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 lim-
its (other than maximum entry size) imposed on the number of
entries in the inittab file. The entry fields are:
id One or two characters used to uniquely identify an
entry.
rstate Define 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(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 warn-
ing 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
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 lev-
els. They are killed only if their line in init-
tab 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 (continue scanning
the inittab file), and when the pro-
cess dies, restart the process. If
the process 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 termi-
nation. 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
restart 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 termination;
when it dies, it 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 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 continu-
ing 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 terminating
the process with the kill signal
SIGKILL. If the process is nonex-
istent, ignore the entry.
ondemand This instruction is really a synonym
for the respawn action. It is func-
tionally identical to respawn but is
given a different keyword in order
to divorce its association with run
levels. 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
continuously). 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 con-
sole (that is, before the Console
Login: prompt). It is expected that
this entry will be used only to ini-
tialize 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 pro-
cess field is prefixed with exec and passed to a
forked sh as sh -c 'exec command'. For this rea-
son, 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)