How to Manage Systemd Services with Systemctl on Linux

Manage Sockets with Systemctl

You can also manage sockets using the Systemctl command.
To list all available system sockets, run the following command:

$ systemctl list-unit-files --type=socket
UNIT FILE                        STATE    VENDOR PRESET
acpid.socket                     enabled  enabled      
avahi-daemon.socket              enabled  enabled
ssh.socket                       disabled enabled            
cups.socket                      enabled  enabled      
dbus.socket                      static   enabled      
dm-event.socket                  enabled  enabled      
lvm2-lvmpolld.socket             enabled  enabled      
saned.socket                     disabled enabled      
snapd.socket                     enabled  enabled      
syslog.socket                    static   disabled     
systemd-coredump.socket          static   enabled      
systemd-fsckd.socket             static   enabled      
systemd-initctl.socket           static   enabled      

To start the SSH socket, run the following command:

$ systemctl start ssh.socket

To stop the SSH socket, run the following command:

$ systemctl stop ssh.socket

To restart the SSH socket, run the following command:

$ systemctl restart ssh.socket

To check the status of the SSH socket, run the following command:

$ systemctl status ssh.socket

To enable and disable the SSH socket at boot time, run the following command:

$ systemctl enable ssh.socket
$ systemctl disable ssh.socket

Control System Runlevels

How to start a system rescue mode.

# systemctl rescue

Broadcast message from root@tecmint on pts/0 (Wed 2015-04-29 11:31:18 IST):

The system is going down to rescue mode NOW!
How to enter into emergency mode.

$ systemctl emergency
Welcome to emergency mode! After logging in, type "journalctl -xb" to view
system logs, "systemctl reboot" to reboot, "systemctl default" to try again
to boot into default mode.

List current run levels in use.

$ systemctl get-default

multi-user.target

How to start Runlevel 5 aka graphical mode.

$ systemctl isolate runlevel5.target
OR
$ systemctl isolate graphical.target

How to start Runlevel 3 aka multiuser mode (command line).

$ systemctl isolate runlevel3.target
OR
$ systemctl isolate multiuser.target

How to set multiuser mode or graphical mode as default run level.

$ systemctl set-default runlevel3.target
OR
$ systemctl set-default runlevel5.target

How to reboot, halt, suspend, hibernate, or put a system in hybrid-sleep.

$ systemctl reboot
$ systemctl halt
$ systemctl suspend
$ systemctl hibernate
$ systemctl hybrid-sleep

For those who may not be aware of run levels and what it does.

Conclusion

In the above guide, you learned how to manage and control systemd service on Linux. I hope this will helps you to interact with and control your systemd instance. Feel free to ask me if you have any questions.

See also: How to Kill a Process in Linux