I have an old iBook (2003, G4) with a burnt-out harddrive. Being a poor academic, I don't want to bother with replacing the drive. I'd like to use an external USB drive in place of the harddrive. I managed to get a copy of MacOSX (it was Tiger at the time of the burnout) onto a USB before the harddrive completely gave out (it seemed to be a problem with overheating so I took it into the coldest part of the house and copied it there). But all my experiments in the open firmware came to naught: it seems that my iBook is too old to be able to boot directly from a USB.
Under Linux, this is not a problem. I can put the kernel and boot stuff onto a CD. The iBook will happily boot from a CD. Then I can tell the kernel to find its root device from the USB stick (via a UUID). This works well, and is my current system.
But I miss Mac OSX ... a little. More so now that I have an iPad and don't want to have to use Windows to sync stuff with it. Plus, I hate the fact that I got so close and yet couldn't quite get it to work.
So ... is it possible to specify a different root device to a MacOSX kernel than the device it is booted from?