terse and somewhat arcane. An inittab entry has this general format: label:runlevel:action:process The label is a one- to four-character tag that identifies the entry. Some systems support only two-character labels. For this reason, most people limit all labels to two characters. The labels can be any arbitrary character string, but in practice, certain labels are commonly used. The label for a getty or other login process is usually the numeric suffix of the tty to which the process is attached. Other labels used in the Red Hat Linux distribution are id for the line that defines the default runlevel used by init si for the system initialization process ln where n is a number from 1 to 6 that indicates the runlevel being initialized by this process ud for the update process ca for the process run when Ctrl+Alt+Del is pressed pf for the process run when the UPS indicates a power failure pr for the process run when power is restored by the UPS before the system is fully shut down x for the process that turns the system into an X terminal The runlevel field indicates the runlevels to which the entry applies. For example, if the field contains a 3, the process identified by the entry must be run for the system to initialize runlevel 3. More than one runlevel can be specified, as illustrated in the sample file by the pr entry. Entries that have an empty runlevel field are not involved in initializing specific runlevels. For example, an entry that is invoked by a special event, such as the three-finger salute (Ctrl+Alt+Del), does not have a value in the runlevel field. The action field defines the conditions under which the process is run. Table 1.1 lists all of the valid action values and the meaning of each one. Table 1.1: Valid Action Values Action Meaning Boot Runs when the system boots. Ignores runlevel. Bootwait Runs when the system boots, and init waits for the process to complete. Runlevels are ignored. Ctrlaltdel Runs when Ctrl+Alt+Del is pressed, which passes the SIGINT signal to init. Runlevels are ignored. Initdefault Doesn’t execute a process. It sets the default runlevel. Kbrequest Runs when init receives a signal from the keyboard. This requires that a key combination be mapped to KeyBoardSignal. Off Disables the entry so the process is not run. Once Runs one time for every runlevel. Ondemand Runs when the system enters one of the special runlevels A, B, or C. Powerfail Runs when init receives the SIGPWR signal. Powerokwait Runs when init receives the SIGPWR signal and the file /etc/ powerstatus contains the word OK. Powerwait Runs when init receives the SIGPWR signal, and init waits for the process to complete. Respawn Restarts the process whenever it terminates. 27
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