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inittab(4)							    inittab(4)

NAME    [Toc]    [Back]

     inittab - script for the init process

DESCRIPTION    [Toc]    [Back]

     The /etc/inittab file supplies the	script to init's role as a general
     process dispatcher.  The process that constitutes the majority of init's
     process dispatching activities is the line	process	/etc/getty that
     initiates individual terminal lines.  Other processes typically
     dispatched	by init	are daemons and	the shell.

     The inittab file is composed of entries that are position dependent and
     have the following	format:


     Each entry	is started with	a character other than # and ended by a
     newline.  Lines starting with # are ignored.  A backslash (\) preceding a
     newline indicates a continuation of the entry.  Up	to 512 characters per
     entry are permitted.  Comments can	be inserted in the process field using
     the sh(1) convention for comments.	 Comments in the process field of
     lines that	spawn gettys are displayed by the who(1) command.  Such
     process field comments can	contain	information about the line such	as its
     location.	There are no limits (other than	maximum	entry size) imposed on
     the number	of entries within the inittab file.  The entry fields are:

     id	       This field, of up to four characters, is	used to	uniquely
	       identify	an entry.

     rstate    This defines the	run-level in which this	entry is to be
	       processed.  Run-levels effectively correspond to	a
	       configuration of	processes in the system.  That is, each
	       process spawned by init is assigned a run-level or run-levels
	       in which	it is allowed to exist.

	       The run-levels are represented by the letter s (or S), or a
	       number ranging from 0 through 6.	 As an example,	if the system
	       is in run-level 1, only those entries having a 1	in the rstate
	       field are processed.

	       When init is requested to change	run-levels, all	processes that
	       do not have an entry in the rstate field	for the	target runlevel
 are sent the warning signal (SIGTERM) and allowed a grace
	       period (see init(1M) for	the length of this grace period),
	       before being forcibly terminated	by a kill signal (SIGKILL).

	       The rstate field	can define multiple run-levels for a process
	       by selecting more than one run-level in any combination from
	       0-6, s, and S.  If no run-level is specified, the process is
	       assumed to be valid at all run-levels.

									Page 1

inittab(4)							    inittab(4)

	       There are three other values, a,	b, and c, that can appear in
	       the rstate field, even though they are not true run-levels.
	       Entries that have these characters in the rstate	field are
	       processed only when the telinit (see init(1M)) process requests
	       them to be run (regardless of the current run-level of the
	       system).	 They differ from run-levels in	that init can never
	       enter run-level a, b, or	c.  Also, a request for	the execution
	       of any of these processes does not change the current runlevel.
  Furthermore, a process started by an a, b, or c command
	       is not killed when init changes levels.	They are only killed
	       if their	line in	/etc/inittab is	marked off in the action
	       field, their line is deleted entirely from /etc/inittab,	or
	       init goes into the SINGLE USER state.

     action    Key words in this field tell init how to	treat the process
	       specified in the	process	field.	The actions recognized by init
	       are as follows:

	       respawn	    If the process does	not exist then start the
			    process.  Do not wait for its termination
			    (continue scanning the inittab file) and when it
			    dies restart the process.  If the process
			    currently exists then do nothing and continue
			    scanning the inittab file.

	       wait	    Upon init's	entering the run-level that matches
			    the	entry's	rstate,	start the process and wait for
			    its	termination.  All subsequent reads of the
			    inittab file while init is in the same run-level
			    causes init	to ignore this entry.

	       once	    Upon init's	entering a run-level that matches the
			    entry's rstate, start the process, do not wait for
			    its	termination.  When it dies, do not restart the
			    process.  If upon entering a new run-level,	the
			    process is still running from a previous run-level
			    change, the	program	is not restarted.

	       boot	    The	entry is to be processed only at init's	boottime
 read of the inittab file.  init is to start
			    the	process	and not	wait for its termination.
			    When it dies, init does not	restart	the process.
			    In order for this instruction to be	meaningful,
			    the	rstate should be the default or	it must	match
			    init's run-level at	boot time.  This action	is
			    useful for an initialization function following a
			    hardware reboot of the system.

	       bootwait	    The	entry is to be processed the first time	init
			    goes from single-user to multi-user	state after
			    the	system is booted.  (If initdefault is set to
			    2, the process runs	right after the	boot.)	init

									Page 2

inittab(4)							    inittab(4)

			    starts the process,	waits for its termination and,
			    when it dies, does not restart the process.

	       powerfail    Execute the	process	associated with	this entry
			    only when init receives a power fail signal
			    (SIGPWR, see signal(2)).

	       powerwait    Execute the	process	associated with	this entry
			    only when init receives a power fail signal
			    (SIGPWR) and wait until it terminates before
			    continuing any processing of inittab.

	       off	    If the process associated with this	entry is
			    currently running, send the	warning	signal
			    (SIGTERM) and wait 20 seconds before forcibly
			    terminating	the process via	the kill signal
			    (SIGKILL).	If the process is nonexistent, ignore
			    the	entry.

	       ondemand	    This instruction is	really a synonym for the
			    respawn action.  It	is functionally	identical to
			    respawn but	is given a different keyword in	order
			    to divorce its association with run-levels.	 This
			    is used only with the a, b or c values described
			    in the rstate field.

	       initdefault  An entry with this action is only scanned when
			    init initially invoked.  init uses this entry, if
			    it exists, to determine which run-level to enter
			    initially.	It does	this by	taking the highest
			    run-level specified	in the rstate field and	using
			    that as its	initial	state.	If the rstate field is
			    empty, this	is interpreted as 0123456 and so init
			    enters run-level 6.	 Additionally, if init does
			    not	find an	initdefault entry in /etc/inittab, it
			    requests an	initial	run-level from the user	at
			    reboot time.

	       sysinit	    Entries of this type are executed before init
			    tries to access the	console	(before	the Console
			    Login: prompt).  It	is expected that this entry
			    will be used only to initialize devices on which
			    init might try to ask the run-level	question.
			    These entries are executed and waited for before

     process   This is a sh command to be executed.  The entire	process	field
	       is prefixed with	exec and passed	to a forked sh as sh -c	'exec
	       command'.  For this reason, any legal sh	syntax can appear in
	       the process field.  Comments can	be inserted with the
	       ; #comment syntax.

									Page 3

inittab(4)							    inittab(4)

FILES    [Toc]    [Back]


SEE ALSO    [Toc]    [Back]

     getty(1M),	init(1M), sh(1), who(1), exec(2), open(2), signal(2).

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