[Bug 1711428] Re: cloud-init sometimes fails on dpkg lock due to concurrent apt-daily-upgrade.service execution

[Julian Andres Klode]

Not that if B has After=A does not imply that the two don't run at the
same time. If B is already running, A will be started as well. That's
the reason why we added a lock file in apt:

if [ "$1" = "lock_is_held" ]; then
    shift
else
    # Maintain a lock on fd 3, so we can't run the script twice at the same
    # time.
    eval $(apt-config shell StateDir Dir::State/d)
    exec 3>${StateDir}/daily_lock
    if ! flock -w 3600 3; then
        echo "E: Could not acquire lock" >&2
        exit 1
    fi

    # We hold the lock.  Rerun this script as a child process, which
    # can run without propagating an extra fd to all of its children.
    "$0" lock_is_held "$@" 3>&-
    exit $?
fi

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https://bugs.launchpad.net/bugs/1711428

Title:
  cloud-init sometimes fails on dpkg lock due to concurrent apt-daily-
  upgrade.service execution

Status in cloud-init:
  Incomplete
Status in apt package in Ubuntu:
  Incomplete

Bug description:
  This is the same problem as https://bugs.launchpad.net/cloud-
  init/+bug/1693361, but with a different APT invoking service.  In this
  case it is apt-daily-upgrade.service.

  So, I guess add apt-daily-upgrade.service to the Before line in
  /lib/systemd/system/cloud-final.service along side apt-daily.service.

  Or wait for an APT fix.  Or retry APT commands when executing
  "packages:"

  Reporting this to save someone else trouble, but I think we'll be
  rolling back to Trusty at this point.  Hopefully the B LTS will have
  an alternative to systemd.

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