Find Block Device
Plug-in your USB stick and find what "/dev/diskN" it is mapped to by opening Terminal (where "N" stands for "disk0", "disk1", "disk2" etc). To do so, please execute:
This will print out the list of currently mapped devices/partitions. Find the USB using "NAME" column. Then note the corresponding /dev/diskN, where "N" is for index of your disk. For example:
/dev/disk2 #: TYPE NAME SIZE IDENTIFIER 0: FAT32 2.0 GB disk0 1: USB2 2.0 GB disk0s1 In this case "/dev/disk2" is the one we want.
Unmount USB Stick
#diskutil unmountDisk /dev/diskN
Where /dev/diskN is the one you have found in previous step as per our example it would be "/dev/disk2".
Write ISO to USB
# sudo dd if=/path/to/downloaded.iso of=/dev/rdiskN bs=4k
/dev/rdiskN is the same disk you have found previously, with an r in front. r is for raw disk, as writing to /dev/rdisk2 is much faster than writing to /dev/disk2. You will be prompted for the administrator's password.