In may day job, we have some 20 old iMac G5 standing around. Those are no longer supported by Apple and the newest Version of Mac OS X that runs on them is so old, that it is so fun anymore. To revive these things (actually to setup a wisebed) we had to install any kind of Linux on it. Turns out, that Debian Linux will run on almost everything including those iMacs. You will need a USB stick to hold the Debian net installer, a USB keyboard and Internet connectivity to download to packages.
1. Download the Debian CD
2. Put the iso onto the USB stick
People recommend to use UNetbooin for this. I have never tried it though.
I always use dd, but one has to be very careful:
dd if=debian-testing-powerpc-netinst.iso | pv | dd of=/dev/rdisk1 bs=1m # check, if your stick is mounted to /dev/disk1
3. Connect the stick to the first (the highest) USB port on the iMac
4. Boot the Mac into the open firmware prompt
Turn the Mac off. Now press and hold command-option-O-F and turn the Mac on. Keep pressing the keys (all at once!) until you end up in the open firmware prompt.
5. Boot from the USB stick
In the Prompt type:
6. Complete the Debian setup
If your Mac has an open firmware password that you do not remember, resetting it is “easy”: