Linux Yocto
Release Cadence
Each release of the Yocto Project, roughly every six months, includes two versions of the Linux kernel with a broad range of hardware support. While tooling is provided to use any Linux kernel you wish, the linux-yocto Linux kernel recipes are tested with all the emulated targets, the core hardware BSPs, and some vendor layers.
While the timing of Linux kernel releases is the domain of the upstream kernel maintainers and beyond the control of the linux-yocto maintainers, making version roadmaps predictions at best, the Yocto Project commits to providing a near-current and a latest LTSI [1] linux-yocto version with each release of the Yocto Project. The final selection of the versions is made approximately six weeks prior to the development cutoff of the final development milestone.
Prior Releases
Reviewing prior releases is illustrative of the process:
- Yocto Project 1.4
- linux-yocto_3.4
- linux-yocto_3.8
- Yocto Project 1.5
- linux-yocto_3.4
- linux-yocto_3.10
- Yocto Project 1.6
- linux-yocto_3.10
- linux-yocto_3.14
Version Lifecycle / Support
While we make every effort to select a longterm Linux kernel for each new release kernel, occasionally our releases do not align with those of the Linux kernel, as was the case with the Yocto Project 1.4 release and the 3.8 kernel. In these cases, the non-longterm kernel version will be dropped in the subsequent release, rather than becoming the next LTSI kernel. This can be seen int he 1.5 release where 3.8 was effectively dropped, 3.4 remained as the LTSI kernel, and 3.10 was added as the new release kernel.
In terms of support, the linux-yocto recipes are treated the same as all the other recipes in a given release. They are supported for the life of that release.
FAQ
- Q: Why don't you support an LTSI kernel across new Yocto Project releases for as long as the that LTSI kernel is supported by the LTSI project?
- A: A new LTSI kernel is selected once per year and supported for two years. This allows for multiple active LTSI kernels at any point in time. It would be infeasible purely from a support and QA perspective to support all of them in every release of the Yocto Project. Furthermore, the LTSI kernel is targeted at productization teams that want to minimize change across the life of their product. It stands to reason if the kernel version must remain static, then so should the OS stack on top of it. For these reasons, LTSI kernel versions are supported for the life of the release they originally ship with.
