NAME

inittab − script for the init process

DESCRIPTION

The inittab file supplies the script to init’s role as a general process dispatcher (see init(1M)). 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 1024 characters per entry are permitted.  Comments can be inserted in the process field using the sh(1) convention for comments. 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.  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 runlevel in which this entry is to be processed. Run levels correspond to a configuration of processes in the system where each process spawned by init is assigned a run level or run levels in which it is allowed to exist.  run levels are represented by a number ranging from 0 through 6.  For example, if the system is in runlevel 1, only those entries having a 1 in their rstate field are processed. 

When 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).  The rstate field 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, the process is assumed to be valid at 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 the telinit (see init(1M)) process requests them to be run (regardless of the current system runlevel).  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.  Processes are killed only 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.  Actions recognized by init are as follows:

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. 

wait Upon init’s entering 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 init is in the same run level 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 init enters a new run level but the process is still running from a previous run level change, the program is not restarted. 

boot Process the entry only at init’s boot-time read of the inittab file.  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 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 at init’s boot-time read of the inittab file.  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(5)).

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 using that as its initial state.  If the rstate field is empty, this is interpreted as 0123456 causing init to enter run level 6. 

The initdefault entry cannot specify that init start in the Single-User state.  Additionally, if init does not find an initdefault entry in /etc/inittab, it requests an initial run level from the user at reboot time. 

sysinit Entries of this type are executed before init tries to access the console.  It is expected that this entry will be only used to initialize devices on which init might attempt to obtain run level information.  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 sh syntax that can legally follow exec can appear in the process field.  Comments can be inserted by using ; #comment syntax. 

In the HP Clustered environment, /etc/inittab is a context-dependent file (CDF) because different cnodes have different initialization requirements.  See cdf(4).

WARNINGS

The 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 /etc/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

SEE ALSO

sh(1), getty(1M), exec(2), open(2), signal(5). 

Hewlett-Packard Company  —  HP-UX Release 9.0: August 1992