Upgrading from Ubuntu 10.04 to 10.10 on Xen? Watch out on reboot!

If you were running Ubuntu 10.04 or or lower on Xen, you may be accustomed to passing root=/dev/xvda1 or similar so that the kernel would find the Xen block device and use it as the root partition. New kernels in Ubuntu 10.10 “Maverick Meerkat” now give Xen block devices the same device names as other mass storage – e.g. /dev/sda – so you may need to update the configuration in PVGRUB or your other bootloader of choice. PVGRUB / GRUB Legacy (0.97):

$ sudo vim /boot/grub/menu.lst

### BEGIN AUTOMAGIC KERNELS LIST
# <snip\>
## default kernel options
# <snip\>
# kopt=root=/dev/sda1 ro
## optional compat. option for lucid kernel in case of regressions
## (you may need to adjust this for your running kernel)
# kopt_2_6_32=root=/dev/xvda1 ro

$ sudo update-grub