By a USB bootable Ubuntu code example
Example: ubuntu create bootable usb from iso command line
$ sudo umount /dev/sdb1
$ sudo dd bs=4M if=/home/sana/Downloads/ubuntu-18.04.2-live-server-amd64.iso of=/dev/sdb1 status=progress oflag=sync$ sudo umount /dev/sdb1
$ sudo dd bs=4M if=/home/sana/Downloads/ubuntu-18.04.2-live-server-amd64.iso of=/dev/sdb1 status=progress oflag=sync