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. 3.4) 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.
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:
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.
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.
Codenames are associated with major releases because a Yocto Project release number (e.g. 3.4) 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 Migration Guides 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.
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.
Stable release branches have strong maintenance for about a year after their initial release. Should significant issues be found for any release regardless of its age, fixes could be backported to older releases. For issues that are not backported given an older release, Community LTS trees and branches allow community members to share patches for older releases. However, these types of patches do not go through the same release process as do point releases. You can find more information about stable branch maintenance at https://wiki.yoctoproject.org/wiki/Stable_branch_maintenance.
3.4 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.bbclass: This automatically included class checks the build environment for missing tools (e.g.
gcc) or common misconfigurations such as MACHINE set incorrectly.
insane.bbclass: 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.bbclass: 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-selftestcan run all tests by default or can run selected tests or test suites.
oe-selftestrequires host packages beyond the “Essential” grouping. See the Required Packages for the Build Host section for more information.
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 (OE-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
“ross/mut” branch in the
poky-contrib repository (i.e. the
master-under-test branch) or in the “master-next” branch in the
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.
no-x11 and and so forth),
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.
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.