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Background

I've successfully installed Ubuntu 64bit 14.04.03 Desktop on my old White Core 2 Duo iMac

  • Linux is a second OS, with OS X 10.7.5 still in place and usable.

  • The only install recipe I found to work was amd64+mac option from an external CD drive - internal is broken, USB didn't work

  • "Try Ubuntu" from Live CD works fine

  • refind 0.10.2

  • I selected install grub to the specific partition during installation

Problem

Refind boot menu with a Linux boot option shown. However selecting it causes a black screen for 10 seconds approx and then rapid flashing white cursor in top left hand corner, caps lock unresponsive, CTRL-alt-Delete has no effect

Things I've tried

  • using live CD to adjust default grub linux params to include nomodeset noapic acpi=off
  • complete power off instead of reboot
  • searching google for many hours
  • holding down option key during boot - only existing OS X + recovery are shown
  • putting the nomodeset noapic acpi=off options in the refind boot parameters via the F2 editor

Conclusions

  • My older iMac will only boot Linux in Legacy aka BIOS mode. This is how the live CD works, I checked /sys/firmware/efi and its not present
  • I don't believe Refind is even trying to do a legacy boot, it is using a EFI boot
  • There is this thing called hybrid MBR which the author of Refind hates with a passion, however this might be the only way forward

Questions

  • Is it possible to force legacy BIOS boot from refind?
  • Do I even need grub? Does Refind bypass this and boot the kernel itself?
  • will I have to resort to this hybrid MBR thing?
  • Is it possible to put refind into some kind of debug mode so I can see exactly what is happening, whether Ubuntu is even starting?
  • Should I even need Refind - is it possible to get partition to show up in Boot+Hold option key startup?
Adam
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  • Does this answer help you understand what's actually going wrong in Ubuntu (but not Fedora)? Another related answer I wrote in case you just want to boot any Ubuntu installation on an older Mac (probably as a workaround): Add a partition for Macs on an installation with GPT I cannot say that Rod hates things with a passion, he is helping users and explaining their problems one by one, were I would have given up and others opt for a one size fits (not) all solution. – LiveWireBT Jan 29 '16 at 07:25

1 Answers1

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AFAIK, Macs will not boot in BIOS/CSM/legacy mode from legal GPT disks; they require an MBR or hybrid MBR to boot in BIOS mode. rEFInd, though, doesn't check for this detail; it tries to start a BIOS-mode boot when asked to do so, even if the disk uses GPT. From your description, I suspect that this is what's happening. Thus, if you've got a BIOS-mode installation on a GPT disk, it won't work; you must create a hybrid MBR. Note that rEFInd will only attempt an EFI-mode boot if it detects an EFI-mode boot loader, which it sounds like you have not installed. Thus, rEFInd is almost certainly not attempting an EFI-mode boot of Ubuntu.

BTW, I'm the author of GPT fdisk and maintainer of rEFInd. Hybrid MBRs are dangerous things -- I've answered far too many questions from people who've wiped out their disks because of hybrid MBRs. Unfortunately, Apple designed its firmware to use them as a "key" to unlock BIOS-mode booting, so you're pretty much stuck with them if that's what you need.

Backing up a bit, most Macs will boot Linux in EFI mode just fine. Given your description, though, you may have a 32-bit EFI. You can check this in rEFInd by reading the About/Info page; it should identify your firmware as being 32-bit or 64-bit (check the Platform: line). If you have a 32-bit EFI, you must use a 32-bit boot loader to boot Linux in EFI mode. This is difficult to do for various reasons -- the installers for 32-bit versions of Ubuntu can't be booted in EFI mode, and the installers for 64-bit versions of Ubuntu come with nothing but the 64-bit EFI boot loader. There are ways around this, but they involve significant hoop-jumping. See this question for more on this subject.

Rod Smith
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