GRUB2 (packaged with Ubuntu 12.10) won't boot OS X

[Alex Kanavin]

Hi,

I've installed Ubuntu 12.10 on a late-2009 Mac Mini with OS X 10.6.8, and while the computer's firmware loads Grub fine, and Grub loads Ubuntu without problems (except Ubuntu's splash screen is missing, I can live with that), I get kernel panics when trying to load OS X in either 32 or 64 bit mode. The menu entries for them were generated from standard scripts in /etc/grub.d/.

Have a look at screenshots (apologies for the blur, if you need exact messages, I can try to take sharper pictures):
http://sensi.org/~ak/tmp/12110004.jpg
http://sensi.org/~ak/tmp/12110006.jpg

I have also attempted to boot OS X via simple EFI chainloading:

address@hidden:~$ cat /boot/grub/custom.cfg 
menuentry "OS X" {
    insmod hfsplus
    insmod part_gpt
    insmod chain
    set root='(hd0,gpt2)'
    chainloader /System/Library/CoreServices/boot.efi
}

but I'm getting this error: "not a valid root device". 

I assure you that gpt2 is a perfectly valid and bootable OS X partition - I can still boot it from Mac's firmware by holding Alt during boot :)

Any ideas how to diagnose this further?

-- 
Alexander