3 Yocto Project Releases and the Stable Release Process

The Yocto Project release process is predictable and consists of both major and minor (point) releases. This brief chapter provides information on how releases are named, their life cycle, and their stability.

3.1 Major and Minor Release Cadence

The Yocto Project delivers major releases (e.g. 4.2.999) using a six month cadence roughly timed each April and October of the year. Following are examples of some major YP releases with their codenames also shown. See the “Major Release Codenames” section for information on codenames used with major releases.

  • 4.1 (“Langdale”)

  • 4.0 (“Kirkstone”)

  • 3.4 (“Honister”)

While the cadence is never perfect, this timescale facilitates regular releases that have strong QA cycles while not overwhelming users with too many new releases. The cadence is predictable and avoids many major holidays in various geographies.

The Yocto project delivers minor (point) releases on an unscheduled basis and are usually driven by the accumulation of enough significant fixes or enhancements to the associated major release. Following are some example past point releases:

  • 4.1.3

  • 4.0.8

  • 3.4.4

The point release indicates a point in the major release branch where a full QA cycle and release process validates the content of the new branch.

Note

Realize that there can be patches merged onto the stable release branches as and when they become available.

3.2 Major Release Codenames

Each major release receives a codename that identifies the release in the Yocto Project Source Repositories. The concept is that branches of Metadata with the same codename are likely to be compatible and thus work together.

Note

Codenames are associated with major releases because a Yocto Project release number (e.g. 4.2.999) could conflict with a given layer or company versioning scheme. Codenames are unique, interesting, and easily identifiable.

Releases are given a nominal release version as well but the codename is used in repositories for this reason. You can find information on Yocto Project releases and codenames at https://wiki.yoctoproject.org/wiki/Releases.

Our Release Information detail how to migrate from one release of the Yocto Project to the next.

3.3 Stable Release Process

Once released, the release enters the stable release process at which time a person is assigned as the maintainer for that stable release. This maintainer monitors activity for the release by investigating and handling nominated patches and backport activity. Only fixes and enhancements that have first been applied on the “master” branch (i.e. the current, in-development branch) are considered for backporting to a stable release.

Note

The current Yocto Project policy regarding backporting is to consider bug fixes and security fixes only. Policy dictates that features are not backported to a stable release. This policy means generic recipe version upgrades are unlikely to be accepted for backporting. The exception to this policy occurs when there is a strong reason such as the fix happens to also be the preferred upstream approach.

3.4 Long Term Support Releases

While stable releases are supported for a duration of seven months, some specific ones are now supported for a longer period by the Yocto Project, and are called Long Term Support (LTS) releases.

When significant issues are found, LTS releases allow to publish fixes not only for the current stable release, but also to the LTS releases that are still supported. Older stable releases which have reached their End of Life (EOL) won’t receive such updates.

This started with version 3.1 (“Dunfell”), released in April 2020, which the project initially committed to supporting for two years, but this duration was later extended to four years. Similarly, the following LTS release, version 4.0 (“Kirkstone”), was released two years later in May 2022 and the project committed to supporting it for four years too.

Therefore, a new LTS release is made every two years and is supported for four years. This offers more stability to project users and leaves more time to upgrade to the following LTS release.

See https://wiki.yoctoproject.org/wiki/Stable_Release_and_LTS for details about the management of stable and LTS releases.

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Note

In some circumstances, a layer can be created by the community in order to add a specific feature or support a new version of some package for an LTS release. This is called a Mixin layer. These are thin and specific purpose layers which can be stacked with an LTS release to “mix” a specific feature into that build. These are created on an as-needed basis and maintained by the people who need them.

Policies on testing these layers depend on how widespread their usage is and determined on a case-by-case basis. You can find some Mixin layers in the meta-lts-mixins repository. While the Yocto Project provides hosting for those repositories, it does not provides testing on them. Other Mixin layers may be released elsewhere by the wider community.

3.5 Testing and Quality Assurance

Part of the Yocto Project development and release process is quality assurance through the execution of test strategies. Test strategies provide the Yocto Project team a way to ensure a release is validated. Additionally, because the test strategies are visible to you as a developer, you can validate your projects. This section overviews the available test infrastructure used in the Yocto Project. For information on how to run available tests on your projects, see the “Performing Automated Runtime Testing” section in the Yocto Project Development Tasks Manual.

The QA/testing infrastructure is woven into the project to the point where core developers take some of it for granted. The infrastructure consists of the following pieces:

  • bitbake-selftest: A standalone command that runs unit tests on key pieces of BitBake and its fetchers.

  • sanity: This automatically included class checks the build environment for missing tools (e.g. gcc) or common misconfigurations such as MACHINE set incorrectly.

  • insane: This class checks the generated output from builds for sanity. For example, if building for an ARM target, did the build produce ARM binaries. If, for example, the build produced PPC binaries then there is a problem.

  • testimage: This class performs runtime testing of images after they are built. The tests are usually used with QEMU to boot the images and check the combined runtime result boot operation and functions. However, the test can also use the IP address of a machine to test.

  • ptest: Runs tests against packages produced during the build for a given piece of software. The test allows the packages to be run within a target image.

  • oe-selftest: Tests combination BitBake invocations. These tests operate outside the OpenEmbedded build system itself. The oe-selftest can run all tests by default or can run selected tests or test suites.

Originally, much of this testing was done manually. However, significant effort has been made to automate the tests so that more people can use them and the Yocto Project development team can run them faster and more efficiently.

The Yocto Project’s main Autobuilder (https://autobuilder.yoctoproject.org) publicly tests each Yocto Project release’s code in the openembedded-core, poky and bitbake repositories. The testing occurs for both the current state of the “master” branch and also for submitted patches. Testing for submitted patches usually occurs in the in the “master-next” branch in the poky repository.

Note

You can find all these branches in the Yocto Project Source Repositories.

Testing within these public branches ensures in a publicly visible way that all of the main supposed architectures and recipes in OE-Core successfully build and behave properly.

Various features such as multilib, sub architectures (e.g. x32, poky-tiny, musl, no-x11 and and so forth), bitbake-selftest, and oe-selftest are tested as part of the QA process of a release. Complete testing and validation for a release takes the Autobuilder workers several hours.

Note

The Autobuilder workers are non-homogeneous, which means regular testing across a variety of Linux distributions occurs. The Autobuilder is limited to only testing QEMU-based setups and not real hardware.

Finally, in addition to the Autobuilder’s tests, the Yocto Project QA team also performs testing on a variety of platforms, which includes actual hardware, to ensure expected results.