Re: Why it's so difficult to fix PowerMac booting for good
Hello Ben,
On 5/30/23 7:16 AM, Ben Westover wrote:
> Hello,
>
> On May 30, 2023 6:45:03 AM EDT, Linux User #330250 <linuxuser330250@gmx.net> wrote:
>>> The last time I installed Debian SID with GRUB on a PowerBook Pismo, the
>>> Apple_Bootstrap partition was mounted as /boot/grub (it might have been
>>> /boot, I don't remember now). But it was a persistent mount. Everything
>>> worked, except Mac OS and Mac OS X volumes could not be boot from the
>>> menu (booting Mac OS X also doesn't work on an Intel Core 2 Duo system).
>>
>> Actually, I was able to boot Mac OS X from GRUB. But if I remember
>> correctly, I had to play with it a bit as it isn't intuitive...
>> os-prober might be helpful as a starting point.
>
> The GRUB Manual [1] says that the PPC port of GRUB only supports booting Linux at the moment. AFAIK booting macOS with GRUB on x86 machines works by just chainloading macOS' UEFI bootloader. I assume this is what yaboot does as well, telling Open Firmware to load OS X's blessed binary instead of the second stage of yaboot and Linux from there. All we need to do is find a way to support Open Firmware chainloading from within GRUB.
>
Thanks for the information. GRUB chainloading support works for x86 (to
boot Windows and NetBSD). Despite considerable effort, I've never been
able to get chainloading to work on New World PowerMacs (consistent with
the link you sent). Surprisingly, I also couldn't get Mac OS X booting
to work on x86_64 (e.g. Intel Core 2 Duo MacBook) systems. To undo the
automatic updating of GRUB during Debian "apt-upgrade" and "apt
dist-upgrade", I have a working grub.cfg files on x86 (e.g. i686) and
x86_64 systems that don't need to run Mac OS X -- for such systems, I
can simply copy my known-good grub.cfg.save to grub.cfg and re-run "grub
install /dev/sda" (for x86) or just "grub-install" for EFI-based x86_64
systems that don't need to run Mac OS X. Even if holding the option key
at boot works on all Macs, I consider that a fallback and don't
necessarily want to be at the system console to pick an OS. An expert
knowledgeable in both GRUB and yaboot could probably figure out how to
get GRUB to do what yaboot has done for decades.
I only bring these points up whenever anyone goes on about how easy it
is to get GRUB working on New World PowerMacs. GRUB will never be an
acceptable replacement for some yaboot users as long as booting Mac OS
isn't supported (os-picker via holding the option key at boot isn't
sufficient). If you don't need to boot Mac OS and GRUB already does
everything you need, you should of course choose GRUB for a new
installation instead of the no-longer-maintained yaboot.
I'll test a new installation of the latest Debian SID (with GRUB) on a
PowerBook Pismo with an unformatted disk and send an update in a
different thread (I specifically want to test whether the partition that
holds the real grub.cfg is normally hidden).
-Stan
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