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

[Chris Murphy]

On Nov 8, 2012, at 11:27 AM, Alex Kanavin <address@hidden> wrote:

> 2012/11/8 Chris Murphy <address@hidden>:
>> You are EFI booted. You might find out what created that inhospitable hybrid 
>> MBR. Oh I bet you prepared the drive using Boot Camp Assistant first,
>> didn't you? If you did and don't also have Windows on the computer, you 
>> might use gdisk to create a new protective MBR, and write out a new GPT.
>> The hybrid MBR is fraught with problems and technically right now you have a 
>> stale and invalid GPT.
> 
> Er, no :) I never even ran boot camp assistant, I reduced the size of
> OS X partition with Disk Utility, and then proceeded to Ubuntu
> installation. That's when the hybrid MBR was created, probably.

If the Ubuntu installer was booted in EFI mode, and thus installed an EFI 
capable bootloader, it makes no sense it would created a hybrid MBR. If it did, 
it's a bug.

I sooner expect that Disk Utility, which depends on diskutil resizevolume, 
probably made by default an MS-DOS (FAT32) volume from the newly freed up space 
from your resized JHFS+ volume. Whenever FAT32 is created by diskutil, a hybrid 
MBR is created.


> I know
> hybrid MBR is a hack made for one specific purpose of booting Windows,
> but it doesn't seem to give me trouble, I'll probably just leave it
> there.

Fortunately both XNU and linux will defer to the GPT, but technically a hybrid 
MBR's mere existence is supposed to invalidate the GPT. Apple's own technote on 
this says that such a disk should be proscribed from further partition changes.

Honestly, for EFI booting, GRUB2 is not a good option, I think it's overly 
complicated and you'd be better off using rEFInd (rEFIt is no longer 
maintained), and using the linux efistub as your bootloader. It's much more 
sane.

Chris Murphy