Dear Federico,

can't easily find the following information:

- Criteria to select a kernel version for a Debian release. It looks to me you
are following LTS releases, but as you know kernel LTS is a moving target in
terms of duration. So, how you choose?

this depends on the Debian release cycle, which the Debian release
team sets. This is announced in the debian-release mailing list.
Once the release date cycle are known, the Debian kernel
team tries to optimise to have a recent enough LTS release balanced
with conservative exposure to enough hardware.

- How much a Debian kernel diverges from kernel.org release overtime?

The stable kernel does not in general add hardware backports.
The amount in debian depends on the vested interests. If we
get enough bug reports or someone making it easy in gitlab
to merge newer hardware support that happens too. The driver
has to be released in mainline to qualify.

- I see you explain how to build and run any kernel from kernel.org, but I do
not see and discouragement in doing so. Is this because you do not see any
known incompatibilities ?

For security maintenance we encourage to use the Debian one.
Of course if you have in house capabilities to follow whatever
LTS release you choose there will not be trouble (unless you set HZ to
some funny value or disable features glibc assumes).

We did optimize certain architectures for size but due to the
involved time constraints this got dropped.

Hope this helps, do not hesitate to follow-up.


Thank you for your interest (:
maximilian

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Hi Federico!

I'm a CERN employee currently evaluating Debian as a possible solution for our
systems in use to control particle accelerators. I would like to know more about
how the Debian community handles the Linux kernel integration. In particular, I
can't easily find the following information:

Cool, if you have more specific followup questions, don't hesitate to ask.

- Criteria to select a kernel version for a Debian release. It looks to me you
are following LTS releases, but as you know kernel LTS is a moving target in
terms of duration. So, how you choose?

Debian releases happen every two years at approximately the end of the second quarter of uneven years. kernel.org LTS releases are usually announced/picked by end of each calendar year and the latest kernel.org LTS gets picked as the kernel version for Debian. Debian 9 has 4.9.x, Debian 10 had 4.19.x, Debian
11 and 5.10 and Debian 12 will have 6.1.

- How much a Debian kernel diverges from kernel.org release overtime?

Not much, you can have a look yourself for the current patches applied
to the 6.1.27 kernel which will be part of the initial Debian 12 release
(and future updates will rebase to 6.1.x LTS releases): https://salsa.debian.org/kernel-team/linux/-/tree/sid/debian/patches

Anything in bugfix are cherrypicked bugfixes, debian/ contains a small
set of Debian-specific patches (for narrow toolchain or software freedom issues) and feature contains a small set of backports (e.g. currently
for improved support for some non-x86 systems). In the past that also
included backported support for some NICs or RAID controllers (but these usually only appear later in a release cycle).

- I see you explain how to build and run any kernel from kernel.org, but I do
not see and discouragement in doing so. Is this because you do not see any
known incompatibilities ?

Generally running a patched or bespoke kernel is supported. It's mostly
a matter of people power to do it properly (since one needs to rebase to security updates and applying custom patches might need rebases if underlying kernel code for updated).

Some parts of the OS (e.g. systemd) expectsa given set of kernel
features to be present to operate properly, but usually these are
quite common and unlikely to be absent in custom configs anyway.

If you start with the current Debian kernel config as a base (found
under /boot/config-VERSION) you won't run into any surprises.

Cheers,
Moritz

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