Automatic Security Updates on Ubuntu

Run the following to install the unattended-upgrades package:

sudo apt update
sudo apt install unattended-upgrades

Now edit the file /etc/apt/apt.conf.d/50unattended-upgrades. Ensure that the line with "${distro_id}:${distro_codename}-security" is uncommented.

You may also want to uncomment "Unattended-Upgrade::Automatic-Reboot "true";" further down.