Install the unattended upgrade package
sudo apt-get install unattended-upgrades
Edit this file accordingly
vim /etc/apt/apt.conf.d/50unattended-upgrades
Install the Update Notifier
The update-notifier daemon notifies about package updates and other useful information (like reboot required messages)
This package is required if you have the “Unattended-Upgrade::Automatic-Reboot” configuration directive set to true.
apt-get install update-notifier-common
Finding out which updates are available:
/usr/lib/update-notifier/apt-check --human-readable
Mail and Notification
There are at least two options available to send email notifications
Option 1:
You can set the “Unattended-Upgrade::Mail” flag in /etc/apt/apt.conf.d/50unattended-upgrades to allow mail notifications.
Note that you must have the package “update-notifier-common” installed for this option to work.
Option 2:
You can use Apticron. “apticron will configure a cron job to email an administrator information about any packages on the system that have updates available, as well as a summary of changes in each package.”
apt install apticron
and update the configuration file (/etc/apticron/apticron.conf) accordingly.
NOTE:
About update-notifier
“If you want the script to automatically reboot when needed, you not only need to set Unattended-Upgrade::Automatic-Reboot "true", but you also need to have the “update-notifier-common” package installed. On minimal installations this is not installed by default and without it the automatic updater will never reboot and will not even tell you that you need to reboot manually if you have email notifications configured!“
“The files in /etc/apt/apt.conf.d/ are evaluated in lexicographical order with each file capable of overriding values set in earlier files. This makes it insufficient to view the setting in /etc/apt/apt.conf.d/20auto-upgrades and why it is recommended to use apt-config.”
Resources
https://help.ubuntu.com/community/AutomaticSecurityUpdates
https://www.techrepublic.com/article/how-to-enable-automatic-security-updates-on-centos-7-with-yum-cron/