This is the story:

I've got a spare 20Gb on my main drive, so I partitioned 10Gb of it and put ReiserFS on it. Then I did a single partition install of the latest stable Debian to that logical partition (/dev/hde7). I skipped the bootloader installation because I'd planned to use the already installed Gentoo bootloader to load it.

So, after installing Debian to /dev/hde7 (which went flawlessly), I rebooted into Gentoo and edited grub.conf to add an entry to boot Debian.

The entry looks like this:

title=Debian
root (hd0,6)
kernel /vmlinuz root=/dev/hde7

When I select debian from the boot menu however, the kernel loads and starts booting up, but then it stops with the following error messages:

VFS: Cannot open root device "hde7" or 21:07
Please append a correct "root=" boot option
Kernel panic: VFS: Unable to mount root fs on 21:07

Any ideas what's going wrong? I can still boot into Gentoo fine...

Here are the relevant lines from a Sarge menu.lst:

title Sarge
root (hd0,6)
kernel /boot/vmlinuz-2.6.8-2-686 root=/dev/hde7 ro
initrd /boot/initrd.img-2.6.8-2-686
savedefault
boot

I fixed it.

The problem was that I was missing the "initrd" command in grub.conf.

I have two symlinks in "/" called "vmlinuz" and "initrd.img" which point to files in "/boot".

Anyways, I was going to move the kernel to my Gentoo "/boot" partition when I noticed the initrd.img file, so I looked up "initrd" in the grub manual and found out I had to add the initrd command in grub.conf.

So now my Debian entry in grub.conf looks like this:

title=Debian
root (hd0,6)
kernel /vmlinuz root=/dev/hde7
initrd /initrd.img

Thanks!