18.04: a stop job is running for unattended upgrades shutdown
回答1
Be patient. Wait for Unattended Upgrades to finish.
DO NOT interrupt Unattended Upgrades while it is upgrading your system. Doing so might break your system quite horribly, including possibly making your system unbootable.
Generally, U-U will only run for a minute or two. If it's taking longer, then ensure your system has good, strong network connectivity. That speeds U-U up a lot.
回答2
I think the real answer is here: https://ostechnix.com/how-to-disable-unattended-upgrades-on-ubuntu/
Disable Unattended Upgrades with $ sudo dpkg-reconfigure unattended-upgrades or remove them completely with $ sudo apt remove unattended-upgrades. This is pretty much necessary to preserve sanity if you only use Ubuntu occasionally in a VM or similar.