[Bug 1654600] Re: unattended-upgrade-shutdown hangs when /var is a separate filesystem

[Launchpad Bug Tracker]

This bug was fixed in the package unattended-upgrades - 0.90ubuntu0.10

---------------
unattended-upgrades (0.90ubuntu0.10) xenial-security; urgency=medium

  * No change rebuild in the -security pocket (See LP #1686470)

 -- Marc Deslauriers <marc.deslauriers at ubuntu.com>  Fri, 18 Jan 2019
13:34:27 -0500

** Changed in: unattended-upgrades (Ubuntu Xenial)
       Status: Fix Committed => Fix Released

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Title:
  unattended-upgrade-shutdown hangs when /var is a separate filesystem

Status in unattended-upgrades package in Ubuntu:
  Fix Released
Status in unattended-upgrades source package in Xenial:
  Fix Released
Status in unattended-upgrades source package in Yakkety:
  Fix Released
Status in unattended-upgrades source package in Zesty:
  Fix Released
Status in unattended-upgrades package in Debian:
  Fix Released

Bug description:
  [SRU justification]
  This fix is needed to make sure that the system does not hang on shutdown when /var is a speparate file system

  [Impact]
  System can hang up to 10 minutes if not fixed.

  [Fix]
  Change the systemd unit's ExecStart to an ExecStop so the unit is correctly sequenced.
  Change WantedBy to multi-user.target. This requires working around Debian Bug #797108 which causes the new unit not to be enabled.
  Remove the unneeded override_dh_isntallinit
  Add Default-Start levels to the SysV initscript
  Improve DEP8 testing

  [Test Case]
  In a VM with /var separated from the / file system, shutdown the VM. It will hang for 10 minutes

  [Regression]
  Upgrade has been tested on Xenial, Yakkety, Zesty. do-release-upgrade has been tested from Trusty to Xenial. All behave as expected.

  A change of behavior may occur now that the systemd unit is correctly
  enabled, which would make functionalities like InstallOnShutdown to
  work as expected whereas it could have been broken previously. This
  cannot be considered as a regression as it is expected behavior.

  Shutdown may be slowed down as it now correctly depends on /var and
  /boot to be available so the unit will run earlier than previously.

  [Original description of the problem]
  The systemd unit file unattended-upgrades.service is used to stop a running unattended-upgrade
  process during shutdown. This unit file is running together with all filesystem
  unmount services.

  The unattended-upgrades service checks if the lockfile for unattended-upgrade
  (in /var/run) exists, and if it does, there is an unattended-upgrade in progress
  and the service will wait until it finishes (and therefore automatically wait at
  shutdown).

  However, if /var is a separate filesystem, it will get unmounted even though /var/run
  is a tmpfs that's still mounted on top of the /var/run directory in the /var filesystem.
  The unattended-upgrade script will fail to find lockfile, sleeps for 5 seconds, and
  tries to check the lockfile again. After 10 minutes (the default timeout), it will finally
  exit and the system will continue shutdown.

  The problem is the error handling in /usr/share/unattended-upgrades/unattended-upgrade-shutdown
  where it tries to lock itself:

      while True:
          res = apt_pkg.get_lock(options.lock_file)
          logging.debug("get_lock returned %i" % res)
          # exit here if there is no lock
          if res > 0:
              logging.debug("lock not taken")
              break
          lock_was_taken = True

  The function apt_pkg.get_lock() either returns a file descriptor, or -1 on an error.
  File descriptors are just C file descriptors, so they are always positive integers.
  The code should check the result to be negative, not positive. I have attached a patch
  to reverse the logic.

  Additional information:

  1)
  Description:	Ubuntu 16.04.1 LTS
  Release:	16.04

  2)
  unattended-upgrades:
    Installed: 0.90ubuntu0.3
    Candidate: 0.90ubuntu0.3
    Version table:
   *** 0.90ubuntu0.3 500
          500 http://nl.archive.ubuntu.com/ubuntu xenial-updates/main amd64 Packages
          500 http://nl.archive.ubuntu.com/ubuntu xenial-updates/main i386 Packages
          100 /var/lib/dpkg/status
       0.90 500
          500 http://nl.archive.ubuntu.com/ubuntu xenial/main amd64 Packages
          500 http://nl.archive.ubuntu.com/ubuntu xenial/main i386 Packages
  3)
  Fast reboot
  4)
  Very slow reboot (after a 10 minutes timeout)

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