inittab(4) FILE FORMATS 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 per entry are permitted. Com-
ments may be inserted in the process field using the conven-
tion 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 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 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 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 pro-
cessed. When init is requested to change run lev-
els, 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 combina-
tion from 0 through 6. If no run level is speci-
fied, 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).
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
1
inittab(4) FILE FORMATS inittab(4)
change the current run level. Furthermore, a pro-
cess 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 init-
tab, 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,
not wait for its termination; and
when it dies, not restart the pro-
cess. 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 initializa-
tion function following a hardware
reboot of the system.
bootwait The entry is to be processed the
2
inittab(4) FILE FORMATS inittab(4)
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 sig-
nal(2)].
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, if it exists,
to determine which run level to
enter initially. It does this by
taking the highest run level speci-
fied 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 6. This
will cause the system to loop, that
is, it will go to firmware and
reboot continuously. Additionally,
if init does not find an initdefault
3
inittab(4) FILE FORMATS inittab(4)
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 (i.e., before the Console
Login: prompt). It is expected that
this entry will be only used to ini-
tialize devices on which init might
try to ask the run level question.
These entries are executed and
waited for before continuing.
process This is 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
init(1M), ttymon(1M), exec(2), open(2), signal(2) sh(1),
who(1) in the User's Reference Manual
4