CentOS 6.5 system shutdown and restart command usage

1. shutdown command (root permission required)

Usage: shutdown [OPTION]... TIME [MESSAGE]
OPTION: OPTION
TIME: TIME
MESSAGE: warning MESSAGE sent to all users
Options:
-R: restart the system after the system service is stopped.
-H: shut down the system immediately after the service is stopped.
-H: shut down the system immediately after the service is stopped (that is,-h)
-P: immediately shut down the system after the service is stopped (that is,-h)
-C: cancels an ongoing shutdown process.
-K: only sending warning messages, not actually shutting down

Example:

Shutdown-r now restart now
Shutdown-h now shut down immediately

Shutdown-h 'I will shutdown' system shut down at today. If the current time is after, shutdown again at the next day and send the I wil shutdown message
Shutdown-h + 30 system shutdown after 30 minutes

II. Shutdown command halt

Age: halt [OPTION]...

-N: do not execute sync before shutdown or restart (data synchronization is written to the disk)
-F: shutdown or restart without calling shutdown.
-P: This option is the default option, that is, poweroff is called during shutdown.
-W: not a real restart or shutdown, but a wtmp (/var/log/wtmp) record.

III. Shutdown command poweroff

Same as halt

IV. Switch execution level init

Switch execution level

Init 0: Shutdown
Init 6: Restart

V. Restart command reboot

Same as halt

The preceding commands can be viewed by man, for example:

Man shutdown