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 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 process
ing 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 sys
tem, runlevel 6 is used to reboot the system, and runlevel
1 is used to put to system into a state where administra
tive tasks can be performed; this is the default if nei
ther 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 mes
sages 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 dis
couraged, 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 mes
sage on the command line that will be sent to all
users.
time 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 creates the advi
sory 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 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 filesystems
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 filesys
tems.
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 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 com
pares 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
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/init.d/halt
/etc/init.d/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 per
cent of all cases this argument will be the word now.
AUTHOR
Miquel van Smoorenburg, miquels@cistron.nl
SEE ALSO
fsck(8), init(1), halt(8), poweroff(8), reboot(8)
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