On the weekend I was installing the new version of Mythbuntu (More interesting screenshots here) and I had a weird error, “No root file system is defined”. At first I thought it must have been something to do with failing to recognise the existing partitions or possibly they were corrupt. “fdisk -l” worked, returning sda, sda1-sda4, which was correct however “mount” would always fail. It turned out that it was just our old friend dmraid was breaking in new and unexpected ways. Here is how to worked around it:
Boot into live CD mode
Remove dmraid via Package Manager
Run Install Mythbuntu from the desktop shortcut
On multiple distributions and motherboards I consistently have problems with dmraid not finding/incorrectly identifying partitions/drives. I’m not the only one with these problems. I’m sure I am having these problems because I have raid hardware but am not using raid. Surely raid is an advanced enough feature that people with raid should be expected to know to install/add it? Perhaps the install could be attempted without raid support and the installer can say “Do you use raid?” or “Are these devices correct?” and at this point the installation restarts/redetects with dmraid enabled.