sudo diskutil unmountDisk /dev/diskN
Format the disk in Disk Utility, with the correct MBR Open Disk Utilty Select the USB device Click Partition Select 1 partition in the partition layout Select “Master Boot Record” in the options Select MS-DOS (FAT) in the format type. Click Apply, then Partition Close Disk Utility This will wipe the USB disk and set it up with the correct boot record Install the MBR binary from the SysLinux project Use the command line diskutil to find the device name for your USB drive. diskutil list Unmount the USB drive with the command line. NB: Be sure to swap the device reference (in my case it is /dev/SOMEdisk2) with the correct one for your usb key that you identified in the previous step – this will change for each machine. diskutil unmountDisk /dev/SOMEdisk2 Mark the partition active, then unmount it again sudo fdisk -e /dev/SOMEdisk2 print f 1 write print exit diskutil unmountDisk /dev/SOMEdisk2 Download Syslinux and extract the mbr.bin file Install the MBR sudo dd conv=notrunc bs=440 count=1 if=mbr.bin of=/dev/SOMEdisk2 NB: see my full instructions if you need further help with steps 4 & 5. Use UnetBootin to install your OS install files Download and install UnetBootin if you haven’t already Load the application, choose your preferred distribution, and then click OK When it’s finished, eject the USB key and use it