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`systemctl`

Control systemd: start, stop, enable and check services and other units, change targets, reboot and power off.

Niveau: RHCSA-examen
Groep: Services en opstarten
Root nodig: Voor wijzigingen
Pakket: systemd

Dit deel is nog niet vertaald. Je ziet de Engelse tekst.

Wat het doet

systemctl COMMAND UNIT is the main tool for services on RHEL. start/stop/restart act now; enable/disable decide what starts at boot; status shows the state and the last log lines. Without a type, a name means .service.

It also lists units, shows and edits unit files (cat, edit), sets the default boot target, and powers the system off or reboots it. With --user it manages the services of your own user session.

Zo schrijf je het

systemctl [OPTION]... COMMAND [UNIT]...

Belangrijkste delen

Units now

start UNIT...: Start units.
stop UNIT...: Stop units.
restart UNIT...: Stop and start.
try-restart UNIT...: Restart only if running.
reload UNIT...: Re-read the config without stopping.
reload-or-restart UNIT...: Reload if possible, else restart.
kill UNIT...: Send a signal to the processes of a unit.
clean UNIT...: Remove cache, logs, state of a unit.
freeze / thaw UNIT...: Pause / continue all processes of a unit.
isolate TARGET: Start this target and stop all others.

Boot

enable UNIT...: Start at boot (--now also starts now).
disable UNIT...: Do not start at boot.
reenable UNIT...: Disable and enable again (new links).
preset UNIT...: Set enabled/disabled to the preset of the vendor.
mask UNIT...: Block the unit completely (link to /dev/null).
unmask UNIT...: Remove the block.
get-default: Show the default boot target.
set-default TARGET: Set the default boot target.

State

status [UNIT...|PID...]: State, PID, cgroup and last log lines.
is-active UNIT...: Print active/inactive (exit code 0 = active).
is-enabled UNIT...: Print enabled/disabled/static/masked.
is-failed UNIT...: Check for the failed state.
is-system-running: Overall state: running, degraded …
list-units: Loaded units (-t type, --state).
list-unit-files: Installed unit files and their enable state.
list-dependencies UNIT: Dependency tree.
list-sockets, list-timers, list-jobs, list-automounts, list-paths: Lists of these types.
show UNIT: All properties (-p some).

Unit files

cat UNIT...: Show the unit file and drop-ins.
edit UNIT: Create a drop-in override (--full = whole copy).
revert UNIT...: Remove your overrides.
daemon-reload: Reload all unit files after manual changes.
set-property UNIT NAME=VALUE...: Change resource settings (like MemoryMax) at run time and keep them.
link FILE, add-wants, add-requires: Other unit file commands.
set-environment, unset-environment, show-environment: Environment of the manager.

System

reboot: Reboot.
poweroff: Power off.
halt: Stop the system without power off.
suspend, hibernate, hybrid-sleep: Sleep modes.
rescue: Go to rescue mode.
emergency: Go to emergency mode.
default: Go to the default target.
soft-reboot: Restart user space only (newer systemd).
reset-failed [UNIT...]: Clear the failed state.

Opties 57

Meest gebruikt

Select

-t, --type=TYPE: Unit type: service, socket, target, timer, mount …
--state=STATE: Only units in this state: running, failed, enabled …
-a, --all: Also inactive units and empty properties.
--failed: Same as --state=failed.
-r, --recursive: Also units of containers.
--reverse: With list-dependencies: who depends on this unit.
--after, --before: With list-dependencies: order instead of needs.
--with-dependencies: Also act on the dependencies.

Output

-p, --property=NAME: Only these properties with show.
-P NAME: Only the value of one property.
--value: With show: only the values.
-l, --full: Do not cut long lines.
-n, --lines=N: Number of log lines in status.
-o, --output=MODE: Format of the log lines (short, json, cat …).
--plain: Lists without tree lines.
--no-legend, --legend=BOOL: Without header and footer.
--no-pager: Do not use a pager.
--timestamp=FORMAT: Format of time stamps.
--show-types: Show the type of sockets.
-q, --quiet: Less output.
--no-warn: No warnings.

Behaviour

--now: With enable/disable/mask: also start or stop now.
--user: Manage your user services.
--system: Manage system services (default).
--global: With enable: for all users.
--runtime: Change only until the next reboot.
--no-block: Do not wait for the job to finish.
--wait: Wait until the started units end.
--job-mode=MODE: How to handle other queued jobs.
-T, --show-transaction: Show all jobs that a start adds.
--dry-run: Show what would happen.
--no-reload: With enable/disable: no daemon-reload.
--no-ask-password: Do not ask for passwords.
--no-wall: No message to users at reboot.
--message=TEXT: A reason for reboot or poweroff (logged).
--when=TIME: Plan a reboot or poweroff at this time (newer systemd).
-f, --force: Force (with enable: overwrite links; reboot -ff: now).
-i, --check-inhibitors=MODE: Respect or ignore inhibitor locks.
--fail: With start: fail if other jobs conflict.
--kill-whom=main|control|all: With kill: which processes.
-s, --signal=SIGNAL: With kill: the signal.
--kill-value=INT: A value with the signal.
--what=TYPE: With clean: which data (cache, logs, state …).
--preset-mode=MODE: With preset: full, enable-only, disable-only.
--firmware-setup: Reboot into the UEFI setup.
--boot-loader-menu=TIME: Show the boot menu at the next boot.
--boot-loader-entry=ID: Boot this entry next time.
--reboot-argument=ARG: Argument for the reboot.
--mkdir: Create folders with bind/start.
--marked: Act on units marked for restart.
--read-only: Bind mounts read only.
--drop-in=NAME: Name of the file for edit.
--root=PATH, --image=PATH, --image-policy=POLICY: Work on another root or image.
-H, --host=HOST: Control another host over SSH.
-M, --machine=NAME: Control a container.
-h, --help: Show help.
--version: Show the version.

Voorbeelden 15

$ als gewone gebruiker# als root (of met sudo)

1Start a service now and at boot

#systemctl enable --now httpd
Created symlink '/etc/systemd/system/multi-user.target.wants/httpd.service' → '/usr/lib/systemd/system/httpd.service'.

The RHCSA way: running now and after reboot.

2Status of a service
```
$systemctl status sshd
```
Loaded/enabled, Active, Main PID and the last 10 log lines.

3Short checks for scripts

$systemctl is-active httpd; systemctl is-enabled httpd
active
enabled

The exit code is 0 when the answer is yes.

4Restart and reload
```
#systemctl restart httpd
#systemctl reload httpd
```
reload keeps open connections; not every service supports it.
5Find failed services
```
$systemctl --failed
```
Start here after a boot with problems.

6List running services

$systemctl list-units -t service --state=running

What runs now.

7Which services start at boot?
```
$systemctl list-unit-files -t service --state=enabled
```
Review this list: fewer services = smaller attack surface.
8Override settings safely
```
#systemctl edit httpd
#systemctl cat httpd
```
The drop-in goes to /etc/systemd/system/httpd.service.d/.
9Block a service
```
#systemctl mask --now cups
```
Not even a dependency can start it.

10Default boot target

$systemctl get-default
#systemctl set-default multi-user.target

Text mode at the next boot.

11Show some properties
```
$systemctl show sshd -p MainPID,ActiveState,Restart
```
Good for scripts and checks.
12Limit memory of a service at run time
```
#systemctl set-property httpd MemoryMax=1G
```
Kept after reboot (use --runtime for a test).
13Rate the security of a service
```
$systemd-analyze security sshd
```
Exposure score from 0 (safe) to 10 (unsafe).
14Your own user services
```
$systemctl --user list-units -t service
```
Services in your session (like podman containers with Quadlet).
15Reboot with a reason
```
#systemctl reboot --message="Kernel update KB-2026-10"
```
The reason goes to the journal.

Let op

start alone does not survive a reboot; enable alone does not start now.
After editing unit files by hand, run systemctl daemon-reload.
isolate stops everything that is not part of the target (also your SSH session in rescue).

Bestanden

/usr/lib/systemd/system/: Unit files from packages.
/etc/systemd/system/: Your units, overrides and enable links.
/run/systemd/system/: Run-time units.
~/.config/systemd/user/: User units.

Exitcodes

0 :: Done (is-active/is-enabled: yes). 1 :: Failed or not active/enabled (also used by status for a dead unit with a pid file). 3 :: status: the unit is not active. 4 :: No such unit.

Volledige handleiding

Deze pagina legt het commando uit in eenvoudige woorden. De originele handleiding heeft elk detail.

In je terminal: man systemctl

Open de man-pagina (linux.die.net)www.freedesktop.org

systemctl

Wat het doet

Zo schrijf je het

Belangrijkste delen

Units now

Boot

State

Unit files

System

Opties 57

Select

Output

Behaviour

Voorbeelden 15

1Start a service now and at boot

2Status of a service

3Short checks for scripts

4Restart and reload

5Find failed services

6List running services

7Which services start at boot?

8Override settings safely

9Block a service

10Default boot target

11Show some properties

12Limit memory of a service at run time

13Rate the security of a service

14Your own user services

15Reboot with a reason

Let op

Bestanden

Exitcodes

Verwante commando's

Gebruikt in deze lessen

Gebruikt in deze labs

Volledige handleiding

`systemctl`