Use dd to write an iso the your flash drive. Here's an example:
sudo dd if=trisquel_6.0_amd64.iso of=/dev/sdd 'if' stands for input file, or the iso you wish to copy "of" stands for output file, or where you wish to write the iso file to.The device name of your flash drive may not be /dev/sdd as in the comand above. Once plugged in, you can use 'fdisk -l', as root or using sudo, to find the device name of the flash drive, then alter the command above as necessary.
