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SHUTDOWN(8) Linux System Administrator’s Manual SHUTDOWN(8)
NAME
shutdown - bring the system down
SYNOPSIS
/sbin/shutdown [-t sec] [-arkhncfF] 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 immediately or after a specified delay. All processes are first noti-
fied that the system is going down by the signal SIGTERM. This gives programs like
vi(1) the time to save the file being edited, mail and news processing programs a
chance to exit cleanly, etc. shutdown does its job by signalling the init process,
asking it to change the runlevel. Runlevel 0 is used to halt the system, runlevel
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 for these runlevels in the file /etc/inittab.
OPTIONS
-a Use /etc/shutdown.allow.
-t sec Tell init(8) to wait sec seconds between sending processes the warning and
the kill signal, before changing to another runlevel.
-k Don’t really shutdown; only send the warning messages to everybody.
-r Reboot after shutdown.
-h Halt after shutdown.
-n [DEPRECATED] Don’t call init(8) to do the shutdown but do it ourself. The
use of this option is discouraged, and its results are not always what you’d
expect.
-f Skip fsck on reboot.
-F Force fsck on reboot.
-c Cancel an already running shutdown. With this option it is of course not
possible to give the time argument, but you can enter a explanatory 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.
If shutdown is called with a delay, it creates the advisory file /etc/nologin which
causes programs such as login(1) to not allow new user logins. Shutdown removes
this file if it is stopped before it can signal init (i.e. it is cancelled or some-
thing goes wrong). It also removes it before calling init to change the runlevel.
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 -F flag means ‘force fsck’. This only creates an advisory file /forcefsck
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 to run fsck(1) with a special ‘force’ flag
so that even properly unmounted filesystems get checked. After that, the boot pro-
cess should remove /forcefsck.
The -n flag causes shutdown not to call init, but to kill all running processes
itself. shutdown will then turn off quota, accounting, and 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 authorized user is logged in on one of the virtual
consoles. If shutdown is called with the -a argument (add this to the invocation of
shutdown in /etc/inittab), 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/shutdown.allow is one user
name per line. Empty lines and comment lines (prefixed by a #) are allowed. Cur-
rently there is a limit of 32 users in this file.
Note that if /etc/shutdown.allow is not present, the -a argument is ignored.
FILES
/fastboot
/etc/inittab
/etc/init.d/halt
/etc/init.d/reboot
/etc/shutdown.allow
NOTES
A lot of users forget to give the time argument and are then puzzled by the error
message shutdown produces. The time argument is mandatory; in 90 percent of all
cases this argument will be the word now.
Init can only capture CTRL-ALT-DEL and start shutdown in console mode. If the sys-
tem is running the X window System, the X server processes all key strokes. Some
X11 environments make it possible to capture CTRL-ALT-DEL, but what exactly is done
with that event depends on that environment.
Shutdown wasn’t designed to be run setuid. /etc/shutdown.allow is not used to find
out who is executing shutdown, it ONLY checks who is currently logged in on (one of
the) console(s).
AUTHOR
Miquel van Smoorenburg, miquels AT cistron.nl
SEE ALSO
fsck(8), init(8), halt(8), poweroff(8), reboot(8)
Juli 31, 2001 SHUTDOWN(8)
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