shutdown
provides an automated shutdown procedure for superusers
to nicely notify users when the system is shutting down,
saving them from system administrators, hackers, and gurus, who
would otherwise not bother with such niceties.
When the
shutdown
command is issued without options the system is placed in single
user mode at the indicated time after shutting down all system
services.
The options are as follows:
-d
When used with
-h
or
-r
causes system to perform a dump.
This option is useful for debugging system dump procedures or capturing the
state of a corrupted or misbehaving system.
See
savecore(8)
for information on how to recover this dump.
-f
Create the file
/fastboot
so that the file systems will
not
be checked by
fsck(8)
during the next boot.
(See
rc(8/)).
-h
The system is halted at the specified
time
when
shutdown
execs
halt(8).
-k
Kick everybody off.
The
-k
option
does not actually halt the system, but leaves the
system multi-user with logins disabled (for all but superuser).
-n
When used with
-h
or
-r
prevents the normal
sync(2)
before stopping the system.
-p
The
-p
flag is passed on to
halt(8),
causing machines which support automatic power down to do so after halting.
time
is the time at which
shutdown
will bring the system down and
may be the word
now
(indicating an immediate shutdown) or
specify a future time in one of two formats:
+number,
or
yymmddhhmm,
where the year, month, and day may be defaulted
to the current system values.
The first form brings the system down in
number
minutes and the second at the absolute time specified.
warning-message
Any other arguments comprise the warning message that is broadcast
to users currently logged into the system.
-
If
‘-’
is supplied as an option, the warning message is read from the standard
input.
At intervals, becoming more frequent as apocalypse approaches
and starting at ten hours before shutdown, warning messages are displayed
on the terminals of all users logged in.
Five minutes before
shutdown, or immediately if shutdown is in less than 5 minutes,
logins are disabled by creating
/etc/nologin
and copying the
warning message there.
If this file exists when a user attempts to log in,
login(1)
prints its contents and exits.
The file is removed just before
shutdown
exits.
At shutdown time a message is written in the system log, containing the
time of shutdown, who initiated the shutdown and the reason.
A terminate
signal is then sent to
init
to bring the system down to single-user state (depending on above
options).
The time of the shutdown and the warning message
are placed in
/etc/nologin
and should be used to
inform the users about when the system will be back up
and why it is going down (or anything else).
You can cancel a scheduled shutdown with the
kill(1)
command by killing the shutdown process.