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Tuesday, April 12, 2011

Booting the Linux Kernel from Grub2

Recently a good friend of mine managed to uninstall all the kernels from his Ubuntu machine (what can I say - Monday morning and no coffee is a deadly combination). Luckily he had the install CD on hand so we did the following:

  1. Boot from the CD (we had Internet connection)
  2. Mount the Linux partition and chroot into it
  3. sudo su
    cd /media/..
    chroot .
  4. Reinstall the kernel with aptitude
  5. Reboot and go into Grub2 command mode
  6. Now do the following (commands need to be adjusted to match your partition - also, tab completion works, so you don't have to guess)
    insmod part_msdos
    insmod ext2
    set root=(hd0,3)
    linux /boot/vmlinuz- root=/dev/sda3 ro
    initrd /boot/initrd.img-2.6.38-6-686

It seems that most of the examples on the 'net are for Grub 1 and little is out there for Grub 2. I found the following three: How to use Grub2 to boot Linux manually, The Grub 2 Guide, GRUB 2 bootloader - Full tutorial. Also, I didn't perform steps 4-5 because he just reinstalled Ubuntu (it was a fresh install anyway), but I tried it out separately on my laptop and it works.



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