Linux.

Notes

  • For information on how to build an image using Toaster, see the Toaster User Manual.

  • For information on how to use devtool to build images, see the "Using devtool in Your SDK Workflow" section in the Yocto Project Application Development and the Extensible Software Development Kit (eSDK) manual.

  • For a quick example on how to build an image using the OpenEmbedded build system, see the Yocto Project Quick Build document.

The build process creates an entire Linux distribution from source and places it in your Build Directory under tmp/deploy/images. For detailed information on the build process using BitBake, see the "Images" section in the Yocto Project Overview and Concepts Manual.

The following figure and list overviews the build process:

  1. Set up Your Host Development System to Support Development Using the Yocto Project: See the "Setting Up to Use the Yocto Project" section for options on how to get a build host ready to use the Yocto Project.

  2. Initialize the Build Environment: Initialize the build environment by sourcing the build environment script (i.e. oe-init-build-env):

         $ source oe-init-build-env [build_dir]
                            

    When you use the initialization script, the OpenEmbedded build system uses build as the default Build Directory in your current work directory. You can use a build_dir argument with the script to specify a different build directory.

    Tip

    A common practice is to use a different Build Directory for different targets. For example, ~/build/x86 for a qemux86 target, and ~/build/arm for a qemuarm target.

  3. Make Sure Your local.conf File is Correct: Ensure the conf/local.conf configuration file, which is found in the Build Directory, is set up how you want it. This file defines many aspects of the build environment including the target machine architecture through the MACHINE variable, the packaging format used during the build (PACKAGE_CLASSES), and a centralized tarball download directory through the DL_DIR variable.

  4. Build the Image: Build the image using the bitbake command:

         $ bitbake target
                            

    Note

    For information on BitBake, see the BitBake User Manual.

    The target is the name of the recipe you want to build. Common targets are the images in meta/recipes-core/images, meta/recipes-sato/images, and so forth all found in the Source Directory. Or, the target can be the name of a recipe for a specific piece of software such as BusyBox. For more details about the images the OpenEmbedded build system supports, see the "Images" chapter in the Yocto Project Reference Manual.

    As an example, the following command builds the core-image-minimal image:

         $ bitbake core-image-minimal
                            

    Once an image has been built, it often needs to be installed. The images and kernels built by the OpenEmbedded build system are placed in the Build Directory in tmp/deploy/images. For information on how to run pre-built images such as qemux86 and qemuarm, see the Yocto Project Application Development and the Extensible Software Development Kit (eSDK) manual. For information about how to install these images, see the documentation for your particular board or machine.

7.10.2. Building Targets with Multiple Configurations

Bitbake also has functionality that allows you to build multiple targets at the same time, where each target uses a different configuration.

In order to accomplish this, you setup each of the configurations you need to use in parallel by placing the configuration files in your current build directory alongside the usual local.conf file.

Follow these guidelines to create an environment that supports multiple configurations:

  • Create Configuration Files: You need to create a single configuration file for each configuration for which you want to add support. These files would contain lines such as the following:

         MACHINE = "A"
                            

    The files would contain any other variables that can be set and built in the same directory.

    Note

    You can change the TMPDIR to not conflict.

    Furthermore, the configuration file must be located in the current build directory in a directory named multiconfig under the build's conf directory where local.conf resides. The reason for this restriction is because the BBPATH variable is not constructed until the layers are parsed. Consequently, using the configuration file as a pre-configuration file is not possible unless it is located in the current working directory.

  • Add the BitBake Multi-Config Variable to you Local Configuration File: Use the BBMULTICONFIG variable in your conf/local.conf configuration file to specify each separate configuration. For example, the following line tells BitBake it should load conf/multiconfig/configA.conf, conf/multiconfig/configB.conf, and conf/multiconfig/configC.conf.

         BBMULTICONFIG = "configA configB configC"
                            

  • Launch BitBake: Use the following BitBake command form to launch the build:

         $ bitbake [multiconfig:multiconfigname:]target [[[multiconfig:multiconfigname:]target] ... ]
                            

    Following is an example that supports building a minimal image for configuration A alongside a standard core-image-sato, which takes its configuration from local.conf:

         $ bitbake multiconfig:configA:core-image-minimal core-image-sato
                            

Support for multiple configurations in this current release of the Yocto Project (Sumo 2.5) has some known issues:

  • No inter-multi-configuration dependencies exist.

  • Shared State (sstate) optimizations do not exist. Consequently, if the build uses the same object twice in, for example, two different TMPDIR directories, the build will either load from an existing sstate cache at the start or build the object twice.

7.10.3. Building an Initial RAM Filesystem (initramfs) Image

An initial RAM filesystem (initramfs) image provides a temporary root filesystem used for early system initialization (e.g. loading of modules needed to locate and mount the "real" root filesystem).

Note

The initramfs image is the successor of initial RAM disk (initrd). It is a "copy in and out" (cpio) archive of the initial filesystem that gets loaded into memory during the Linux startup process. Because Linux uses the contents of the archive during initialization, the initramfs image needs to contain all of the device drivers and tools needed to mount the final root filesystem.

Follow these steps to create an initramfs image:

  1. Create the initramfs Image Recipe: You can reference the core-image-minimal-initramfs.bb recipe found in the meta/recipes-core directory of the Source Directory as an example from which to work.

  2. Decide if You Need to Bundle the initramfs Image Into the Kernel Image: If you want the initramfs image that is built to be bundled in with the kernel image, set the INITRAMFS_IMAGE_BUNDLE variable to "1" in your local.conf configuration file and set the INITRAMFS_IMAGE variable in the recipe that builds the kernel image.

    Tip

    It is recommended that you do bundle the initramfs image with the kernel image to avoid circular dependencies between the kernel recipe and the initramfs recipe should the initramfs image include kernel modules.

    Setting the INITRAMFS_IMAGE_BUNDLE flag causes the initramfs image to be unpacked into the ${B}/usr/ directory. The unpacked initramfs image is then passed to the kernel's Makefile using the CONFIG_INITRAMFS_SOURCE variable, allowing the initramfs image to be built into the kernel normally.

    Note

    If you choose to not bundle the initramfs image with the kernel image, you are essentially using an Initial RAM Disk (initrd). Creating an initrd is handled primarily through the INITRD_IMAGE, INITRD_LIVE, and INITRD_IMAGE_LIVE variables. For more information, see the image-live.bbclass file.

  3. Optionally Add Items to the initramfs Image Through the initramfs Image Recipe: If you add items to the initramfs image by way of its recipe, you should use PACKAGE_INSTALL rather than IMAGE_INSTALL. PACKAGE_INSTALL gives more direct control of what is added to the image as compared to the defaults you might not necessarily want that are set by the image or core-image classes.

  4. Build the Kernel Image and the initramfs Image: Build your kernel image using BitBake. Because the initramfs image recipe is a dependency of the kernel image, the initramfs image is built as well and bundled with the kernel image if you used the INITRAMFS_IMAGE_BUNDLE variable described earlier.

7.10.4. Building a Tiny System

Very small distributions have some significant advantages such as requiring less on-die or in-package memory (cheaper), better performance through efficient cache usage, lower power requirements due to less memory, faster boot times, and reduced development overhead. Some real-world examples where a very small distribution gives you distinct advantages are digital cameras, medical devices, and small headless systems.

This section presents information that shows you how you can trim your distribution to even smaller sizes than the poky-tiny distribution, which is around 5 Mbytes, that can be built out-of-the-box using the Yocto Project.

7.10.4.1. Overview

The following list presents the overall steps you need to consider and perform to create distributions with smaller root filesystems, achieve faster boot times, maintain your critical functionality, and avoid initial RAM disks:

7.10.4.2. Goals and Guiding Principles

Before you can reach your destination, you need to know where you are going. Here is an example list that you can use as a guide when creating very small distributions:

  • Determine how much space you need (e.g. a kernel that is 1 Mbyte or less and a root filesystem that is 3 Mbytes or less).

  • Find the areas that are currently taking 90% of the space and concentrate on reducing those areas.

  • Do not create any difficult "hacks" to achieve your goals.

  • Leverage the device-specific options.

  • Work in a separate layer so that you keep changes isolated. For information on how to create layers, see the "Understanding and Creating Layers" section.

7.10.4.3. Understand What Contributes to Your Image Size

It is easiest to have something to start with when creating your own distribution. You can use the Yocto Project out-of-the-box to create the poky-tiny distribution. Ultimately, you will want to make changes in your own distribution that are likely modeled after poky-tiny.

Note

To use poky-tiny in your build, set the DISTRO variable in your local.conf file to "poky-tiny" as described in the "Creating Your Own Distribution" section.

Understanding some memory concepts will help you reduce the system size. Memory consists of static, dynamic, and temporary memory. Static memory is the TEXT (code), DATA (initialized data in the code), and BSS (uninitialized data) sections. Dynamic memory represents memory that is allocated at runtime: stacks, hash tables, and so forth. Temporary memory is recovered after the boot process. This memory consists of memory used for decompressing the kernel and for the __init__ functions.

To help you see where you currently are with kernel and root filesystem sizes, you can use two tools found in the Source Directory in the scripts/tiny/ directory:

  • ksize.py: Reports component sizes for the kernel build objects.

  • dirsize.py: Reports component sizes for the root filesystem.

This next tool and command help you organize configuration fragments and view file dependencies in a human-readable form:

  • merge_config.sh: Helps you manage configuration files and fragments within the kernel. With this tool, you can merge individual configuration fragments together. The tool allows you to make overrides and warns you of any missing configuration options. The tool is ideal for allowing you to iterate on configurations, create minimal configurations, and create configuration files for different machines without having to duplicate your process.

    The merge_config.sh script is part of the Linux Yocto kernel Git repositories (i.e. linux-yocto-3.14, linux-yocto-3.10, linux-yocto-3.8, and so forth) in the scripts/kconfig directory.

    For more information on configuration fragments, see the "Creating Configuration Fragments" section in the Yocto Project Linux Kernel Development Manual.

  • bitbake -u taskexp -g bitbake_target: Using the BitBake command with these options brings up a Dependency Explorer from which you can view file dependencies. Understanding these dependencies allows you to make informed decisions when cutting out various pieces of the kernel and root filesystem.

7.10.4.4. Trim the Root Filesystem

The root filesystem is made up of packages for booting, libraries, and applications. To change things, you can configure how the packaging happens, which changes the way you build them. You can also modify the filesystem itself or select a different filesystem.

First, find out what is hogging your root filesystem by running the dirsize.py script from your root directory:

     $ cd root-directory-of-image
     $ dirsize.py 100000 > dirsize-100k.log
     $ cat dirsize-100k.log
                    

You can apply a filter to the script to ignore files under a certain size. The previous example filters out any files below 100 Kbytes. The sizes reported by the tool are uncompressed, and thus will be smaller by a relatively constant factor in a compressed root filesystem. When you examine your log file, you can focus on areas of the root filesystem that take up large amounts of memory.

You need to be sure that what you eliminate does not cripple the functionality you need. One way to see how packages relate to each other is by using the Dependency Explorer UI with the BitBake command:

     $ cd image-directory
     $ bitbake -u taskexp -g image
                    

Use the interface to select potential packages you wish to eliminate and see their dependency relationships.

When deciding how to reduce the size, get rid of packages that result in minimal impact on the feature set. For example, you might not need a VGA display. Or, you might be able to get by with devtmpfs and mdev instead of udev.

Use your local.conf file to make changes. For example, to eliminate udev and glib, set the following in the local configuration file:

     VIRTUAL-RUNTIME_dev_manager = ""
                    

Finally, you should consider exactly the type of root filesystem you need to meet your needs while also reducing its size. For example, consider cramfs, squashfs, ubifs, ext2, or an initramfs using initramfs. Be aware that ext3 requires a 1 Mbyte journal. If you are okay with running read-only, you do not need this journal.

Note

After each round of elimination, you need to rebuild your system and then use the tools to see the effects of your reductions.

7.10.4.5. Trim the Kernel

The kernel is built by including policies for hardware-independent aspects. What subsystems do you enable? For what architecture are you building? Which drivers do you build by default?

Note

You can modify the kernel source if you want to help with boot time.

Run the ksize.py script from the top-level Linux build directory to get an idea of what is making up the kernel:

     $ cd top-level-linux-build-directory
     $ ksize.py > ksize.log
     $ cat ksize.log
                    

When you examine the log, you will see how much space is taken up with the built-in .o files for drivers, networking, core kernel files, filesystem, sound, and so forth. The sizes reported by the tool are uncompressed, and thus will be smaller by a relatively constant factor in a compressed kernel image. Look to reduce the areas that are large and taking up around the "90% rule."

To examine, or drill down, into any particular area, use the -d option with the script:

     $ ksize.py -d > ksize.log
                    

Using this option breaks out the individual file information for each area of the kernel (e.g. drivers, networking, and so forth).

Use your log file to see what you can eliminate from the kernel based on features you can let go. For example, if you are not going to need sound, you do not need any drivers that support sound.

After figuring out what to eliminate, you need to reconfigure the kernel to reflect those changes during the next build. You could run menuconfig and make all your changes at once. However, that makes it difficult to see the effects of your individual eliminations and also makes it difficult to replicate the changes for perhaps another target device. A better method is to start with no configurations using allnoconfig, create configuration fragments for individual changes, and then manage the fragments into a single configuration file using merge_config.sh. The tool makes it easy for you to iterate using the configuration change and build cycle.

Each time you make configuration changes, you need to rebuild the kernel and check to see what impact your changes had on the overall size.

7.10.4.6. Remove Package Management Requirements

Packaging requirements add size to the image. One way to reduce the size of the image is to remove all the packaging requirements from the image. This reduction includes both removing the package manager and its unique dependencies as well as removing the package management data itself.

To eliminate all the packaging requirements for an image, be sure that "package-management" is not part of your IMAGE_FEATURES statement for the image. When you remove this feature, you are removing the package manager as well as its dependencies from the root filesystem.

7.10.4.7. Look for Other Ways to Minimize Size

Depending on your particular circumstances, other areas that you can trim likely exist. The key to finding these areas is through tools and methods described here combined with experimentation and iteration. Here are a couple of areas to experiment with:

  • glibc: In general, follow this process:

    1. Remove glibc features from DISTRO_FEATURES that you think you do not need.

    2. Build your distribution.

    3. If the build fails due to missing symbols in a package, determine if you can reconfigure the package to not need those features. For example, change the configuration to not support wide character support as is done for ncurses. Or, if support for those characters is needed, determine what glibc features provide the support and restore the configuration.

    4. Rebuild and repeat the process.

  • busybox: For BusyBox, use a process similar as described for glibc. A difference is you will need to boot the resulting system to see if you are able to do everything you expect from the running system. You need to be sure to integrate configuration fragments into Busybox because BusyBox handles its own core features and then allows you to add configuration fragments on top.

7.10.4.8. Iterate on the Process

If you have not reached your goals on system size, you need to iterate on the process. The process is the same. Use the tools and see just what is taking up 90% of the root filesystem and the kernel. Decide what you can eliminate without limiting your device beyond what you need.

Depending on your system, a good place to look might be Busybox, which provides a stripped down version of Unix tools in a single, executable file. You might be able to drop virtual terminal services or perhaps ipv6.

7.10.5. Building Images for More than One Machine

A common scenario developers face is creating images for several different machines that use the same software environment. In this situation, it is tempting to set the tunings and optimization flags for each build specifically for the targeted hardware (i.e. "maxing out" the tunings). Doing so can considerably add to build times and package feed maintenance collectively for the machines. For example, selecting tunes that are extremely specific to a CPU core used in a system might enable some micro optimizations in GCC for that particular system but would otherwise not gain you much of a performance difference across the other systems as compared to using a more general tuning across all the builds (e.g. setting DEFAULTTUNE specifically for each machine's build). Rather than "max out" each build's tunings, you can take steps that cause the OpenEmbedded build system to reuse software across the various machines where it makes sense.

If build speed and package feed maintenance are considerations, you should consider the points in this section that can help you optimize your tunings to best consider build times and package feed maintenance.

  • Share the Build Directory: If at all possible, share the TMPDIR across builds. The Yocto Project supports switching between different MACHINE values in the same TMPDIR. This practice is well supported and regularly used by developers when building for multiple machines. When you use the same TMPDIR for multiple machine builds, the OpenEmbedded build system can reuse the existing native and often cross-recipes for multiple machines. Thus, build time decreases.

    Note

    If DISTRO settings change or fundamental configuration settings such as the filesystem layout, you need to work with a clean TMPDIR. Sharing TMPDIR under these circumstances might work but since it is not guaranteed, you should use a clean TMPDIR.

  • Enable the Appropriate Package Architecture: By default, the OpenEmbedded build system enables three levels of package architectures: "all", "tune" or "package", and "machine". Any given recipe usually selects one of these package architectures (types) for its output. Depending for what a given recipe creates packages, making sure you enable the appropriate package architecture can directly impact the build time.

    A recipe that just generates scripts can enable "all" architecture because there are no binaries to build. To specifically enable "all" architecture, be sure your recipe inherits the allarch class. This class is useful for "all" architectures because it configures many variables so packages can be used across multiple architectures.

    If your recipe needs to generate packages that are machine-specific or when one of the build or runtime dependencies is already machine-architecture dependent, which makes your recipe also machine-architecture dependent, make sure your recipe enables the "machine" package architecture through the MACHINE_ARCH variable:

         PACKAGE_ARCH = "${MACHINE_ARCH}"
                            

    When you do not specifically enable a package architecture through the PACKAGE_ARCH, The OpenEmbedded build system defaults to the TUNE_PKGARCH setting:

         PACKAGE_ARCH = "${TUNE_PKGARCH}"
                            

  • Choose a Generic Tuning File if Possible: Some tunes are more generic and can run on multiple targets (e.g. an armv5 set of packages could run on armv6 and armv7 processors in most cases). Similarly, i486 binaries could work on i586 and higher processors. You should realize, however, that advances on newer processor versions would not be used.

    If you select the same tune for several different machines, the OpenEmbedded build system reuses software previously built, thus speeding up the overall build time. Realize that even though a new sysroot for each machine is generated, the software is not recompiled and only one package feed exists.

  • Manage Granular Level Packaging: Sometimes cases exist where injecting another level of package architecture beyond the three higher levels noted earlier can be useful. For example, consider how NXP (formerly Freescale) allows for the easy reuse of binary packages in their layer meta-freescale. In this example, the fsl-dynamic-packagearch class shares GPU packages for i.MX53 boards because all boards share the AMD GPU. The i.MX6-based boards can do the same because all boards share the Vivante GPU. This class inspects the BitBake datastore to identify if the package provides or depends on one of the sub-architecture values. If so, the class sets the PACKAGE_ARCH value based on the MACHINE_SUBARCH value. If the package does not provide or depend on one of the sub-architecture values but it matches a value in the machine-specific filter, it sets MACHINE_ARCH. This behavior reduces the number of packages built and saves build time by reusing binaries.

  • Use Tools to Debug Issues: Sometimes you can run into situations where software is being rebuilt when you think it should not be. For example, the OpenEmbedded build system might not be using shared state between machines when you think it should be. These types of situations are usually due to references to machine-specific variables such as MACHINE, SERIAL_CONSOLES, XSERVER, MACHINE_FEATURES, and so forth in code that is supposed to only be tune-specific or when the recipe depends (DEPENDS, RDEPENDS, RRECOMMENDS, RSUGGESTS, and so forth) on some other recipe that already has PACKAGE_ARCH defined as "${MACHINE_ARCH}".

    Note

    Patches to fix any issues identified are most welcome as these issues occasionally do occur.

    For such cases, you can use some tools to help you sort out the situation:

    • sstate-diff-machines.sh: You can find this tool in the scripts directory of the Source Repositories. See the comments in the script for information on how to use the tool.

    • BitBake's "-S printdiff" Option: Using this option causes BitBake to try to establish the closest signature match it can (e.g. in the shared state cache) and then run bitbake-diffsigs over the matches to determine the stamps and delta where these two stamp trees diverge.

7.10.6. Building Software from an External Source

By default, the OpenEmbedded build system uses the Build Directory when building source code. The build process involves fetching the source files, unpacking them, and then patching them if necessary before the build takes place.

Situations exist where you might want to build software from source files that are external to and thus outside of the OpenEmbedded build system. For example, suppose you have a project that includes a new BSP with a heavily customized kernel. And, you want to minimize exposing the build system to the development team so that they can focus on their project and maintain everyone's workflow as much as possible. In this case, you want a kernel source directory on the development machine where the development occurs. You want the recipe's SRC_URI variable to point to the external directory and use it as is, not copy it.

To build from software that comes from an external source, all you need to do is inherit the externalsrc class and then set the EXTERNALSRC variable to point to your external source code. Here are the statements to put in your local.conf file:

     INHERIT += "externalsrc"
     EXTERNALSRC_pn-myrecipe = "path-to-your-source-tree"
                

This next example shows how to accomplish the same thing by setting EXTERNALSRC in the recipe itself or in the recipe's append file:

     EXTERNALSRC = "path"
     EXTERNALSRC_BUILD = "path"
                

Note

In order for these settings to take effect, you must globally or locally inherit the externalsrc class.

By default, externalsrc.bbclass builds the source code in a directory separate from the external source directory as specified by EXTERNALSRC. If you need to have the source built in the same directory in which it resides, or some other nominated directory, you can set EXTERNALSRC_BUILD to point to that directory:

     EXTERNALSRC_BUILD_pn-myrecipe = "path-to-your-source-tree"
                

7.11. Speeding Up a Build

Build time can be an issue. By default, the build system uses simple controls to try and maximize build efficiency. In general, the default settings for all the following variables result in the most efficient build times when dealing with single socket systems (i.e. a single CPU). If you have multiple CPUs, you might try increasing the default values to gain more speed. See the descriptions in the glossary for each variable for more information:

As mentioned, these variables all scale to the number of processor cores available on the build system. For single socket systems, this auto-scaling ensures that the build system fundamentally takes advantage of potential parallel operations during the build based on the build machine's capabilities.

Following are additional factors that can affect build speed:

  • File system type: The file system type that the build is being performed on can also influence performance. Using ext4 is recommended as compared to ext2 and ext3 due to ext4 improved features such as extents.

  • Disabling the updating of access time using noatime: The noatime mount option prevents the build system from updating file and directory access times.

  • Setting a longer commit: Using the "commit=" mount option increases the interval in seconds between disk cache writes. Changing this interval from the five second default to something longer increases the risk of data loss but decreases the need to write to the disk, thus increasing the build performance.

  • Choosing the packaging backend: Of the available packaging backends, IPK is the fastest. Additionally, selecting a singular packaging backend also helps.

  • Using tmpfs for TMPDIR as a temporary file system: While this can help speed up the build, the benefits are limited due to the compiler using -pipe. The build system goes to some lengths to avoid sync() calls into the file system on the principle that if there was a significant failure, the Build Directory contents could easily be rebuilt.

  • Inheriting the rm_work class: Inheriting this class has shown to speed up builds due to significantly lower amounts of data stored in the data cache as well as on disk. Inheriting this class also makes cleanup of TMPDIR faster, at the expense of being easily able to dive into the source code. File system maintainers have recommended that the fastest way to clean up large numbers of files is to reformat partitions rather than delete files due to the linear nature of partitions. This, of course, assumes you structure the disk partitions and file systems in a way that this is practical.

Aside from the previous list, you should keep some trade offs in mind that can help you speed up the build:

  • Remove items from DISTRO_FEATURES that you might not need.

  • Exclude debug symbols and other debug information: If you do not need these symbols and other debug information, disabling the *-dbg package generation can speed up the build. You can disable this generation by setting the INHIBIT_PACKAGE_DEBUG_SPLIT variable to "1".

  • Disable static library generation for recipes derived from autoconf or libtool: Following is an example showing how to disable static libraries and still provide an override to handle exceptions:

         STATICLIBCONF = "--disable-static"
         STATICLIBCONF_sqlite3-native = ""
         EXTRA_OECONF += "${STATICLIBCONF}"
                        

    Notes

    • Some recipes need static libraries in order to work correctly (e.g. pseudo-native needs sqlite3-native). Overrides, as in the previous example, account for these kinds of exceptions.

    • Some packages have packaging code that assumes the presence of the static libraries. If so, you might need to exclude them as well.

7.12. Working With Libraries

Libraries are an integral part of your system. This section describes some common practices you might find helpful when working with libraries to build your system:

7.12.1. Including Static Library Files

If you are building a library and the library offers static linking, you can control which static library files (*.a files) get included in the built library.

The PACKAGES and FILES_* variables in the meta/conf/bitbake.conf configuration file define how files installed by the do_install task are packaged. By default, the PACKAGES variable includes ${PN}-staticdev, which represents all static library files.

Note

Some previously released versions of the Yocto Project defined the static library files through ${PN}-dev.

Following is part of the BitBake configuration file, where you can see how the static library files are defined:

     PACKAGE_BEFORE_PN ?= ""
     PACKAGES = "${PN}-dbg ${PN}-staticdev ${PN}-dev ${PN}-doc ${PN}-locale ${PACKAGE_BEFORE_PN} ${PN}"
     PACKAGES_DYNAMIC = "^${PN}-locale-.*"
     FILES = ""

     FILES_${PN} = "${bindir}/* ${sbindir}/* ${libexecdir}/* ${libdir}/lib*${SOLIBS} \
                 ${sysconfdir} ${sharedstatedir} ${localstatedir} \
                 ${base_bindir}/* ${base_sbindir}/* \
                 ${base_libdir}/*${SOLIBS} \
                 ${base_prefix}/lib/udev/rules.d ${prefix}/lib/udev/rules.d \
                 ${datadir}/${BPN} ${libdir}/${BPN}/* \
                 ${datadir}/pixmaps ${datadir}/applications \
                 ${datadir}/idl ${datadir}/omf ${datadir}/sounds \
                 ${libdir}/bonobo/servers"

     FILES_${PN}-bin = "${bindir}/* ${sbindir}/*"

     FILES_${PN}-doc = "${docdir} ${mandir} ${infodir} ${datadir}/gtk-doc \
                 ${datadir}/gnome/help"
     SECTION_${PN}-doc = "doc"

     FILES_SOLIBSDEV ?= "${base_libdir}/lib*${SOLIBSDEV} ${libdir}/lib*${SOLIBSDEV}"
     FILES_${PN}-dev = "${includedir} ${FILES_SOLIBSDEV} ${libdir}/*.la \
                     ${libdir}/*.o ${libdir}/pkgconfig ${datadir}/pkgconfig \
                     ${datadir}/aclocal ${base_libdir}/*.o \
                     ${libdir}/${BPN}/*.la ${base_libdir}/*.la"
     SECTION_${PN}-dev = "devel"
     ALLOW_EMPTY_${PN}-dev = "1"
     RDEPENDS_${PN}-dev = "${PN} (= ${EXTENDPKGV})"

     FILES_${PN}-staticdev = "${libdir}/*.a ${base_libdir}/*.a ${libdir}/${BPN}/*.a"
     SECTION_${PN}-staticdev = "devel"
     RDEPENDS_${PN}-staticdev = "${PN}-dev (= ${EXTENDPKGV})"
                

7.12.2. Combining Multiple Versions of Library Files into One Image

The build system offers the ability to build libraries with different target optimizations or architecture formats and combine these together into one system image. You can link different binaries in the image against the different libraries as needed for specific use cases. This feature is called "Multilib."

An example would be where you have most of a system compiled in 32-bit mode using 32-bit libraries, but you have something large, like a database engine, that needs to be a 64-bit application and uses 64-bit libraries. Multilib allows you to get the best of both 32-bit and 64-bit libraries.

While the Multilib feature is most commonly used for 32 and 64-bit differences, the approach the build system uses facilitates different target optimizations. You could compile some binaries to use one set of libraries and other binaries to use a different set of libraries. The libraries could differ in architecture, compiler options, or other optimizations.

Several examples exist in the meta-skeleton layer found in the Source Directory:

  • conf/multilib-example.conf configuration file

  • conf/multilib-example2.conf configuration file

  • recipes-multilib/images/core-image-multilib-example.bb recipe

7.12.2.1. Preparing to Use Multilib

User-specific requirements drive the Multilib feature. Consequently, there is no one "out-of-the-box" configuration that likely exists to meet your needs.

In order to enable Multilib, you first need to ensure your recipe is extended to support multiple libraries. Many standard recipes are already extended and support multiple libraries. You can check in the meta/conf/multilib.conf configuration file in the Source Directory to see how this is done using the BBCLASSEXTEND variable. Eventually, all recipes will be covered and this list will not be needed.

For the most part, the Multilib class extension works automatically to extend the package name from ${PN} to ${MLPREFIX}${PN}, where MLPREFIX is the particular multilib (e.g. "lib32-" or "lib64-"). Standard variables such as DEPENDS, RDEPENDS, RPROVIDES, RRECOMMENDS, PACKAGES, and PACKAGES_DYNAMIC are automatically extended by the system. If you are extending any manual code in the recipe, you can use the ${MLPREFIX} variable to ensure those names are extended correctly. This automatic extension code resides in multilib.bbclass.

7.12.2.2. Using Multilib

After you have set up the recipes, you need to define the actual combination of multiple libraries you want to build. You accomplish this through your local.conf configuration file in the Build Directory. An example configuration would be as follows:

     MACHINE = "qemux86-64"
     require conf/multilib.conf
     MULTILIBS = "multilib:lib32"
     DEFAULTTUNE_virtclass-multilib-lib32 = "x86"
     IMAGE_INSTALL_append = " lib32-glib-2.0"
                    

This example enables an additional library named lib32 alongside the normal target packages. When combining these "lib32" alternatives, the example uses "x86" for tuning. For information on this particular tuning, see meta/conf/machine/include/ia32/arch-ia32.inc.

The example then includes lib32-glib-2.0 in all the images, which illustrates one method of including a multiple library dependency. You can use a normal image build to include this dependency, for example:

     $ bitbake core-image-sato
                    

You can also build Multilib packages specifically with a command like this:

     $ bitbake lib32-glib-2.0
                    

7.12.2.3. Additional Implementation Details

Generic implementation details as well as details that are specific to package management systems exist. Following are implementation details that exist regardless of the package management system:

  • The typical convention used for the class extension code as used by Multilib assumes that all package names specified in PACKAGES that contain ${PN} have ${PN} at the start of the name. When that convention is not followed and ${PN} appears at the middle or the end of a name, problems occur.

  • The TARGET_VENDOR value under Multilib will be extended to "-vendormlmultilib" (e.g. "-pokymllib32" for a "lib32" Multilib with Poky). The reason for this slightly unwieldy contraction is that any "-" characters in the vendor string presently break Autoconf's config.sub, and other separators are problematic for different reasons.

For the RPM Package Management System, the following implementation details exist:

  • A unique architecture is defined for the Multilib packages, along with creating a unique deploy folder under tmp/deploy/rpm in the Build Directory. For example, consider lib32 in a qemux86-64 image. The possible architectures in the system are "all", "qemux86_64", "lib32_qemux86_64", and "lib32_x86".

  • The ${MLPREFIX} variable is stripped from ${PN} during RPM packaging. The naming for a normal RPM package and a Multilib RPM package in a qemux86-64 system resolves to something similar to bash-4.1-r2.x86_64.rpm and bash-4.1.r2.lib32_x86.rpm, respectively.

  • When installing a Multilib image, the RPM backend first installs the base image and then installs the Multilib libraries.

  • The build system relies on RPM to resolve the identical files in the two (or more) Multilib packages.

For the IPK Package Management System, the following implementation details exist:

  • The ${MLPREFIX} is not stripped from ${PN} during IPK packaging. The naming for a normal RPM package and a Multilib IPK package in a qemux86-64 system resolves to something like bash_4.1-r2.x86_64.ipk and lib32-bash_4.1-rw_x86.ipk, respectively.

  • The IPK deploy folder is not modified with ${MLPREFIX} because packages with and without the Multilib feature can exist in the same folder due to the ${PN} differences.

  • IPK defines a sanity check for Multilib installation using certain rules for file comparison, overridden, etc.

7.12.3. Installing Multiple Versions of the Same Library

Situations can exist where you need to install and use multiple versions of the same library on the same system at the same time. These situations almost always exist when a library API changes and you have multiple pieces of software that depend on the separate versions of the library. To accommodate these situations, you can install multiple versions of the same library in parallel on the same system.

The process is straightforward as long as the libraries use proper versioning. With properly versioned libraries, all you need to do to individually specify the libraries is create separate, appropriately named recipes where the PN part of the name includes a portion that differentiates each library version (e.g.the major part of the version number). Thus, instead of having a single recipe that loads one version of a library (e.g. clutter), you provide multiple recipes that result in different versions of the libraries you want. As an example, the following two recipes would allow the two separate versions of the clutter library to co-exist on the same system:

     clutter-1.6_1.6.20.bb
     clutter-1.8_1.8.4.bb
                

Additionally, if you have other recipes that depend on a given library, you need to use the DEPENDS variable to create the dependency. Continuing with the same example, if you want to have a recipe depend on the 1.8 version of the clutter library, use the following in your recipe:

     DEPENDS = "clutter-1.8"
                

7.13. Using x32 psABI

x32 processor-specific Application Binary Interface (x32 psABI) is a native 32-bit processor-specific ABI for Intel® 64 (x86-64) architectures. An ABI defines the calling conventions between functions in a processing environment. The interface determines what registers are used and what the sizes are for various C data types.

Some processing environments prefer using 32-bit applications even when running on Intel 64-bit platforms. Consider the i386 psABI, which is a very old 32-bit ABI for Intel 64-bit platforms. The i386 psABI does not provide efficient use and access of the Intel 64-bit processor resources, leaving the system underutilized. Now consider the x86_64 psABI. This ABI is newer and uses 64-bits for data sizes and program pointers. The extra bits increase the footprint size of the programs, libraries, and also increases the memory and file system size requirements. Executing under the x32 psABI enables user programs to utilize CPU and system resources more efficiently while keeping the memory footprint of the applications low. Extra bits are used for registers but not for addressing mechanisms.

The Yocto Project supports the final specifications of x32 psABI as follows:

  • You can create packages and images in x32 psABI format on x86_64 architecture targets.

  • You can successfully build recipes with the x32 toolchain.

  • You can create and boot core-image-minimal and core-image-sato images.

  • RPM Package Manager (RPM) support exists for x32 binaries.

  • Support for large images exists.

To use the x32 psABI, you need to edit your conf/local.conf configuration file as follows:

     MACHINE = "qemux86-64"
     DEFAULTTUNE = "x86-64-x32"
     baselib = "${@d.getVar('BASE_LIB_tune-' + (d.getVar('DEFAULTTUNE', True) \
        or 'INVALID'), True) or 'lib'}"
            

Once you have set up your configuration file, use BitBake to build an image that supports the x32 psABI. Here is an example:

     $ bitbake core-image-sato
            

7.14. Enabling GObject Introspection Support

GObject introspection is the standard mechanism for accessing GObject-based software from runtime environments. GObject is a feature of the GLib library that provides an object framework for the GNOME desktop and related software. GObject Introspection adds information to GObject that allows objects created within it to be represented across different programming languages. If you want to construct GStreamer pipelines using Python, or control UPnP infrastructure using Javascript and GUPnP, GObject introspection is the only way to do it.

This section describes the Yocto Project support for generating and packaging GObject introspection data. GObject introspection data is a description of the API provided by libraries built on top of GLib framework, and, in particular, that framework's GObject mechanism. GObject Introspection Repository (GIR) files go to -dev packages, typelib files go to main packages as they are packaged together with libraries that are introspected.

The data is generated when building such a library, by linking the library with a small executable binary that asks the library to describe itself, and then executing the binary and processing its output.

Generating this data in a cross-compilation environment is difficult because the library is produced for the target architecture, but its code needs to be executed on the build host. This problem is solved with the OpenEmbedded build system by running the code through QEMU, which allows precisely that. Unfortunately, QEMU does not always work perfectly as mentioned in the xxx section.

7.14.1. Enabling the Generation of Introspection Data

Enabling the generation of introspection data (GIR files) in your library package involves the following:

  1. Inherit the gobject-introspection class.

  2. Make sure introspection is not disabled anywhere in the recipe or from anything the recipe includes. Also, make sure that "gobject-introspection-data" is not in DISTRO_FEATURES_BACKFILL_CONSIDERED and that "qemu-usermode" is not in MACHINE_FEATURES_BACKFILL_CONSIDERED. If either of these conditions exist, nothing will happen.

  3. Try to build the recipe. If you encounter build errors that look like something is unable to find .so libraries, check where these libraries are located in the source tree and add the following to the recipe:

         GIR_EXTRA_LIBS_PATH = "${B}/something/.libs"
                            

    Note

    See recipes in the oe-core repository that use that GIR_EXTRA_LIBS_PATH variable as an example.

  4. Look for any other errors, which probably mean that introspection support in a package is not entirely standard, and thus breaks down in a cross-compilation environment. For such cases, custom-made fixes are needed. A good place to ask and receive help in these cases is the Yocto Project mailing lists.

Note

Using a library that no longer builds against the latest Yocto Project release and prints introspection related errors is a good candidate for the previous procedure.

7.14.2. Disabling the Generation of Introspection Data

You might find that you do not want to generate introspection data. Or, perhaps QEMU does not work on your build host and target architecture combination. If so, you can use either of the following methods to disable GIR file generations:

  • Add the following to your distro configuration:

         DISTRO_FEATURES_BACKFILL_CONSIDERED = "gobject-introspection-data"
                            

    Adding this statement disables generating introspection data using QEMU but will still enable building introspection tools and libraries (i.e. building them does not require the use of QEMU).

  • Add the following to your machine configuration:

         MACHINE_FEATURES_BACKFILL_CONSIDERED = "qemu-usermode"
                            

    Adding this statement disables the use of QEMU when building packages for your machine. Currently, this feature is used only by introspection recipes and has the same effect as the previously described option.

    Note

    Future releases of the Yocto Project might have other features affected by this option.

If you disable introspection data, you can still obtain it through other means such as copying the data from a suitable sysroot, or by generating it on the target hardware. The OpenEmbedded build system does not currently provide specific support for these techniques.

7.14.3. Testing that Introspection Works in an Image

Use the following procedure to test if generating introspection data is working in an image:

  1. Make sure that "gobject-introspection-data" is not in DISTRO_FEATURES_BACKFILL_CONSIDERED and that "qemu-usermode" is not in MACHINE_FEATURES_BACKFILL_CONSIDERED.

  2. Build core-image-sato.

  3. Launch a Terminal and then start Python in the terminal.

  4. Enter the following in the terminal:

         >>> from gi.repository import GLib
         >>> GLib.get_host_name()
                            

  5. For something a little more advanced, enter the following:

         http://python-gtk-3-tutorial.readthedocs.org/en/latest/introduction.html
                            

7.14.4. Known Issues

The following know issues exist for GObject Introspection Support:

  • qemu-ppc64 immediately crashes. Consequently, you cannot build introspection data on that architecture.

  • x32 is not supported by QEMU. Consequently, introspection data is disabled.

  • musl causes transient GLib binaries to crash on assertion failures. Consequently, generating introspection data is disabled.

  • Because QEMU is not able to run the binaries correctly, introspection is disabled for some specific packages under specific architectures (e.g. gcr, libsecret, and webkit).

  • QEMU usermode might not work properly when running 64-bit binaries under 32-bit host machines. In particular, "qemumips64" is known to not work under i686.

7.15. Optionally Using an External Toolchain

You might want to use an external toolchain as part of your development. If this is the case, the fundamental steps you need to accomplish are as follows:

  • Understand where the installed toolchain resides. For cases where you need to build the external toolchain, you would need to take separate steps to build and install the toolchain.

  • Make sure you add the layer that contains the toolchain to your bblayers.conf file through the BBLAYERS variable.

  • Set the EXTERNAL_TOOLCHAIN variable in your local.conf file to the location in which you installed the toolchain.

A good example of an external toolchain used with the Yocto Project is Mentor Graphics® Sourcery G++ Toolchain. You can see information on how to use that particular layer in the README file at http://github.com/MentorEmbedded/meta-sourcery/. You can find further information by reading about the TCMODE variable in the Yocto Project Reference Manual's variable glossary.

7.16. Creating Partitioned Images Using Wic

Creating an image for a particular hardware target using the OpenEmbedded build system does not necessarily mean you can boot that image as is on your device. Physical devices accept and boot images in various ways depending on the specifics of the device. Usually, information about the hardware can tell you what image format the device requires. Should your device require multiple partitions on an SD card, flash, or an HDD, you can use the OpenEmbedded Image Creator, Wic, to create the properly partitioned image.

The wic command generates partitioned images from existing OpenEmbedded build artifacts. Image generation is driven by partitioning commands contained in an Openembedded kickstart file (.wks) specified either directly on the command line or as one of a selection of canned kickstart files as shown with the wic list images command in the "Using an Existing Kickstart File" section. When you apply the command to a given set of build artifacts, the result is an image or set of images that can be directly written onto media and used on a particular system.

Note

For a kickstart file reference, see the "OpenEmbedded Kickstart (.wks) Reference" Chapter in the Yocto Project Reference Manual.

The wic command and the infrastructure it is based on is by definition incomplete. The purpose of the command is to allow the generation of customized images, and as such, was designed to be completely extensible through a plug-in interface. See the "Using the Wic Plug-Ins Interface" section for information on these plug-ins.

This section provides some background information on Wic, describes what you need to have in place to run the tool, provides instruction on how to use the Wic utility, provides information on using the Wic plug-ins interface, and provides several examples that show how to use Wic.

7.16.1. Background

This section provides some background on the Wic utility. While none of this information is required to use Wic, you might find it interesting.

  • The name "Wic" is derived from OpenEmbedded Image Creator (oeic). The "oe" diphthong in "oeic" was promoted to the letter "w", because "oeic" is both difficult to remember and to pronounce.

  • Wic is loosely based on the Meego Image Creator (mic) framework. The Wic implementation has been heavily modified to make direct use of OpenEmbedded build artifacts instead of package installation and configuration, which are already incorporated within the OpenEmbedded artifacts.

  • Wic is a completely independent standalone utility that initially provides easier-to-use and more flexible replacements for an existing functionality in OE-Core's image-live class and mkefidisk.sh script. The difference between Wic and those examples is that with Wic the functionality of those scripts is implemented by a general-purpose partitioning language, which is based on Redhat kickstart syntax.

7.16.2. Requirements

In order to use the Wic utility with the OpenEmbedded Build system, your system needs to meet the following requirements:

  • The Linux distribution on your development host must support the Yocto Project. See the "Supported Linux Distributions" section in the Yocto Project Reference Manual for the list of distributions that support the Yocto Project.

  • The standard system utilities, such as cp, must be installed on your development host system.

  • You must have sourced the build environment setup script (i.e. oe-init-build-env) found in the Build Directory.

  • You need to have the build artifacts already available, which typically means that you must have already created an image using the Openembedded build system (e.g. core-image-minimal). While it might seem redundant to generate an image in order to create an image using Wic, the current version of Wic requires the artifacts in the form generated by the OpenEmbedded build system.

  • You must build several native tools, which are built to run on the build system:

         $ bitbake parted-native dosfstools-native mtools-native
                            

  • Include "wic" as part of the IMAGE_FSTYPES variable.

  • Include the name of the wic kickstart file as part of the WKS_FILE variable

7.16.3. Getting Help

You can get general help for the wic command by entering the wic command by itself or by entering the command with a help argument as follows:

     $ wic -h
     $ wic --help
     $ wic help
                

Currently, Wic supports seven commands: cp, create, help, list, ls, rm, and write. You can get help for all these commands except "help" by using the following form:

     $ wic help command
                

For example, the following command returns help for the write command:

     $ wic help write
                

Wic supports help for three topics: overview, plugins, and kickstart. You can get help for any topic using the following form:

     $ wic help topic
                

For example, the following returns overview help for Wic:

     $ wic help overview
                

One additional level of help exists for Wic. You can get help on individual images through the list command. You can use the list command to return the available Wic images as follows:

     $ wic list images
       mpc8315e-rdb                  		Create SD card image for MPC8315E-RDB
       genericx86                    		Create an EFI disk image for genericx86*
       beaglebone-yocto              		Create SD card image for Beaglebone
       edgerouter                    		Create SD card image for Edgerouter
       qemux86-directdisk            		Create a qemu machine 'pcbios' direct disk image
       directdisk-gpt                		Create a 'pcbios' direct disk image
       mkefidisk                     		Create an EFI disk image
       directdisk                    		Create a 'pcbios' direct disk image
       systemd-bootdisk              		Create an EFI disk image with systemd-boot
       mkhybridiso                   		Create a hybrid ISO image
       sdimage-bootpart              		Create SD card image with a boot partition
       directdisk-multi-rootfs       		Create multi rootfs image using rootfs plugin
       directdisk-bootloader-config  		Create a 'pcbios' direct disk image with custom bootloader config
                

Once you know the list of available Wic images, you can use help with the command to get help on a particular image. For example, the following command returns help on the "beaglebone-yocto" image:

     $ wic list beaglebone-yocto help


     Creates a partitioned SD card image for Beaglebone.
     Boot files are located in the first vfat partition.
                

7.16.4. Operational Modes

You can use Wic in two different modes, depending on how much control you need for specifying the Openembedded build artifacts that are used for creating the image: Raw and Cooked:

  • Raw Mode: You explicitly specify build artifacts through Wic command-line arguments.

  • Cooked Mode: The current MACHINE setting and image name are used to automatically locate and provide the build artifacts. You just supply a kickstart file and the name of the image from which to use artifacts.

Regardless of the mode you use, you need to have the build artifacts ready and available.

7.16.4.1. Raw Mode

Running Wic in raw mode allows you to specify all the partitions through the wic command line. The primary use for raw mode is if you have built your kernel outside of the Yocto Project Build Directory. In other words, you can point to arbitrary kernel, root filesystem locations, and so forth. Contrast this behavior with cooked mode where Wic looks in the Build Directory (e.g. tmp/deploy/images/machine).

The general form of the wic command in raw mode is:

     $ wic create wks_file options ...

       Where:

          wks_file:
             An OpenEmbedded kickstart file.  You can provide
             your own custom file or use a file from a set of
             existing files as described by further options.

          optional arguments:
            -h, --help            show this help message and exit
            -o OUTDIR, --outdir OUTDIR
                                  name of directory to create image in
            -e IMAGE_NAME, --image-name IMAGE_NAME
                                  name of the image to use the artifacts from e.g. core-
                                  image-sato
            -r ROOTFS_DIR, --rootfs-dir ROOTFS_DIR
                                  path to the /rootfs dir to use as the .wks rootfs
                                  source
            -b BOOTIMG_DIR, --bootimg-dir BOOTIMG_DIR
                                  path to the dir containing the boot artifacts (e.g.
                                  /EFI or /syslinux dirs) to use as the .wks bootimg
                                  source
            -k KERNEL_DIR, --kernel-dir KERNEL_DIR
                                  path to the dir containing the kernel to use in the
                                  .wks bootimg
            -n NATIVE_SYSROOT, --native-sysroot NATIVE_SYSROOT
                                  path to the native sysroot containing the tools to use
                                  to build the image
            -s, --skip-build-check
                                  skip the build check
            -f, --build-rootfs    build rootfs
            -c {gzip,bzip2,xz}, --compress-with {gzip,bzip2,xz}
                                  compress image with specified compressor
            -m, --bmap            generate .bmap
            --no-fstab-update     Do not change fstab file.
            -v VARS_DIR, --vars VARS_DIR
                                  directory with <image>.env files that store bitbake
                                  variables
            -D, --debug           output debug information
                    

Note

You do not need root privileges to run Wic. In fact, you should not run as root when using the utility.

7.16.4.2. Cooked Mode

Running Wic in cooked mode leverages off artifacts in the Build Directory. In other words, you do not have to specify kernel or root filesystem locations as part of the command. All you need to provide is a kickstart file and the name of the image from which to use artifacts by using the "-e" option. Wic looks in the Build Directory (e.g. tmp/deploy/images/machine) for artifacts.

The general form of the wic command using Cooked Mode is as follows:

     $ wic create wks_file -e IMAGE_NAME

       Where:

          wks_file:
             An OpenEmbedded kickstart file.  You can provide
             your own custom file or use a file from a set of
             existing files provided with the Yocto Project
             release.

          required argument:
             -e IMAGE_NAME, --image-name IMAGE_NAME
                                  name of the image to use the artifacts from e.g. core-
                                  image-sato
                    

7.16.5. Using an Existing Kickstart File

If you do not want to create your own kickstart file, you can use an existing file provided by the Wic installation. As shipped, kickstart files can be found in the Yocto Project Source Repositories in the following two locations:

     poky/meta-yocto-bsp/wic
     poky/scripts/lib/wic/canned-wks
                

Use the following command to list the available kickstart files:

     $ wic list images
       mpc8315e-rdb                  		Create SD card image for MPC8315E-RDB
       genericx86                    		Create an EFI disk image for genericx86*
       beaglebone-yocto              		Create SD card image for Beaglebone
       edgerouter                    		Create SD card image for Edgerouter
       qemux86-directdisk            		Create a qemu machine 'pcbios' direct disk image
       directdisk-gpt                		Create a 'pcbios' direct disk image
       mkefidisk                     		Create an EFI disk image
       directdisk                    		Create a 'pcbios' direct disk image
       systemd-bootdisk              		Create an EFI disk image with systemd-boot
       mkhybridiso                   		Create a hybrid ISO image
       sdimage-bootpart              		Create SD card image with a boot partition
       directdisk-multi-rootfs       		Create multi rootfs image using rootfs plugin
       directdisk-bootloader-config  		Create a 'pcbios' direct disk image with custom bootloader config
                

When you use an existing file, you do not have to use the .wks extension. Here is an example in Raw Mode that uses the directdisk file:

     $ wic create directdisk -r rootfs_dir -b bootimg_dir \
           -k kernel_dir -n native_sysroot
                

Here are the actual partition language commands used in the genericx86.wks file to generate an image:

     # short-description: Create an EFI disk image for genericx86*
     # long-description: Creates a partitioned EFI disk image for genericx86* machines
     part /boot --source bootimg-efi --sourceparams="loader=grub-efi" --ondisk sda --label msdos --active --align 1024
     part / --source rootfs --ondisk sda --fstype=ext4 --label platform --align 1024 --use-uuid
     part swap --ondisk sda --size 44 --label swap1 --fstype=swap

     bootloader --ptable gpt --timeout=5 --append="rootfstype=ext4 console=ttyS0,115200 console=tty0"
                

7.16.6. Using the Wic Plug-Ins Interface

You can extend and specialize Wic functionality by using Wic plug-ins. This section explains the Wic plug-in interface.

Note

Wic plug-ins consist of "source" and "imager" plug-ins. Imager plug-ins are beyond the scope of this section.

Source plug-ins provide a mechanism to customize partition content during the Wic image generation process. You can use source plug-ins to map values that you specify using --source commands in kickstart files (i.e. *.wks) to a plug-in implementation used to populate a given partition.

Note

If you use plug-ins that have build-time dependencies (e.g. native tools, bootloaders, and so forth) when building a Wic image, you need to specify those dependencies using the WKS_FILE_DEPENDS variable.

Source plug-ins are subclasses defined in plug-in files. As shipped, the Yocto Project provides several plug-in files. You can see the source plug-in files that ship with the Yocto Project here. Each of these plug-in files contains source plug-ins that are designed to populate a specific Wic image partition.

Source plug-ins are subclasses of the SourcePlugin class, which is defined in the poky/scripts/lib/wic/pluginbase.py file. For example, the BootimgEFIPlugin source plug-in found in the bootimg-efi.py file is a subclass of the SourcePlugin class, which is found in the pluginbase.py file.

You can also implement source plug-ins in a layer outside of the Source Repositories (external layer). To do so, be sure that your plug-in files are located in a directory whose path is scripts/lib/wic/plugins/source/ within your external layer. When the plug-in files are located there, the source plug-ins they contain are made available to Wic.

When the Wic implementation needs to invoke a partition-specific implementation, it looks for the plug-in with the same name as the --source parameter used in the kickstart file given to that partition. For example, if the partition is set up using the following command in a kickstart file:

     part /boot --source bootimg-pcbios --ondisk sda --label boot --active --align 1024
                

The methods defined as class members of the matching source plug-in (i.e. bootimg-pcbios) in the bootimg-pcbios.py plug-in file are used.

To be more concrete, here is the corresponding plug-in definition from the bootimg-pcbios.py file for the previous command along with an example method called by the Wic implementation when it needs to prepare a partition using an implementation-specific function:

                  .
                  .
                  .
     class BootimgPcbiosPlugin(SourcePlugin):
         """
         Create MBR boot partition and install syslinux on it.
         """

         name = 'bootimg-pcbios'
                  .
                  .
                  .
         @classmethod
         def do_prepare_partition(cls, part, source_params, creator, cr_workdir,
                                  oe_builddir, bootimg_dir, kernel_dir,
                                  rootfs_dir, native_sysroot):
             """
             Called to do the actual content population for a partition i.e. it
             'prepares' the partition to be incorporated into the image.
             In this case, prepare content for legacy bios boot partition.
             """
                  .
                  .
                  .
                

If a subclass (plug-in) itself does not implement a particular function, Wic locates and uses the default version in the superclass. It is for this reason that all source plug-ins are derived from the SourcePlugin class.

The SourcePlugin class defined in the pluginbase.py file defines a set of methods that source plug-ins can implement or override. Any plug-ins (subclass of SourcePlugin) that do not implement a particular method inherit the implementation of the method from the SourcePlugin class. For more information, see the SourcePlugin class in the pluginbase.py file for details:

The following list describes the methods implemented in the SourcePlugin class:

  • do_prepare_partition(): Called to populate a partition with actual content. In other words, the method prepares the final partition image that is incorporated into the disk image.

  • do_configure_partition(): Called before do_prepare_partition() to create custom configuration files for a partition (e.g. syslinux or grub configuration files).

  • do_install_disk(): Called after all partitions have been prepared and assembled into a disk image. This method provides a hook to allow finalization of a disk image (e.g. writing an MBR).

  • do_stage_partition(): Special content-staging hook called before do_prepare_partition(). This method is normally empty.

    Typically, a partition just uses the passed-in parameters (e.g. the unmodified value of bootimg_dir). However, in some cases, things might need to be more tailored. As an example, certain files might additionally need to be taken from bootimg_dir + /boot. This hook allows those files to be staged in a customized fashion.

    Note

    get_bitbake_var() allows you to access non-standard variables that you might want to use for this behavior.

You can extend the source plug-in mechanism. To add more hooks, create more source plug-in methods within SourcePlugin and the corresponding derived subclasses. The code that calls the plug-in methods uses the plugin.get_source_plugin_methods() function to find the method or methods needed by the call. Retrieval of those methods is accomplished by filling up a dict with keys that contain the method names of interest. On success, these will be filled in with the actual methods. See the Wic implementation for examples and details.

7.16.7. Examples

This section provides several examples that show how to use the Wic utility. All the examples assume the list of requirements in the "Requirements" section have been met. The examples assume the previously generated image is core-image-minimal.

7.16.7.1. Generate an Image using an Existing Kickstart File

This example runs in Cooked Mode and uses the mkefidisk kickstart file:

     $ wic create mkefidisk -e core-image-minimal
     INFO: Building wic-tools...
               .
               .
               .
     INFO: The new image(s) can be found here:
       ./mkefidisk-201804191017-sda.direct

     The following build artifacts were used to create the image(s):
       ROOTFS_DIR:                   /home/stephano/build/master/build/tmp-glibc/work/qemux86-oe-linux/core-image-minimal/1.0-r0/rootfs
       BOOTIMG_DIR:                  /home/stephano/build/master/build/tmp-glibc/work/qemux86-oe-linux/core-image-minimal/1.0-r0/recipe-sysroot/usr/share
       KERNEL_DIR:                   /home/stephano/build/master/build/tmp-glibc/deploy/images/qemux86
       NATIVE_SYSROOT:               /home/stephano/build/master/build/tmp-glibc/work/i586-oe-linux/wic-tools/1.0-r0/recipe-sysroot-native

     INFO: The image(s) were created using OE kickstart file:
       /home/stephano/build/master/openembedded-core/scripts/lib/wic/canned-wks/mkefidisk.wks
                    

The previous example shows the easiest way to create an image by running in cooked mode and supplying a kickstart file and the "-e" option to point to the existing build artifacts. Your local.conf file needs to have the MACHINE variable set to the machine you are using, which is "qemux86" in this example.

Once the image builds, the output provides image location, artifact use, and kickstart file information.

Note

You should always verify the details provided in the output to make sure that the image was indeed created exactly as expected.

Continuing with the example, you can now write the image from the Build Directory onto a USB stick, or whatever media for which you built your image, and boot from the media. You can write the image by using bmaptool or dd:

     $ oe-run-native bmaptool copy mkefidisk-201804191017-sda.direct /dev/sdX
                    

or

     $ sudo dd if=mkefidisk-201804191017-sda.direct of=/dev/sdX
                    

Note

For more information on how to use the bmaptool to flash a device with an image, see the "Flashing Images Using bmaptool" section.

7.16.7.2. Using a Modified Kickstart File

Because partitioned image creation is driven by the kickstart file, it is easy to affect image creation by changing the parameters in the file. This next example demonstrates that through modification of the directdisk-gpt kickstart file.

As mentioned earlier, you can use the command wic list images to show the list of existing kickstart files. The directory in which the directdisk-gpt.wks file resides is scripts/lib/image/canned-wks/, which is located in the Source Directory (e.g. poky). Because available files reside in this directory, you can create and add your own custom files to the directory. Subsequent use of the wic list images command would then include your kickstart files.

In this example, the existing directdisk-gpt file already does most of what is needed. However, for the hardware in this example, the image will need to boot from sdb instead of sda, which is what the directdisk-gpt kickstart file uses.

The example begins by making a copy of the directdisk-gpt.wks file in the scripts/lib/image/canned-wks directory and then by changing the lines that specify the target disk from which to boot.

     $ cp /home/stephano/poky/scripts/lib/wic/canned-wks/directdisk-gpt.wks \
          /home/stephano/poky/scripts/lib/wic/canned-wks/directdisksdb-gpt.wks
                    

Next, the example modifies the directdisksdb-gpt.wks file and changes all instances of "--ondisk sda" to "--ondisk sdb". The example changes the following two lines and leaves the remaining lines untouched:

     part /boot --source bootimg-pcbios --ondisk sdb --label boot --active --align 1024
     part / --source rootfs --ondisk sdb --fstype=ext4 --label platform --align 1024 --use-uuid
                    

Once the lines are changed, the example generates the directdisksdb-gpt image. The command points the process at the core-image-minimal artifacts for the Next Unit of Computing (nuc) MACHINE the local.conf.

     $ wic create directdisksdb-gpt -e core-image-minimal
     INFO: Building wic-tools...
                .
                .
                .
     Initialising tasks: 100% |#######################################| Time: 0:00:01
     NOTE: Executing SetScene Tasks
     NOTE: Executing RunQueue Tasks
     NOTE: Tasks Summary: Attempted 1161 tasks of which 1157 didn't need to be rerun and all succeeded.
     INFO: Creating image(s)...

     INFO: The new image(s) can be found here:
       ./directdisksdb-gpt-201710090938-sdb.direct

     The following build artifacts were used to create the image(s):
       ROOTFS_DIR:                   /home/stephano/build/master/build/tmp-glibc/work/qemux86-oe-linux/core-image-minimal/1.0-r0/rootfs
       BOOTIMG_DIR:                  /home/stephano/build/master/build/tmp-glibc/work/qemux86-oe-linux/core-image-minimal/1.0-r0/recipe-sysroot/usr/share
       KERNEL_DIR:                   /home/stephano/build/master/build/tmp-glibc/deploy/images/qemux86
       NATIVE_SYSROOT:               /home/stephano/build/master/build/tmp-glibc/work/i586-oe-linux/wic-tools/1.0-r0/recipe-sysroot-native

     INFO: The image(s) were created using OE kickstart file:
       /home/stephano/poky/scripts/lib/wic/canned-wks/directdisksdb-gpt.wks
                    

Continuing with the example, you can now directly dd the image to a USB stick, or whatever media for which you built your image, and boot the resulting media:

     $ sudo dd if=directdisksdb-gpt-201710090938-sdb.direct of=/dev/sdb
     140966+0 records in
     140966+0 records out
     72174592 bytes (72 MB, 69 MiB) copied, 78.0282 s, 925 kB/s
     $ sudo eject /dev/sdb
                    

7.16.7.3. Using a Modified Kickstart File and Running in Raw Mode

This next example manually specifies each build artifact (runs in Raw Mode) and uses a modified kickstart file. The example also uses the -o option to cause Wic to create the output somewhere other than the default output directory, which is the current directory:

     $ wic create /home/stephano/my_yocto/test.wks -o /home/stephano/testwic \
          --rootfs-dir /home/stephano/build/master/build/tmp/work/qemux86-poky-linux/core-image-minimal/1.0-r0/rootfs \
          --bootimg-dir /home/stephano/build/master/build/tmp/work/qemux86-poky-linux/core-image-minimal/1.0-r0/recipe-sysroot/usr/share \
          --kernel-dir /home/stephano/build/master/build/tmp/deploy/images/qemux86 \
          --native-sysroot /home/stephano/build/master/build/tmp/work/i586-poky-linux/wic-tools/1.0-r0/recipe-sysroot-native

     INFO: Creating image(s)...

     INFO: The new image(s) can be found here:
       /home/stephano/testwic/test-201710091445-sdb.direct

     The following build artifacts were used to create the image(s):
       ROOTFS_DIR:                   /home/stephano/build/master/build/tmp-glibc/work/qemux86-oe-linux/core-image-minimal/1.0-r0/rootfs
       BOOTIMG_DIR:                  /home/stephano/build/master/build/tmp-glibc/work/qemux86-oe-linux/core-image-minimal/1.0-r0/recipe-sysroot/usr/share
       KERNEL_DIR:                   /home/stephano/build/master/build/tmp-glibc/deploy/images/qemux86
       NATIVE_SYSROOT:               /home/stephano/build/master/build/tmp-glibc/work/i586-oe-linux/wic-tools/1.0-r0/recipe-sysroot-native

     INFO: The image(s) were created using OE kickstart file:
       /home/stephano/my_yocto/test.wks
                    

For this example, MACHINE did not have to be specified in the local.conf file since the artifact is manually specified.

7.16.7.4. Using Wic to Manipulate an Image

Wic image manipulation allows you to shorten turnaround time during image development. For example, you can use Wic to delete the kernel partition of a Wic image and then insert a newly built kernel. This saves you time from having to rebuild the entire image each time you modify the kernel.

Note

In order to use Wic to manipulate a Wic image as in this example, your development machine must have the mtools package installed.

The following example examines the contents of the Wic image, deletes the existing kernel, and then inserts a new kernel:

  1. List the Partitions: Use the wic ls command to list all the partitions in the Wic image:

         $ wic ls tmp/deploy/images/qemux86/core-image-minimal-qemux86.wic
         Num     Start        End          Size      Fstype
          1       1048576     25041919     23993344  fat16
          2      25165824     72157183     46991360  ext4
                                

    The previous output shows two partitions in the core-image-minimal-qemux86.wic image.

  2. Examine a Particular Partition: Use the wic ls command again but in a different form to examine a particular partition.

    Note

    You can get command usage on any Wic command using the following form:
         $ wic help command
                                    
    For example, the following command shows you the various ways to use the wic ls command:
         $ wic help ls
                                    

    The following command shows what is in Partition one:

         $ wic ls tmp/deploy/images/qemux86/core-image-minimal-qemux86.wic:1
         Volume in drive : is boot
          Volume Serial Number is E894-1809
         Directory for ::/
    
         libcom32 c32    186500 2017-10-09  16:06
         libutil  c32     24148 2017-10-09  16:06
         syslinux cfg       220 2017-10-09  16:06
         vesamenu c32     27104 2017-10-09  16:06
         vmlinuz        6904608 2017-10-09  16:06
                 5 files           7 142 580 bytes
                                  16 582 656 bytes free
                                

    The previous output shows five files, with the vmlinuz being the kernel.

    Note

    If you see the following error, you need to update or create a ~/.mtoolsrc file and be sure to have the line “mtools_skip_check=1“ in the file. Then, run the Wic command again:
         ERROR: _exec_cmd: /usr/bin/mdir -i /tmp/wic-parttfokuwra ::/ returned '1' instead of 0
          output: Total number of sectors (47824) not a multiple of sectors per track (32)!
          Add mtools_skip_check=1 to your .mtoolsrc file to skip this test
                                    

  3. Remove the Old Kernel: Use the wic rm command to remove the vmlinuz file (kernel):

         $ wic rm tmp/deploy/images/qemux86/core-image-minimal-qemux86.wic:1/vmlinuz
                                 

  4. Add In the New Kernel: Use the wic cp command to add the updated kernel to the Wic image. Depending on how you built your kernel, it could be in different places. If you used devtool and an SDK to build your kernel, it resides in the tmp/work directory of the extensible SDK. If you used make to build the kernel, the kernel will be in the workspace/sources area.

    The following example assumes devtool was used to build the kernel:

         cp ~/poky_sdk/tmp/work/qemux86-poky-linux/linux-yocto/4.12.12+git999-r0/linux-yocto-4.12.12+git999/arch/x86/boot/bzImage \
            ~/poky/build/tmp/deploy/images/qemux86/core-image-minimal-qemux86.wic:1/vmlinuz
                                 

    Once the new kernel is added back into the image, you can use the dd command or bmaptool to flash your wic image onto an SD card or USB stick and test your target.

    Note

    Using bmaptool is generally 10 to 20 times faster than using dd.

7.17. Flashing Images Using bmaptool

A fast and easy way to flash an image to a bootable device is to use Bmaptool, which is integrated into the OpenEmbedded build system. Bmaptool is a generic tool that creates a file's block map (bmap) and then uses that map to copy the file. As compared to traditional tools such as dd or cp, Bmaptool can copy (or flash) large files like raw system image files much faster.

Notes

  • If you are using Ubuntu or Debian distributions, you can install the bmap-tools package using the following command and then use the tool without specifying PATH even from the root account:

         $ sudo apt-get install bmap-tools
                            

  • If you are unable to install the bmap-tools package, you will need to build Bmaptool before using it. Use the following command:

         $ bitbake bmap-tools-native
                            

Following, is an example that shows how to flash a Wic image. Realize that while this example uses a Wic image, you can use Bmaptool to flash any type of image. Use these steps to flash an image using Bmaptool:

  1. Update your local.conf File: You need to have the following set in your local.conf file before building your image:

         IMAGE_FSTYPES += "wic wic.bmap"
                        

  2. Get Your Image: Either have your image ready (pre-built with the IMAGE_FSTYPES setting previously mentioned) or take the step to build the image:

         $ bitbake image
                        

  3. Flash the Device: Flash the device with the image by using Bmaptool depending on your particular setup. The following commands assume the image resides in the Build Directory's deploy/images/ area:

    • If you have write access to the media, use this command form:

           $ oe-run-native bmap-tools-native bmaptool copy build-directory/tmp/deploy/images/machine/image.wic /dev/sdX
                                  

    • If you do not have write access to the media, set your permissions first and then use the same command form:

           $ sudo chmod 666 /dev/sdX
           $ oe-run-native bmap-tools-native bmaptool copy build-directory/tmp/deploy/images/machine/image.wic /dev/sdX
                                  

For help on the bmaptool command, use the following command:

     $ bmaptool --help
            

7.18. Making Images More Secure

Security is of increasing concern for embedded devices. Consider the issues and problems discussed in just this sampling of work found across the Internet:

When securing your image is of concern, there are steps, tools, and variables that you can consider to help you reach the security goals you need for your particular device. Not all situations are identical when it comes to making an image secure. Consequently, this section provides some guidance and suggestions for consideration when you want to make your image more secure.

Note

Because the security requirements and risks are different for every type of device, this section cannot provide a complete reference on securing your custom OS. It is strongly recommended that you also consult other sources of information on embedded Linux system hardening and on security.

7.18.1. General Considerations

General considerations exist that help you create more secure images. You should consider the following suggestions to help make your device more secure:

  • Scan additional code you are adding to the system (e.g. application code) by using static analysis tools. Look for buffer overflows and other potential security problems.

  • Pay particular attention to the security for any web-based administration interface.

    Web interfaces typically need to perform administrative functions and tend to need to run with elevated privileges. Thus, the consequences resulting from the interface's security becoming compromised can be serious. Look for common web vulnerabilities such as cross-site-scripting (XSS), unvalidated inputs, and so forth.

    As with system passwords, the default credentials for accessing a web-based interface should not be the same across all devices. This is particularly true if the interface is enabled by default as it can be assumed that many end-users will not change the credentials.

  • Ensure you can update the software on the device to mitigate vulnerabilities discovered in the future. This consideration especially applies when your device is network-enabled.

  • Ensure you remove or disable debugging functionality before producing the final image. For information on how to do this, see the "Considerations Specific to the OpenEmbedded Build System" section.

  • Ensure you have no network services listening that are not needed.

  • Remove any software from the image that is not needed.

  • Enable hardware support for secure boot functionality when your device supports this functionality.

7.18.2. Security Flags

The Yocto Project has security flags that you can enable that help make your build output more secure. The security flags are in the meta/conf/distro/include/security_flags.inc file in your Source Directory (e.g. poky).

Note

Depending on the recipe, certain security flags are enabled and disabled by default.

Use the following line in your local.conf file or in your custom distribution configuration file to enable the security compiler and linker flags for your build:

     require conf/distro/include/security_flags.inc
                

7.18.3. Considerations Specific to the OpenEmbedded Build System

You can take some steps that are specific to the OpenEmbedded build system to make your images more secure:

  • Ensure "debug-tweaks" is not one of your selected IMAGE_FEATURES. When creating a new project, the default is to provide you with an initial local.conf file that enables this feature using the EXTRA_IMAGE_FEATURES variable with the line:

         EXTRA_IMAGE_FEATURES = "debug-tweaks"
                    

    To disable that feature, simply comment out that line in your local.conf file, or make sure IMAGE_FEATURES does not contain "debug-tweaks" before producing your final image. Among other things, leaving this in place sets the root password as blank, which makes logging in for debugging or inspection easy during development but also means anyone can easily log in during production.

  • It is possible to set a root password for the image and also to set passwords for any extra users you might add (e.g. administrative or service type users). When you set up passwords for multiple images or users, you should not duplicate passwords.

    To set up passwords, use the extrausers class, which is the preferred method. For an example on how to set up both root and user passwords, see the "extrausers.bbclass" section.

    Note

    When adding extra user accounts or setting a root password, be cautious about setting the same password on every device. If you do this, and the password you have set is exposed, then every device is now potentially compromised. If you need this access but want to ensure security, consider setting a different, random password for each device. Typically, you do this as a separate step after you deploy the image onto the device.

  • Consider enabling a Mandatory Access Control (MAC) framework such as SMACK or SELinux and tuning it appropriately for your device's usage. You can find more information in the meta-selinux layer.

7.18.4. Tools for Hardening Your Image

The Yocto Project provides tools for making your image more secure. You can find these tools in the meta-security layer of the Yocto Project Source Repositories.

7.19. Creating Your Own Distribution

When you build an image using the Yocto Project and do not alter any distribution Metadata, you are creating a Poky distribution. If you wish to gain more control over package alternative selections, compile-time options, and other low-level configurations, you can create your own distribution.

To create your own distribution, the basic steps consist of creating your own distribution layer, creating your own distribution configuration file, and then adding any needed code and Metadata to the layer. The following steps provide some more detail:

  • Create a layer for your new distro: Create your distribution layer so that you can keep your Metadata and code for the distribution separate. It is strongly recommended that you create and use your own layer for configuration and code. Using your own layer as compared to just placing configurations in a local.conf configuration file makes it easier to reproduce the same build configuration when using multiple build machines. See the "Creating a General Layer Using the bitbake-layers Script" section for information on how to quickly set up a layer.

  • Create the distribution configuration file: The distribution configuration file needs to be created in the conf/distro directory of your layer. You need to name it using your distribution name (e.g. mydistro.conf).

    Note

    The DISTRO variable in your local.conf file determines the name of your distribution.

    You can split out parts of your configuration file into include files and then "require" them from within your distribution configuration file. Be sure to place the include files in the conf/distro/include directory of your layer. A common example usage of include files would be to separate out the selection of desired version and revisions for individual recipes.

    Your configuration file needs to set the following required variables:

         DISTRO_NAME
         DISTRO_VERSION
                        

    These following variables are optional and you typically set them from the distribution configuration file:

         DISTRO_FEATURES
         DISTRO_EXTRA_RDEPENDS
         DISTRO_EXTRA_RRECOMMENDS
         TCLIBC
                        

    Tip

    If you want to base your distribution configuration file on the very basic configuration from OE-Core, you can use conf/distro/defaultsetup.conf as a reference and just include variables that differ as compared to defaultsetup.conf. Alternatively, you can create a distribution configuration file from scratch using the defaultsetup.conf file or configuration files from other distributions such as Poky or Angstrom as references.
  • Provide miscellaneous variables: Be sure to define any other variables for which you want to create a default or enforce as part of the distribution configuration. You can include nearly any variable from the local.conf file. The variables you use are not limited to the list in the previous bulleted item.

  • Point to Your distribution configuration file: In your local.conf file in the Build Directory, set your DISTRO variable to point to your distribution's configuration file. For example, if your distribution's configuration file is named mydistro.conf, then you point to it as follows:

         DISTRO = "mydistro"
                        
  • Add more to the layer if necessary: Use your layer to hold other information needed for the distribution:

    • Add recipes for installing distro-specific configuration files that are not already installed by another recipe. If you have distro-specific configuration files that are included by an existing recipe, you should add an append file (.bbappend) for those. For general information and recommendations on how to add recipes to your layer, see the "Creating Your Own Layer" and "Following Best Practices When Creating Layers" sections.

    • Add any image recipes that are specific to your distribution.

    • Add a psplash append file for a branded splash screen. For information on append files, see the "Using .bbappend Files in Your Layer" section.

    • Add any other append files to make custom changes that are specific to individual recipes.

7.20. Creating a Custom Template Configuration Directory

If you are producing your own customized version of the build system for use by other users, you might want to customize the message shown by the setup script or you might want to change the template configuration files (i.e. local.conf and bblayers.conf) that are created in a new build directory.

The OpenEmbedded build system uses the environment variable TEMPLATECONF to locate the directory from which it gathers configuration information that ultimately ends up in the Build Directory conf directory. By default, TEMPLATECONF is set as follows in the poky repository:

     TEMPLATECONF=${TEMPLATECONF:-meta-poky/conf}
            

This is the directory used by the build system to find templates from which to build some key configuration files. If you look at this directory, you will see the bblayers.conf.sample, local.conf.sample, and conf-notes.txt files. The build system uses these files to form the respective bblayers.conf file, local.conf file, and display the list of BitBake targets when running the setup script.

To override these default configuration files with configurations you want used within every new Build Directory, simply set the TEMPLATECONF variable to your directory. The TEMPLATECONF variable is set in the .templateconf file, which is in the top-level Source Directory folder (e.g. poky). Edit the .templateconf so that it can locate your directory.

Best practices dictate that you should keep your template configuration directory in your custom distribution layer. For example, suppose you have a layer named meta-mylayer located in your home directory and you want your template configuration directory named myconf. Changing the .templateconf as follows causes the OpenEmbedded build system to look in your directory and base its configuration files on the *.sample configuration files it finds. The final configuration files (i.e. local.conf and bblayers.conf ultimately still end up in your Build Directory, but they are based on your *.sample files.

     TEMPLATECONF=${TEMPLATECONF:-meta-mylayer/myconf}
            

Aside from the *.sample configuration files, the conf-notes.txt also resides in the default meta-poky/conf directory. The script that sets up the build environment (i.e. oe-init-build-env) uses this file to display BitBake targets as part of the script output. Customizing this conf-notes.txt file is a good way to make sure your list of custom targets appears as part of the script's output.

Here is the default list of targets displayed as a result of running either of the setup scripts:

     You can now run 'bitbake <target>'

     Common targets are:
         core-image-minimal
         core-image-sato
         meta-toolchain
         meta-ide-support
            

Changing the listed common targets is as easy as editing your version of conf-notes.txt in your custom template configuration directory and making sure you have TEMPLATECONF set to your directory.

7.21. Conserving Disk Space During Builds

To help conserve disk space during builds, you can add the following statement to your project's local.conf configuration file found in the Build Directory:

     INHERIT += "rm_work"
            

Adding this statement deletes the work directory used for building a recipe once the recipe is built. For more information on "rm_work", see the rm_work class in the Yocto Project Reference Manual.

7.22. Working with Packages

This section describes a few tasks that involve packages:

7.22.1. Excluding Packages from an Image

You might find it necessary to prevent specific packages from being installed into an image. If so, you can use several variables to direct the build system to essentially ignore installing recommended packages or to not install a package at all.

The following list introduces variables you can use to prevent packages from being installed into your image. Each of these variables only works with IPK and RPM package types. Support for Debian packages does not exist. Also, you can use these variables from your local.conf file or attach them to a specific image recipe by using a recipe name override. For more detail on the variables, see the descriptions in the Yocto Project Reference Manual's glossary chapter.

  • BAD_RECOMMENDATIONS: Use this variable to specify "recommended-only" packages that you do not want installed.

  • NO_RECOMMENDATIONS: Use this variable to prevent all "recommended-only" packages from being installed.

  • PACKAGE_EXCLUDE: Use this variable to prevent specific packages from being installed regardless of whether they are "recommended-only" or not. You need to realize that the build process could fail with an error when you prevent the installation of a package whose presence is required by an installed package.

7.22.2. Incrementing a Package Version

This section provides some background on how binary package versioning is accomplished and presents some of the services, variables, and terminology involved.

In order to understand binary package versioning, you need to consider the following:

  • Binary Package: The binary package that is eventually built and installed into an image.

  • Binary Package Version: The binary package version is composed of two components - a version and a revision.

    Note

    Technically, a third component, the "epoch" (i.e. PE) is involved but this discussion for the most part ignores PE.

    The version and revision are taken from the PV and PR variables, respectively.

  • PV: The recipe version. PV represents the version of the software being packaged. Do not confuse PV with the binary package version.

  • PR: The recipe revision.

  • SRCPV: The OpenEmbedded build system uses this string to help define the value of PV when the source code revision needs to be included in it.

  • PR Service: A network-based service that helps automate keeping package feeds compatible with existing package manager applications such as RPM, APT, and OPKG.

Whenever the binary package content changes, the binary package version must change. Changing the binary package version is accomplished by changing or "bumping" the PR and/or PV values. Increasing these values occurs one of two ways:

  • Automatically using a Package Revision Service (PR Service).

  • Manually incrementing the PR and/or PV variables.

Given a primary challenge of any build system and its users is how to maintain a package feed that is compatible with existing package manager applications such as RPM, APT, and OPKG, using an automated system is much preferred over a manual system. In either system, the main requirement is that binary package version numbering increases in a linear fashion and that a number of version components exist that support that linear progression. For information on how to ensure package revisioning remains linear, see the "Automatically Incrementing a Binary Package Revision Number" section.

The following three sections provide related information on the PR Service, the manual method for "bumping" PR and/or PV, and on how to ensure binary package revisioning remains linear.

7.22.2.1. Working With a PR Service

As mentioned, attempting to maintain revision numbers in the Metadata is error prone, inaccurate, and causes problems for people submitting recipes. Conversely, the PR Service automatically generates increasing numbers, particularly the revision field, which removes the human element.

Note

For additional information on using a PR Service, you can see the PR Service wiki page.

The Yocto Project uses variables in order of decreasing priority to facilitate revision numbering (i.e. PE, PV, and PR for epoch, version, and revision, respectively). The values are highly dependent on the policies and procedures of a given distribution and package feed.

Because the OpenEmbedded build system uses "signatures", which are unique to a given build, the build system knows when to rebuild packages. All the inputs into a given task are represented by a signature, which can trigger a rebuild when different. Thus, the build system itself does not rely on the PR, PV, and PE numbers to trigger a rebuild. The signatures, however, can be used to generate these values.

The PR Service works with both OEBasic and OEBasicHash generators. The value of PR bumps when the checksum changes and the different generator mechanisms change signatures under different circumstances.

As implemented, the build system includes values from the PR Service into the PR field as an addition using the form ".x" so r0 becomes r0.1, r0.2 and so forth. This scheme allows existing PR values to be used for whatever reasons, which include manual PR bumps, should it be necessary.

By default, the PR Service is not enabled or running. Thus, the packages generated are just "self consistent". The build system adds and removes packages and there are no guarantees about upgrade paths but images will be consistent and correct with the latest changes.

The simplest form for a PR Service is for it to exist for a single host development system that builds the package feed (building system). For this scenario, you can enable a local PR Service by setting PRSERV_HOST in your local.conf file in the Build Directory:

     PRSERV_HOST = "localhost:0"
                    

Once the service is started, packages will automatically get increasing PR values and BitBake takes care of starting and stopping the server.

If you have a more complex setup where multiple host development systems work against a common, shared package feed, you have a single PR Service running and it is connected to each building system. For this scenario, you need to start the PR Service using the bitbake-prserv command:

     bitbake-prserv --host ip --port port --start
                    

In addition to hand-starting the service, you need to update the local.conf file of each building system as described earlier so each system points to the server and port.

It is also recommended you use build history, which adds some sanity checks to binary package versions, in conjunction with the server that is running the PR Service. To enable build history, add the following to each building system's local.conf file:

     # It is recommended to activate "buildhistory" for testing the PR service
     INHERIT += "buildhistory"
     BUILDHISTORY_COMMIT = "1"
                    

For information on build history, see the "Maintaining Build Output Quality" section.

Note

The OpenEmbedded build system does not maintain PR information as part of the shared state (sstate) packages. If you maintain an sstate feed, its expected that either all your building systems that contribute to the sstate feed use a shared PR Service, or you do not run a PR Service on any of your building systems. Having some systems use a PR Service while others do not leads to obvious problems.

For more information on shared state, see the "Shared State Cache" section in the Yocto Project Overview and Concepts Manual.

7.22.2.2. Manually Bumping PR

The alternative to setting up a PR Service is to manually "bump" the PR variable.

If a committed change results in changing the package output, then the value of the PR variable needs to be increased (or "bumped") as part of that commit. For new recipes you should add the PR variable and set its initial value equal to "r0", which is the default. Even though the default value is "r0", the practice of adding it to a new recipe makes it harder to forget to bump the variable when you make changes to the recipe in future.

If you are sharing a common .inc file with multiple recipes, you can also use the INC_PR variable to ensure that the recipes sharing the .inc file are rebuilt when the .inc file itself is changed. The .inc file must set INC_PR (initially to "r0"), and all recipes referring to it should set PR to "${INC_PR}.0" initially, incrementing the last number when the recipe is changed. If the .inc file is changed then its INC_PR should be incremented.

When upgrading the version of a binary package, assuming the PV changes, the PR variable should be reset to "r0" (or "${INC_PR}.0" if you are using INC_PR).

Usually, version increases occur only to binary packages. However, if for some reason PV changes but does not increase, you can increase the PE variable (Package Epoch). The PE variable defaults to "0".

Binary package version numbering strives to follow the Debian Version Field Policy Guidelines. These guidelines define how versions are compared and what "increasing" a version means.

7.22.2.3. Automatically Incrementing a Package Version Number

When fetching a repository, BitBake uses the SRCREV variable to determine the specific source code revision from which to build. You set the SRCREV variable to AUTOREV to cause the OpenEmbedded build system to automatically use the latest revision of the software:

     SRCREV = "${AUTOREV}"
                    

Furthermore, you need to reference SRCPV in PV in order to automatically update the version whenever the revision of the source code changes. Here is an example:

     PV = "1.0+git${SRCPV}"
                    

The OpenEmbedded build system substitutes SRCPV with the following:

     AUTOINC+source_code_revision
                    

The build system replaces the AUTOINC with a number. The number used depends on the state of the PR Service:

  • If PR Service is enabled, the build system increments the number, which is similar to the behavior of PR. This behavior results in linearly increasing package versions, which is desirable. Here is an example:

         hello-world-git_0.0+git0+b6558dd387-r0.0_armv7a-neon.ipk
         hello-world-git_0.0+git1+dd2f5c3565-r0.0_armv7a-neon.ipk
                                

  • If PR Service is not enabled, the build system replaces the AUTOINC placeholder with zero (i.e. "0"). This results in changing the package version since the source revision is included. However, package versions are not increased linearly. Here is an example:

         hello-world-git_0.0+git0+b6558dd387-r0.0_armv7a-neon.ipk
         hello-world-git_0.0+git0+dd2f5c3565-r0.0_armv7a-neon.ipk
                                

In summary, the OpenEmbedded build system does not track the history of binary package versions for this purpose. AUTOINC, in this case, is comparable to PR. If PR server is not enabled, AUTOINC in the package version is simply replaced by "0". If PR server is enabled, the build system keeps track of the package versions and bumps the number when the package revision changes.

7.22.3. Handling Optional Module Packaging

Many pieces of software split functionality into optional modules (or plug-ins) and the plug-ins that are built might depend on configuration options. To avoid having to duplicate the logic that determines what modules are available in your recipe or to avoid having to package each module by hand, the OpenEmbedded build system provides functionality to handle module packaging dynamically.

To handle optional module packaging, you need to do two things:

  • Ensure the module packaging is actually done.

  • Ensure that any dependencies on optional modules from other recipes are satisfied by your recipe.

7.22.3.1. Making Sure the Packaging is Done

To ensure the module packaging actually gets done, you use the do_split_packages function within the populate_packages Python function in your recipe. The do_split_packages function searches for a pattern of files or directories under a specified path and creates a package for each one it finds by appending to the PACKAGES variable and setting the appropriate values for FILES_packagename, RDEPENDS_packagename, DESCRIPTION_packagename, and so forth. Here is an example from the lighttpd recipe:

     python populate_packages_prepend () {
         lighttpd_libdir = d.expand('${libdir}')
         do_split_packages(d, lighttpd_libdir, '^mod_(.*)\.so$',
                          'lighttpd-module-%s', 'Lighttpd module for %s',
                           extra_depends='')
     }
                    

The previous example specifies a number of things in the call to do_split_packages.

  • A directory within the files installed by your recipe through do_install in which to search.

  • A regular expression used to match module files in that directory. In the example, note the parentheses () that mark the part of the expression from which the module name should be derived.

  • A pattern to use for the package names.

  • A description for each package.

  • An empty string for extra_depends, which disables the default dependency on the main lighttpd package. Thus, if a file in ${libdir} called mod_alias.so is found, a package called lighttpd-module-alias is created for it and the DESCRIPTION is set to "Lighttpd module for alias".

Often, packaging modules is as simple as the previous example. However, more advanced options exist that you can use within do_split_packages to modify its behavior. And, if you need to, you can add more logic by specifying a hook function that is called for each package. It is also perfectly acceptable to call do_split_packages multiple times if you have more than one set of modules to package.

For more examples that show how to use do_split_packages, see the connman.inc file in the meta/recipes-connectivity/connman/ directory of the poky source repository. You can also find examples in meta/classes/kernel.bbclass.

Following is a reference that shows do_split_packages mandatory and optional arguments:

     Mandatory arguments

     root
        The path in which to search
     file_regex
        Regular expression to match searched files.
        Use parentheses () to mark the part of this
        expression that should be used to derive the
        module name (to be substituted where %s is
        used in other function arguments as noted below)
     output_pattern
        Pattern to use for the package names. Must
        include %s.
     description
        Description to set for each package. Must
        include %s.

     Optional arguments

     postinst
        Postinstall script to use for all packages
        (as a string)
     recursive
        True to perform a recursive search - default
        False
     hook
        A hook function to be called for every match.
        The function will be called with the following
        arguments (in the order listed):

        f
           Full path to the file/directory match
        pkg
           The package name
        file_regex
           As above
        output_pattern
           As above
        modulename
           The module name derived using file_regex

     extra_depends
        Extra runtime dependencies (RDEPENDS) to be
        set for all packages. The default value of None
        causes a dependency on the main package
        (${PN}) - if you do not want this, pass empty
        string '' for this parameter.
     aux_files_pattern
        Extra item(s) to be added to FILES for each
        package. Can be a single string item or a list
        of strings for multiple items. Must include %s.
     postrm
        postrm script to use for all packages (as a
        string)
     allow_dirs
        True to allow directories to be matched -
        default False
     prepend
        If True, prepend created packages to PACKAGES
        instead of the default False which appends them
     match_path
        match file_regex on the whole relative path to
        the root rather than just the file name
     aux_files_pattern_verbatim
        Extra item(s) to be added to FILES for each
        package, using the actual derived module name
        rather than converting it to something legal
        for a package name. Can be a single string item
        or a list of strings for multiple items. Must
        include %s.
     allow_links
        True to allow symlinks to be matched - default
        False
     summary
        Summary to set for each package. Must include %s;
        defaults to description if not set.
                     

7.22.3.2. Satisfying Dependencies

The second part for handling optional module packaging is to ensure that any dependencies on optional modules from other recipes are satisfied by your recipe. You can be sure these dependencies are satisfied by using the PACKAGES_DYNAMIC variable. Here is an example that continues with the lighttpd recipe shown earlier:

     PACKAGES_DYNAMIC = "lighttpd-module-.*"
                    

The name specified in the regular expression can of course be anything. In this example, it is lighttpd-module- and is specified as the prefix to ensure that any RDEPENDS and RRECOMMENDS on a package name starting with the prefix are satisfied during build time. If you are using do_split_packages as described in the previous section, the value you put in PACKAGES_DYNAMIC should correspond to the name pattern specified in the call to do_split_packages.

7.22.4. Using Runtime Package Management

During a build, BitBake always transforms a recipe into one or more packages. For example, BitBake takes the bash recipe and produces a number of packages (e.g. bash, bash-bashbug, bash-completion, bash-completion-dbg, bash-completion-dev, bash-completion-extra, bash-dbg, and so forth). Not all generated packages are included in an image.

In several situations, you might need to update, add, remove, or query the packages on a target device at runtime (i.e. without having to generate a new image). Examples of such situations include:

  • You want to provide in-the-field updates to deployed devices (e.g. security updates).

  • You want to have a fast turn-around development cycle for one or more applications that run on your device.

  • You want to temporarily install the "debug" packages of various applications on your device so that debugging can be greatly improved by allowing access to symbols and source debugging.

  • You want to deploy a more minimal package selection of your device but allow in-the-field updates to add a larger selection for customization.

In all these situations, you have something similar to a more traditional Linux distribution in that in-field devices are able to receive pre-compiled packages from a server for installation or update. Being able to install these packages on a running, in-field device is what is termed "runtime package management".

In order to use runtime package management, you need a host or server machine that serves up the pre-compiled packages plus the required metadata. You also need package manipulation tools on the target. The build machine is a likely candidate to act as the server. However, that machine does not necessarily have to be the package server. The build machine could push its artifacts to another machine that acts as the server (e.g. Internet-facing). In fact, doing so is advantageous for a production environment as getting the packages away from the development system's build directory prevents accidental overwrites.

A simple build that targets just one device produces more than one package database. In other words, the packages produced by a build are separated out into a couple of different package groupings based on criteria such as the target's CPU architecture, the target board, or the C library used on the target. For example, a build targeting the qemux86 device produces the following three package databases: noarch, i586, and qemux86. If you wanted your qemux86 device to be aware of all the packages that were available to it, you would need to point it to each of these databases individually. In a similar way, a traditional Linux distribution usually is configured to be aware of a number of software repositories from which it retrieves packages.

Using runtime package management is completely optional and not required for a successful build or deployment in any way. But if you want to make use of runtime package management, you need to do a couple things above and beyond the basics. The remainder of this section describes what you need to do.

7.22.4.1. Build Considerations

This section describes build considerations of which you need to be aware in order to provide support for runtime package management.

When BitBake generates packages, it needs to know what format or formats to use. In your configuration, you use the PACKAGE_CLASSES variable to specify the format:

  1. Open the local.conf file inside your Build Directory (e.g. ~/poky/build/conf/local.conf).

  2. Select the desired package format as follows:

         PACKAGE_CLASSES ?= “package_packageformat

    where packageformat can be "ipk", "rpm", "deb", or "tar" which are the supported package formats.

    Note

    Because the Yocto Project supports four different package formats, you can set the variable with more than one argument. However, the OpenEmbedded build system only uses the first argument when creating an image or Software Development Kit (SDK).

If you would like your image to start off with a basic package database containing the packages in your current build as well as to have the relevant tools available on the target for runtime package management, you can include "package-management" in the IMAGE_FEATURES variable. Including "package-management" in this configuration variable ensures that when the image is assembled for your target, the image includes the currently-known package databases as well as the target-specific tools required for runtime package management to be performed on the target. However, this is not strictly necessary. You could start your image off without any databases but only include the required on-target package tool(s). As an example, you could include "opkg" in your IMAGE_INSTALL variable if you are using the IPK package format. You can then initialize your target's package database(s) later once your image is up and running.

Whenever you perform any sort of build step that can potentially generate a package or modify existing package, it is always a good idea to re-generate the package index after the build by using the following command:

    $ bitbake package-index
                    

It might be tempting to build the package and the package index at the same time with a command such as the following:

    $ bitbake some-package package-index
                    

Do not do this as BitBake does not schedule the package index for after the completion of the package you are building. Consequently, you cannot be sure of the package index including information for the package you just built. Thus, be sure to run the package update step separately after building any packages.

You can use the PACKAGE_FEED_ARCHS, PACKAGE_FEED_BASE_PATHS, and PACKAGE_FEED_URIS variables to pre-configure target images to use a package feed. If you do not define these variables, then manual steps as described in the subsequent sections are necessary to configure the target. You should set these variables before building the image in order to produce a correctly configured image.

When your build is complete, your packages reside in the ${TMPDIR}/deploy/packageformat directory. For example, if ${TMPDIR} is tmp and your selected package type is RPM, then your RPM packages are available in tmp/deploy/rpm.

7.22.4.2. Host or Server Machine Setup

Although other protocols are possible, a server using HTTP typically serves packages. If you want to use HTTP, then set up and configure a web server such as Apache 2, lighttpd, or SimpleHTTPServer on the machine serving the packages.

To keep things simple, this section describes how to set up a SimpleHTTPServer web server to share package feeds from the developer's machine. Although this server might not be the best for a production environment, the setup is simple and straight forward. Should you want to use a different server more suited for production (e.g. Apache 2, Lighttpd, or Nginx), take the appropriate steps to do so.

From within the build directory where you have built an image based on your packaging choice (i.e. the PACKAGE_CLASSES setting), simply start the server. The following example assumes a build directory of ~/poky/build/tmp/deploy/rpm and a PACKAGE_CLASSES setting of "package_rpm":

     $ cd ~/poky/build/tmp/deploy/rpm
     $ python -m SimpleHTTPServer
                    

7.22.4.3. Target Setup

Setting up the target differs depending on the package management system. This section provides information for RPM, IPK, and DEB.

7.22.4.3.1. Using RPM

The Dandified Packaging Tool (DNF) performs runtime package management of RPM packages. In order to use DNF for runtime package management, you must perform an initial setup on the target machine for cases where the PACKAGE_FEED_* variables were not set as part of the image that is running on the target. This means if you built your image and did not not use these variables as part of the build and your image is now running on the target, you need to perform the steps in this section if you want to use runtime package management.

Note

For information on the PACKAGE_FEED_* variables, see PACKAGE_FEED_ARCHS, PACKAGE_FEED_BASE_PATHS, and PACKAGE_FEED_URIS in the Yocto Project Reference Manual variables glossary.

On the target, you must inform DNF that package databases are available. You do this by creating a file named /etc/yum.repos.d/oe-packages.repo and defining the oe-packages.

As an example, assume the target is able to use the following package databases: all, i586, and qemux86 from a server named my.server. The specifics for setting up the web server are up to you. The critical requirement is that the URIs in the target repository configuration point to the correct remote location for the feeds.

Tip

For development purposes, you can point the web server to the build system's deploy directory. However, for production use, it is better to copy the package directories to a location outside of the build area and use that location. Doing so avoids situations where the build system overwrites or changes the deploy directory.

When telling DNF where to look for the package databases, you must declare individual locations per architecture or a single location used for all architectures. You cannot do both:

  • Create an Explicit List of Architectures: Define individual base URLs to identify where each package database is located:

         [oe-packages]
         baseurl=http://my.server/rpm/i586 http://my.server/rpm/qemux86 http://my.server/rpm/all
                                    

    This example informs DNF about individual package databases for all three architectures.

  • Create a Single (Full) Package Index: Define a single base URL that identifies where a full package database is located:

         [oe-packages]
         baseurl=http://my.server/rpm
                                    

    This example informs DNF about a single package database that contains all the package index information for all supported architectures.

Once you have informed DNF where to find the package databases, you need to fetch them:

     # dnf makecache
                        

DNF is now able to find, install, and upgrade packages from the specified repository or repositories.

Note

See the DNF documentation for additional information.

7.22.4.3.2. Using IPK

The opkg application performs runtime package management of IPK packages. You must perform an initial setup for opkg on the target machine if the PACKAGE_FEED_ARCHS, PACKAGE_FEED_BASE_PATHS, and PACKAGE_FEED_URIS variables have not been set or the target image was built before the variables were set.

The opkg application uses configuration files to find available package databases. Thus, you need to create a configuration file inside the /etc/opkg/ direction, which informs opkg of any repository you want to use.

As an example, suppose you are serving packages from a ipk/ directory containing the i586, all, and qemux86 databases through an HTTP server named my.server. On the target, create a configuration file (e.g. my_repo.conf) inside the /etc/opkg/ directory containing the following:

     src/gz all http://my.server/ipk/all
     src/gz i586 http://my.server/ipk/i586
     src/gz qemux86 http://my.server/ipk/qemux86
                        

Next, instruct opkg to fetch the repository information:

     # opkg update
                        

The opkg application is now able to find, install, and upgrade packages from the specified repository.

7.22.4.3.3. Using DEB

The apt application performs runtime package management of DEB packages. This application uses a source list file to find available package databases. You must perform an initial setup for apt on the target machine if the PACKAGE_FEED_ARCHS, PACKAGE_FEED_BASE_PATHS, and PACKAGE_FEED_URIS variables have not been set or the target image was built before the variables were set.

To inform apt of the repository you want to use, you might create a list file (e.g. my_repo.list) inside the /etc/apt/sources.list.d/ directory. As an example, suppose you are serving packages from a deb/ directory containing the i586, all, and qemux86 databases through an HTTP server named my.server. The list file should contain:

     deb http://my.server/deb/all ./
     deb http://my.server/deb/i586 ./
     deb http://my.server/deb/qemux86 ./
                        

Next, instruct the apt application to fetch the repository information:

     # apt-get update
                        

After this step, apt is able to find, install, and upgrade packages from the specified repository.

7.22.5. Generating and Using Signed Packages

In order to add security to RPM packages used during a build, you can take steps to securely sign them. Once a signature is verified, the OpenEmbedded build system can use the package in the build. If security fails for a signed package, the build system aborts the build.

This section describes how to sign RPM packages during a build and how to use signed package feeds (repositories) when doing a build.

7.22.5.1. Signing RPM Packages

To enable signing RPM packages, you must set up the following configurations in either your local.config or distro.config file:

     # Inherit sign_rpm.bbclass to enable signing functionality
     INHERIT += " sign_rpm"
     # Define the GPG key that will be used for signing.
     RPM_GPG_NAME = "key_name"
     # Provide passphrase for the key
     RPM_GPG_PASSPHRASE = "passphrase"
                    

Note

Be sure to supply appropriate values for both key_name and passphrase

Aside from the RPM_GPG_NAME and RPM_GPG_PASSPHRASE variables in the previous example, two optional variables related to signing exist:

  • GPG_BIN: Specifies a gpg binary/wrapper that is executed when the package is signed.

  • GPG_PATH: Specifies the gpg home directory used when the package is signed.

7.22.5.2. Processing Package Feeds

In addition to being able to sign RPM packages, you can also enable signed package feeds for IPK and RPM packages.

The steps you need to take to enable signed package feed use are similar to the steps used to sign RPM packages. You must define the following in your local.config or distro.config file:

     INHERIT += "sign_package_feed"
     PACKAGE_FEED_GPG_NAME = "key_name"
     PACKAGE_FEED_GPG_PASSPHRASE_FILE = "path_to_file_containing_passphrase"
                    

For signed package feeds, the passphrase must exist in a separate file, which is pointed to by the PACKAGE_FEED_GPG_PASSPHRASE_FILE variable. Regarding security, keeping a plain text passphrase out of the configuration is more secure.

Aside from the PACKAGE_FEED_GPG_NAME and PACKAGE_FEED_GPG_PASSPHRASE_FILE variables, three optional variables related to signed package feeds exist:

  • GPG_BIN: Specifies a gpg binary/wrapper that is executed when the package is signed.

  • GPG_PATH: Specifies the gpg home directory used when the package is signed.

  • PACKAGE_FEED_GPG_SIGNATURE_TYPE: Specifies the type of gpg signature. This variable applies only to RPM and IPK package feeds. Allowable values for the PACKAGE_FEED_GPG_SIGNATURE_TYPE are "ASC", which is the default and specifies ascii armored, and "BIN", which specifies binary.

7.22.6. Testing Packages With ptest

A Package Test (ptest) runs tests against packages built by the OpenEmbedded build system on the target machine. A ptest contains at least two items: the actual test, and a shell script (run-ptest) that starts the test. The shell script that starts the test must not contain the actual test - the script only starts the test. On the other hand, the test can be anything from a simple shell script that runs a binary and checks the output to an elaborate system of test binaries and data files.

The test generates output in the format used by Automake:

     result: testname
                

where the result can be PASS, FAIL, or SKIP, and the testname can be any identifying string.

For a list of Yocto Project recipes that are already enabled with ptest, see the Ptest wiki page.

Note

A recipe is "ptest-enabled" if it inherits the ptest class.

7.22.6.1. Adding ptest to Your Build

To add package testing to your build, add the DISTRO_FEATURES and EXTRA_IMAGE_FEATURES variables to your local.conf file, which is found in the Build Directory:

     DISTRO_FEATURES_append = " ptest"
     EXTRA_IMAGE_FEATURES += "ptest-pkgs"
                    

Once your build is complete, the ptest files are installed into the /usr/lib/package/ptest directory within the image, where package is the name of the package.

7.22.6.2. Running ptest

The ptest-runner package installs a shell script that loops through all installed ptest test suites and runs them in sequence. Consequently, you might want to add this package to your image.

7.22.6.3. Getting Your Package Ready

In order to enable a recipe to run installed ptests on target hardware, you need to prepare the recipes that build the packages you want to test. Here is what you have to do for each recipe:

  • Be sure the recipe inherits the ptest class: Include the following line in each recipe:

         inherit ptest
                                

  • Create run-ptest: This script starts your test. Locate the script where you will refer to it using SRC_URI. Here is an example that starts a test for dbus:

         #!/bin/sh
         cd test
         make -k runtest-TESTS
                                

  • Ensure dependencies are met: If the test adds build or runtime dependencies that normally do not exist for the package (such as requiring "make" to run the test suite), use the DEPENDS and RDEPENDS variables in your recipe in order for the package to meet the dependencies. Here is an example where the package has a runtime dependency on "make":

         RDEPENDS_${PN}-ptest += "make"
                                

  • Add a function to build the test suite: Not many packages support cross-compilation of their test suites. Consequently, you usually need to add a cross-compilation function to the package.

    Many packages based on Automake compile and run the test suite by using a single command such as make check. However, the host make check builds and runs on the same computer, while cross-compiling requires that the package is built on the host but executed for the target architecture (though often, as in the case for ptest, the execution occurs on the host). The built version of Automake that ships with the Yocto Project includes a patch that separates building and execution. Consequently, packages that use the unaltered, patched version of make check automatically cross-compiles.

    Regardless, you still must add a do_compile_ptest function to build the test suite. Add a function similar to the following to your recipe:

         do_compile_ptest() {
            oe_runmake buildtest-TESTS
         }
                                

  • Ensure special configurations are set: If the package requires special configurations prior to compiling the test code, you must insert a do_configure_ptest function into the recipe.

  • Install the test suite: The ptest class automatically copies the file run-ptest to the target and then runs make install-ptest to run the tests. If this is not enough, you need to create a do_install_ptest function and make sure it gets called after the "make install-ptest" completes.

7.23. Efficiently Fetching Source Files During a Build

The OpenEmbedded build system works with source files located through the SRC_URI variable. When you build something using BitBake, a big part of the operation is locating and downloading all the source tarballs. For images, downloading all the source for various packages can take a significant amount of time.

This section shows you how you can use mirrors to speed up fetching source files and how you can pre-fetch files all of which leads to more efficient use of resources and time.

7.23.1. Setting up Effective Mirrors

A good deal that goes into a Yocto Project build is simply downloading all of the source tarballs. Maybe you have been working with another build system (OpenEmbedded or Angstrom) for which you have built up a sizable directory of source tarballs. Or, perhaps someone else has such a directory for which you have read access. If so, you can save time by adding statements to your configuration file so that the build process checks local directories first for existing tarballs before checking the Internet.

Here is an efficient way to set it up in your local.conf file:

     SOURCE_MIRROR_URL ?= "file:///home/you/your-download-dir/"
     INHERIT += "own-mirrors"
     BB_GENERATE_MIRROR_TARBALLS = "1"
     # BB_NO_NETWORK = "1"
                

In the previous example, the BB_GENERATE_MIRROR_TARBALLS variable causes the OpenEmbedded build system to generate tarballs of the Git repositories and store them in the DL_DIR directory. Due to performance reasons, generating and storing these tarballs is not the build system's default behavior.

You can also use the PREMIRRORS variable. For an example, see the variable's glossary entry in the Yocto Project Reference Manual.

7.23.2. Getting Source Files and Suppressing the Build

Another technique you can use to ready yourself for a successive string of build operations, is to pre-fetch all the source files without actually starting a build. This technique lets you work through any download issues and ultimately gathers all the source files into your download directory build/downloads, which is located with DL_DIR.

Use the following BitBake command form to fetch all the necessary sources without starting the build:

     $ bitbake -c target runall="fetch"
                

This variation of the BitBake command guarantees that you have all the sources for that BitBake target should you disconnect from the Internet and want to do the build later offline.

7.24. Selecting an Initialization Manager

By default, the Yocto Project uses SysVinit as the initialization manager. However, support also exists for systemd, which is a full replacement for init with parallel starting of services, reduced shell overhead and other features that are used by many distributions.

If you want to use SysVinit, you do not have to do anything. But, if you want to use systemd, you must take some steps as described in the following sections.

7.24.1. Using systemd Exclusively

Set the these variables in your distribution configuration file as follows:

     DISTRO_FEA