Comment 0 for bug 1803137

[Impact]

 * Unattended-upgrades may keep running during shutdown even beyond unmounting local filesystems potentially leaving a broken installation behind.
 * The fix reverts the original fix of LP: #1778219 and applies a different one startin unattended-upgrades-shutdown _before_ the shutdown transaction starts/

[Test Case]

 * Run unattended-upgrades in InstallOnShutdown mode and observe it being finished installing a few packages _before_ the shutdown transaction starts:

$ lxc launch ubuntu:18.10 cc-uu-onshutdown
Creating cc-uu-onshutdown
Starting cc-uu-onshutdown
$ lxc shell cc-uu-onshutdown
mesg: ttyname failed: No such device
root@cc-uu-onshutdown:~# apt update -qq
33 packages can be upgraded. Run 'apt list --upgradable' to see them.
root@cc-uu-onshutdown:~# echo 'Unattended-Upgrade::InstallOnShutdown "true";' > /etc/apt/apt.conf.d/51unattended-upgrades-on-shutdown
root@cc-uu-onshutdown:~# dbus-send --system --print-reply --dest=org.freedesktop.login1 /org/freedesktop/login1 "org.freedesktop.login1.Manager.Reboot" boolean:false
method return time=1542112922.046290 sender=:1.4 -> destination=:1.13 serial=27 reply_serial=2

Session terminated, terminating shell...$
$ lxc shell cc-uu-onshutdown
mesg: ttyname failed: No such device
root@cc-uu-onshutdown:~# journalctl -l
...
Nov 13 12:50:10 cc-uu-shutdown systemd[1]: Started Unattended Upgrades Shutdown.
Nov 13 12:51:17 cc-uu-shutdown systemd-logind[228]: System is rebooting.

...
root@cc-uu-shutdown:~# cat /var/log/unattended-upgrades/unattended-upgrades-shutdown.log
...
2018-11-13 12:51:13,835 WARNING - Running unattended-upgrades in shutdown mode
2018-11-13 12:51:13,852 WARNING - Unattended-upgrade in progress during shutdown, please don't turn off the computer
2018-11-13 12:51:15,482 WARNING - Unattended-upgrade in progress during shutdown, please don't turn off the computer
2018-11-13 12:51:17,151 WARNING - Unattended-upgrade in progress during shutdown, please don't turn off the computer
2018-11-13 12:51:17,166 INFO - All upgrades installed

[Regression Potential]

 * The change reverts the behavior of unattended-upgrades-shutdown to be close to the behavior observed in Ubuntu 18.04, blocking the shutdown process reliably until is unattended-upgrades finished, but it starts _before_ shutdown triggered by the PrepareForShutdown() signal. Due to the shutdown not fully starting yet users may not get visual notification of unattended-upgrades running in some system configuration (testing that is WIP).
 * The reversion of unattended-upgrades.service was not complete in u-u 1.7 and needed a further fix in 1.7ubuntu1 (which fix is already included in 1.5ubuntu4). This part may be source of potential regressions.
 * The fix itself rewrites big part of unattended-upgrades-shutdown and this rewrite could cause regressions in running unattended-upgrades in InstallOnShutdown mode, but also this mode was extensively tested.
 * The fix includes increasing logind's InhibitDelayMaxSec to 30s to give u-u enough time to gracefully stop in normal mode and install packages in InstallOnShutdown mode. The delay is global, thus any other program holding the lock can delay shutdown or sleep by 30s instead of the original 5s default. This regression is hard to avoid and the 30s was chosen to minimize the regression potential while still giving more than 5s to u-u to finish actions. Bugs reporting increased delay to sleep or shutdown should be monitored to catch other programs misbehaving with this new default.

[Other Info]

This is a regression of introduced in LP: #1778219 and can be observed in a cosmic lxd container easily:

$ lxc launch ubuntu:18.10 cc-uu-onshutdown
Creating cc-uu-onshutdown
Starting cc-uu-onshutdown
$ lxc shell cc-uu-onshutdown
mesg: ttyname failed: No such device
root@cc-uu-onshutdown:~# apt update -qq
33 packages can be upgraded. Run 'apt list --upgradable' to see them.
root@cc-uu-onshutdown:~# echo 'Unattended-Upgrade::InstallOnShutdown "true";' > /etc/apt/apt.conf.d/51unattended-upgrades-on-shutdown
root@cc-uu-onshutdown:~# dbus-send --system --print-reply --dest=org.freedesktop.login1 /org/freedesktop/login1 "org.freedesktop.login1.Manager.Reboot" boolean:false
method return time=1542112922.046290 sender=:1.4 -> destination=:1.13 serial=27 reply_serial=2

Session terminated, terminating shell...$
$ lxc shell cc-uu-onshutdown
mesg: ttyname failed: No such device
root@cc-uu-onshutdown:~# journalctl -l
...
Nov 13 12:42:02 cc-uu-onshutdown systemd[1]: Stopped target Local File Systems.
Nov 13 12:42:02 cc-uu-onshutdown systemd[1]: unattended-upgrades.service: Failed to reset devices.list: Operation not permitted
Nov 13 12:42:02 cc-uu-onshutdown systemd[1]: Starting Unattended Upgrades Shutdown...
..