[Bug 1732703] Re: MAAS does not detect properly if Ubuntu is using upstart/systemd

[Dimitri John Ledkov]

It is correct, in general, to check for /run/systemd/system to detect if
systemd manages pid 1.

Imho deputy systemd (used by snapd, on trusty, with xenial-lts kernel)
should not have been creating that, however I fear that without that
directory snapd and snaps therein may get confused (in classic
confinment).

It is true that trusty only uses upstart as pid1 with no other options;
and any system systemd jobs are inert (deputy systemd only looks for
deputy things).

Note that although xenial ships both upstart & systemd; only systemd is
supported as pid1 on all form-factors. (upstart as pid1 is only
supported on xenial ubuntu touch product, which is now end-of-life).

Possibly we could create one more directory e.g. /run/dsystemd/system or
some such, which maas can check for to destinguish "systemd or deputy-
systemd".

However, checking /sbin/init like done in the proposed merge proposal is
very adequate for maas needs, and should yield correct results. As far
as I can tell, since on xenial either upstart-sysv or systemd-sysv may
provide /sbin/init, with systemd-sysv being the default everywhere.
(upstart-sysv on xenial is for ubuntu touch only).

Ideally, I do not want to touch deputy systemd uploads.

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https://bugs.launchpad.net/bugs/1732703

Title:
  MAAS does not detect properly if Ubuntu is using upstart/systemd

Status in MAAS:
  Won't Fix
Status in MAAS 1.9 series:
  In Progress
Status in maas package in Ubuntu:
  New
Status in snapd package in Ubuntu:
  Won't Fix
Status in systemd package in Ubuntu:
  New
Status in maas source package in Trusty:
  New
Status in snapd source package in Trusty:
  New
Status in systemd source package in Trusty:
  New

Bug description:
  [impact]
  Since Trusty uses upstart by default, MAAS manages its services with upstart. However, when a user installs systemd (even if it is not used as the init system), MAAS detects systemd installed and tries to manage its services via systemd. This obviously creates issues and prevents MAAS from working.

  [Test Case]
  1. Install & configure MAAS
  2. Add machines
  3. install systemd
  4. MAAS will fail to manage machines

  [Regression potential]
  Minimal. This just ensures that upstart is detected correctly even if systemd is installed (but not used).

  [Original bug report]
  Trusty uses upstart by default, and installing snapd (e.g. for livepatch purposes), pulls systemd too. In this setup, upstart is _not_ replaced by systemd, but MAAS "detects" systemd as init because of the existence of /run/systemd/system:

  @src/provisioningserver/utils/__init__.py:505

  SYSTEMD_RUN_PATH = '/run/systemd/system'

  def get_init_system():
      """Returns 'upstart' or 'systemd'."""
      if os.path.exists(SYSTEMD_RUN_PATH):
          return 'systemd'
      else:
          return 'upstart'

  One possible solution would be to check if /sbin/init is a symlink
  pointing to /lib/systemd/systemd:

  def get_init_system():
      """Returns 'upstart' or 'systemd'."""
      initpath = os.readlink("/sbin/init")
      if (initpath == "/lib/systemd/systemd"):
          return 'systemd'
      else:
      return 'upstart'

  Other affected parts of the code are the postinst files for maas-proxy
  and maas-dhcp (debian/maas-proxy.postinst debian/maas-dhcp.postinst),
  throwing an error if maas is installed after systemd in Trusty

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