Mac: Create Bootable SD from ISO

Using Ubuntu as an example: https://www.ubuntu.com/download downloaded to Downloads folder.

Download Ubuntu and Create img file

• Download iso:
  http://releases.ubuntu.com/16.04.2/ubuntu-16.04.2-desktop-amd64.iso
• Create img file in Terminal:
• cd Downloads
• hdiutil convert -format UDRW -o ubuntu-16.04.2-desktop-amd64.img ubuntu-16.04.2-desktop-amd64.iso
• Rename it (OSX puts dmg suffix on):
  mv ubuntu-16.04.2-desktop-amd64.img.dmg ubuntu-16.04.2-desktop-amd64.img

Create Bootable SD from img file

• Disk Utility: Erase the SD Card (not sub partition) select:
    Name: (Optional) e.g. UBUNTU
    Format: MS-DOS (FAT)
    Scheme: GUID Partition Map
• Unmount any partitions, but leave the drive itself mounted
• Terminal: cd to location of downloaded img
  cd Downloads (ls to check)
• List disks:
  sudo diskutil list
• Note identifier of SD card found by disk size e.g. disk3s2
• Unmount:
  sudo umount disk3 && sudo umount disk3s1 && sudo umount disk3s2
• Copy image across:
  sudo dd bs=4m if=ubuntu-16.04.2-desktop-amd64.img of=/dev/disk3
• WAIT: It could take around 20 minutes with little indication it's happening.

Now try your boot: Reboot and hold down Alt/Option key to select the boot disk.