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. Reinstall the kernel with aptitude
  4. Reboot and go into Grub2 command mode
  5. 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.