Copyright (c) 1980 Regents of the University of California. All rights reserved. The Berkeley software License Agreement specifies the terms and conditions for redistribution.
/usr/ucb/shutdown [-fhknr] time [warning-message]...
shutdown provides an automated procedure to notify users when the system is to be shut down. time specifies when shutdown will bring the system down; it may be the word now (indicating an immediate shutdown), or it may specify a future time in one of two formats: +number and hour:min. The first form brings the system down in number minutes, and the second brings the system down at the time of day indicated in 24-hour notation.
At intervals that get closer as the apocalypse approaches, warning messages are displayed at terminals of all logged-in users, and of users who have remote mounts on that machine.
At shutdown time a message is written to the system log daemon, syslogd(8), containing the time of shutdown, the instigator of the shutdown, and the reason. Then a terminate signal is sent to init, which brings the system down to single-user mode.
As an alternative to the above procedure, these options can be specified: -f
Arrange, in the manner of fastboot(1B), that when the system is rebooted, the file systems will not be checked.
Execute halt(8).
Simulate shutdown of the system. Do not actually shut down the system.
Prevent the normal sync(2) before stopping.
Execute reboot(8).
remote mounted file system table
login (1), fastboot (1B), sync (2), rmtab (5), attributes (7), halt (8), reboot (8), syslogd (8)
Only allows you to bring the system down between now and 23:59 if you use the absolute time for shutdown.