Grub entry:

title Fedora Core 5 Xen (2.6.15-1.2054_FC5) init 3
        root (hd0,4)
        kernel /boot/xen.gz-2.6.15-1.2054_FC5 noreboot
        module /boot/vmlinuz-2.6.15-1.2054_FC5xen0 ro root=/dev/hda5 selinux=0 init 3
        module /boot/initrd-2.6.15-1.2054_FC5xen0.img

/boot/* above all exist ok on /dev/hda5 and are readable. /dev/hda5 is my usual / for FC5 and boots fine with a non-Xen kernel and conventional grub entry. First stage grub (the bootsector) actual lives on /dev/hda3 but this has always worked fine. I don't use LVM.

When I try to boot the above ("noreboot" added so I can see the error), it seems to
get as far as mounting the real root on /dev/hda5, but then panics with:

WARNING: can't access
exec of init () failed!!!: no such file or directory

- there's genuinely nothing after the word "access" above, not even "(null)" which seems unusual.