How can we make F17 be able to boot on Macs (with or without reFit)

[Chris Murphy]

Responding to my own email on various boot behaviors, with some editorialization.

EFI vs CSM-BIOS:

EFI boot produces highly variable results between Apple models, while CSM-BIOS boot is very consistent between Apple models.

Windows 7 will not boot in UEFI mode on Apple hardware. I have searched thoroughly and have found no success stories so far. Even if it has been done, it's outside of what normal people are willing or able to do. Yet CSM-BIOS booting works fine on all of Apple's hardware for the past 4-5 years. This makes some sense, because Microsoft says they explicitly support UEFI 2.x and higher only, while Apple's firmware is based on Intel EFI 1.10, not UEFI 2.x.

CSM-BIOS boot is not ideal. But it's also not ideal to support a flakey EFI boot scenario that may take a lot of effort for low efficacy.

Also consider Mac users are running into the BIOS-MBR 2.2TB limit on Apple hardware. It stands to reason Apple will need to make some modifications to their EFI implementation to deal with this eventually. This accommodation of Windows (U)EFI requirements may be good for linux, or may be bad for linux. I think investing in Apple EFI unknowns is risky.

Further, consider CSM-BIOS has the best chance of supporting Fedora when Apple releases new hardware. It may take months or years to support the peculiarities of each model's EFI.

So if I were voting, I'd suggest a constrained type of support for CSM-BIOS boot, both Fedora only (atypical) and dual boot (typical).


Triple Boot:

This is possible, I've done it with several combinations, but it's non-trivial. I question if gptsync is at all appropriate for making sure the resulting hybrid MBR and GPT aren't a disaster (more often than not gptsync produces ill advised hybrid MBRs, more so than they already are).

The big gotcha with triple boot support, is that the most common situation is the existence of Mac OS and Windows, which means there is a hybrid MBR and GPT. This means a Fedora installation must make sure both an appropriate MBR and GPT are produced not merely so that all three systems to boot as expected, but to ensure neither of the previously working systems become unbootable. Today this is not the case with Fedora 16. Anaconda+parted blow away such a hybrid MBR in favor of GPT only with protective MBR, the result of which is an unbootable Windows (Mac OS remains bootable).

Even refusing to install Fedora (or a warning about the consequences) would be a much needed improvement here.


A bit about Apple's philosophy:

Apple doesn't sell hardware. They don't sell operating systems. They sell an experience that combines both. That's how they see it. The two are inseparable. 

At best they "tolerate" Windows support, and not just any Windows, only Windows 7 is supported for the better part of a year now. I have zero doubt they'd be baffled by the idea anyone would want to run linux on a Mac, and would not care one single bit if it could not be done with either EFI or CSM-BOOT modes. 

This is the hallmark company that does not believe users have any right to boot an operating system of their choice on any hardware they produce. People who buy Apple hardware today cannot even run the most recent previous version of Mac OS 10.6.8 (released July 28 2011) - it simply won't boot on their hardware.

I am leery of excessive amounts of effort, which in effect is a kind of turd polishing, to deal with Apple's non-standard EFI. I don't like being relegated to CSM-BIOS mode booting, but it does work, with well understood limitations.


Chris Murphy