shutdown
Hurricane Electric Internet Services
NAME
shutdown - bring the system down
SYNOPSIS
/sbin/shutdown [-t sec] [-rkhncf] time [warning-message]
DESCRIPTION
Shutdown brings the system down in a secure way. All
logged in users are notified that the system is going
down, and login(1) is blocked. It is possible to shut the
system down immideately, or after a delay. All processes
are first notified that the system is going down by the
signal SIGTERM. This gives programs like vi(1) the time
to save the file being editted, mail and news processing
programs a chance to exit cleanly, etc. Shutdown does it's
job by signalling the init process, asking it to change
the runlevel. Runlevel 0 is used to halt the system, run-
level 6 is used to reboot the system and runlevel 1 is
used to put to system into a state where administrative
tasks can be performed; this is the default if neither the
-h or -r flag is given to shutdown. To see which actions
are taken on halt or reboot see the appropriate entries of
these runlevels in the file /etc/inittab.
OPTIONS
-t sec Tell init to wait sec seconds between sending pro-
cesses the warning and the kill signal, before
changing to another runlevel.
-k Don't really shutdown; only send the warning mes-
sages to everybody.
-r Reboot after shutdown.
-h Halt after shutdown.
-n [DEPRECIATED] Don't call init to do the shutdown
but do it ourself. The use of this option is dis-
couraged, and its results are not always what you'd
expect.
-f Do a `fast' reboot.
-c Cancel an already running shutdown. With this
option it is ofcourse not possible to give the time
argument, but you can enter a explanitory message
on the command line that will be sent to all users.
time When to shutdown.
warning-message
Message to send to all users.
The time argument can have different formats. First, it
can be an absolute time in the format hh:mm, in which hh
is the hour (1 or 2 digits) and mm is the minute of the
hour (in two digits). Second, it can be in the format +m,
in which m is the number of minutes to wait. The word now
is an alias for +0.
The -f flag means `reboot fast'. This only creates an
advisory file /fastboot which can be tested by the system
when it comes up again. The boot rc file can test if this
file is present, and decide not to run fsck(1) since the
system has been shut down in the proper way. After that,
the boot process should remove /fastboot.
The -n flag causes shutdown not to call init, but to kill
all running processes itself. After all processes are
killed, shutdown will try to run the script
/etc/rc.d/rc.halt fast (or rc.reboot). It also tests for
the presence of the equivalent files rc.0 and rc.6. If
this script returns or can't be executed (because it's not
present for example) shutdown will turn off quota and
accounting, turn off swapping and unmount all filesystems.
Access Control
Shutdown can be called from init(8) when the magic keys
CTRL-ALT-DEL are pressed, by creating an appropriate entry
in /etc/inittab. This means that everyone who has physical
access to the console keyboard can shut the system down.
To prevent this, shutdown can check to see if an autho-
rized user is logged in on one of the virtual consoles. If
shutdown is called from init, it checks to see if the file
/etc/shutdown.allow is present. It then compares the
login names in that file with the list of people that are
logged in on a virtual console (from /var/run/utmp). Only
if one of those authorized users or root is logged in, it
will proceed. Otherwise it will write the message
shutdown: no authorized users logged in
to the (physical) system console. The format of /etc/shut-
down.allow is one user name per line. Empty lines and com-
ment lines (prefixed by a #) are allowed. Currently there
is a limit of 32 users in this file.
FILES
/fastboot
/etc/inittab
/etc/rc.d/rc.halt
/etc/rc.d/rc.reboot
/etc/shutdown.allow
BUGS
Not really a bug, but most users forget to give the time
argument and are then puzzled by the error message shut-
down produces. The time argument is mandatory; in 90
percent of all cases this argument will be the word now.
AUTHOR
Miquel van Smoorenburg, miquels@drinkel.ow.org
SEE ALSO
fsck(8), init(1), halt(8), reboot(8)
Hurricane Electric Internet Services
Copyright (C) 1998
Hurricane Electric.
All Rights Reserved.