Special runlevels "s", "emergency", "init=/bin/sh" and single user mode (runlevel 1)
- Runlevel "1" — will run /etc/rc.d/rc1.d
- Runlevel "s" — do not need /etc/inittab and will open root shell on /dev/console
- Runlevel "emergency" — boot single user mode without startup scripts, root filesystem will be mount in read only mode.
- Runlevel "init=/bin/sh" — run /bin/sh instead of /sbin/init