inittab - Controls the initialization process
The inittab file provides the init program with instructions for creating and running initialization processes. The init program reads the inittab file each time init is invoked. The file typically contains instructions for the default initialization, the creation and control of processes at each run level, and the getty command, which controls the activation of terminal lines.
Each line in the inittab file contains an entry that has four fields; each field is separated by a colon. There is no limit to the number of entries in the inittab file. The entry syntax is as follows: Identifier:Runlevel:Action:Command
Specifies a fourteen character field used to uniquely identify an object. Specifies a twenty character field that defines the run levels in which the object is to be processed. Runlevel corresponds to a configuration of processes in a system. Each process spawned by the init command is assigned one or more run levels in which it is allowed to exist. The run levels are as follows: Specifies the halt state. Specifies multiuser state without network services. Specifies multiuser state with network services. Specifies single-user state. You can define multiple run levels for a process by specifying more than one run level character in any combination. Specifies a twenty character field that tells init how to treat the specified process. init recognizes the following Action values: Specifies that if the process does not exist or if it dies, init starts it. If the process exists, init continues to process the inittab file. Specifies that if init enters a run level that matches the run level specified in the inittab file entry, it starts the process and waits for its termination. As long as init continues in this run level, it does not act on subsequent reads of the entry in the inittab file. Specifies that if init enters a run level that matches the run level specified in the inittab file, it starts the process and does not wait for its termination. When the process stops, init does not restart it. If init enters a new run level where the process is still running from a previous runlevel change, init does not restart the process. Specifies that when init first executes and reads the inittab file, it processes this entry. The init program starts the process and does not wait for its termination. When the process stops, init does not restart it. The run level specified in this inittab file entry should be the default run level, or it must match the run level in which init operates at boot time. Specifies that when init first executes and reads the inittab file, it processes this inittab file entry. The init program starts the process, waits for its termination and, when it dies, does not restart the process. (This value exists only for SVID3/SVR4 compatibility.) Specifies that if init receives the SIGPWR power fail signal, it executes the process associated with this line. (This value exists only for SVID3/SVR4 compatibility.) Specifies that if init receives the SIGPWR power fail signal, it executes the process associated with this line and waits until the process terminates before continuing processing the inittab file. Specifies that if the process associated with this line is currently running, init sends the warning signal SIGTERM and waits 20 seconds before sending the kill signal SIGKILL. If the process does not existent, init ignores the inittab entry. Specifies that a line with this action is processed when init is originally invoked. The init program uses this line to determine the run level to enter originally. It determines this by taking the highest run level specified in the run level field and using that as its initial state. If the run level field is empty, this is interpreted as 0s23, causing init to enter run level 3. If init does not find an initdefault entry in the inittab file, it requests an initial run level from the operator. Specifies that entries of this type are executed before init tries to access the console. This inittab file entry should be used only to initialize devices on which init could attempt to request a run level. Specifies a 1024 character field that contains the sh command to be executed. The command is prefixed with exec. Any legitimate sh syntax can appear in the command field. Comments can be inserted be specifying a number sign (#). The line continuation character \ can be placed at the end of a line.
The following is an example of an inittab file entry for a terminal line: tty01:23:respawn:/usr/sbin/getty /dev/tty08 9600 vt100
Specifies the command that initializes and controls terminal lines.
Commands: init(8), getty(8)
Functions: kill(2) delim off