How to Manage Systemd Services with Systemctl on Linux

Systemd a standard process for managing start-up services in Linux operating systems. It is used for controlling which programs run when the Linux system boots up. It is a system manager and has become the new standard for Linux operating systems. Systemd allows you to create a custom systemd service to run and manage any process. In this tutorial, we will explain how to manage services with systemd on Linux.

Prerequisites

  • A server running Linux with Systemd, I will use Ubuntu 20.04 server here.
  • A root password is configured the server.

Verify Systemd

By default, Systemd comes pre-installed in all major operating systems. You can verify the installed version of Systemd with the following command:

systemctl --version

You should see the following output:

systemd 245 (245.4-4ubuntu3)
+PAM +AUDIT +SELINUX +IMA +APPARMOR +SMACK +SYSVINIT +UTMP +LIBCRYPTSETUP +GCRYPT +GNUTLS +ACL +XZ +LZ4 +SECCOMP +BLKID +ELFUTILS +KMOD +IDN2 -IDN +PCRE2 default-hierarchy=hybrid

You can find the location of the Systemd with the following command:

whereis systemd

You should get the following output:

systemd: /usr/bin/systemd /usr/lib/systemd /etc/systemd /usr/share/systemd /usr/share/man/man1/systemd.1.gz

To find systemctl location, run the following command:

whereis systemctl

You should get the following output:

systemctl: /usr/bin/systemctl /usr/share/man/man1/systemctl.1.gz

You can also verify whether the Systemd is running or not with the following command:

ps -eaf | grep systemd

You should get the following output:

root         269       1  0 09:57 ?        00:00:01 /lib/systemd/systemd-journald
root         294       1  0 09:57 ?        00:00:00 /lib/systemd/systemd-udevd
systemd+     297       1  0 09:57 ?        00:00:00 /lib/systemd/systemd-networkd
message+     319       1  0 09:57 ?        00:00:00 /usr/bin/dbus-daemon --system --address=systemd: --nofork --nopidfile --systemd-activation --syslog-only
root         329       1  0 09:57 ?        00:00:00 /lib/systemd/systemd-logind
systemd+     382       1  0 09:57 ?        00:00:00 /lib/systemd/systemd-resolved
root        1128       1  0 10:47 ?        00:00:00 /lib/systemd/systemd --user
root        1177    1152  0 10:48 pts/0    00:00:00 grep --color=auto systemd

You can also analyze the time taken by each process at system boot with the following command:

systemd-analyze blame

You should get the following output:

3.662s csm.service                         
1.899s apt-daily-upgrade.service           
1.798s dev-sda1.device                     
1.400s systemd-logind.service              
1.336s fstrim.service                      
1.207s systemd-networkd.service            
1.131s systemd-resolved.service            
 856ms man-db.service                      
 842ms systemd-journald.service            
 415ms e2scrub_reap.service                
 320ms keyboard-setup.service              
 295ms networkd-dispatcher.service         
 239ms systemd-udev-trigger.service 

To analyze the critical chain at boot with the following command:

systemd-analyze critical-chain

You should get the following output:

The time when unit became active or started is printed after the "@" character.
The time the unit took to start is printed after the "+" character.

graphical.target @4.948s
??multi-user.target @4.946s
  ??csm.service @1.282s +3.662s
    ??basic.target @1.277s
      ??sockets.target @1.276s
        ??dbus.socket @1.274s
          ??sysinit.target @1.257s
            ??systemd-update-utmp.service @1.247s +8ms
              ??systemd-tmpfiles-setup.service @1.228s +17ms
                ??systemd-journal-flush.service @1.201s +24ms
                  ??systemd-journald.service @356ms +842ms
                    ??systemd-journald.socket @313ms
                      ??system.slice @225ms
                        ??-.slice @225ms

Manage Services with Systemd

Systemctl provides an easier way to manage the systemd services.

To start the Apache service, run the following command:

systemctl start apache2

To restart the Apache service, run the following command:

systemctl restart apache2

To stop the Apache service, run the following command:

systemctl stop apache2

To reload the Apache service, run the following command:

systemctl reload apache2

To enable the Apache service to start after system reboot, run the following command:

systemctl enable apache2

To remove the Apache service from the system start up, run the following command:

systemctl disable apache2

To kill the Apache service, run the following command:

systemctl kill apache2

To mask the Apache service, run the following command:

systemctl mask apache2

To unmask the Apache process, run the following command:

systemctl unmask apache2

To check whether the Apache service is enabled or not, run the following command:

systemctl is-enabled apache2

To check the status of the Apache service, run the following command:

systemctl status apache2

If the service is running, you should get the following output:

? apache2.service - The Apache HTTP Server
     Loaded: loaded (/lib/systemd/system/apache2.service; enabled; vendor preset: enabled)
     Active: active (running) since Sat 2021-01-09 10:53:12 UTC; 26s ago
       Docs: https://httpd.apache.org/docs/2.4/
   Main PID: 1708 (apache2)
      Tasks: 55 (limit: 2353)
     Memory: 5.8M
     CGroup: /system.slice/apache2.service
             ??1708 /usr/sbin/apache2 -k start
             ??1709 /usr/sbin/apache2 -k start
             ??1710 /usr/sbin/apache2 -k start

Jan 09 10:53:12 ubuntu2004 systemd[1]: Starting The Apache HTTP Server...

After renaming or deleting any systemd file, you will need to reload it to apply the changes. To reload the systemd service file, run the following command:

systemctl daemon-reload

Manage Systemd Unit Files

The above commands will be useful for managing single services. However, it can not used to find the current state of the system. There are lot of other commands that are useful for providing this information.

To see a list of all available units, run the following command:

systemctl list-unit-files

You should see a list of all unit files in the following output:

UNIT FILE                              STATE           VENDOR PRESET
proc-sys-fs-binfmt_misc.automount      static          enabled      
-.mount                                generated       enabled      
dev-hugepages.mount                    static          enabled      
dev-mqueue.mount                       static          enabled      
proc-sys-fs-binfmt_misc.mount          disabled        enabled      
sys-fs-fuse-connections.mount          static          enabled      
sys-kernel-config.mount                static          enabled      
sys-kernel-debug.mount                 static          enabled      
sys-kernel-tracing.mount               static          enabled      
acpid.path                             enabled         enabled      
ntp-systemd-netif.path                 enabled         enabled      
systemd-ask-password-console.path      static          enabled      
systemd-ask-password-wall.path         static          enabled      
session-2.scope                        transient       enabled      
acpid.service                          disabled        enabled      
apt-daily-upgrade.service              static          enabled      
apt-daily.service                      static          enabled      
[email protected]                        enabled         enabled      
console-getty.service                  disabled        disabled     
console-setup.service                  enabled         enabled      
[email protected]               static          enabled      
cron.service                           enabled         enabled      
cryptdisks-early.service               masked          enabled      
cryptdisks.service                     masked          enabled      
csm.service                            enabled         enabled      
dbus-org.freedesktop.hostname1.service static          enabled      
dbus-org.freedesktop.locale1.service   static          enabled      

To see a list of all active units, run the following command:

systemctl list-units

You should see the following output:

  UNIT                                                                                        LOAD   ACTIVE SUB       DESCRIPTION             >
  proc-sys-fs-binfmt_misc.automount                                                           loaded active waiting   Arbitrary Executable Fil>
  sys-devices-pci0000:00-0000:00:03.0-virtio0-net-eth0.device                                 loaded active plugged   Virtio network device   >
  sys-devices-pci0000:00-0000:00:04.0-virtio1-net-eth1.device                                 loaded active plugged   Virtio network device   >
  sys-devices-pci0000:00-0000:00:05.0-virtio2-host2-target2:0:0-2:0:0:0-block-sda-sda1.device loaded active plugged   QEMU_HARDDISK 1         >
  sys-devices-pci0000:00-0000:00:05.0-virtio2-host2-target2:0:0-2:0:0:0-block-sda.device      loaded active plugged   QEMU_HARDDISK           >
  sys-devices-platform-serial8250-tty-ttyS1.device                                            loaded active plugged   /sys/devices/platform/se>
  sys-devices-platform-serial8250-tty-ttyS10.device                                           loaded active plugged   /sys/devices/platform/se>
  sys-devices-platform-serial8250-tty-ttyS11.device                                           loaded active plugged   /sys/devices/platform/se>
  sys-devices-platform-serial8250-tty-ttyS12.device                                           loaded active plugged   /sys/devices/platform/se>
  sys-devices-platform-serial8250-tty-ttyS13.device                                           loaded active plugged   /sys/devices/platform/se>
  sys-devices-platform-serial8250-tty-ttyS14.device                                           loaded active plugged   /sys/devices/platform/se>
  sys-devices-platform-serial8250-tty-ttyS15.device                                           loaded active plugged   /sys/devices/platform/se>
  sys-devices-platform-serial8250-tty-ttyS16.device                                           loaded active plugged   /sys/devices/platform/se>
  sys-devices-platform-serial8250-tty-ttyS17.device                                           loaded active plugged   /sys/devices/platform/se>
  sys-devices-platform-serial8250-tty-ttyS18.device                                           loaded active plugged   /sys/devices/platform/se>
  sys-devices-platform-serial8250-tty-ttyS19.device                                           loaded active plugged   /sys/devices/platform/se>
  sys-devices-platform-serial8250-tty-ttyS2.device                                            loaded active plugged   /sys/devices/platform/se>
  sys-devices-platform-serial8250-tty-ttyS20.device                                           loaded active plugged   /sys/devices/platform/se>
  sys-devices-platform-serial8250-tty-ttyS21.device                                           loaded active plugged   /sys/devices/platform/se>
  sys-devices-platform-serial8250-tty-ttyS22.device                                           loaded active plugged   /sys/devices/platform/se>
  sys-devices-platform-serial8250-tty-ttyS23.device                                           loaded active plugged   /sys/devices/platform/se>
  sys-devices-platform-serial8250-tty-ttyS24.device                                           loaded active plugged   /sys/devices/platform/se>
  sys-devices-platform-serial8250-tty-ttyS25.device                                           loaded active plugged   /sys/devices/platform/se>
  sys-devices-platform-serial8250-tty-ttyS26.device                                           loaded active plugged   /sys/devices/platform/se>
  sys-devices-platform-serial8250-tty-ttyS27.device                                           loaded active plugged   /sys/devices/platform/se>
  sys-devices-platform-serial8250-tty-ttyS28.device                                           loaded active plugged   /sys/devices/platform/se>
  sys-devices-platform-serial8250-tty-ttyS29.device                                           loaded active plugged   /sys/devices/platform/se>
  sys-devices-platform-serial8250-tty-ttyS3.device                                            loaded active plugged   /sys/devices/platform/se>
  sys-devices-platform-serial8250-tty-ttyS30.device                                           loaded active plugged   /sys/devices/platform/se>
  sys-devices-platform-serial8250-tty-ttyS31.device                                           loaded active plugged   /sys/devices/platform/se>

To see a list of all failed units, run the following command:

systemctl --failed

To list all services including enabled and disabled services, run the following command:

systemctl list-unit-files --type=service

You should see the following output:

UNIT FILE                              STATE           VENDOR PRESET
acpid.service                          disabled        enabled      
apache-htcacheclean.service            disabled        enabled      
[email protected]           disabled        enabled      
apache2.service                        enabled         enabled      
[email protected]                       disabled        enabled      
apt-daily-upgrade.service              static          enabled      
apt-daily.service                      static          enabled      
[email protected]                        enabled         enabled      
console-getty.service                  disabled        disabled     
console-setup.service                  enabled         enabled      
[email protected]               static          enabled      
cron.service                           enabled         enabled      
cryptdisks-early.service               masked          enabled      
cryptdisks.service                     masked          enabled      
csm.service                            enabled         enabled      
dbus-org.freedesktop.hostname1.service static          enabled      
dbus-org.freedesktop.locale1.service   static          enabled      
dbus-org.freedesktop.login1.service    static          enabled      
dbus-org.freedesktop.resolve1.service  enabled         enabled      
dbus-org.freedesktop.timedate1.service static          enabled      
dbus-org.freedesktop.timesync1.service masked          enabled      
dbus.service                           static          enabled      
debug-shell.service                    disabled        disabled     
dmesg.service                          enabled         enabled      
[email protected]                       static          enabled      
e2scrub_all.service                    static          enabled      
[email protected]                  static          enabled      
e2scrub_reap.service                   enabled         enabled      
emergency.service                      static          enabled      
fstrim.service                         static          enabled      
getty-static.service                   static          enabled      
[email protected]                         enabled         enabled      

You can see the properties of SSH unit, run the following command:

systemctl show sshd.service

You should see the following output:

Id=sshd.service
Names=sshd.service
Requires=basic.target
Wants=system.slice
WantedBy=multi-user.target
Conflicts=shutdown.target
Before=shutdown.target multi-user.target
After=syslog.target network.target auditd.service systemd-journald.socket basic.target system.slice
Description=OpenSSH server daemon

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

You should see the following output:

UNIT FILE                        STATE    VENDOR PRESET
acpid.socket                     enabled  enabled      
dbus.socket                      static   enabled      
ssh.socket                       disabled enabled      
syslog.socket                    static   disabled     
systemd-fsckd.socket             static   enabled      
systemd-initctl.socket           static   enabled      
systemd-journald-audit.socket    static   enabled      
systemd-journald-dev-log.socket  static   enabled      
[email protected] static   enabled      
systemd-journald.socket          static   enabled      
[email protected]         static   enabled      
systemd-networkd.socket          disabled enabled      
systemd-rfkill.socket            static   enabled      
systemd-udevd-control.socket     static   enabled      
systemd-udevd-kernel.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

Systemctl Additional Commands

You can perform several tasks using the systemctl command. If you want to put the system into single-user mode, run the following command:

systemctl rescue

To halt the system, run the following command:

systemctl halt

To shutdown the system, run the following command:

systemctl poweroff

To restart the system, run the following command:

systemctl reboot

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.

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