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
(\) preceding a newline indicates a continuation of the
entry. Up to 512 characters for each entry are permitted.
Comments may be inserted in the process field using the con-
vention for comments described in sh(1). There are no limits
(other than maximum entry size) imposed on the number of
entries in the inittab file. The entry fields are:
id One to four characters used to uniquely identify an
entry. Do not use the characters "r" or "t" as the
first or only character in this field. These charac-
ters are reserved for the use of rlogin(1) and tel-
net(1).
rstate
Define the run level in which this entry is to be pro-
cessed. Run-levels effectively correspond to a confi-
guration of processes in the system. That is, each
process spawned by init is assigned a run level(s) in
which it is allowed to exist. The run levels are
represented by a number ranging from 0 through 6. For
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 lev-
els 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 system). See init(1M).
These 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
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 (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 and not wait for its termina-
tion; when it dies, it does not restart the pro-
cess. In order for this instruction to be mean-
ingful, 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
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(3C)).
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.
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 SIG-
KILL. 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
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 will
enter run level 6. This will cause the system to
loop (it will go to firmware and reboot continu-
ously). Additionally, 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 (that is, before the
Console Login: prompt). It is expected that this
entry will be used only to initialize devices
that
init might try to ask the run level question.
These entries are executed and init waits for
their completion before continuing.
process
Specify 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.
SEE ALSO
sh(1), who(1), init(1M), ttymon(1M), exec(2), open(2),
signal(3C)
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