File: inittab.5

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.\"{{{}}}
.\"{{{  Title
.TH INITTAB 5 "Dec 4, 2001" "" "Linux System Administrator's Manual"
.\"}}}
.\"{{{  Name
.SH NAME
inittab \- format of the inittab file used by the sysv-compatible init
process
.\"}}}
.\"{{{  Description
.SH DESCRIPTION
The \fBinittab\fP file describes which processes are started at bootup and
during normal operation (e.g.\& /etc/init.d/boot, /etc/init.d/rc, gettys...).
.BR Init (8)
distinguishes multiple \fIrunlevels\fP, each of which can have its own set of
processes that are started.  Valid runlevels are \fB0\fP\-\fB6\fP plus
\fBA\fP, \fBB\fP, and \fBC\fP for \fBondemand\fP entries.  An entry in the
\fBinittab\fP file has the following format:
.RS
.sp
\fIid\fP:\fIrunlevels\fP:\fIaction\fP:\fIprocess\fP
.sp
.RE
Lines beginning with `#' are ignored.
.\"{{{  id
.IP \fIid\fP
is a unique sequence of 1-4 characters which identifies an entry in
.B inittab 
(for versions of sysvinit compiled with the \fIold\fP libc5 (< 5.2.18) or
a.out libraries the limit is 2 characters).
.sp
Note: traditionally, for getty and other login processes, the value of the
\fIid\fP field is kept the same as the suffix of the corresponding tty, e.g.\&
\fB1\fP for \fBtty1\fP. Some ancient login accounting programs might
expect this, though I can't think of any.
.\"}}}
.\"{{{  runlevels
.IP \fIrunlevels\fP
lists the runlevels for which the specified action should be taken.
.\"}}}
.\"{{{  action
.IP \fIaction\fP
describes which action should be taken.
.\"}}}
.\"{{{  process
.IP \fIprocess\fP
specifies the process to be executed.  If the process field starts with
a `+' character, 
.B init 
will not do utmp and wtmp accounting for that process.  This is needed for 
gettys that insist on doing their own utmp/wtmp housekeeping.  This is also 
a historic bug.
.\"}}}
.PP
The \fIrunlevels\fP field may contain multiple characters for different
runlevels.  For example, \fB123\fP specifies that the process should be 
started in runlevels 1, 2, and 3.
The \fIrunlevels\fP for \fBondemand\fP entries may contain an \fBA\fP,
\fBB\fP, or \fBC\fP.  The \fIrunlevels\fP field of \fBsysinit\fP,
\fBboot\fP, and \fBbootwait\fP entries are ignored.
.PP
When the system runlevel is changed, any running processes that are not
specified for the new runlevel are killed, first with \s-2SIGTERM\s0,
then with \s-2SIGKILL\s0.
.PP
Valid actions for the \fIaction\fP field are:
.\"{{{  respawn
.IP \fBrespawn\fP
The process will be restarted whenever it terminates (e.g.\& getty).
.\"}}}
.\"{{{  wait
.IP \fBwait\fP
The process will be started once when the specified runlevel is entered and 
.B init 
will wait for its termination.
.\"}}}
.\"{{{  once
.IP \fBonce\fP
The process will be executed once when the specified runlevel is
entered.
.\"}}}
.\"{{{  boot
.IP \fBboot\fP
The process will be executed during system boot.  The \fIrunlevels\fP
field is ignored.
.\"}}}
.\"{{{  bootwait
.IP \fBbootwait\fP
The process will be executed during system boot, while 
.B init 
waits for its termination (e.g.\& /etc/rc).  
The \fIrunlevels\fP field is ignored.
.\"}}}
.\"{{{  off
.IP \fBoff\fP
This does nothing.
.\"}}}
.\"{{{  ondemand
.IP \fBondemand\fP
A process marked with an \fBondemand\fP runlevel will be executed
whenever the specified \fBondemand\fP runlevel is called.  However, no
runlevel change will occur (\fBondemand\fP runlevels are `a', `b',
and `c').
.\"}}}
.\"{{{  initdefault
.IP \fBinitdefault\fP
An \fBinitdefault\fP entry specifies the runlevel which should be
entered after system boot.  If none exists, 
.B init
will ask for a runlevel on the console. The \fIprocess\fP field is ignored.
.\"}}}
.\"{{{  sysinit
.IP \fBsysinit\fP
The process will be executed during system boot. It will be
executed before any \fBboot\fP or \fB bootwait\fP entries.
The \fIrunlevels\fP field is ignored.
.\"}}}
.\"{{{  powerwait
.IP \fBpowerwait\fP
The process will be executed when the power goes down. Init is usually
informed about this by a process talking to a UPS connected to the computer.
\fBInit\fP will wait for the process to finish before continuing.
.\"}}}
.\"{{{  powerfail
.IP \fBpowerfail\fP
As for \fBpowerwait\fP, except that \fBinit\fP does not wait for the process's
completion.
.\"}}}
.\"{{{  powerokwait
.IP \fBpowerokwait\fP
This process will be executed as soon as \fBinit\fP is informormed that the
power has been restored.
.\"}}}
.\"{{{  powerfailnow
.IP \fBpowerfailnow\fP
This process will be executed when \fBinit\fP is told that the battery of
the external UPS is almost empty and the power is failing (provided that the
external UPS and the monitoring process are able to detect this condition).
.\"}}}
.\"{{{  ctrlaltdel
.IP \fBctrlaltdel\fP
The process will be executed when \fBinit\fP receives the SIGINT signal.
This means that someone on the system console has pressed the
\fBCTRL\-ALT\-DEL\fP key combination. Typically one wants to execute some
sort of \fBshutdown\fP either to get into single\-user level or to
reboot the machine.
.\"}}}
.\"{{{  kbrequest
.IP \fBkbrequest\fP
The process will be executed when \fBinit\fP receives a signal from the
keyboard handler that a special key combination was pressed on the
console keyboard.
.sp
The documentation for this function is not complete yet; more documentation
can be found in the kbd-x.xx packages (most recent was kbd-0.94 at
the time of this writing). Basically you want to map some keyboard
combination to the "KeyboardSignal" action. For example, to map Alt-Uparrow
for this purpose use the following in your keymaps file:
.RS
.sp
alt keycode 103 = KeyboardSignal
.sp
.RE
.\"}}}
.\"}}}
.\"{{{  Examples
.SH EXAMPLES
This is an example of a inittab which resembles the old Linux inittab:
.RS
.sp
.nf
.ne 7
# inittab for linux
id:1:initdefault:
rc::bootwait:/etc/rc
1:1:respawn:/etc/getty 9600 tty1
2:1:respawn:/etc/getty 9600 tty2
3:1:respawn:/etc/getty 9600 tty3
4:1:respawn:/etc/getty 9600 tty4
.fi
.sp
.RE
This inittab file executes \fB/etc/rc\fP during boot and starts gettys
on tty1\-tty4.
.PP
A more elaborate \fBinittab\fP with different runlevels (see the comments
inside):
.RS
.sp
.nf
.ne 19
# Level to run in
id:2:initdefault:

# Boot-time system configuration/initialization script.
si::sysinit:/etc/init.d/rcS

# What to do in single-user mode.
~:S:wait:/sbin/sulogin

# /etc/init.d executes the S and K scripts upon change
# of runlevel.
#
# Runlevel 0 is halt.
# Runlevel 1 is single-user.
# Runlevels 2-5 are multi-user.
# Runlevel 6 is reboot.

l0:0:wait:/etc/init.d/rc 0
l1:1:wait:/etc/init.d/rc 1
l2:2:wait:/etc/init.d/rc 2
l3:3:wait:/etc/init.d/rc 3
l4:4:wait:/etc/init.d/rc 4
l5:5:wait:/etc/init.d/rc 5
l6:6:wait:/etc/init.d/rc 6

# What to do at the "3 finger salute".
ca::ctrlaltdel:/sbin/shutdown -t1 -h now

# Runlevel 2,3: getty on virtual consoles
# Runlevel   3: getty on terminal (ttyS0) and modem (ttyS1)
1:23:respawn:/sbin/getty tty1 VC linux
2:23:respawn:/sbin/getty tty2 VC linux
3:23:respawn:/sbin/getty tty3 VC linux
4:23:respawn:/sbin/getty tty4 VC linux
S0:3:respawn:/sbin/getty -L 9600 ttyS0 vt320
S1:3:respawn:/sbin/mgetty -x0 -D ttyS1

.fi
.sp
.RE
.\"}}}
.\"{{{  Files
.SH FILES
/etc/inittab
.\"}}}
.\"{{{  Author
.SH AUTHOR
\fBInit\fP was written by Miquel van Smoorenburg 
(miquels@cistron.nl).  This manual page was written by 
Sebastian Lederer (lederer@francium.informatik.uni-bonn.de) and modified
by Michael Haardt (u31b3hs@pool.informatik.rwth-aachen.de).
.\"}}}
.\"{{{  See also
.SH "SEE ALSO"
.BR init (8),
.BR telinit (8)
.\"}}}