How to: Install OS X Leopard on a PPC Mac using an external USB device

iMac G5 Rebuilding

I recently got hold of a iMac G5 (PPC) that was heading for the recycling centre. I thought I’d have a go at restoring it.

Internet recovery or even local recovery wasn’t a thing until we got to Lion. Optical media was the way of the world when this bad boy was in service.

I didn’t have a Dual Layer DVD so, instead, I needed to install from a USB pen drive (8Gb or larger required). Again, with Snow Leopard and later OS X Operating Systems, it was relatively simple to make a bootable USB pen drive and install from it. Not the case with Leopard.

I had an image of the Leopard installation media in a DMG file. Despite using SuperDuper! and the standard Disk Utility Restore feature to try to make a bootable USB stick, the iMac wasn’t interested in seeing my USB device as bootable media when I powered up holding down the option key.

I spent some quality time with Google before managing to get the Operating System to re-install. Given all the hassle I had, I felt it worth sharing here:

1. Make sure your installation media (in my case the Mac OS X Install DVD 10.5.dmg file) is readily available on another Mac.

2. Connect your external drive to the Mac containing your source files and launch Disk Utility.

3. Select the drive in Disk Utility and then select the Partition tab. Make sure that the drive is formatted using an Apple Partition Map scheme, not GUID or MBR (you may need to reformat your drive to get it in this form).

4. Highlight the newly formatted drive within Disk Utility and select the Restore option under the Edit menu

5. Browse to your source DMG file

6. Click on restore. This may take a while to complete.

7. Determine the partition where your bootable image it situated. This might be disk1s3 in which case the partition number is 3. Also you can check it on Disk Utility, select the drive click the Info button and write down the ‘Partition Number.’

8. Eject the USB drive safely from your Mac and pop it into the iMac

9. Restart your iMac while holding down Command+Option+O+F. This will place you in Open Firmware.

10. Type dev / ls to get the device tree list.

Look for something in the output like:


As we’re talking about a tree here, write down the complete path to this node. In my case it would be:


11. Type devalias ud /ht/pci@2/usb@b,1/disk@1. In other words: make ‘ud’ equal to the path you found in step 10.

12. Now verify you got the right disk:

dir ud:3,\ 

(3 is the partition number you wrote down in step 7). And look for a file with tbxi attribute, probably in:

\System\Library\CoreServices\BootX, e.g.:

dir ud:3,\System\Library\CoreServices

13. Then boot from it:

boot ud:3,\System\Library\CoreServices\BootX


14. Wait a little bit – while the iMac restarts and if you see the Leopard Installer begin, you’re done.

Source materials that got me started are here


Photo credit for cover image: Matthew Pearce (Flickr) Creative Commons