unattended-upgrades.This unattended-upgrades package is installed by default on Ubuntu (but not on Linux Mint for example) and Debian 9+ with Gnome, and while it's a nice feature to have, quite a few users complain about it and the Microsoft Windows-like behavior of installing updates with no input from the user. Especially when you want to shutdown or reboot your system while in a hurry, and you get this:
This is the case not only for Ubuntu with Gnome, but other Ubuntu flavors as well, including Kubuntu, Ubuntu MATE, and so on.
As a side note, if you force a shutdown / reboot while installing updates, your computer may fail to boot into Ubuntu / Debian, and apt will probably get broken, showing the
E: Could not get lock /var/lib/dpkg/lock or E: dpkg was interrupted, you must manually run 'sudo dpkg --configure -a' to correct the problem errors.Those wanting to get rid of this behavior of automatically installing updates on Ubuntu or Debian 9+ with Gnome, have 2 options: remove the
unattended-upgrades or configure it so it does not install updates automatically.