The following instructions are intended as a step-by-step guide to configuring Ubuntu/OSX/MorphOS triple-boot using yaboot on the mac-mini.
It should be applicable to triple-booting on any NewWorld Mac, but has only been tested on Mac-mini so far.

Apologies if this seems a bit disorganised, I was writing in response to a PM and thought it would probably be more useful here.

The timbre and flow of the prose could use some work - it's not quite iambic pentameter. Who knows, eventually I may tidy it up and post it to the library.

START

For the installation of MorphOS & MacOSX, follow Jacadcap's guide, but with the following modifications:

When setting up MorphOS, create an additional small HFS partition at the beginning of the disk (This will be used for the Ubuntu bootloader) - around 32MB will do.
You cannot use the same partition for both the MorphOS bootloader and the Ubuntu bootloader.
You will also need to leave space on the disk (anywhere on the disk) for 1) your ext2 (Ubuntu) partition and 2) a swap area for Ubuntu.

Whilst Ext3/4 can be used for the Ubuntu partition, I used ext2 purely because it could be accessed by MorphOS and used for exchanging files between the OSes.

You don't need to create your Ubuntu/Swap/Boot partitions at this stage, just leave enough space for later - the Ubuntu installer will allow you to create these partitions correctly.
(For guidance, the ext2 Ubuntu partition took up around 10GB space on my drive after a clean installation, I left around 5GB for swap.)

/End of modifications to Jacadcap's guide

Download and burn-to-disk Ubuntu for PPC.
Begin booting the 'live' installation from the disk (this can be selected from the boot menu by holding 'ATL' when booting).
When booted, double-click the 'install' icon on the desktop, and follow the instructions until you are prompted to choose the installation destination.

I recommend using the 'manual' partitioning method as I was not sure if the 'boot side-by-side' option would pick-up on the MorphOS installation. The following instructions assume you have done the same. (NB, I have not tried the 'boot side-by-side' option - it may work, it may not)

Mount your ext2 area as '/' (not '/etc' or '/usr'). Designate your Newworldboot partition and swap partitions (create partitions now if required).

Follow the instructions to install Ubuntu, and reboot into Ubuntu when prompted (you may have to hold 'alt' upon reboot and select it from the list).

At this point, check the partition numbers using the disk utility (available in Ubuntu's menu): on my installation, 32kb of free space at the start of the disk was 'recognised' as a partition, and my first 'real' partition became hda2. You have been warned.

To configure yaboot, open a terminal window and type 'sudo gedit /etc/yaboot.conf'. This will bring up a text editor which allows you to modify the bootloader config file.

Most of the script can be ignored (although type 'yaboot.conf man' into a terminal if you want to know the details)

Add/modify the following lines:
delay=# (where # is the delay time (in seconds) from the menu appearing to autobooting).
enableofboot (enables booting to openfirmware prompt from yaboot menu)
enablecdboot (enables CD booting option in yaboot menu)
macos=/dev/hda# (where # is the number of the partition containing the MorphOS boot.img)
macosx=/dev/hda# (where # is the number of the partition containing MacOSX)

Don't worry, we'll hack something later so that it displays MorphOS (not MacOS) in the menu

Save the file and close gedit.

At a terminal type 'sudo ybin --nonvram -v'

(The '--nonvram' option prevents ybin from messing with openfirmware's variables (I prefer to do this manually), the -v switch puts the output into verbose mode (just for confirmation everything went ok)).

Once this has run, reboot holding down 'Command + Option + O + F' to get to the openfirmware prompt.

Type 'printenv' at the prompt. This will display your current environment variables.

Type 'setenv boot-command boot hd#,//:tbxi' (where # is the NewWorld boot partition) - you can ignore the 'boot-device' line, it is overridden by the 'boot-command' line. (The tbxi tells openfirmware to look for a 'blessed' file. As there can only be one 'blessed' file per partition, the filename does not need to be specified. This is also the reason why MorphOS and Ubuntu bootloaders require separate partitions.)

Reboot into MorphOS (either from yaboot, or by holding 'alt' whilst rebooting).

Mount your NewWorld boot partition (using tools/mounter, if it has not been automatically mounted).
Using your favourite text editor, edit the following lines of <drive>/ofboot.b (where <drive> is the name of your mounted NewWorld boot partition)

(Around line 10)
: boot macos "Booting MacOS..." etc...
change to
: boot macos "Booting MorphOS..." etc...

(Around line 34)
" m for MacOS," etc
change to
" m for MorphOS," etc

Save and exit.

Open a CLI

Type 'hfssetmacboot <drive>:ofboot.b' (where <drive> is the name of your mounted NewWorld boot partition). This 'blesses' the file to allow openfirmware to identify that it is bootable.

All done.
Upon reboot, the menu should load automatically, and should offer you MorphOS, Mac OSX, Ubuntu, CD boot and Openfirmware boot.

Now, that wasn't so hard was it?

[ Edited by boot_wb on 2010/8/26 14:11 ]