Boot iMac G5 from USB

Like with all the other PPC Macintoshes, actually yes, you can boot from USB on the iMac G5. Here it is the procedure:

1. prepare a USB key with the netinstall image using dd

2. hold Command + Option + O + F while booting until you get the OpenFirmware command line

3. type the following command boot usb<N>/disk@<n>:,\<path-to-bootloader>

Replace with the USB port number you are using. On the iMac G5 they go from 0 (top) to 2 (bottom).

Replace with the disk number assigned. This is usually 0 or 1.

Replace with the full path to the grub bootloader.

In practice, assuming that you have the USB key in the top USB port.

boot usb0/disk@1:,\boot\grub\powerpc.elf

How do you find this yourself? Using dev / ls you get the hardware layout (device tree). In there you will see a node under a PCI endpoint named disk@<n>. Remember type devalias, and you will see that a usb<N> name is mapped to the PCI endpoint you found before.