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How to Manage Systemd Services with Systemctl on Linux

ComputingPost
7 min readDec 17, 2022

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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      

autovt@.service                        enabled         enabled      

console-getty.service                  disabled        disabled     

console-setup.service                  enabled         enabled      

container-getty@.service               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      

apache-htcacheclean@.service           disabled        enabled      

apache2.service                        enabled         enabled      

apache2@.service                       disabled        enabled      

apt-daily-upgrade.service              static          enabled      

apt-daily.service                      static          enabled      

autovt@.service                        enabled         enabled      

console-getty.service                  disabled        disabled     

console-setup.service                  enabled         enabled      

container-getty@.service               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      

e2scrub@.service                       static          enabled      

e2scrub_all.service                    static          enabled      

e2scrub_fail@.service                  static          enabled      

e2scrub_reap.service                   enabled         enabled      

emergency.service                      static          enabled      

fstrim.service                         static          enabled      

getty-static.service                   static          enabled      

getty@.service                         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      

systemd-journald-varlink@.socket static   enabled      

systemd-journald.socket          static   enabled      

systemd-journald@.socket         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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ComputingPost

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