shutdown arranges for the system to be brought down in a safe way. All logged-in users are notified that the system is going down and, within the last five minutes of TIME, new logins are prevented.
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.
Once TIME has elapsed, shutdown sends a request to the init daemon to bring the system down into the appropriate runlevel. This is performed by emitting the runlevel event, which includes the new runlevel in the RUNLEVEL environment variable as well as the previous runlevel (obtained from the environment or from /var/run/utmp) in the PREVLEVEL variable. An additional INIT_HALT variable may be set, this will contain the value HALT when bringing the system down for halt and POWEROFF when bringing the system down for power off.
shutdown [OPTION]... TIME [MESSAGE]
-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 scripts.