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Mac mini (Macmini2,1) EFI boot 64 bit [SOLVED]
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gabrielg
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PostPosted: Sun Nov 18, 2012 1:30 pm    Post subject: Mac mini (Macmini2,1) EFI boot 64 bit [SOLVED] Reply with quote

Hi,

Has anybody managed to successfully boot a Mac mini with a 64 bit kernel in EFI mode? This is a Core 2 Duo (I think 2007 model, first one with 64 bit CPU's), I tried System Rescue CD with no luck, and I have just managed to boot a Fedora Live CD in 32 bits.

I know that apple is very particular with "standards", and perhaps my firmware doesn't support 64 bit boots for whatever reason.

Let me know your thoughts - I'm just looking at the options I've got I guess.


Gabriel


Last edited by gabrielg on Sun Nov 25, 2012 12:05 pm; edited 2 times in total
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gabrielg
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PostPosted: Sun Nov 18, 2012 2:36 pm    Post subject: Reply with quote

I think I found my answer:
- Mac minis like mine have an EFI firmware which is a 32bit one. Further upgrades aren't available, unless you perhaps manage to "force" them, which I don't think I'll try. So, for EFI, you're stuck with 32 bits.
- In legacy mode (emulated BIOS), it is possible to boot a 64bit kernel (like the one that comes in the Gentoo install CD).

I am not yet sure how well it will run in either mode, so I guess I've got something to play now, and it would be beyond the scope of this forum.
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srs5694
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PostPosted: Sun Nov 18, 2012 4:14 pm    Post subject: Reply with quote

You could look into installing a 32-bit version of GRUB (EFI) and using it to load a 64-bit kernel. In theory that should work; however, my understanding is that you'll lose access to EFI runtime variables. The biggest problem with that is that you won't be able to use the efibootmgr utility -- but it's been reported to cause firmware corruption on some Macs under some circumstances, so that's not really the biggest drawback.
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gabrielg
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PostPosted: Sun Nov 25, 2012 12:06 pm    Post subject: Reply with quote

Yes - 32 bit boot loader and 64 bit kernel did it, finally. Worth mentioning that this Mac apparently wants a hybrid MBR/GPT disk and an HFS+ EFI partition, otherwise it won't boot.

Thanks!
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srs5694
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PostPosted: Sun Nov 25, 2012 3:20 pm    Post subject: Reply with quote

I've never heard of a Mac requiring a hybrid MBR except to boot a BIOS-based OS. When booting in EFI mode, a standard GPT setup should work fine. Thus, it's conceivable that you're doing a BIOS-mode boot and not realizing it; or maybe there was some other problem with your partition table and rewriting the protective MBR as a hybrid MBR fixed that problem.

As to an HFS+ ESP, that also is very peculiar. Perhaps filesystem corruption on a previous FAT ESP could have caused problems, though....
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gabrielg
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PostPosted: Sun Nov 25, 2012 3:51 pm    Post subject: Reply with quote

I'm pretty certain that I'm booting EFI, since grub is just an EFI executable, and rEFIt detected it as such. The kernel then boots up extremely quickly, which is another "symptom" of EFI boot. Like you said, no access to EFI vars, but I did see them while booting on i686 Fedora 17, and managed to use efibootmgr without issues. I'm also considering build a USB key or CD with a Gentoo 32bit that would boot EFI for emergencies (I'm suspecting that accessing the EFI vars would be useful).

As for the partition, well, I thought about what you said, I did repartition while trying this out and couldn't get it to work. Unfortunately, I'm more interested in getting this machine working than experimenting, so I won't be able to tell what really happened. I did do some repartitioning (removing Fedora's LVM and replacing it with ext4) and will do more in future - nothing has broken yet. What I reckon I will not do is reformat the EFI partition.

Two things that I thought peculiar while going through this process:
1. On rEFIt's shell, a FAT16 or 32 partition would be inaccessible.
2. _Sometimes_ (without rEFIt), I'd get stuck in the grey screen when the Mac boots - unfortunately, seeing nothing. Maybe there was an obvious error behind that screen that I could have sorted out.

Ah, well, this is an old model anyway, hopefully the newer ones are better standardised and people shouldn't be bumping into these issues.
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srs5694
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PostPosted: Sun Nov 25, 2012 8:26 pm    Post subject: Reply with quote

gabrielg wrote:
Two things that I thought peculiar while going through this process:
1. On rEFIt's shell, a FAT16 or 32 partition would be inaccessible.


That's extremely strange. The only thought I have, offhand, is that the filesystem may have been damaged, or perhaps it was created using a tool that set things up strangely so that the firmware couldn't read it.

FWIW, I've got a first-generation Intel Mac Mini, which has a 32-bit EFI and a 32-bit CPU. I use a FAT32 ESP and have rEFInd installed on it, and this all works well, although the Linux kernel hangs when loaded from a FAT partition on this system.

Quote:
Ah, well, this is an old model anyway, hopefully the newer ones are better standardised and people shouldn't be bumping into these issues.


This provoked an almost hysterical (but short) laugh from me. As rEFInd's maintainer I see lots of queries from Mac users with bizarre and system-specific problems, using computers that range from the first-generation Intel boxes to the very latest ones. Sadly, Apple's EFI rulebook is constantly being re-written.
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gabrielg
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PostPosted: Sun Nov 25, 2012 9:08 pm    Post subject: Reply with quote

srs5694 wrote:
gabrielg wrote:
Two things that I thought peculiar while going through this process:
1. On rEFIt's shell, a FAT16 or 32 partition would be inaccessible.


That's extremely strange. The only thought I have, offhand, is that the filesystem may have been damaged, or perhaps it was created using a tool that set things up strangely so that the firmware couldn't read it.

Well... I used Gentoo's mkfs.vfat and Fedora's to try. I'm thinking that at some point I tried to run grub2-install but it didn't have the right 32bit EFI files. Maybe that broke something. Having said that, I tried several times to just boot whatever comes with the Fedora Live CD which boots EFI perfectly.

Quote:
FWIW, I've got a first-generation Intel Mac Mini, which has a 32-bit EFI and a 32-bit CPU. I use a FAT32 ESP and have rEFInd installed on it, and this all works well, although the Linux kernel hangs when loaded from a FAT partition on this system.

Yeap, have one of those too, tried to install Gentoo but something is broken with the HW (the laptop was completely replaced by the "geniuses", except for the screen). One day I'll try replacing the RAM and give it another go - it should be simpler as everything is 32 bits.

Quote:
Quote:
Ah, well, this is an old model anyway, hopefully the newer ones are better standardised and people shouldn't be bumping into these issues.


This provoked an almost hysterical (but short) laugh from me. As rEFInd's maintainer I see lots of queries from Mac users with bizarre and system-specific problems, using computers that range from the first-generation Intel boxes to the very latest ones. Sadly, Apple's EFI rulebook is constantly being re-written.

:-) There was a little bit of sarcasm in my comment to be honest for the ones who know, and a little bit of hope for the rest, glad it made you laugh at least.
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