Forcing PowerPC iMac to boot from USB

Submitted by Darren Oh on Mon, 04/30/2018 - 08:47

Yesterday, a friend brought me a second-hand iMac G5 that he could not get the password for. He wanted to erase and reinstall the operating system. We had ordered a Leopard install disk, but the iMac kept ejecting it. I copied the install disk to a USB flash drive, but it did not appear in the list of startup disks. The instructions on the page Boot a PowerPC Apple from USB provided a workaround:

  1. Create a bootable USB flash drive. Use Disk Utility to create an APM, not GUID or MBR, partition. If Disk Utility does not allow you to partition the flash drive, go to the View menu and choose Show All Devices. You have to erase the flash drive itself, not the volume it contains.
    Disk Utility screen shot showing the flash drive selected rather than the volume that it contains
    The flash drive is selected in the side bar.
  2. Make note of the partition containing the installation volume. In my case it was disk2s3. The number at the end of the device name is the partition number (3 in this case).
    Disk Utility screen shot showing the installation partition on the USB flash drive
    The device name in the lower right of the table identifies the partition.
  3. Restart iMac while holding the Command-Option-O-F key combination to enter Open Firmware.
  4. Type
    dev / ls
    to get the list of devices. Find the path to the USB drive. In my case, it was
    /ht/pci@2/usb@b/disk@2
    I was able to verify the path with the following command:
    dev /ht/pci@2/usb@b/disk@2 ls
  5. Create a device alias for the USB drive, using the path from step 4:
    devalias ud /ht/pci@2/usb@b/disk@2
  6. Verify that the installation partition on the USB drive contains the BootX file (ud is the device alias from step 5, 3 is the partition number from step 2):
    dir ud:3,\System\Library\CoreServices
  7. Boot from the USB drive:
    boot ud:3,\System\Library\CoreServices\BootX

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