I see this issue reported a lot but all the accepted solutions have not worked for me.
I have created a bootable USB stick using UNetbootin with a Debian image. The USB stick is FAT32 formatted with a GUID partition table.
When I reboot with the usb stick plugged in and hold down option I'm only presented with the MacOS hard drive to boot from.
I've successfully reset the PRAM using option+cmd+p+r keys but this has had no effect.
I've not found any other suggested solutions to the problem. What am I doing wrong?
Best Answer
If you have succesfully made a bootable linux USB stck before with your method, try a different USB stick or image. It sounds like you have done this before, which suggests perhaps that the image is not right in some way.
A GUID partition table and FAT format are correct.
Other things to try:
1. Try Etcher: It's simple and free. You can find a tutorial from Ubuntu regarding making a bootable Ubuntu drive with it, but all it really says is "use Etcher."
2. Try Mac Linux USB Loader. It costs ~ $5, and while it only supports certain OSes, Ubuntu is one, so Debian probably works.
3. Try dd - note it is /dev/diskx not /dev/diskxs3 (partition 3 or other on disk x). Another tutorial also has you convert the image; I haven't used that method but it seems to work for people:
I like to know what dd's progress is, so I use pv, which you can get using Homebrew or Macports:
You'll probably have to put sudo before each dd command.
I hope that helps - you'll definitely get something to work eventually, whether it's the image, method, or USB stick.