systemd

systemd is a suit of basic building blocks for a linux system. It provides a system and service manager that runs as PID 1 and starts the rest of the system.

Basic systemctl usage

The main command used to introspect and control systemd is systemctl. Some of its uses are examinig the system state and managing the system and services.

Using units

Units commonly include, but are not limited to, services (.service), mount points (.mount), devices (.device) and sockets (.socket). When using systemctl, you generally have to specify the complete name of the unit file, including suffix, for example sshd.socket. There are a few short forms when specifying the unit int the following systemctl commands:

• If you do not specify the suffix, systemctl will assume .service
• Mount points will automatically be translated into the appropriate .mount unit. For example /home is equivalent to home.mount
• Similar to mount points, devices are automatically translated into the appropriate .device unit. Therefore specifying /dev/sda2 is equivalent to dev-sda2.device

Action	Command	Note
Show system status	systemctl status
List running units	systemctl or systemctl list-units
List failing units	systemctl --failed
List installed unit files	systemctl list-unit-files
Show process status for a PID	systemctl status pid	cgroup slice, memory and parent
Show a manual page associated with a unit	systemctl help unit	as supported by the unit
Status of a unit	systemctl status unit	including whether it is running or not
Check whether a unit is enabled	systemctl is-enabled unit
Start a unit immediately	systemctl start unit
Stop a unit immediately	systemctl stop unit
Restart a unit	systemctl restart unit
Reload a unit and its configuration	systemctl reload unit
Enable a unit to start auatomatically at boot	systemctl enable unit
Enable a unit to start auatomatically at boot and start it immediately	systemctl enable --now unit
Disable a unit to no longer to start at boot	systemctl disable unit
Reenable a unit	systemctl reenable unit	i.e. disable and enable anew