I was messing with my GRUB2 boot settions from the Grub UI Manager and I removed the grub menu link to Ubuntu, so that when I rebooted I couldn’t get into Ubuntu again! Doooh!
To fix you have to get into the GRUB CLI bu pressing ‘C’ at the boot menu.
Next you’ll get presented with a command line with “grub >” as the prompt.
Now you need to see what partitions you have and where your linux image file will be.
you should see something like
(hd0) (hd0,msdos3) (hd0.msdos4) (fd0)
My linux partion was on (hd0,msdos8) or (hd0,8).
set root=(hd0,8) linux /boot/vml(press the tap key here)ro root=/dev/sda8 initrd /boot/ini(press the tap key here) boot
Pick out the most recent image from above (you’ll see it once you tab).
If you have no idea which partition your image is on, then simply set root(hd0,x) for each partition shown on the “ls” command and you’ll find it eventually.
Once back into to Ubuntu I reset my Grub menu from the Grub UI Manager and I was back in business.
All the above was sourced from here..