systemctl

Mental model

• systemd manages units. Most are .service, but also .socket, .timer (cron replacement), .target (runlevels), .mount, .device.
• Two independent axes — this is the #1 confusion:
• enabled = starts at boot?
• active = running right now?
• enable ≠ start. Use --now to do both at once.
• Unit files: /lib/systemd/system/ (shipped by packages) and /etc/systemd/system/ (your overrides — wins). Don't edit the shipped ones directly; use systemctl edit.
• --user targets units in your own login session instead of system-wide.

Everyday

Command	What it does
systemctl status <unit>	running? + recent log tail
systemctl start <unit>	start now
systemctl stop <unit>	stop now
systemctl restart <unit>	stop + start
systemctl reload <unit>	re-read config without full restart
systemctl enable <unit>	start at boot (doesn't start now)
systemctl disable <unit>	don't start at boot
systemctl enable --now <unit>	enable and start now

Inspecting

Command	What it does
systemctl list-units --type=service	active services
systemctl list-unit-files	all units + their enabled state
systemctl --failed	what's broken
systemctl is-active <unit>	quick active check (scriptable)
systemctl is-enabled <unit>	quick boot check
systemctl cat <unit>	show the unit file
systemctl show <unit>	every property
systemctl list-dependencies <unit>	what it pulls in

Editing units

Command	What it does
systemctl edit <unit>	create a drop-in override (recommended)
systemctl edit --full <unit>	edit a full copy into /etc
systemctl daemon-reload	reload after editing any unit file
systemctl revert <unit>	throw away your overrides
systemctl mask <unit>	fully disable — can't even be started

Timers (cron replacement)

Command	What it does
systemctl list-timers	all timers + next/last run
systemctl status <t>.timer	one timer's schedule + state

Targets & power

Command	What it does
systemctl get-default	boot target (graphical / multi-user)
systemctl set-default multi-user.target	boot to CLI, no GUI
systemctl reboot / poweroff	restart / shut down
systemctl suspend	sleep

Gotchas

• enable ≠ start. Enabling only affects boot; the service isn't running until you start it (or use --now).
• daemon-reload after editing unit files — otherwise systemd runs the old version.
• A masked unit can't be started at all until unmask — different from merely disabled.

See also

• [[journalctl]] — read a unit's logs (journalctl -u <unit>)