Rescue mode has a option to mount as read only and single mode defaults to read only. Why read only mode?

Why use emergency mode over rescue mode(off cd or fdd)?

Can anyone point me to a detail document explained the run levels(1-5)

Sorry for n00b questions....

The Red Hat documentation, specifically the Customization guide Chapter 9. Basic System Recovery would be the place to start.

I think you're probably wanting to look through the Rute guide as well. I suggest downloading it as well.

Actually I have read the the guides, granted I might be dense or missing something but everything you would use single or emergency mode for you could do through rescue mode.
I dont have a stong linux background but im trying and I guss I dont want to move until I under stand this... Thanks if you can get me straight on this.

Linux single boots with the prompt having full root powers but with no networking and the system mounted normally, I think. It has been a couple of years since I have used linux single.

Rescue boots into a kernel and bash, nothing mounted (some distros differ) and everything is done manually, mounting drives, mounting the /proc directory to a mounted system so that you can chroot into it and actually do processes such as compiling. I tend to use rescue and do stuff by hand, myself.

I haven't used emergency mode, so I am unfamiliar with it.

It just depends on what you need to do and learning the fastest and easiest ways to do what needs to be done.