INITTAB(4) INITTAB(4)
NAME
inittab - script for the init process
DESCRIPTION
The inittab file supplies the script to init's role as a
general process dispatcher. The process that constitutes the
majority of init's process dispatching activities is the
line process /etc/getty that initiates individual terminal
lines. Other processes typically dispatched by init are
daemons and the shell.
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
sh(1) convention for comments. Comments for lines that
spawn gettys are displayed by the who(1) command. It is
expected that they will contain some information about the
line such as the location. There are no limits (other than
maximum entry size) imposed on the number of entries within
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 will be
processed. When init is requested to change run-
levels, all processes which do not have an entry
in the rstate field for the target run-level will
be sent the warning signal (SIGTERM) and allowed a
20-second grace period before being forcibly
terminated by a 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 0-6. If no run-level is
specified, then the process is assumed to be valid
at all run-levels 0-6. There are three other
values, a, b and c, which can appear in the rstate
field, even though they are not true run-levels.
Page 1 (last mod. 8/20/87)
INITTAB(4) INITTAB(4)
Entries which have these characters in the rstate
field are processed only when the telinit [see
init(1M)] process requests them to be run
(regardless of the current run-level of the
system). 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 only killed if their line in /etc/inittab
is marked off in the action field, their line is
deleted entirely from /etc/inittab, or init goes
into the 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 it dies
restart the process. If the process
currently exists then do nothing and
continue scanning the inittab file.
wait Upon init's entering 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 will cause init
to ignore this entry.
once Upon init's entering 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 upon
entering a new run-level, where the
process is still running from a
previous run-level change, the
program will not be 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
Page 2 (last mod. 8/20/87)
INITTAB(4) INITTAB(4)
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 will run
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
continuing any processing of
inittab.
off If the process associated with this
entry is currently running, send the
warning signal (SIGTERM) and wait 20
seconds before forcibly terminating
the process via 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 is used only
with the a, b or c values described
in the rstate field.
initdefault An entry with this action is only
scanned when init 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
Page 3 (last mod. 8/20/87)
INITTAB(4) INITTAB(4)
using that as its initial state. If
the rstate field is empty, this is
interpreted as 0123456 and so init
will enter run-level 6.
Additionally, if init does not find
an initdefault entry in
/etc/inittab, then it will request
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 sh 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. Comments can be inserted with the
; #comment syntax.
FILES
/etc/inittab
SEE ALSO
exec(2), open(2), signal(2).
getty(1M), init(1M) in the System Administrator's Reference
Manual.
sh(1), who(1) in the User's Reference Manual.
ORIGIN
AT&T V.3
Page 4 (last mod. 8/20/87)