inittab(4) DG/UX 4.30 inittab(4)
NAME
inittab - script for the init process
DESCRIPTION
The inittab file contains the instructions used by the
init(1M) program which is the general process dispatcher in
the DG/UX system. Most of init's process dispatching is for
the line process /etc/getty, which initiates individual
terminal lines. Other processes typically invoked by init
are daemons and the shell.
The inittab file is composed of entries with the following
format:
id:level:action:process
Each entry is delimited by a New Line, however, a backslash
(\) preceding a New Line indicates a continuation of the
entry. Up to 512 characters per entry are permitted. You
can insert comments in the process field using the sh(1)
convention for comments. Comments for lines that spawn
getty(1M) processes are displayed by the who(1) command.
Comments should contain some information about the line,
such as its location. Maximum entry size is the only limit
imposed on the number of entries within the inittab file.
The entry fields are:
id One to four characters used to uniquely identify an
entry. For tty lines, the entry must begin with the
number of the given tty line, such as
04::respawn:/etc/getty tty04 9600.
level
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. For example, if the system is in run level
1, only those entries having a 1 in the level field are
processed. When init(1M) is requested to change run
levels, all processes without an entry in the level
field for the target run level will be sent the warning
signal (SIGTERM). They are given a 20-second grace
period before being forcibly terminated by a kill
signal (SIGKILL). The level 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.
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Three other values, a, b, and c, can appear in the
level field, even though they are not true run levels .
Entries with these characters in the level 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(1M) 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(1M) 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(1M) goes into the single-
user state.
action
Key words in this field tell init(1M) how to treat the
process specified in the process field. The actions
recognized by init(1M) are as follows:
respawn If the process does not exist, then
start it. Do not wait for its
termination (continue scanning the
inittab file); when the process
dies, restart it. If the process
currently exists, then do nothing
and continue scanning the inittab
file.
wait When init(1M) enters the run level
that matches the entry's level,
start the process and wait for its
termination. All subsequent reads
of the inittab file while init(1M)
is in the same run-level will cause
init(1M) to ignore this entry.
once When init(1M) enters a run level
that matches the entry's level,
start the process. Do not wait for
its termination. When it dies, do
not restart the process. Upon
entering a new run level, if 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
when init(1M) reads inittab at boot
time. Init starts the process and
does not wait for its termination.
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inittab(4) DG/UX 4.30 inittab(4)
When the process dies, init does not
restart it. The level must be the
default or match init's run level at
boot time. This action is useful
for an initialization function
following a hardware reboot of the
system.
bootwait Process the entry only when init
reads inittab at boot time. Init
starts the process, waits for its
termination and, when it dies, does
not restart the process.
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 A synonym for the respawn action.
It is given a different keyword to
break its association with run
levels. Ondemand is used only with
the a, b, or c values described in
the level field.
initdefault An entry with this action is only
scanned 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 level field and
using that as its initial state. If
the level field is empty, this is
interpreted as 0123456 and init will
enter run level 6. 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. This entry should only be
used to initialize devices on which
init might try to ask the run level
question. These entries are
executed and waited for before
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continuing.
process This keyword is a sh(1) command to be executed.
The entire process field is prefixed with exec and
passed to a forked sh(1) as sh -c 'exec command'.
For this reason, any legal sh(1) 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), initrc(1M), sh(1), who(1)
Installing and Managing the DG/UX System
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