Comment 24 for bug 1778219

Verified 1.5ubuntu3.18.10.0 on cosmic with installing apport, rather than snapd:

...
root@uu-shutdown-test:~# echo 'Unattended-Upgrade::InstallOnShutdown "true";' > /etc/apt/apt.conf.d/51unattended-upgrades-on-shutdown
root@uu-shutdown-test:~# echo 'Unattended-Upgrade::Allowed-Origins:: "${distro_id}:${distro_codename}-updates";' > /etc/apt/apt.conf.d/51unattended-upgrades-updates-too
root@uu-shutdown-test:~# unattended-upgrade --download-only
root@uu-shutdown-test:~# dbus-send --system --print-reply --dest=org.freedesktop.login1 /org/freedesktop/login1 "org.freedesktop.login1.Manager.Reboot" boolean:false
method return time=1543423811.418244 sender=:1.4 -> destination=:1.27 serial=81 reply_serial=2
root@uu-shutdown-test:~#
Session terminated, terminating shell... ...terminated.
rbalint@yogi:~$ lxc shell uu-shutdown-test
mesg: ttyname failed: No such device
root@uu-shutdown-test:~# cat /var/log/unattended-upgrades/unattended-upgrades-dpkg.log
Log started: 2018-11-28 16:50:13
(Reading database ... 28278 files and directories currently installed.)
Preparing to unpack .../apport_2.20.10-0ubuntu13.1_all.deb ...
Unpacking apport (2.20.10-0ubuntu13.1) over (2.20.10-0ubuntu13) ...
Processing triggers for systemd (239-7ubuntu10.4) ...
Setting up apport (2.20.10-0ubuntu13.1) ...
apport-autoreport.service is a disabled or a static unit, not starting it.
Processing triggers for man-db (2.8.4-2) ...
Log ended: 2018-11-28 16:50:16

Installing apport locked up during shutdown when downgrading u-u to 1.4ubuntu2. Latest unfixed u-u in cosmic does not lock up because the system shuts down earlier with u-u still running (LP: #1803137), but this is fixed, too.