"systemctl status/start/stop/enable/disable" Commands

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∟"systemctl status/start/stop/enable/disable" Commands

This section provides a quick introduction of the 'systemctl' command, which allows you to start or stop a system service, check the status of a service, and enable or disable a service at the boot time.

What Is "systemctl" Command? "systemctl" is a command to interact with "systemd", the system and service manager.

The most common tasks you can perform with the "systemctl" command are:

1. "systemctl status service_name" - To check the status of a given service. By the way, the ".service" postfix of a service name can be omitted when specifying the service name.

herong$ sudo systemctl status cockpit
* cockpit.service - Cockpit Web Service
   Loaded: loaded (/usr/lib/systemd/system/cockpit.service; static; ...
   Active: active (running) since Tue ...
     Docs: man:cockpit-ws(8)
  Process: 7282 ExecStartPre=/usr/sbin/remotectl certificate --ensure ...
 Main PID: 7285 (cockpit-ws)
    Tasks: 2 (limit: 26213)
   Memory: 1.5M
   CGroup: /system.slice/cockpit.service
           |-7285 /usr/libexec/cockpit-ws

localhost.localdomain systemd[1]: Starting Cockpit Web Service...
localhost.localdomain systemd[1]: Started Cockpit Web Service.
localhost.localdomain cockpit-ws[7285]: Using certificate: \
   /etc/cockpit/ws-certs.d/0-self-signed.cert

systemctl status cockpit.service
(same output as above)

2. "systemctl start service_name" - To start a given service.

3. "systemctl stop service_name" - To stop a given service.

4. "systemctl enable service_name" - To enable a given service at system boot time.

herong$ sudo systemctl enable cockpit.socket
Created symlink /etc/systemd/system/sockets.target.wants/cockpit.socket ->
  /usr/lib/systemd/system/cockpit.socket.

5. "systemctl disable service_name" - To disable a given service at system boot time. The "disabled" status of the service file will be displayed in the "systemctl status" command output.

herong$ sudo systemctl disable cockpit.socket
Removed /etc/systemd/system/sockets.target.wants/cockpit.socket.

herong$ systemctl status cockpit.socket
* cockpit.socket - Cockpit Web Service Socket
   Loaded: loaded (/usr/lib/systemd/system/cockpit.socket; disabled; ...
   Active: inactive (dead)
     Docs: man:cockpit-ws(8)
   Listen: [::]:9090 (Stream)

5. "systemctl --all list-units" - To list all services, including inactive ones. The output bellow shows 457 services with different statuses on my CentOS computer.

herong$ systemctl --all list-units | wc
    457    3173  106109

herong$ systemctl --all list-units
  UNIT                  LOAD   ACTIVE   SUB     DESCRIPTION
  dev-block-8:19.device loaded active   plugged TOSHIBA_DT01ACA2 primary
  dev-cl-home.device    loaded active   plugged /dev/cl/home
  -.mount               loaded active   mounted Root Mount
  boot.mount            loaded active   mounted /boot
  firewalld.service     loaded active   running firewalld - dynamic ...
  nfs-mountd.service    loaded active   running NFS Mount Daemon
  nfs-server.service    loaded active   exited  NFS server and services
  nfs-utils.service     loaded inactive dead    NFS server and client ...
* ypserv.service     not-found inactive dead    ypserv.service
  ...

6. "systemctl --all list-unit-files" - To list all service definition file.

herong$ systemctl list-unit-files | wc
    496     993   26206

herong$ systemctl list-unit-files *httpd*
NIT FILE                                   STATE
boot.mount                                 generated
dev-mqueue.mount                           static
home.mount                                 generated
cockpit.service                            static
console-getty.service                      disabled
crond.service                              enabled
sssd-sudo.service                          indirect
...