I did a dumb thing... I forgot that Ubuntu 10.04 (Lucid) switched to Grub2 which puts a ton of *.mod files (kernel modules) in /boot/grub. I thought they were soundtrack files put there erroneously and moved them. Needless to say, the next reboot was traumatic. I was presented with something I had no memory of ever seeing... a 'grub rescue>' prompt.

With the help of how-to-fix-error-unknown-filesystem-grub-rescue however, I was able to recover...

• Discovered that Grub Rescue does not have 'cd', 'cp' or any other filesystem commands except its own variation of 'ls'.

• So first I had to find the partition with the /boot directory containing vmlinuz... and other boot image files... (failed attempts not shown)

  grub rescue>  ls  
  (hd0,4) (hd0,3) (hd0,2) (hd0,1)  
   grub rescue>  ls (hd0,2)/boot
  ... grub ... initrd.img-2.6.32-33-generic ... vmlinuz-2.6.32-33-generic 
  

• Then manually boot from 'grub rescue>' prompt (no command history either!)...

  grub rescue>  set root=(hd0,2)/boot  
  grub rescue>  insmod linux  
  grub rescue>  linux (hd0,2)/boot/vmlinuz-2.6.32-33-generic  
  grub rescue>  initrd (hd0,2)/boot/initrd.img-2.6.32-33-generic  
  grub rescue>  boot  
  

• This boots and crashes to the BusyBox prompt which DOES have some rudimentary filesystem commnds.

• Then I moved the *.mod files back to the /boot/grub directory...

  busybox>  cd /boot  
  busybox>  mv mod/* grub
  busybox>  reboot
  

• The reboot was successful but that was a lot of work.

Is there an easier way?