inittab format, id, runlevels, action, process, respawn, wait, once, boot, bootwait, ondemand, initdefault, sysinit, powerwait, powerfail, Powerokwait, ctrlaltdel
The format of each line in inittab file is as follows:
id:runlevels:action:process
• 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 |
Description |
respawn |
The process will be restarted whenever it terminates. |
wait |
The process will be started once when the runlevel is entered, and init will wait for its completion. |
once |
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. |
boot |
The process will be executed at system boot. The runlevels field is ignored in this case. |
bootwait |
The process will be executed at system boot, and init will wait for completion of the boot before |
ondemand |
The process will be executed when a specific runlevel request occurs. (These runlevels are a, b, |
initdefault |
Specifies the default runlevel for init on startup. If no default is specified, the user is prompted for a runlevel on console. |
sysinit |
The process will be executed during system boot, before any of the boot or bootwait entries. |
powerwait |
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. |
powerfail |
Same as powerwait, except that init will not wait for the process to finish. |
Powerokwait |
This process will be executed as soon as init is informed that the power has been restored. |
ctrlaltdel |
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. |