The format of each line in inittab file is as follows:
• id: A unique sequence of one to four characters that identifies this entry in the /etc/inittab file.
• runlevels: The runlevels at which the process should be invoked. For example, the runlevels entry 123 specifies something that runs at runlevels 1, 2, or 3.
• action: Describes what action should be taken. Options for this field are explained in the next table.
• Process: Names the process (or program) to execute when the runlevel is entered.
The following table specifies some valid actions for the action field.
Action Field in inittab file
The process will be restarted whenever it terminates.
The process will be started once when the runlevel is entered, and init will wait for its completion.
The process will be started once when the runlevel is entered; however, init won’t wait for termination of the process before possibly executing additional programs to be run at that particular runlevel.
The process will be executed at system boot. The runlevels field is ignored in this case.
The process will be executed at system boot, and init will wait for completion of the boot before
advancing to the next process to be run.
The process will be executed when a specific runlevel request occurs. (These runlevels are a, b,
and c.) No change in runlevel occurs.
Specifies the default runlevel for init on startup. If no default is specified, the user is prompted for a runlevel on console.
The process will be executed during system boot, before any of the boot or bootwait entries.
If init receives a signal from another process that there are problems with the power, this process will be run. Before continuing, init will wait for this process to finish.
Same as powerwait, except that init will not wait for the process to finish.
This process will be executed as soon as init is informed that the power has been restored.
The process is executed when init receives a signal indicating that the user has pressed the ctrl-alt-del key combination. Keep in mind that most X Window System servers capture this key combination, and thus init may not receive this signal if the X Window System is active.