Ubuntu – How to Repair Grub while dual booting ( win7 / ubuntu 11.10)


I've installed windows 7 and then Ubuntu 11.10, and then set up everything on easyBCD.

When I select Ubuntu on the boot menu, I end-up in grub prompt (like "grub>" in a black screen) instead of loading Ubuntu directly.

I have to run:

grub>  root (dh0,4)
grub>  kernel /vmlinuzblahblah root=/dev/sda6
grub>  boot

Every time to boot Ubuntu(where vmlinuz is a long filename I always tab).

How could I skip this process?

Best Answer

My "Fix-Grub-routine" is as follows:

  1. Boot from an Ubuntu LiveCD (USB key usually)
  2. Mount the /root and /boot partition of my original install in the live environment. Lets say my root is mounted in /tmp/myRoot/ and boot in /tmp/myBoot/
  3. Mount/bind a few important directories
    sudo mount --bind /dev /tmp/myRoot/dev
    sudo mount --bind /proc /tmp/myRoot/proc
    sudo mount --bind /sys /tmp/myRoot/sys
    sudo mount --bind /tmp/myBoot /tmp/myRoot/boot
  4. Chroot into my original installation
    sudo chroot /tmp/myRoot/
  5. Now I'd usually do update-grub but since you messed up your bootsystem using some weird third-party application, I think it might be better to re-install grub using grub-install /dev/sda *.
  6. When done, exit the chroot and reboot the system (without your live-media)

Note: Replace /dev/sda with the drive you want grub to be installed on!

Note2: Most of this information used to be on an Ubuntu wikipage called RecoveringUbuntuAfterInstallingWindows. While finding this page to link to in this post I noticed the page has had quite a change. The chrooting and stuff is not described anymore but instead a boot-repair utility is available on some live cds. I have not experience with it, but I suppose it's worth a shot.

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