Christopher Friedt writes:
Just in case anyone wants to use UNetbootin to create e.g. an Ubuntu Live USB device and it isn’t working, there are two key steps that are not performed by the UNetbootin binary for OS X.
After downloading the ISO, use Disk Utility to partition your USB device. Ensure that you’ve selected Options -> MBR . After formatting the disk…
1) Ensure that you’ve marked the partition active
fdisk -e /dev/rdisk1
2) Download syslinux and write the critical mbr binary your device.
dd conv=notrunc bs=440 count=1 if=mbr.bin of=/dev/rdisk1
After that, just use UNetbootin as usual.
I got away with just doing the fdisk to activate the partition, otherwise it just comes up with “Missing Operating System“.
This worked for BackTrack5 r3.