First download your desired .img / iso file to be written on the drive.
Open a Terminal (under Utilities)
Run the following command to get the current list of devices
- diskutil list
Insert your flash media
Run the diskutil list again and determine the device node assigned to your flash media (e.g. /dev/disk2)
Run (diskN is to be replaced with your device node name)
- diskutil unmountDisk /dev/diskN
- sudo dd if=/path/to/downloaded.img of=/dev/diskN bs=1m
- diskutil eject /dev/diskN
and remove your flash media when the command completes.