I dunno Jimmy, can you use
Google to find the answers to some of the easier questions?
The problem is that runlevels can be different depending on which unix you're looking at. Solaris for example. Run level 5 is a system power down. On Linux boxes, run level 5 brings you into the windowing system.
Some runlevels are consistent even if they're not really official standards. Run level 2 and 3 for example.
Plus some systems use rc
n.d directories where others use rc scripts.
There are other run levels too.
S - Single user mode
0 - System Shutdown
1 - Single user mode
2 - Start most services
3 - Multi-user mode startup (apache, nfs server and snmp start here on solaris)
4 - ?
5 - X-Windows on linux, Powerdown on Sun
6 - ?
7 - ?
8 - ?
9 - ?
If you have a directory and have a specific need to start something extra, like a web server but you don't want it starting in 3, then you can put Apache in run level 4 for example, but not on Sun.
See in Linux, each rc directory stands on its own. init throws you right to the /etc/rc3.d directory. So all your startup scripts for run level 3 need to be in /etc/rc3.d. However on Sun systems, /etc/rc2.d is processed and
then /etc/rc3.d and potentially /etc/rc4.d if you had something in there.
Did that help?
Carl