SHUTDOWN(8) manual page
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shutdown - bring the system down
/sbin/shutdown
[-akrhPHfFnc] [-t sec] time [warning message]
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.
- -a
- Use /etc/shutdown.allow.
- -k
- Don’t really shutdown; only send the
warning messages to everybody.
- -r
- Reboot after shutdown.
- -h
- Halt or power
off after shutdown.
- -P
- Halt action is to turn off the power.
- -H
- 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.
- -f
- Skip fsck on reboot.
- -F
- Force fsck on reboot.
- -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.
- -c
- Cancel a waiting shutdown. ("shutdown
now" is no longer waiting.) With this option it is of course not possible
to give the time argument, but you can enter explanatory message arguments
on the command line that will be sent to all users.
- -t sec
- Tell init(8)
to wait sec seconds between sending processes the warning and the kill
signal, before changing to another runlevel.
- 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 will create the advisory file /run/nologin 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.
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.
/fastboot
/etc/inittab
/etc/init.d/halt
/etc/init.d/reboot
/etc/shutdown.allow
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 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).
Miquel van Smoorenburg, miquels@cistron.nl
fsck(8)
, init(8)
, halt(8)
, poweroff(8)
, reboot(8)
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