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 (\)
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 convention 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 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 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 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
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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 process 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 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 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 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(2)].
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powerwait Execute the process associated with this
entry only when init receives a power fail
signal, SIGPWR, and wait until it terminates
before continuing 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 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
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 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 6. 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 (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 question. 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.
SEE ALSO
init(1M), ttymon(1M), exec(2), open(2), signal(2)
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inittab(4) inittab(4)
sh(1), who(1) in the User's Reference Manual
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