Man page of SHUTDOWN
Section: Linux System Administrator's Manual (8)
Updated: November 12, 2003
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shutdown - bring the system down
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 notified 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.
- -t sec
Tell init(8) to wait sec seconds between sending processes the
warning and the kill signal, before changing to another runlevel.
Don't really shutdown; only send the warning messages to everybody.
Reboot after shutdown.
Halt or power off after shutdown.
Modifier to the -h flag. Halt action is to halt or drop into boot
monitor on systems that support it. Must be used with the -h flag.
Halt action is to turn off the power.
[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
Skip fsck on reboot.
Force fsck on reboot.
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.
When to shutdown.
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 will create the advisory file
which causes programs such as login(1) to not allow new user
logins. This file is created five minutes before the shutdown sequence
starts. Shutdown removes this file if it is stopped before it
can signal init (i.e. it is cancelled or something 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 file systems get checked.
After that, the boot process 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 file systems.
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. Currently there is a limit of 32 users in this file.
Note that if /etc/shutdown.allow is not present, the -a
argument is ignored.
HALT OR POWEROFF
The -H option just sets the init environment variable
INIT_HALT to HALT, and the -P option just sets
that variable to POWEROFF. The shutdown script that calls
halt(8) as the last thing in the shutdown sequence should
check these environment variables and call halt(8) with
the right options for these options to actually have any effect.
Debian 3.1 (sarge) supports this.
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 system 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
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).
Miquel van Smoorenburg, email@example.com
- ACCESS CONTROL
- HALT OR POWEROFF
- SEE ALSO
This document was created by
using the manual pages.
Time: 04:17:50 GMT, September 24, 2010