+
++For scientific reasons I was recently forced to figure out how to install an +older OS X version on my iBook G4. +This is easy as long as you still know where your original installer DVD is, +but if like me you are stuck with only an .iso backup there are really +only two options: + +
+While it sounds trivial today, I spent almost a day on getting the Mac OS X +Leopard installer booting from USB on my newly acquired iBook G4. + +
+There are plenty of guides and Youtube videos describing the process but not +a single one of those fully worked for me. +Here is a summary of how I got it working in the hopes it helps future me or +anyone else who ended up here. + +
+Apple's OpenFirmware shipped on PowerMacs does in theory support USB booting but +it is incredibly picky when it comes to accepting USB disks and very fragile +in general. My first advice is: Don't give up too easily. If it doesn't work +right away, try a combination of different USB drives and ports. + +
+The best way to find out if a particular device is supported is to plug it in +while the device is turned off, then power it on and hold +Option + Command + O + F. +This should boot you into the Open Firmware shell. +From there, run: + +
+> probe-usb +> dev / ls ++ +
+to get a dump of the device topology. +If the USB disk was detected it should show up as a /disk node under +one of the USB port such as in: + +
+... + /usb@1a + /usb@1b + /usb@1b,1 + /disk@1 + /usb@1b,2 +... ++ +
+No /disk node means you may have to try rerunning probe-usb, try a +different USB drive or another port. + +
+Once we have found a working drive we have to format our it to be bootable +on Power Macs. +We can either do this using the graphical Disk Utility or on the command line +with +diskutil(8). +For the sake of simplicity I will only document the second, especially because +other than the GUI, the command line API has been pretty stable since at least +OS X 10.5. + +
+First, plug in your USB drive and find your disk ID using: + +
+% diskutil list +... +/dev/disk6 (external, physical): + #: TYPE NAME SIZE IDENTIFIER +... ++ +
+Make sure the disk is unmounted or the next step will fail. + +
+% diskutil unmountDisk disk6 ++ +
+You need to format the disk using the APM partition scheme with a HFS+ file +system partition to make it suitable for booting from Open Firmware. + +
+% diskutil partitionDisk disk6 APM HFS+ OSX 8G ++ +
+I created a 8GB partition since that was enough to fit my OS X 10.5 installer +image. + +
+Now that the USB drive is technically ready to boot you need to get our iso +on there. +macOS really wants the iso to be mounted before restoring it to another disk. +hdiutil(1) +can be used to mount the iso file from the command line: + +
+% hdiutil mount ~/OSX_10_5_LEOPARD.iso +/dev/disk7 Apple_partition_scheme +/dev/disk7s1 Apple_partition_map +/dev/disk7s2 Apple_Driver_ATAPI +/dev/disk7s3 Apple_HFS /Volumes/Mac OS X Install DVD ++ +
+Alternatively, double clicking the file in finder should also automatically +mount it. +Finally restore the Mac OS X Installer partition from the iso to your +USB disk using asr(8): + +
+# asr restore --source /dev/disk7s3 --target /dev/disk6s3 --erase ++ +
+Back to step one: make sure Open Firmware detects your USB drive using the +methods documented above. + +
+> probe-usb +> dev / ls ++ +
+Once the drive shows up you can enter the magical USB boot command. + +
+> boot usb$DEV/disk:$PART,\\:tbxi ++ +
+Where $DEV is the ID of the usb device (usually it is enough to just try +0 and 1) and $PART is the disk partition. +This is the same partition ID we used previously to restore the installer image +to disk. + +
+In my case the disk was /dev/disk6s3 so this would be 3 (which +also seems to be the default first actual partition when using APM). + +
+> probe-usb +> boot usb0/disk:3,\\:tbxi ++ +
+If everything goes well, you will be greeted with a grey apple logo screen for
+a while before the actual Mac OS X installer pops up.
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+PS: If anyone knows of a simpler way I would be happy to learn about it and update +this guide. + + + +