The hardware used, as already said, is a MacBook Pro 3,1 and a Western Digital My Passport Essential 500GB USB hard disk. Other combination may work, but I don't guarantee this, as always. Also you should be warned that anything I describe here could destroy your existing installation and I'm not responsible for that. Doing some kind of backup might be a good idea. Time Machine is easy to use .

Before we start, as usual, the credits for some sites I get my information from. This is mainly the Produnis blog, the Blog of Chris, the Ubuntu wiki and of course the guys around the Grub2 development.

Creating the EFI boot loader

Apple doesn't use the legacy BIOS to boot their machines, they use the Extensible Firmware Interface (EFI). This new way of booting operation systems is very flexible, as the name suggest, but has several drawbacks, like most of the standard operation system doesn't speaks it language. Although Linux can be configured to use EFI directly we will emulate a legacy BIOS in the following. For this we need a connector which makes EFI and Linux happy and let them both work smoothly together. This connector is Grub2, which is in development for several years now. It's the successor of Grub and is the standard in many popular Linux distributions these days. We have to build a version our self, for which an existing Linux installation is really helpful. I used my 64-bit Gentoo installation. First you have to find out if the EFI installation on your target Apple machine is 64 or 32-bit. You can do this by executing:

ioreg -l -p IODeviceTree | grep firmware-abi

This will return EFI64 or EFI32 respectively. In my case I need the 64-bit version, which is a little bit surprising when I consider that my MacBook Pro isn't able to boot a 64-bit Snow Leopard. Anyway, grab the latest version of Grub2 and unpack it on the Linux machine. Please note that you need a gcc with multilib support if you are targeting an architecture which isn't the same as the host one. Use the following to configure Grub2 and to build it. Of course you have to adjust the target architecture if it is a different one.

./configure --with-platform=efi --target=x86_64 --disable-werror
make

When this is finished you create the EFI package by executing

./grub-mkimage -d . -o bootx86.efi *.mod

Here I included all modules which are available. If size matter for you, you could of course make a selective choice on the modules included. I didn't test this myself, so you have to find out yourself which one are important.

Whipping the USB hard disk into shape

Next we have to prepare the USB hard disk for the new installation. In the following I assume your USB hard disk doesn't contain any valid data and could be reformatted without data lose. Make a backup of your data first if this isn't the case on your side. Apple uses the GUID Partition Table scheme to organize their partitions on a hard disk. This specification is part of EFI and remove many limitations of the Master boot record (MBR) scheme, which is widely used in the PC world. That is e.g. the disk size limitation of 2TB or the maximum of 4 primary partitions. You reformat your disk, using the Disk Utility application of Mac OS X. Make sure all existing partitions on the disk are unmounted. When necessary, change the partition scheme from MBR to GUID in the Options dialog of the Partitions window. Select the partitions count you want to use. You need at least 3 partitions to make Linux works fine. My partition scheme looks like in the following: As you can see I have 5 partitions configured. The first one is an additional Snow Leopard installation for testing. I also added a Data partition at the end for making the data transfer between the different operation systems as easy as possibly. LINUXBOOT is a small partition which will contain the EFI boot loader (size it 50MB or something like that). Linux Swap, obviously, will become the swap partition of the Linux installation. DISK1S5 is the Linux root partition itself. The Data partition has to be formated as Mac OS Extended. Don't use the Journaled version of HFS+, cause this makes trouble on the Linux side. The other partitions have to be formatted as MS-DOS (FAT).

After applying the changes we can add the EFI boot loader to the LINUXBOOT partition. The Apple EFI implementation is searching for a file with the efi extensions on all bootable hard disks. Mount LINUXBOOT and create a efi/boot directory on the root path. Copy the bootx86.efi file into the boot/ directory. As bootx86.efi is a Grub2 boot loader we need a valid Grub2 configuration file. The following grub.cfg shows the configuration for a Ubuntu 9.10 i386 installation. For the 64-bit version or any other version of Ubuntu the settings might be slightly different.

menuviewer="text"
timeout=10
default=0
set F1=ctrl-x
menuentry "ubuntu-9.10-desktop-i386"
{
 fakebios
 search --set -f /boot/vmlinuz-2.6.31-14-generic
 linux /boot/vmlinuz-2.6.31-14-generic root=UUID=4e140981-4ab3-41a2-a2fb-26b1287beb87 ro quiet splash noefi video=efifb
 initrd /boot/initrd.img-2.6.31-14-generic
}
menuentry "ubuntu-9.10-desktop-i386 single"
{
 fakebios
 search --set -f /boot/vmlinuz-2.6.31-14-generic
 linux /boot/vmlinuz-2.6.31-14-generic root=UUID=4e140981-4ab3-41a2-a2fb-26b1287beb87 ro noefi video=efifb single
 initrd /boot/initrd.img-2.6.31-14-generic
}
menuentry "ubuntu-9.10-desktop-i386 text"
{
 fakebios
 search --set -f /boot/vmlinuz-2.6.31-14-generic
 linux /boot/vmlinuz-2.6.31-14-generic root=UUID=4e140981-4ab3-41a2-a2fb-26b1287beb87 ro noefi vga=normal
 initrd /boot/initrd.img-2.6.31-14-generic
}
menuentry "Mac OS X"
{
 search --set -f /usr/standalone/i386/boot.efi
 chainloader /usr/standalone/i386/boot.efi
}
menuentry "CD"
{
 appleloader CD
}
menuentry "mbr"
{
 appleloader HD
}
menuentry "reboot"
{
 reboot
}

You have to change the root UUID to the one the Ubuntu installer will assign to your hard disk after installation. Just check the fstab file when the installation has finished. The first entry boots Linux with a splash image enabled. The second one is for the single user mode in the case something went wrong. Please note the video=efifb option, which enables the graphical mode in the boot phase.

Installing Ubuntu

Most of the installation process is straight forward and doesn't need any special attention. Download the version of your choice from one of the mirrors, burn it on CD and start the installation. You can select the CD as boot medium by pressing Alt when your Mac starts. When the installer ask for the partition scheme, you have to switch to "manual choice". Select the DISK1S5 (your what it is in your case) as the root / partition and change the filesystem type to ext3. Also remember the path to the system partition, cause you will need it later again. Select the swap partition and change its type to swap. Proceed with the rest of the installation until the last dialog. There select "advanced settings" and change the boot loader target from hd0 to /dev/sdXX, where you replace XX to the path you used previously in the partition tool.

If all went right you should be able to select the LINUXBOOT partition by pressing Alt when your Mac starts. After that Grub2 should shows up, you will be able to boot into your freshly installed Ubuntu.

Conclusion

In this post I showed how to easily add the possibility to boot Linux on your MacBook Pro. With the external USB hard disk solution, no internal valuable space is wasted. Of course the speed isn't the same as if the OS would be installed on the internal drive, but for testing software on different operation systems this is satisfactory. To increase the speed a little bit more, an external FireWire hard disk could be used.