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.
After an update (Upgrade?) a while ago I couldn’t boot into Fedora, it had the text mode bar graph and after getting to 100% it failed with this error message:
Cannot open /dev/sda1: Device or resource busy
It turned out that this was a dmraid problem. It would appear that something changed when updating and added or enabled dmraid. So I had to find a way to remove or disable it, the simplest solution I found that worked was disabling it via the arguments to the kernel in GRUB.
Edit menu.lst (Or grub.conf, my menu.lst is a symbolic link to grub.conf)
Find the entry that you are currently booting into and add “nodmraid” to the end of the “kernel” line:
kernel /vmlinuz-126.96.36.199-166.fc12.x86_64 ro root=UUID=7129c2cc-03c5-4b7a-8472-bb9d314446b3 LANG=en_US.UTF-8 SYSFONT=latarcyrheb-sun16 KEYBOARDTYPE=pc KEYTABLE=us rhgb quiet nodmraid
I also like to add a timeout and remove hiding of the menu (This is in the general entry at the top of the file):
My final menu.lst/grub.conf file looks like this:
title Fedora (188.8.131.52-166.fc12.x86_64)
kernel /vmlinuz-184.108.40.206-166.fc12.x86_64 ro root=UUID=7129c2cc-03c5-4b7a-8472-bb9d314446b3 LANG=en_US.UTF-8 SYSFONT=latarcyrheb-sun16 KEYBOARDTYPE=pc KEYTABLE=us rhgb quiet
Why Chris, your grub.conf is so puny, only one entry in it. Leave me alone, I only just reinstalled.