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Ch. 3 Grub- editing grub.cfg on centos 7 during boot


Just an FYI in case anyone else has this issue with the Ch 3 labs on GRUB. I couldnt figure out where to edit the line to add the number 3 to boot to runlevel 3 non graphical mode. Some google searching found a page that helped a bit. If you are running Centos 7, you boot up, and stop at the GRUB menu, select the kernel you want to boot, hit 'e'- and now look for the following line and add the number 3 after "/centos-root".


linux16 /vmlinuz-3.10.0-229.1.2.el7.x86_64 root=/dev/mapper/centos-root 3 ro rd.lvm.lv=centos/root rd.lvm.lv=centos/swap crashkernel=auto rhgb quiet LANG=en_US.UTF-8 systemd.debug initrd16 /initramfs-3.10.0-229.1.2.el7.x86_64.img

There may be other things after "/centos-root" but just put a space at the end and add the number 3 in between.

If I have made any mistakes with this info let me know.



  • coop
    coop Posts: 915
    AFAIK, placement on the line is irrelevant, and I have just been adding "3" at the end of the line after a blank space for many years.

    THe way it works is the kernel parses the command line (everything after "linux" or linux16" depending on grub version and distribution) and compares the arguments against a built-in list of parameter possibilities. These can either be "tag=value" types (like "root=/dev/sda1") or just parameters (like "ro"). Anything left over goes to whatever PID=1 (init) program is run, and if the order were to matter it would be up to the init program, but it should not matter.

    Anything that init doesn't consume is simply discarded, as far as I know.

    You should all keep in mind that the exact choice of boot parameters, and how the
    initramfs/initrd are build is quite distro-dependent, which can be a great annoyance, but every distro things they have the best solutions.
  • ultraninja
    ultraninja Posts: 20
    Thanks for the tip. I was having some trouble and found that adding "3" worked.

    I was able to get into text-only rescue mode by following the tip on:
    Change the ro line to rw and add init=/sysroot/bin/sh

    rw init=/sysroot/bin/sh

    However, that wasn't exactly what the lab was supposed to do. Thanks again.

  • PCTek254
    PCTek254 Posts: 1
    edited January 2017

    Thanks for the post.  I've googled and search via youtube as well and no search results come close

    to your tip.  I followed your example by adding the "3" after root, "/centos-root 3".  I can move forward with the lesson.  Thanks again.


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