NAME

inittab − script for 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. 

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 512 characters per entry are permitted.  Comments may be inserted in the process field using the sh(1) convention for comments. Comments for lines that spawn gettys are displayed by the who(1) command.  It is expected that they 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 This is one or two characters used to uniquely identify an entry. 

rstate This defines the run-level in which this entry is going 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.  As an example, if the system is in run-level 1, only those entries having a 1 in the rstate field are processed.  When init is requested to change run-levels, all processes which 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 0−6.  If no run-level is specified, then the process is assumed to be valid at all run-levels 0−6.  There are three other values, a, b and c, which can appear in the rstate field, even though they are not true run-levels. Entries which have 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 run-level of the system).  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.  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 goes into the SINGLE USER state. 

action Key words in this field tell init how to treat the process specified in the process field.  The actions recognized by init are:

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 entry’s rstate, start the process and wait for its termination. All 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 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 entry is 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 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 The entry is to be processed the first time init goes from single-user to multi-user state after the system is booted.  (If initdefault is set to 2, the process runs right after the boot.)  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(2)].

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 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 rstate field and using that as its initial state.  If the rstate field is empty, this is interpreted as 0123456 and so init enters run-level 6.  Additionally, if init does not find an initdefault entry in /etc/inittab, then 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 (i.e., before the Console Login: prompt).  It is expected that this entry is used only 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 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 legal sh syntax can appear in the process field.  Comments can be inserted with the ; #comment syntax. 

FILES

/etc/inittab

SEE ALSO

exec(2), getty(1M), init(1M), open(2), sh(1), signal(2), who(1)

September 02, 1992