respawn	Restart the process whenever it terminates. Usually used for getty processes, which monitor for logins.
wait	Start the process once when the specified runlevel is entered and wait for its termination before init proceeds.
once	Start the process once when the specified runlevel is entered.
initdefault	Specifies the runlevel to enter after system boot.
ctrlaltdel	Execute the associated process when init receives the SIGINT signal, for example, when someone on the system console presses CTRL-ALT-DEL.