man 8 shutdown

SHUTDOWN(8)                        shutdown                        SHUTDOWN(8)

NAME
       shutdown - Halt, power off or reboot the machine

SYNOPSIS
       shutdown [OPTIONS...] [TIME] [WALL...]

DESCRIPTION
       shutdown may be used to halt, power off, or reboot the machine.

       The first argument may be a time string (which is usually "now").
       Optionally, this may be followed by a wall message to be sent to all
       logged-in users before going down.

       The time string may either be in the format "hh:mm" for hour/minutes
       specifying the time to execute the shutdown at, specified in 24h clock
       format. Alternatively it may be in the syntax "+m" referring to the
       specified number of minutes m from now.  "now" is an alias for "+0",
       i.e. for triggering an immediate shutdown. If no time argument is
       specified, "+1" is implied.

       Note that to specify a wall message you must specify a time argument,
       too.

       If the time argument is used, 5 minutes before the system goes down the
       /run/nologin file is created to ensure that further logins shall not be
       allowed.

OPTIONS
       The following options are understood:

       --help
           Print a short help text and exit.

       -H, --halt
           Halt the machine.

       -P, --poweroff
           Power the machine off (the default).

       -r, --reboot
           Reboot the machine.

       -h
           The same as --poweroff, but does not override the action to take if
           it is "halt". E.g.  shutdown --reboot -h means "poweroff", but
           shutdown --halt -h means "halt".

       -k
           Do not halt, power off, or reboot, but just write the wall message.

       --no-wall
           Do not send wall message before halt, power off, or reboot.

       -c
           Cancel a pending shutdown. This may be used to cancel the effect of
           an invocation of shutdown with a time argument that is not "+0" or
           "now".

       --show
           Show a pending shutdown action and time if there is any.

EXIT STATUS
       On success, 0 is returned, a non-zero failure code otherwise.

COMPATIBILITY
       The
        shutdown command in previous init systems (including sysvinit)
       defaulted to single-user mode instead of powering off the machine. To
       change into single-user mode, use systemctl rescue instead.

SEE ALSO
       systemd(1), systemctl(1), halt(8), wall(1)

systemd 252                                                        SHUTDOWN(8)