Two EFI Boot images showing up

Question

I made a Bootable usb stick with linux mint using terminal with the dd command. When I boot my mac and hold the alt key I see my Macintosh HD and I see two times an EFI Boot. Can it be I did something wrong? Or can I just pick one?

Answer 1

Several possibilities occur to me:

• A Mint disk made in the way you describe should be bootable in both BIOS/CSM/legacy mode and in EFI mode. Despite the fact that both those options are labeled "EFI Boot," it could be one is for each mode, and one is simply mis-labeled.
• The Mint .iso image file format is a Frankenstein's Monster sort of thing, and may be confusing the Mac's firmware, thus causing it to show two duplicate entries.
• It could be that one of those entries refers to something other than the USB drive -- for instance, there might be a boot loader on your hard disk's EFI System Partition (ESP) that's being detected.
• There could be a bug in the Mac's firmware that's causing it to display two entries.

I recommend you simply try one entry, but instead of selecting the option to install Mint immediately, pick the one to try Mint without installing. (This assumes that Mint's options mirror those of Ubuntu; they may be different.) When you boot up, open a Terminal window and use ls to look for a directory called /sys/firmware/efi. If it's present, you've booted in EFI mode; if it's absent, you've booted in BIOS/CSM/legacy mode. If you've booted in EFI mode, proceed with the install; but if you've booted in BIOS mode, reboot and try the other option.

Of course, some of the possible causes could result in a failed boot, so if that happens, you should reboot and try again with the other option. A failed boot is very unlikely to cause any serious and permanent damage to your existing OS X installation. Such damage can occur because of bugs or mistakes unrelated to this issue, though, so you should back up your entire hard disk, or at least your important personal data, before proceeding.

Answer 2

Had the same issue with Ubuntu 18.10 on an iMac.

I tried the left one. It froze. Power cycled. Tried the right one. It worked.

FYI.