I have installed usermode-sources-2.6.12-r2. According to uml guide, i need to change /etc/fstab and use /dev/ubd/0 and /dev/ubd/1 respectively. But it failed on 2.6.12-r2. I used /dev/ubda and /dev/ubdb and it runs fine. Perhaps you should check again to see whether it's correct and update the document if needed?
Maybe because the guide assumed devfs-compatible names and you use udev? Should be fixed, anyway :-).
Yes, i used udev.
Thanks, the guide is now updated.