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Can I use openfirmware to boot without yaboot?
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Travis86
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PostPosted: Mon Mar 07, 2011 7:18 pm    Post subject: Can I use openfirmware to boot without yaboot? Reply with quote

I'm (planning on) installing Gentoo on my G5, but I don't want to change the default OS X setup in any way. In particular, I don't want to replace the Apple bootloader with yaboot. Is there a way to use openfirmware to boot a partition? (I know this will be a lot more work every time I start up.)

Thanks.
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JoseJX
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PostPosted: Mon Mar 14, 2011 4:15 am    Post subject: Reply with quote

There's absolutely no need. Installing yaboot does *not* change the "Apple Bootloader". So then, what happens when an Apple PowerPC machine boots?

More or less, Open Firmware looks for a "blessed" HFS or HFS+ partition, in order on the disk. When it finds a valid one, it starts executing the open firmware boot instructions (yaboot uses ofboot.b which is a script which loads the correct binary and displays the penguin icon when selecting the boot device).

As long as you don't change your OSX drive, there is nothing to worry about since there isn't a real "boot loader" like on x86. If you press and hold "option" on boot, it will show you the available drives to boot from. So, feel free to add a Linux partition / boot partition / etc. As long as you don't change the OSX partition, there's nothing you can do to damage it or prevent booting.
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Travis86
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PostPosted: Wed Mar 16, 2011 1:43 am    Post subject: Reply with quote

Yaboot is not a normal bootloader? So the Apple bootloader calls yaboot, which calls the Linux bootloader? I guess that's one way to do it, but that wasn't what I thought yaboot did. So, I don't have anything to worry about, then.

But, that aside, I sort of got it to work "my way". While researching the nature of yaboot, I found a hint in the PPC64 FAQ that I thought might help. Here's what I did:

First, I copied the PPC64 Live CD to the third partition on my second hard drive, just to see if I could get anything running.

Then I changed the first line of /boot/yaboot.conf from:
Code:
device=cd:

- to -
Code:
device=/ht@0,f2000000/pci@5/k2-sata-root@c/k2-sata@1/disk@0:

(Which is the Open Firmware path to that disk.)

Then booting into Open Firmware, I ran:
Code:
devalias hd /ht@0,f2000000/pci@5/k2-sata-root@c/k2-sata@1/disk@0
boot hd:3,\boot\yaboot


And, it almost booted. Eventually, Linux got to some "Media not found" errors and couldn't boot further. Yaboot scolded me for the partition type not being Apple_Bootstrap, but other than that, it worked fine.

I'm sure there's a reason the partition needs to be Apple_Bootstrap, but it appears to work without it....
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JoseJX
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PostPosted: Thu Mar 17, 2011 5:10 am    Post subject: Reply with quote

As I said above, if you want Open Firmware to recognize the partition as bootable, you need a blessed HFS partition (the bootstrap). It will boot without it, but you'll need to type in the Open Firmware commands every time.
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