$ runlevel
N 2

# runlevel
N 3
		

$ sudo vim /etc/init.d/rcS
#! /bin/sh
#
# rcS
#
# Call all S??* scripts in /etc/rcS.d/ in numerical/alphabetical order
#

exec /etc/init.d/rc S
		

the default is S (/etc/rcS.d/)

the redhat linux in the /etc/inittab

switch runlevel

/etc/init.d/rc 3