1. Load GRUB from the boot disc boot section (OS selection menu)
2. GRUB loads Linux core vmlinuz (so the OS is alive)
3. execute command init
3.1 /etc/rc.d/rc.sysinit (share with all run level, e.g. ip address, mount fs)
3.2 /etc/rc.d/rc $runlevel
execute files /etc/rc.d/rc$runlevel.d/K* with parameter “stop”, order by sequence asc
execute files /etc/rc.d/rc$runlevel.d/S* with parameter “start”, order by sequence asc
(files in /etc/rc.d/rc$runlevel.d are symbolic link to /etc/rc.d/init.d)
(/etc/rc.d/rc.local is linked by “S99local -> ../rc.local” in rc2.d, rc3.d, rc4.d, rc5.d, )
4. execute command mingetty
runlevel: /etc/inittab
init: user level process(command) which is started by OS core (vmlinuz)