UUIDS

["mick.crane" <mick.crane@gmail.com>]

I'm sure it used to be that you could swap linux discs between PCs and 
it would sort itself out but I try swapping disks about and booting and 
they complain
"Cannot find UUID..lots of identifying numbers"
and gives intramfs prompt.
Am I supposed to be able to sort it out from there?
like how?
mick