Bug#985446: release-notes: cgroupv2 is the default cgroup hierarchy

[Michael Biebl <biebl@debian.org>]

Package: release-notes
Severity: normal
X-Debbugs-Cc: pkg-systemd-maintainers@lists.alioth.debian.org

Starting with bullseye, the default cgroup hierarchy will be unified,
ie. cgroupv2 only.

We have this section in our systemd.NEWS file:

systemd (247.2-2) unstable; urgency=medium

  systemd now defaults to the "unified" cgroup hierarchy (i.e. cgroupv2).
  This change reflects the fact that cgroups2 support has matured
  substantially in both systemd and in the kernel.
  All major container tools nowadays should support cgroupv2.
  If you run into problems with cgroupv2, you can switch back to the previous,
  hybrid setup by adding "systemd.unified_cgroup_hierarchy=false" to the
  kernel command line.
  You can read more about the benefits of cgroupv2 at
  https://www.kernel.org/doc/html/latest/admin-guide/cgroup-v2.html

 -- Michael Biebl <biebl@debian.org>  Mon, 21 Dec 2020 18:40:10 +0100


We should add something similar to the release notes.
The above text could be a good starting point.


We track issues related to cgroupv2 via user tags [1].
Some tools, most notably probably is libcgroup [2], don't support
cgroupv2 yet.

Regards,
Michael

[1] https://bugs.debian.org/cgi-bin/pkgreport.cgi?users=pkg-systemd-maintainers@lists.alioth.debian.org;tag=cgroupv2
[2] https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=959022