runlevel and ring level ?

[sam111]

I know the only possible ring levels are 0 , 1, 2,3
corresponding to the 2bit Privilege field in the global descriptor table.

I am curious in linux why we have runlevels 0 - 6.
Are the runlevels not the same as ring levels ?


when I issue runlevel at the command line it gives me
N 2

That means I am in ring 2 or the third ring from the bottom up.

Correct me if I am wrong?

[rcgreen]

I think they are not related. Ring level has to do with the privilege
that code has running on the processor. Run level is a linux feature that
controls whether the OS is running in single user mode, multi user
mode, graphical mode, or whatever.

[sam111]

I kind of figured that.

But I am curious when you switch to these different runlevels will it switch to a different ring level?
I know runlevel 0 and 6 are just to shutdown or restart the computer but I wasn't sure if the other runlevels are mapped to the same ring level and the difference is just the multilevel , single mode level , graphics,...etc modes.

Or if a particular runlevel is associate to a different ring level while switching runlevels.... or if anybody knew for sure with out me having to dig into the init code of linux source.

Now that I think about it windows and linux machines only use ring 0 or ring 3 "I think"
so if the runlevel was not in 3 it would probably only be in ring 0.