Because my old hard drive was failing, I installed a new one and installed Fedora 9 on it. After a lot of problems I decided to go back to Fedora 8. I copied my old installation with tar, changed the fstab, and added entries in my new grub.conf to point to my Fedora 8 installation.

My grub.conf looks like this:

title Fedora (2.6.26.3-14.fc8)
root (hd1,2)
kernel /boot/vmlinuz-2.6.26.3-14.fc8 ro root=LABEL=fc8 rhgb quiet usbcore.autosuspend=-1
initrd /boot/initrd-2.6.26.3-14.fc8.img
title Fedora (2.6.25.14-69.fc8)
root (hd1,2)
kernel /boot/vmlinuz-2.6.25.14-69.fc8 ro root=LABEL=fc8 rhgb quiet usbcore.autosuspend=-1
initrd /boot/initrd-2.6.25.14-69.fc8.img
title Fedora (2.6.26.5-45.fc9.x86_64)
root (hd1,0)
kernel /boot/vmlinuz-2.6.26.5-45.fc9.x86_64 ro root=UUID=e72c6d16-9923-4532-92d3-f6c4a1fe026b rhgb quiet
initrd /boot/initrd-2.6.26.5-45.fc9.x86_64.img

The problem is that Fedora 8 won't boot. When I try I get:

mount: could not find filesystem '/dev/root'
setuproot: mounting /dev failed: No such file or directory
setuproot: error mounting /proc: No such file or directory
setuproot: error mounting /sys: No such file or directory
switchroot: mount failed: No such file or directory
hub 1-0:1.0: over-current change on port 5
hub 1-0:1.0: over-current change on port 6

and then nothing else happens. I've tried doing a fresh mkinitrd and doing "mknod /dev/root b 8 3" but neither helped any. Does anybody have any idea what's going on here?

From your new grub.conf, it looks like you moved the root of Fedora 8 to the 3rd partition of your second drive (hd1,2). Is there another drive in the system, which would be detected first as hd0? You may need to fix /boot/grub/device.map by hand.

Also, could you explain the title of your post? Did you boot from the rescue disk, attempt to chroot, and have a problem?

Yes, both 9 and 8 are on the same drive now.
Yes, the device.map (which resides on my Fedora 9 partition) is correct.
I can boot to Fedora 9 and chroot (which is how I did the mkinitrd and mknod) but when booting the system when I select the Fedora 8 entry from the grub boot menu I get those errors.

Somehow it isn't finding your root partition. Check and see if the fedora 8 root partition is correctly labeled as "fc8", using fsck. In any case, you could change root=LABEL=fc8 to root=/dev/sdb3 or hdb3, as the case may be, and try booting again. I would try removing the LABEL reference in fstab as well.

[root@jks-desktop /home/jks]# e2label /dev/sda3
fc8

fsck reports no problems.

I tried passing root=/dev/sda3 to the kernel but that didn't work either.

If you can chroot into it from a working system then it is odd that mkinitrd is not doing it right. How exactly are you doing that? I do this:

boot up linux livecd or separete partition

mount partition to /mnt
cd /mnt
mount -t proc proc /mnt/proc
mount --bind /dev /mnt/dev
mount --bind /sys /mnt/sys

chroot /mnt /bin/bash

mkinitrd ...

Either way, it could also be some mismatch in /etc/modprobe.conf
Or it can be the case even after success with chroot/mkinitrd once you try to boot a new mkinitrd created on that initrd restored system, like for a new kernel.

If you compare the modprobe.conf of a system that can mkinitrd correctly for the give drive, compare it against your old one, particularly the 'alias scsi_hostadapter' parts. For instance one drive may need ata_generic while another atiixp. Once that is sorted out, you should be able to rebuild initrd on that system any time. At least that's what I've done before.