Suppose you want to try out Xen for the first time, and you're a bit
paranoid careful because, well, you don't want to break your system. No problem, just download the Xen 3.0 Demo CD Image (a live CD). Or so I thought; it took me a loong time to even find a download link for that beast. There seems to be no ISO image for 3.0.4, but only for 3.0.3 (gah!).
Anyways, the live CD seems to try to mount
/dev/sda as my CDROM drive, which is... um... stupid, as that's a harddrive. A SATA harddrive to be more specific. A dm-crypt'ed hard drive to be even more specific. So there's no way the live CD can ever mount that. I was dropped into a minimalist shell, but couldn't figure out how to fix anything from there, and a quick look at the docs didn't reveal anything either.
So here's my fix:
qemu -cdrom /dev/cdrom -boot d
Nice huh? QEMU's hard drive is an IDE drive, it's called
/dev/hda (instead of
/dev/sda), thus the live CD works fine.
(Yes, I'm sure this could be fixed "the right way" too, but this is a nice way to get quick results, i.e. a working Xen test setup)