If you execute
systemctl without arguments, the default behavior is
List known units (subject to limitations specified with
-t). If one or more PATTERNs are specified, only units matching one of them are shown.
This is the default command.
If you specify the option
Show terse runtime status information about one or more units, followed by most recent log data from the journal. If no units are specified, show system status. If combined with
--all, also show the status of all units (subject to limitations specified with
-t). If a PID is passed, show information about the unit the process belongs to.
This function is intended to generate human-readable output. If you are looking for computer-parsable output, use show instead. By default, this function only shows 10 lines of output and ellipsizes lines to fit in the terminal window. This can be changed with
--full, see above. In addition,
journalctl --unit=NAME or
journalctl --user-unit=NAME use a similar filter for messages and might be more convenient.