inittab(4)
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inittab File Format
script for the init process
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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
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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.
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. When the process
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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
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
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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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