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NAMEinittab — script for the boot init process DESCRIPTIONThe
/etc/inittab
file supplies the script to the boot
init
daemon in its role as a general process dispatcher (see
init(1M)).
The process that constitutes the majority of boot
init's
process dispatching activities is the line process
/usr/sbin/getty
that initiates individual terminal lines.
Other processes typically dispatched by boot
init
are daemons and shells. The
inittab
file is composed of entries that are position-dependent
and have the following format:
Each entry is delimited by a newline;
however, a backslash
(\)
preceding a newline indicates a continuation of the entry.
Up to 1024 characters per entry are permitted.
Comments can be inserted in the
process
field by starting a "word" with a
#
(see
sh(1)).
Comments for lines that spawn
gettys
are displayed by the
who
command (see
who(1)).
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
A one- to four-character value used to uniquely identify an entry.
Duplicate entries cause an error message to be issued,
but are otherwise ignored.
The use of a four-character value to identify an entry
is strongly recommended (see WARNINGS below). - rstate
Defines the
run level
in which this entry is to be processed.
Run levels correspond to a configuration of processes in the system
where each process spawned by boot
init
is assigned one or more run levels in which it is allowed to exist.
Run levels are represented by a number in the range
0
through
6.
For example, if the system is in run level
1,
only those entries having a
1
in their
rstate
field are processed. When boot
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 20-second grace period
before being forcibly terminated by a kill signal
(SIGKILL).
You can specify multiple run levels for a process
by entering more than one run level value in any combination.
If no run level is specified,
the process is assumed to be valid for all run levels,
0
through
6. Three other values,
a,
b
and
c,
can also appear in the
rstate
field, even though they are not true run levels.
Entries having these characters in the
rstate
field are processed only when a user
init
process requests them to be run (regardless of the current system run level).
They differ from run levels in that boot
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 numeric run level. Furthermore, a process started by an
a,
b,
or
c
option is not killed when boot
init
changes levels.
A process is killed only if its line in
inittab
is marked
off
in the
action
field, its line is deleted entirely from
inittab,
or boot
init
goes into the
single-user
state. - action
A keyword in this field tells boot
init
how to treat the process specified in the
process
field.
The following actions can be specified:
- boot
Process the entry only at boot
init's
boot-time read of the
inittab
file.
Boot
init
starts the process, does not wait for its termination,
and when it dies, does not restart the process.
In order for this instruction to be meaningful, the
rstate
should be the default or it must match boot
init's
run level at boot time.
This action is useful for an initialization function
following a hardware boot of the system. - bootwait
Process the entry only at boot
init's
boot-time read of the
inittab
file.
Boot
init
starts the process, waits for its termination, and,
when it dies, does not restart the process. - initdefault
An entry with this
action
is only scanned when boot
init
is initially invoked.
Boot
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, boot
init
enters run level
6. The
initdefault
entry cannot specify that boot
init
start in the single-user state.
Additionally, if boot
init
does not find an
initdefault
entry in
inittab,
it requests an initial run level from the user at boot time. - 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. - once
When boot
init
enters a run level that matches the entry's
rstate,
start the process and do not wait for its termination.
When it dies, do not restart the process.
If boot
init
enters a new run level
but the process is still running from a previous run level change,
the process is not restarted. - 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. - powerfail
Execute the process associated with this entry only when boot
init
receives a power-fail signal
(SIGPWR
see
signal(5)). - powerwait
Execute the process associated with this entry only when boot
init
receives a power-fail signal
(SIGPWR)
and wait until it terminates before continuing any processing of
inittab. - respawn
If the process does not exist, start the process;
do not wait for its termination (continue scanning the
inittab
file).
When it dies, restart the process.
If the process currently exists, do nothing and continue scanning the
inittab
file. - sysinit
Entries of this type are executed before boot
init
tries to access the console.
It is expected that this entry will be only used
to initialize devices on which boot
init
might attempt to obtain run level information.
These entries are executed and waited for before continuing. - wait
When boot
init
enters the run level that matches the entry's
rstate,
start the process and wait for its termination.
Any subsequent reads of the
inittab
file while boot
init
is in the same run level cause boot
init
to ignore this entry.
- 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
sh
syntax that can legally follow
exec
can appear in the
process
field.
Comments can be inserted by using the
; #comment
syntax.
WARNINGSThe use of a four-character
id
is strongly recommended.
Many pty servers use the last two characters of the pty name as an
id.
If an
id
chosen by a pty server collides with one used in the
inittab
file, the
/etc/utmp
file can become corrupted.
A corrupt
/etc/utmp
file can cause commands such as
who
to report inaccurate information. FILES- /etc/inittab
File of processes dispatched by boot
init.
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