Plug in USB key and get device name:
$ df -h
Filesystem Size Used Avail Use% Mounted on
/dev/sda1 110G 34G 71G 33% /
udev 7.9G 4.0K 7.9G 1% /dev
tmpfs 1.6G 1.5M 1.6G 1% /run
none 5.0M 0 5.0M 0% /run/lock
none 7.9G 69M 7.8G 1% /run/shm
none 100M 28K 100M 1% /run/user
/dev/sdc1 2.4G 2.4G 0 100% /media/XXXXXXXXXXX
Run dd - BE CAREFUL!:
$ sudo dd if=/path/to/iso of=/dev/sdc
To monitor progress, in another terminal:
$ ps fax | grep dd
$ sudo kill -USR1 PID_OF_DD_PROCESS