08-C.8.1: Managing Linux Services - systemctl

The systemctl Command

systemctl is used to examine and control the state of “systemd” system and service manager.

systemd is system and service manager for Unix like operating systems (most of the distributions, not all). As the system boots up, the first process created, i.e., init process with PID = 1, is systemd system that initiates the userspace services.

Syntax :

systemctl [ OPTIONS ] COMMAND [NAME...]

Command Options:

Option	Meaning
-t, --type=	The argument in this case should be comma-separated list of unit types such as service and socket.
--state=	This is used to show only specified states, for example --state=failed, will show only failed units.
-a, --all	Show all units, regardless of their states.
-r, --recursive	While listing units, show units of local containers also.
--show-types	Shows types of sockets along with showing sockets.
--job-mode	This option controls how to deal with already queued jobs in case of queuing a new job.
--fail	Similar to --job-mode=fail.
-i, --ignore-inhibitors	When you request system shutdown or sleep state, it ignores inhibitor locks.
-q, --quite	Suppresses printing of results of various commands and the hints about the truncated lines.
--no-block	Don't wait synchronously for process to finish.
--user	Talk to service manager of calling user, instead of system.
--no-wall	Don't send wall message before power-off, halt or reboot.
-f, --force	When used with enable, override any conflicting symlinks.
--message=	When used with halt, poweroff, reboot, kexec, you can display a short message specifying reason of operation.
-n, --lines	When used with status, controls the number of journal lines to show.
-H, --host=	Execute operation remotely.

systemctl has numerous sub-commands to assist in managing the various services. The following example shows the command's syntax, the command, followed by a sub-command (in the example it is stop), and then the service (NetworkManager.service):

systemctl stop NetworkManager.service
OR
systemctl stop NetworkManager

Below are some of the common sub-commands available. See the systemctl man page for more details.

systemctl Sub-commands:

Subcommand	Meaning
systemctl start foobar.service	Used to start a service (not reboot persistent).
systemctl stop foobar.service	Used to stop a service (not reboot persistent).
systemctl restart foobar.service	Used to stop and then start a service.
systemctl reload foobar.service	When supported, reloads the config file without interrupting pending operations.
systemctl condrestart foobar.service	Restarts if the service is already running.
systemctl status foobar.service	Tells whether a service is currently running.
ls /lib/systemd/system/*.service /etc/systemd/system/*.service	Used to list the services that can be started or stopped.
systemctl enable foobar.service	Turns the service on, for start at next boot, or other trigger.
systemctl disable foobar.service	Turns the service off for the next reboot, or any other trigger.
systemctl is-enabled foobar.service	Used to check whether a service is configured to start or not in the current environment.

Some example output - notice that the command only used "ssh" and not "sshd.service" - this is valid syntax.

pbmac@pbmac-server $ systemctl status sshd
● ssh.service - OpenBSD Secure Shell server
   Loaded: loaded (/lib/systemd/system/ssh.service; enabled; vendor preset: enab
   Active: active (running) since Wed 2020-08-19 08:11:43 PDT; 1 weeks 1 days ag
 Main PID: 1132 (sshd)
    Tasks: 1 (limit: 4915)
   CGroup: /system.slice/ssh.service
           └─1132 /usr/sbin/sshd -D

Adapted from:
"systemctl in Unix" by Mandeep Singh, Geeks for Geeks is licensed under CC BY-SA 4.0