inittab(4) CLIX inittab(4)
NAME
inittab - Script file for init process
DESCRIPTION
The /etc/inittab file supplies the script for the init command to act as a
general process dispatcher. The process that constitutes the majority of
the process dispatching activities for init is /etc/getty, which 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:
id:rstate:action:process
Each entry is delimited by a newline, however, a backslash (\) preceding a
newline indicates a continuation of the entry. Up to 512 characters per
entry are permitted. Comments may be inserted in the process field using
the sh convention for comments. Comments for lines that spawn getty
processes are displayed by the who command. It is expected that they will
contain some information about the line such as the location. There are
no limits (other than maximum entry size) imposed on the number of entries
within the inittab file. The entry fields are as follows:
id Specifies one or two characters used to uniquely identify an
entry.
rstate 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 run-levels in which it is allowed to exist. For
example, if the system is in run-level 1, only those entries
having a 1 in the rstate field will be processed. The run-
levels are represented by a number ranging from 0 through 6.
When init is requested to change run-levels, all processes that
do not have an entry in the rstate field for the target run-
level will be sent the warning signal (SIGTERM) and allowed a
20-second 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.
If no run-level is specified, then the process is assumed to be
valid at all run-levels.
There are three other values (a, b and c) which can appear in
the rstate field, even though they are not true run-levels.
Entries which have these characters in the rstate field are
processed only when the telinit (see init(8)) process requests
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them to be run. They differ from true 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
run-level. Processes started by an a, b or c command are not
killed when init changes levels. They are only killed on the
following conditions:
⊕ Their line in the inittab file is marked off in the action
field.
⊕ Their line is deleted entirely from inittab.
⊕ The init command 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 Starts the process if it does not exist. The init
command does not wait for the process to terminate
(it continues scanning the inittab file). If the
process dies, it is restarted. If the process
currently exists then init does nothing and
continues scanning the inittab file.
wait Starts the process and waits for its termination
when init enters the run-level that matches the
entry's rstate. All subsequent reads of the
inittab file while init is in the same run-level
will cause init to ignore this entry.
once Starts the process and does not wait for its
termination when init enters a run-level that
matches the entry's rstate. When the process
dies, it is not restarted. If init enters a new
run-level where the process is still running from
a previous run-level change, the program will not
be restarted.
boot Processes the entry only at boot-time when init
reads the inittab file. The init command starts
the process and does not wait for its termination.
When it dies, the process is not restarted. In
order for this instruction to be meaningful, the
rstate should be the default or it must match the
run-level of init at boot time. This action is
useful for an initialization function following a
hardware reboot of the system.
bootwait Processes the entry the first time init goes from
single-user to multiuser state after the system is
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booted. (If initdefault is set to 2, the process
will run right after the system is booted.) The
init command starts the process, waits for its
termination and, when it dies, does not restart
the process.
powerfail Executes the process associated with this entry
only when init receives a power fail signal
(SIGPWR). See signal(2).
powerwait Executes the process associated with this entry
only when init receives a power fail signal
(SIGPWR) and waits until it terminates before
continuing any processing of inittab.
off If the process associated with this entry is
currently running, sends the warning signal
(SIGTERM) and waits 20 seconds before forcibly
terminating the process with the kill signal
(SIGKILL). If the process is nonexistent, ignores
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 separate 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 is initially invoked. The init command 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, so init will enter run-level 6.
Additionally, if init does not find an initdefault
entry in the inittab file, then it will request an
initial run-level from the user at reboot time.
sysinit Entries of this type are executed before init
tries to access the console (that is, before the
Console Login: prompt). It is expected that this
entry will be only used to initialize devices on
which init might try to ask the run-level
question. These entries are executed and waited
for before continuing.
process Indicates a sh command to be executed. The entire process field
is prefixed with exec and passed to a forked sh as sh -c '"exec"
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" command"'. For this reason, any legal sh syntax can appear in
the process field. Comments can be inserted with the ``; #
comment'' syntax.
FILES
/etc/inittab
RELATED INFORMATION
Commands: getty(8), init(8), sh(1), who(1)
Functions: exec(2), open(2), signal(2)
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