In the previous post I wrote about systemd timers.
The problem with such configuration is that, upon reboot, timers are not started automatically.

Obviously, like other services, we need to specify in which case start the systemd unit (WantedBy=) and we need to enable it.

[Install]
WantedBy=base.target

Then

sudo vi /etc/systemd/system/test.timer

[Unit]
Description=Run test.service every day at midnight

[Timer]
OnCalendar=Mon..Sun *-*-* 00:00:00

[Install]
WantedBy=base.target

And finally enable the timer:

sudo systemctl enable test.timer