I just confirmed that InstallOnShutdown does work, it is triggered by PrepareForShutdown(), not the TERM signal:
balint@yogi:~$ lxc launch ubuntu:cosmic cc-lp-1806463 Creating cc-lp-1806463 Starting cc-lp-1806463 rbalint@yogi:~$ lxc shell cc-lp-1806463 root@cc-lp-1806463:~# apt update ... root@cc-lp-1806463:~# apt install unattended-upgrades ... root@cc-lp-1806463:~# reboot ... # enable InstallOnShutdown: root@cc-lp-1806463:~# vi /etc/apt/apt.conf.d/50unattended-upgrades root@cc-lp-1806463:~# dbus-send --system --print-reply --dest=org.freedesktop.login1 /org/freedesktop/login1 "org.freedesktop.login1.Manager.Reboot" boolean:false method return time=1543938923.733435 sender=:1.2 -> destination=:1.14 serial=32 reply_serial=2 root@cc-lp-1806463:~# top ... PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND 547 root 20 0 257324 86180 49460 S 1.0 0.5 0:02.81 unattended-upgr 567 root 20 0 258132 73168 36236 S 0.0 0.5 0:00.08 unattended-upgr 237 root 20 0 627388 30768 16548 S 0.0 0.2 0:00.34 snapd 233 root 20 0 125852 21016 12980 S 0.0 0.1 0:00.09 unattended-upgr 229 root 20 0 47400 17436 9696 S 0.0 0.1 0:00.09 networkd-dispat 578 root 20 0 18760 11192 2748 D 19.0 0.1 0:00.34 dpkg ... root@cc-lp-1806463:~# Session terminated, terminating shell...logout ...terminated. rbalint@yogi:~$ lxc shell cc-lp-1806463 mesg: ttyname failed: No such device root@cc-lp-1806463:~# cat /var/log/unattended-upgrades/unattended-upgrades unattended-upgrades-dpkg.log unattended-upgrades-shutdown.log unattended-upgrades.log root@cc-lp-1806463:~# cat /var/log/unattended-upgrades/unattended-upgrades-shutdown.log 2018-12-04 15:54:11,587 WARNING - SIGTERM or SIGHUP received, stopping unattended-upgradesonly if it is running 2018-12-04 15:55:23,748 WARNING - Running unattended-upgrades in shutdown mode 2018-12-04 15:55:23,765 WARNING - Unattended-upgrade in progress during shutdown, please don't turn off the computer Progress: 0.0025 % (perl-base,perl-modules-5.26,libperl5.26,perl) 2018-12-04 15:55:26,737 WARNING - Unattended-upgrade in progress during shutdown, please don't turn off the computer Progress: 0.0 % (perl-modules-5.26) 2018-12-04 15:55:29,740 WARNING - Unattended-upgrade in progress during shutdown, please don't turn off the computer Progress: 20.0 % (perl-modules-5.26) 2018-12-04 15:55:32,742 WARNING - Unattended-upgrade in progress during shutdown, please don't turn off the computer Progress: 80.0 % (perl-modules-5.26) 2018-12-04 15:55:35,746 WARNING - Unattended-upgrade in progress during shutdown, please don't turn off the computer Progress: 46.1538 % (perl) 2018-12-04 15:55:38,747 WARNING - Unattended-upgrade in progress during shutdown, please don't turn off the computer Progress: 92.3077 % (perl) 2018-12-04 15:55:41,752 WARNING - Unattended-upgrade in progress during shutdown, please don't turn off the computer Progress: 92.3077 % (perl) 2018-12-04 15:55:41,769 INFO - All upgrades installed For more details please see the /usr/share/doc/unattended-upgrades/NEWS.Debian.gz, the changelog, and LP: #1803137. ** Changed in: unattended-upgrades (Ubuntu) Status: New => Incomplete -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1806463 Title: Unattended-Upgrade::InstallOnShutdown "true" not working To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/unattended-upgrades/+bug/1806463/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs