inittab(4) inittab(4)
NAME
inittab - script for init
DESCRIPTION
The file /etc/inittab controls process dispatching by init. The
processes most typically dispatched by init are daemons.
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 (\) preced-
ing a newline indicates a continuation of the entry. Up to 512 charac-
ters per entry are permitted. Comments may be inserted in the process
field using the # character.
The entry fields are:
id This is one or two characters used to uniquely identify an
entry.
rstate This defines the run level in which this entry is to be pro-
cessed. 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 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 run level are sent the warning
signal SIGTERM and allowed a 5-second grace period before
being forcibly terminated by the 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
through 6. If no run level is specified, then the process is
assumed to be valid at all run levels 0 through 6. 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 an init or telinit process requests them
to be run (regardless of the current run level of the sys-
tem), [see init(1M)]. 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 run level. Furthermore, a process started by an
a, b or c command is not killed when init changes levels.
They are killed only if their line in inittab is marked off
in the action field, their line is deleted entirely from
inittab, or init goes into singleuser state.
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inittab(4) inittab(4)
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 (con-
tinue scanning the inittab file), and when the
process dies, restart the process. If the pro-
cess currently exists, do nothing and continue
scanning the inittab file.
wait When init enters 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
cause init to ignore this entry.
once When init enters a run level that matches the
entry's rstate, start the process, do not wait
for its termination. When it dies, do not res-
tart the process. If init enters a new run level
and 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
boot-time read of the inittab file. init is to
start the process, not wait for its termination;
and when it dies, 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 singleuser to multiuser state after
the system is booted. (If initdefault is set to
2, the process runs right after the boot.) init
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 con-
tinuing any processing of inittab.
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off If the process associated with this entry is
currently running, send the warning signal
SIGTERM and wait 5 seconds before forcibly ter-
minating the process with 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 lev-
els. This instruction is used only with the a, b
or c values described in the rstate field.
initdefault An entry with this action is scanned only when
init is 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 init therefore enters run level 0.
This will cause the system to stop. Addition-
ally, if init does not find an initdefault entry
in 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 (i.e. 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 ques-
tion. These entries are executed and waited for
before continuing.
process This is a 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.
Comment can be appended to the process entry and is intro-
duced with #.
A maximum of 2,500 processes can be entered.
SEE ALSO
who(1), init(1M), ttymon(1M), exec(2), open(2), signal(2).
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