Consider wisely, if you really want this, as it can result in unexpected behavior. I do this for a notebook which I don’t depend on and backup regularly. Also I usually do updates without looking into to the installing packages for this machine anyway…

Prerequisites

Check if the necessary service is up and running:

systemctl status unattended-upgrades

(This should be the case on default Ubuntu installations, if not do a sudo apt install unattended-upgrades.)

Configuration

Edit the file /etc/apt/apt.conf.d/50unattended-upgrades with root to configure what and how the auto-upgrades happen:

• In the first block Unattended-Upgrade::Allowed-Origins remove the line comments for the package types that you want to have installed automatically. By default, only security and ESM are enabled.
• (Optional) Add any packages that you don’t want to install automatically to the blacklist block Unattended-Upgrade::Package-Blacklist. Useful for packages that restart/quit during upgrades.
• (Optional) Uncomment Unattended-Upgrade::AutoFixInterruptedDpkg "true" to try an autofix in case of interrupted upgrades.
• (Optional) Uncomment Unattended-Upgrade::MinimalSteps "true"; to make the upgrades more robust against e.g. user reboots during upgrades.
• (Optional) Uncomment and configure Acquire::http::Dl-Limit "500"; to limit the network bandwidth for the updates. I like setting this to a third of my available internet speed, so I barely notice the upgrades.

Edit /etc/apt/apt.conf.d/20auto-upgrades with root to define how often the upgrade gets started:

• To upgrade daily, set APT::Periodic::Update-Package-Lists "1";and APT::Periodic::Unattended-Upgrade "1";
• If you want to do additional weekly cleanup, you can add as third line APT::Periodic::AutocleanInterval "7";.