you can type
shutdown --help in a terminal to see various options
Usage: shutdown [OPTION]... TIME [MESSAGE]
Bring the system down.
-r reboot after shutdown
-h halt or power off after shutdown
-H halt after shutdown (implies -h)
-P power off after shutdown (implies -h)
-c cancel a running shutdown
-k only send warnings, don't shutdown
-q, --quiet reduce output to errors only
-v, --verbose increase output to include informational messages
--help display this help and exit
--version output version information and exit
TIME may have different formats, the most common is simply the word
'now' which will bring the system down immediately. Other valid
formats are +m, where m is the number of minutes to wait until
shutting down and hh:mm which specifies the time on the 24hr clock.
Logged in users are warned by a message sent to their terminal, you
may include an optional MESSAGE included with this. Messages can be
sent without actually bringing the system down by using the -k option.
If TIME is given, the command will remain in the foreground until the
shutdown occurs. It can be cancelled by Control-C, or by another user
using the -c option.
The system is brought down into maintenance (single-user) mode by
default, you can change this with either the -r or -h option which
specify a reboot or system halt respectively. The -h option can be
further modified with -H or -P to specify whether to halt the system,
or to power it off afterwards. The default is left up to the shutdown
to make run you will need
sudo shutdown now for instance will shut the computer down right away.
hope this helps.