File: shutdown.8

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.\"{{{}}}
.\"{{{  Title
.TH SHUTDOWN 8 "November 12, 2003" "" "Linux System Administrator's Manual"
.\"}}}
.\"{{{  Name
.SH NAME
shutdown \- bring the system down
.\"}}}
.\"{{{  Synopsis
.SH SYNOPSIS
.B /sbin/shutdown
.RB [ \-t
.IR sec ]
.RB [ \-arkhncfFHP ]
.I time
.RI [ warning-message ]
.\"}}}
.\"{{{  Description
.SH DESCRIPTION
\fBshutdown\fP brings the system down in a secure way.  All logged-in users are
notified that the system is going down, and \fBlogin\fP(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 \s-2SIGTERM\s0.  This gives programs like \fBvi\fP(1)
the time to save the file being edited, 
mail and news processing programs a chance to exit cleanly, etc. 
\fBshutdown\fP does its job by signalling the \fBinit\fP process, 
asking it to change the runlevel.
Runlevel \fB0\fP is used to halt the system, runlevel \fB6\fP is used
to reboot the system, and runlevel \fB1\fP is used to put to system into
a state where administrative tasks can be performed; this is the default
if neither the \fI-h\fP or \fI-r\fP flag is given to \fBshutdown\fP.
To see which actions are taken on halt or reboot see the appropriate
entries for these runlevels in the file \fI/etc/inittab\fP.
.\"}}}
.\"{{{  Options
.SH OPTIONS
.\"{{{  -a
.IP "\fB\-a\fP
Use \fB/etc/shutdown.allow\fP.
.\"}}}
.\"{{{  -t sec
.IP "\fB\-t\fP \fIsec\fP"
Tell \fBinit\fP(8) to wait \fIsec\fP seconds between sending processes the 
warning and the kill signal, before changing to another runlevel.
.\"}}}
.\"{{{  -k
.IP \fB\-k\fP
Don't really shutdown; only send the warning messages to everybody.
.\"}}}
.\"{{{  -r
.IP \fB\-r\fP
Reboot after shutdown.
.\"}}}
.\"{{{  -h
.IP \fB\-h\fP
Halt or poweroff after shutdown.
.\"}}}
.\"{{{  -H
.IP \fB\-H\fP
Halt action is to halt or drop into boot monitor on systems that
support it.
.\"}}}
.\"{{{  -P
.IP \fB\-P\fP
Halt action is to turn off the power.
.\"}}}
.\"{{{  -n
.IP \fB\-n\fP
[DEPRECATED] Don't call \fBinit\fP(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
.IP \fB\-f\fP
Skip fsck on reboot.
.\"}}}
.\"{{{  -F
.IP \fB\-F\fP
Force fsck on reboot.
.\"}}}
.\"{{{  -c
.IP \fB\-c\fP
Cancel an already running shutdown. With this option it is of course
not possible to give the \fBtime\fP argument, but you can enter a
explanatory message on the command line that will be sent to all users.
.\"}}}
.\"{{{  time
.IP \fItime\fP
When to shutdown.
.\"}}}
.\"{{{  warning-message
.IP \fIwarning-message\fP
Message to send to all users.
.\"}}}
.PP
The \fItime\fP argument can have different formats.  First, it can be an
absolute time in the format \fIhh:mm\fP, in which \fIhh\fP is the hour
(1 or 2 digits) and \fImm\fP is the minute of the hour (in two digits).
Second, it can be in the format \fB+\fP\fIm\fP, in which \fIm\fP is the
number of minutes to wait.  The word \fBnow\fP is an alias for \fB+0\fP.
.PP
If shutdown is called with a delay, it creates the advisory file
.I /etc/nologin
which causes programs such as \fIlogin(1)\fP 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.
.PP
The \fB\-f\fP flag means `reboot fast'.  This only creates an advisory
file \fI/fastboot\fP 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 \fBfsck\fP(1) since the system has been shut down in the proper way.  
After that, the boot process should remove \fI/fastboot\fP.
.PP
The \fB\-F\fP flag means `force fsck'.  This only creates an advisory
file \fI/forcefsck\fP 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 \fBfsck\fP(1) with a special `force' flag so that even properly
unmounted filesystems get checked.
After that, the boot process should remove \fI/forcefsck\fP.
.PP
The \fB-n\fP flag causes \fBshutdown\fP not to call \fBinit\fP, 
but to kill all running processes itself. 
\fBshutdown\fP will then turn off quota, accounting, and swapping
and unmount all filesystems.
.\"}}}
.\"{{{  Files
.SH ACCESS CONTROL
\fBshutdown\fP can be called from \fBinit\fP(8) when the magic keys
\fBCTRL-ALT-DEL\fP are pressed, by creating an appropriate entry in
\fI/etc/inittab\fP. This means that everyone who has physical access
to the console keyboard can shut the system down. To prevent this,
\fBshutdown\fP can check to see if an authorized user is logged in on
one of the virtual consoles. If \fBshutdown\fP is called with the \fB-a\fP
argument (add this to the invocation of shutdown in /etc/inittab),
it checks to see if the file \fI/etc/shutdown.allow\fP 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 \fI/var/run/utmp\fP). Only
if one of those authorized users \fBor root\fP is logged in, it will
proceed. Otherwise it will write the message
.sp 1
.nf
\fBshutdown: no authorized users logged in\fP
.fi
.sp 1
to the (physical) system console. The format of \fI/etc/shutdown.allow\fP
is one user name per line. Empty lines and comment lines (prefixed by a
\fB#\fP) are allowed. Currently there is a limit of 32 users in this file.
.sp 1
Note that if \fI/etc/shutdown.allow\fP is not present, the \fB-a\fP
argument is ignored.
.SH HALT OR POWEROFF
The \fB-H\fP option just sets the \fIinit\fP environment variable
\fIINIT_HALT\fP to \fIHALT\fP, and the \fB-P\fP option just sets
that variable to \fIPOWEROFF\fP. The shutdown script that calls
\fBhalt\fP(8) as the last thing in the shutdown sequence should
check these environment variables and call \fBhalt\fP(8) with
the right options for these options to actually have any effect.
Debian 3.1 (sarge) supports this.
.SH FILES
.nf
/fastboot
/etc/inittab
/etc/init.d/halt
/etc/init.d/reboot
/etc/shutdown.allow
.fi
.\"}}}
.SH NOTES
A lot of users forget to give the \fItime\fP argument
and are then puzzled by the error message \fBshutdown\fP produces. The
\fItime\fP argument is mandatory; in 90 percent of all cases this argument
will be the word \fBnow\fP.
.PP
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.
.PP
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
.SH AUTHOR
Miquel van Smoorenburg, miquels@cistron.nl
.\"}}}
.\"{{{  See also
.SH "SEE ALSO"
.BR fsck (8),
.BR init (8),
.BR halt (8),
.BR poweroff (8),
.BR reboot (8)
.\"}}}