[Bug 1850667] Re: Switch to "unified" cgroup hierarchy (cgroupv2)

[Lukas Märdian]

After enabling the unified cgroups hierarchy in systemd and running some
tests, I can confirm that most things are working as expected, except
for snapd.

https://bileto.ubuntu.com/excuses/4602/impish.html

The Bileto autopkgtests show (ignoring two unrelated/flaky failures in
universe packages: suricata & mosquitto) that:

* The systemd "tests-in-lxd" test fails, for snapd's "WARNING: cgroup v2
is not fully supported yet, proceeding with partial confinement" stderr
output. If that stderr output is muted/ignored (by modifying
autopkgtests itself) the test passes, as tested locally.

* The snapd "autopkgtest:adt-local:tests/smoke/sandbox" spread test
fails with an "all ubuntu systems must have strict confinement" error
message.

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https://bugs.launchpad.net/bugs/1850667

Title:
  Switch to "unified" cgroup hierarchy (cgroupv2)

Status in lxc:
  Fix Released
Status in lxd:
  Fix Released
Status in snapd:
  Confirmed
Status in docker.io package in Ubuntu:
  Fix Released
Status in lxc package in Ubuntu:
  Fix Released
Status in snapd package in Ubuntu:
  In Progress
Status in systemd package in Ubuntu:
  Confirmed
Status in lxc package in Debian:
  Fix Released
Status in systemd package in Debian:
  Fix Released

Bug description:
  Systemd upstream switched the default cgroup hierarchy to unified with
  v243. This change is reverted by the Ubuntu systemd packages, but as
  unified is the way to go per upstream support should be added to all
  relevant Ubuntu packges (and snaps):

  https://github.com/systemd/systemd/blob/v243/NEWS#L56

          * systemd now defaults to the "unified" cgroup hierarchy setup during
            build-time, i.e. -Ddefault-hierarchy=unified is now the build-time
            default. Previously, -Ddefault-hierarchy=hybrid was the default. This
            change reflects the fact that cgroupsv2 support has matured
            substantially in both systemd and in the kernel, and is clearly the
            way forward. Downstream production distributions might want to
            continue to use -Ddefault-hierarchy=hybrid (or even =legacy) for
            their builds as unfortunately the popular container managers have not
            caught up with the kernel API changes.

  
  Systemd is rebuilt using the new default and is available from the following PPA for testing:

  https://launchpad.net/~rbalint/+archive/ubuntu/systemd-unified-cgh

  The autopkgtest results against other packges are available here:

  https://objectstorage.prodstack4-5.canonical.com/v1/AUTH_77e2ada1e7a84929a74ba3b87153c0ac/autopkgtest-
  eoan-rbalint-systemd-unified-cgh/?format=plain

  https://objectstorage.prodstack4-5.canonical.com/v1/AUTH_77e2ada1e7a84929a74ba3b87153c0ac/autopkgtest-
  focal-rbalint-systemd-unified-cgh/?format=plain

  lxc autopkgtest failing:

  https://objectstorage.prodstack4-5.canonical.com/v1/AUTH_77e2ada1e7a84929a74ba3b87153c0ac/autopkgtest-
  eoan-rbalint-systemd-unified-
  cgh/eoan/amd64/d/docker.io/20191030_155944_2331e@/log.gz

  snapd autopkgtest failing:

  https://objectstorage.prodstack4-5.canonical.com/v1/AUTH_77e2ada1e7a84929a74ba3b87153c0ac/autopkgtest-
  eoan-rbalint-systemd-unified-
  cgh/eoan/amd64/s/snapd/20191030_161354_94b26@/log.gz

  
  docker.io autopkgtest failing:

  https://objectstorage.prodstack4-5.canonical.com/v1/AUTH_77e2ada1e7a84929a74ba3b87153c0ac/autopkgtest-
  eoan-rbalint-systemd-unified-
  cgh/eoan/amd64/d/docker.io/20191030_155944_2331e@/log.gz

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