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

[Chris Murphy]

On Nov 7, 2012, at 8:51 PM, Alex Kanavin <address@hidden> wrote:

> 2012/11/7 Chris Murphy <address@hidden>:
>>> EFI I guess. How do I find out and switch between modes?
>> 
>> What are you using as the first boot manager? The built-in one using option 
>> key at startup chime, or rEFIt/rEFInd?
> 
> I'm not using anything specifically; when I switch on or reboot the
> computer, it goes straight into the Grub menu. I think Ubuntu wrote
> some magic into NVRAM during installation to make that happen, and
> firmware is able to pick up the grub bootloder from EFI system
> partition (which is FAT32). Just as it should be :)

Well that's debatable, because it's inherently fragile to depend on NVRAM for 
this. "Zapping the PRAM" is a common (if not sometimes mystical) 
troubleshooting technique on Macs, and the instant you do this your computer 
cannot be made to revert to the behavior you now have. So it's not only 
fragile, but it's obscured, and also it's basically broken your ability to boot 
the primary OS: OS X.

> 
> If I do hold the option key, I get two choices: either rEFInd
> (installed on OS X partition), or "Windows". If I choose 'Windows'
> (which I've never had on the machine, and I never used Boot Camp
> either) I get a "No operating system error" after some time.

Weird. The Windows option is hard wired and requires three things to be true: 
the first 440 bytes of the MBR contain boot loader code, the MBR contains more 
than one entry, one of the entries other than the first entry in the MBR has an 
active flag set.

So something has done those three things. The Windows options is the gateway to 
the Apple EFI activating the CSM-BIOS, so that would seem to indicate you're 
booting CSM-BIOS, but the fact it's a dead end with "no operating system" 
rather than going to GRUB possibly means you're booting EFI, in which case why 
do you have a hybrid MBR, and code in the MBR bootloader region.

What do you get for:

dmesg | grep -i efi


Chris Murphy