INITTAB(5,F) AIX Technical Reference INITTAB(5,F)
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inittab
PURPOSE
Describes the information used by 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.
Note: If the Transparent Computing Facility is installed, each cluster site
has its own version of inittab (/etc/inittab is a symbolic link into the
local file system).
File Format
The inittab file consists of one or more named stanzas separated by blank
lines. Each stanza begins with its name followed by a colon, and contains
assignments of values to keyword attributes. The values, in turn, may be
alphanumeric strings or arbitrary character strings enclosed in double quotes.
Note: In the multibyte environment, the inittab file stanzas may contain only
ASCII characters.
inittab Parameters
The inittab keywords and their meanings are as follows:
id This is one to four characters used to uniquely identify an entry.
level This defines the run-level in which this stanza 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 to 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 stanzas
having a 1 in the level keyword are processed. When init is
requested to change run-levels, all processes which do not have an
entry in the level keyword 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 level
keyword 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 action will be taken on this process
for all run-levels 0-6. There are three other values, a, b, and c,
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which can appear in the level keyword, even though they are not true
run-levels. Stanzas which have these characters in the level
keyword are processed only when the telinit (see the init command in
AIX Operating System Commands Reference) process requests them to be
run (regardless of the current run-level of the system). They
differ from run-levels in that the system is only in these states
for as long as it takes to execute all the stanzas associated with
the states. A process started by an a, b or c command is not killed
when init changes levels. They are only killed if their stanza in
/etc/inittab is marked off in the action keyword, their stanza is
deleted entirely from /etc/inittab, or init goes into the SINGLE
USER state.
action Values for this keyword tell init how to treat the process specified
in the command keyword. 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
stanza's level, 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 stanza.
once Upon init's entering a run-level that matches the
stanza's level, start the process, do not wait for its
termination and 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 is not restarted.
boot The stanza 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 level 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 stanza is to be processed only at init's boot-time
read of the inittab file. init is to start the process,
wait for its termination and, when it dies, not restart
the process.
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powerfail Execute the process associated with this stanza only
when init receives a power fail signal (SIGPWR); see
"sigaction, sigvec, signal."
powerwait Execute the process associated with this stanza 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 stanza 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 stanza.
ondemand This instruction is really a synonym of the respawn
action. It is functionally identical to respawn but is
given a different name in order to divorce its
association with run-levels. This is used only with the
a, b or c values described in the level keyword.
initdefault A stanza 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 keyword and using that as its initial state.
If the level keyword is empty, this is interpreted as
0123456 and so init will enter a run-level 6. Also, the
stanza with the initdefault action can specify s or S in
the level keyword to indicate that init is to start in
the SINGLE USER state. Additionally, if init doesn't
find an initdefault stanza in /etc/inittab, then it will
request an initial run-level from the user at reboot
time.
sysinit Stanzas with this action are executed before init tries
to access the console. It is expected that this stanza
will be used to initialize devices on which init might
try to ask the run-level question. These stanzas are
executed and waited for before continuing.
command This is an sh command to be executed.
comment The text that follows is a comment. If the text includes a space
(you have two or more words), then the test must be quoted. The
commands WHO -l and WHO -u print the comment.
EXAMPLE
The following example of an inittab file illustrates some of its features:
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*
idef:
id = idef
level = 2
action = initdefault
command = "# default state: multi user"
*
sys1:
id = sys1
level = NULL
action = sysinit
command = "/etc/init.dir/shx Boot2singl"
*
mul1:
id = mul1
level = 2
action = wait
command = "/bin/kill -9 -1"
*
mul2:
id = mul2
level = 2
action = wait
command = "/etc/init.dir/shx Singl2multi"
*
sin1:
id = sin1
level = 03
action = wait
command = "/etc/init.dir/shx Multi2singl"
*
sin2:
id = sin2
level = 03
action = wait
command = "/bin/kill -15 -1"
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*
sin3:
id = sin3
level = 03
action = wait
command = "sleep 10"
*
*
sin4:
id = sin4
level = 03
action = wait
command = "/bin/kill -9 -1"
*
sin5:
id = sin5
level = 03
action = wait
command = "/etc/init.dir/shx Filesystems down"
*
sin6:
id = sin6
level = 3
action = wait
command = "/etc/init s </dev/console >/dev/console 2>&1"
*
hlt0:
id = hlt0
level = 0
action = wait
command = "/etc/haltsys"
*
lds:
id = lds
level = 4
action = respawn
command = "/etc/loadserver"
*
console:
id = con
action = respawn
level = 14
command = "/etc/getty console"
*
tty00:
id = tt0
action = respawn
level = 14
command = "/etc/getty tty00"
*
*
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tty01:
id = tt1
action = off
level = 14
command = "/etc/getty tty01"
comment = "modem line"
FILES
/etc/inittab
/etc/locks
RELATED INFORMATION
In this book: "attributes," "connect.con," "environment," and "termio."
The su, pstart, pdisable, getty, login, init, and stty commands in AIX
Operating System Commands Reference.
"Introduction to International Character Support" in Managing the AIX Operating
System.
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