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Part of Linux Commands Cheat Sheet

Systemd is an init system and system manager for Linux machines.

In systemd, the target of most actions are "units", which are resources that systemd knows how to manage. Units are categorized by the type of resource they represent and they are defined with files known as unit files. The type of each unit can be inferred from the suffix on the end of the file.

List units:


systemctl # list active units
systemctl --all # list all services
systemctl --type=service
systemctl --state=failed

States:

  • inactive
  • active: start succeed
  • failed: start failed

List unit files:


systemctl list-unit-files
systemctl list-unit-files --type=service
systemctl list-unit-files --state=enabled

States:

  • enabled: start at boot.
  • disabled: not start at boot.
  • masked: cannot be started.
  • static: cannot be enabled.

Unit file management:


systemctl cat nginx.service
systemctl mask nginx.service # make it unstartable
systemctl unmask nginx.service

Editing unit file:

Create a snippet in a directory (default /etc/systemd/system/nginx.service.d/*), override the original configuration file:


systemctl edit nginx.service

To undo the modification:


rm -r /etc/systemd/system/nginx.service.d

Create a copy in /etc/systemd/system/nginx.service, take place of the original configuration file (default /lib/systemd/system/nginx.service):


systemctl edit --full nginx.service

To undo the modification:


rm /etc/systemd/system/nginx.service

After modification, run the following command to reload configuration:


systemctl daemon-reload

Service management:


systemctl status nginx
systemctl is-active nginx
systemctl is-enabled nginx
systemctl is-failed nginx

Operations:


systemctl start nginx.service # start nginx service
systemctl start nginx # .service suffix can be left off
systemctl stop nginx
systemctl restart nginx
systemctl reload nginx # reload configuration files without restarting
systemctl enable nginx # start nginx automatically at boot
systemctl disable nginx

How To Use Systemctl to Manage Systemd Services and Units - DigitalOcean

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