I know this question has been answered earlier, but none of the answers were clear enough for a newbie in Ubuntu. So the problem is I have installed Ubuntu on a flash drive, using another flash drive, containing Ubuntu live installation. I am able to boot this flash from a Windows based pc, but when I insert the flash to my MacBook Air and restart while holding down option key I only get to choose to boot into Macintosh HD or Windows (on bootcamp) how do I make my Ubuntu USB drive visible in the boot options? Please help :)
The problem is that apple has a proprietary boot manager. When you installed to your USB drive, Ubuntu tried to make some changers to the boot manager, which Apple happily ignored.
Here's what you need to do:
Boot into OSX. If you are working with an apple machine, DO NOT run this in anything but OSX.
Decompress it, navigate to the directory and run
reboot osx, with your USB install of ubuntu plugged in.
You should now see a slightly less slick looking bootup screen, and an option to boot into Ubuntu. If this doesn't work the first time, try booting one or two more times until it does.
It's remarkable how simple this is... and how hard that information was to find. I hope that this helps!