Cheatsheet Pages / systemd Cheatsheet
How to enable a systemd timer — enable the TIMER, not the service
The classic trap: you enabled the .service and nothing ever runs — the timer is the thing that must be enabled and started.
Most management commands need sudo, and systemctl only works on a system actually booted with systemd — inside containers it fails with “System has not been booted with systemd as init system”. Every command was checked against systemd 255, and the example units pass systemd-analyze verify.
sudo systemctl enable --now backup.timer # start the countdown + enable at boot
systemctl list-timers --all # confirm it shows a NEXT time
# the classic trap: enabling backup.service does nothing useful here —
# the timer is the thing that must be enabled and running