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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 ...
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  1. #1
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    runlevel and ring level ?


    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?

  2. #2
    Linux Engineer rcgreen's Avatar
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    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.

  3. #3
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    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.
    Last edited by sam111; 03-02-2012 at 04:43 AM.

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