OK here's an easy way to burn a USB Key (Bootable) from iso image.
First, find out what the USB Key is appearing as in a list of your drives by executing fdisk -l.
In this case, mine is an old 1GB USB Drive: /dev/sdb
donmc@T510:~$ sudo fdisk -l Disk /dev/sdb: 984 MiB, 1031798784 bytes, 2015232 sectors Units: sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disklabel type: gpt Disk identifier: 2CBA5013-16E7-4D41-B75D-544A6474498B Device Start End Sectors Size Type /dev/sdb1 64 539 476 238K Microsoft basic data /dev/sdb2 540 6299 5760 2.8M EFI System /dev/sdb3 6300 1341303 1335004 651.9M Apple HFS/HFS+ /dev/sdb4 1341304 1341903 600 300K Microsoft basic data donmc@T510:~$ sudo dd bs=4M if=/full/path/to/file/some.iso of=/dev/sdb 163+1 records in 163+1 records out 687079424 bytes (687 MB, 655 MiB) copied, 378.456 s, 1.8 MB/s