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How to Manage Systemd Services with Systemctl on Linux

How to control System and Services 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.

Starting with Systemtd and Systemctl Basics

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

It’s clear from the above example, that we have systemd 245 version Installed.
Check where the binaries and libraries of systemd and systemctl are installed.

$ whereis systemd
systemd: /usr/bin/systemd /usr/lib/systemd /etc/systemd /usr/share/systemd /usr/share/man/man1/systemd.1.gz
$ whereis systemctl
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
root         417       1  0 Jan30 ?        00:00:00 /lib/systemd/systemd-journald
root         464       1  0 Jan30 ?        00:00:01 /lib/systemd/systemd-udevd
systemd+     713       1  0 Jan30 ?        00:00:03 /lib/systemd/systemd-resolved
message+     825       1  0 Jan30 ?        00:00:02 /usr/bin/dbus-daemon --system --address=systemd: --nofork --nopidfile --systemd-activation --syslog-only
root         852       1  0 Jan30 ?        00:00:00 /lib/systemd/systemd-logind
rasho       1043       1  0 Jan30 ?        00:00:00 /lib/systemd/systemd --user
rasho       1112    1043  0 Jan30 ?        00:00:02 /usr/bin/dbus-daemon --session --address=systemd: --nofork --nopidfile --systemd-activation --syslog-only
rasho      18275   18094  0 13:32 pts/0    00:00:00 grep --color=auto systemd
Note: systemd is running as parent daemon (PID=1). In the above command ps with -e select all Processes, -a select all processes except session leaders and -f for full format listing (i.e. -eaf).
You can also analyze the time taken by each process at system boot with the following command:

$ systemd-analyze blame
2.508s dev-sda2.device                                      
1.903s snapd.service                                        
1.419s fwupd-refresh.service                                
1.275s fwupd.service                                                                   
 915ms lm-sensors.service                                   
 857ms man-db.service                                       
 831ms networkd-dispatcher.service                          
 664ms logrotate.service                                    
 587ms udisks2.service                                      
 576ms systemd-logind.service
..............

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

$ systemd-analyze critical-chain
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 @6.768s
└─multi-user.target @6.768s
  └─snapd.seeded.service @6.722s +44ms
    └─snapd.service @4.817s +1.903s
      └─basic.target @4.752s
        └─sockets.target @4.752s
          └─snapd.socket @4.751s +1ms
            └─sysinit.target @4.745s
              └─snapd.apparmor.service @4.592s +152ms
                └─apparmor.service @4.397s +191ms
                  └─local-fs.target @4.395s
                    └─run-user-1000.mount @6.540s
                      └─local-fs-pre.target @2.187s
                        └─systemd-tmpfiles-setup-dev.service @2.053s +134ms
                          └─systemd-sysusers.service @1.863s +186ms
                            └─systemd-remount-fs.service @1.747s +112ms
                              └─systemd-journald.socket @1.730s
                                └─system.slice @1.726s
                                  └─-.slice @1.726s

List all the available units.

$ systemctl list-unit-files
UNIT FILE                                  STATE           VENDOR PRESET
proc-sys-fs-binfmt_misc.automount          static          enabled      
-.mount                                    generated       enabled      
boot-efi.mount                             generated       enabled      
dev-hugepages.mount                        static          enabled      
dev-mqueue.mount                           static          enabled      
proc-sys-fs-binfmt_misc.mount              disabled        enabled      
snap-android\x2dstudio-99.mount            enabled         enabled      

List all running units.

$ systemctl list-units
  UNIT                                                                                        LOAD   ACTIVE     SUB       DESCRIPTION                                                                >
  proc-sys-fs-binfmt_misc.automount                                                           loaded active     waiting   Arbitrary Executable File Formats File System Automount Point              >
  dev-fuse.device                                                                             loaded activating tentative /dev/fuse                                                                  >
  sys-devices-pci0000:00-0000:00:02.0-drm-card0-card0\x2dLVDS\x2d1-intel_backlight.device     loaded active     plugged   /sys/devices/pci0000:00/0000:00:02.0/drm/card0/card0-LVDS-1/intel_backlight>
  sys-devices-pci0000:00-0000:00:16.3-tty-ttyS4.device                                        loaded active     plugged   7 Series/C210 Series Chipset Family KT Controller                          >
  sys-devices-pci0000:00-0000:00:19.0-net-enp0s25.device                                      loaded active     plugged   82579LM Gigabit Network Connection (Lewisville)                            >
  sys-devices-pci0000:00-0000:00:1b.0-sound-card0.device                                      loaded active     plugged   7 Series/C216 Chipset Family High Definition Audio Controller              >
  sys-devices-pci0000:00-0000:00:1c.3-0000:03:00.0-net-wlo1.device                            loaded active     plugged   Centrino Advanced-N 6235 (AGN)                                             >
  sys-devices-pci0000:00-0000:00:1d.0-usb2-2\x2d1-2\x2d1.6-2\x2d1.6:1.0-bluetooth-hci0.device loaded active     plugged   /sys/devices/pci0000:00/0000:00:1d.0/usb2/2-1/2-1.6/2-1.6:1.0/bluetooth/hci>
  sys-devices-pci0000:00-0000:00:1f.2-ata1-host0-target0:0:0-0:0:0:0-block-sda-sda1.device    loaded active     plugged   PNY_CS900_120GB_SSD EFI\x20System\x20Partition                             >
  sys-devices-pci0000:00-0000:00:1f.2-ata1-host0-target0:0:0-0:0:0:0-block-sda-sda2.device    loaded active     plugged   PNY_CS900_120GB_SSD 2                                                      >
  sys-devices-pci0000:00-0000:00:1f.2-ata1-host0-target0:0:0-0:0:0:0-block-sda.device         loaded active     plugged   PNY_CS900_120GB_SSD

List all failed units.

$ systemctl --failed
  UNIT                  LOAD   ACTIVE SUB    DESCRIPTION                           
● fwupd-refresh.service loaded failed failed Refresh fwupd metadata and update motd

LOAD   = Reflects whether the unit definition was properly loaded.
ACTIVE = The high-level unit activation state, i.e. generalization of SUB.
SUB    = The low-level unit activation state, values depend on unit type.

1 loaded units listed.
The output has the following columns :
UNIT: The systemd service unit name
LOAD: Shows whether the unit definition was properly read and loaded
ACTIVE: Describes if the unit is active.
SUB: Low-level activation state of the unit, giving more detailed information about the unit. This will vary by unit type.
DESCRIPTION: The service unit’s description.

Manage Services with Systemd

Systemctl provides an easier way to manage the systemd services.
List all services (including enabled and disabled).

$ systemctl list-unit-files --type=service
UNIT FILE                                  STATE           VENDOR PRESET
accounts-daemon.service                    enabled         enabled      
acpid.service                              disabled        enabled      
alsa-restore.service                       static          enabled      
alsa-state.service                         static          enabled      
alsa-utils.service                         masked          enabled      
anacron.service                            enabled         enabled      
apparmor.service                           enabled         enabled      
apt-daily-upgrade.service                  static          enabled      
apt-daily.service                          static          enabled      
[email protected]                            enabled         enabled      
avahi-daemon.service                       enabled         enabled      
blk-availability.service                   enabled         enabled      
bluetooth.service                          enabled         enabled      
bolt.service                               static          enabled
...................

To start a systemd service, use the systemctl start command:

$ sudo systemctl start name.service

You can leave .service suffix. For example, to start the apache server on Ubuntu:

$ sudo systemctl start apache2

To stop a running service:

$ sudo systemctl stop apache2

To restart the Apache service, run the following command:

$ systemctl restart 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

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
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