Upgraded udev on a Gentoo Xen guest recently? Easy fix.

Wednesday, January 27, 2010

I guess some time in the last few months, I updated udev on my Gentoo Xen Guest. Normally, this wouldn’t be a problem and it wasn’t since I didn’t need to reboot the system until yesterday. It wouldn’t come back up automatically, so I consoled the domain with xm, and saw this:

* Mounting proc at /proc ... [ ok ]
* Mounting sysfs at /sys ... [ ok ]
* Your kernel is too old to work with this version of udev.
* Current udev only supports Linux kernel 2.6.25 and newer.
* Could not create /dev/pts!
* Checking root filesystem ...Failed to open the device '/dev/hda2': No such file or directory

* Filesystem couldn't be fixed 
[ !! ]
Give root password for maintenance
(or type Control-D to continue):

Of course I didn’t read the obvious error at first, and started messing around with other things before finally realizing the kernel the Xen domain is booting from is still at version 2.6.18. I had two options:
1) upgrade the domu kernel from xen-sources (>2.6.18-r12 still being masked on this system) and copy it to the xen host for the vm to boot from.
2) downgrade udev and pretend it never happened.

I chose #2, mainly because it’d take less time and work.
In short, here’s what I did:
Note: This is all from root on the Xen Dom0, not the guest machine.. since it wouldn’t boot yet.

root@Dom-0:# mount /dev/sde5 /mnt/gentoo
root@Dom-0:# mount -t proc none /mnt/gentoo/proc
root@Dom-0:# mount -o bind /dev /mnt/gentoo/dev
root@Dom-0:# chroot /mnt/gentoo /bin/bash
root@Dom-0:# env-update; source /etc/profile; export PS1="(chroot) $PS1"
root@Dom-0:# echo ">=sys-fs/udev-141" >> /etc/portage/package.mask
root@Dom-0:# emerge -avDu udev

And that was it! Started up the gentoo xen domain again, and it booted right up.