near disaster averted - "can not find /dev/by-id/xxxx"

[O. Sinclair]

Have no idea what happened but if this helps someone landing in the same
trouble then it is worth the effort of documenting it.

I am still on Karmic with all updates. Last night I was online and left
the computer on over the night. No problems, all worked this morning.
Shut it down to take it to where I am currently working (it is a laptop
and I am currently travelling).

On next boot I get to the splash and then I get "BSOD" - Black Screen of
Death. A black monitor, no activity or message or anything.

Reboot and go to "recovery option" that after a while ends up with the line:
...can not find /dev/by-id/xxxx long string of UUID here

I am dropped into Busybox shell and can do nothing worthwhile. I reboot
with a usb flash I have and can see that all works and the disks are
there (one disk, 3 partitions including swap). I check grub.cfg, I check
/etc/fstab and all LOOKS perfect. But no boot.

I tried the 3-4 kernels and none worked. Scouted around internet for a
solution and there were a few suggestion ranging from rebuilding the
kernel to what eventually worked and was simple:

on bootup get into the Grub menu by hitting ESC, Shift or both
choose a "recovery kernel",  I chose an earlier than the latest just to
be on safe side
press "e" to get to edit mode
replace all UUID-strings with /dev/sda(your root number), in my case
/dev/sda2
press ctrl+x to boot with those settings
drop to a root shell
run update-grub
reboot
all worked as before.... except now grub.cfg points to /dev/sda2 instead
of /dev/uuid-string

Phew,
Sinclair