I recently did a major number of updates of my system. One of the updates must have been to Grub, because after I restarted and grub came up, it wouldn't boot my other OS correctly, Archlinux. Here is what it wrote into the Grub menuentry for Arch:
It would come up with a message saying it could not find /dev/hda3, waiting 10 seconds. To fix it, I could knew what my configuration was, so I changed this line:
setparams 'arch (on /dev/sda4)'
search --no-floppy --fs-uuid --set=root 72b29576-5eb0-4b76-90c8-755c603e2515
linux /boot/vmlinuz-linux root=/dev/hda3 ro
and it worked fine at boot up. I had to make this a custom menuentry because update-grub keeps coming up with something that does not work. This is workable for the time, I am just curious why Grub did this.
linux /boot/vmlinuz-linux root=/dev/sda4 ro