How to use shutdown ubuntu 12.04 command under Linux

How do I use shutdown command?

The shutdown command can be used to turn off or reboot a computer. Type the command as follows to shutdown server / computer immediately:
$ sudo shutdown -h now
OR
$ sudo shutdown -h 0

How do I shutdown compute at specific time?

To shutdown computer at 6:45pm, enter:
$ sudo shutdown -h 18:45 "Server is going down for maintenance"
At 6:30pm message will go out to all user and 6:45 system will shutdown.
Please note that you can also use halt or poweroff or reboot command for stopping and restarting the system:
$ sudo halt
OR
$ sudo poweroff

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