I'm trying to use a Ubuntu 16.04.3 i386 try/install stick I created on a 2017 iMac. It boots fine on a 2012 Macbook Pro and the USB stick shows up as "Windows". It was created on the 2012 using etcher and setup GUID/FAT. When holding the option key on the iMac 2017, the only option I have is the internal hard drive. If I boot into the MacOS, it see the USB stick as connected but wants to format it because it doesn't recognize the format. How do I get the install stick to boot? Should I use an 64bit disc image instead of i386? Your help is appreciated!
Here is how I managed to boot Ubuntu 18.04 from usb stick on an imac 2017 21,5" (macOS 10.12 Sierra):
I downloaded Ubuntu 18.04 64bit (iso file) and put it to the usb stick from a Debian Stretch computer using the command:
sudo dd bs=4M status=progress if=/home/[username]/Desktop/ubuntu-18.04.1-desktop-amd64.iso of=/dev/sdx conv=fdatasync
[username] with your current username.
/dev/sdx with the appropriate drive letter of your USB stick (find it out using the command
Plug your USB stick in your imac 2017. The imac must be shut down (no power).
Plug a wired keyboard in one of the USB ports of your imac.
Hit the ALT key and hold it as you are powering the imac on and until the EFI boot manager shows two big drive icons:
- Macintosh HDD
- EFI Boot
Click on EFI Boot and then on the up arrow that has appeared as you clicked on the drive icon EFI Boot.
Wait several seconds, maybe about 30 seconds or a little more.
Ubuntu 18.04 should boot from USB stick.
For your information: my imac was completely unmodified as I did this.