So… if you’re looking at this post, it is because you’ve spent the last 2 hours pulling your hair out trying to figure out how to make your Mac’s EFI boot loader recognize a FULL linux install (not a “live” cd) on a USB drive. Something that used to be pretty painless to do for most systems, but the EFI component is driving you up a wall.
I just got done doing it, thanks to a pointer from a co-worker.
You need two items:
1) A thumb drive that you can put an EFI bootable OS onto (the fedora LIVE cd seems to do this automatically)
2) Your *actual* target USB drive
I was able to boot into the smaller thumb drive LIVE environment and then install onto my target USB drive. Doing so created the correct EFI components that allows MacOS to see the drive when you boot up and hold down the option key.
This was done with Fedora. I can’t speak to the other OSes and their LIVE cds.