systemd

Systemd units are tools that manage resources and services. A unit for an apache2 service will be apache2.service.

#linux

Unit Types

1. service → Most common one, for system resources that can be initiated, interrupted and reloaded.
2. socket → Filesystem or a network socket. They have a corresponding service unit loaded when the socket receives a request.
3. device → Associated with a hardware device. udev rule for the purpose must exist.
4. mount → Mount point definition in the filesystem, similar to /etc/fstab.
5. automount → Same as above, but mounted automatically. Has a corresponding mount unit, initiated when automount is accessed.
6. target → Grouping of other units managed as a single unit.
7. snapshot → Saved state of the systemd manager.

Important info

• Unit location configuration: /usr/lib/systemd/system
• Remember to run systemctl daemon-reload after editing some configuration.

Common actions

• systemctl start <unit_name>.service
• systemctl stop <unit_name>.service
• systemctl restart <unit_name>.service
• systemctl status <unit_name>.service
• systemctl is-active <unit_name>.service
• systemctl enable <unit_name>.service
• systemctl disable <unit_name>.service
• systemctl is-enabled <unit_name>.service
• systemctl get-default → gets the default boot target.
• systemctl list-units → lists active units.
• systemctl list-unit-files → lists all units.