I have Debian 8.1 in my system now and the Ubuntu 14.04 LTS as ISO image. I know these pieces of advices for OSX here about making bootable usb in OSX.
Pseudo unsuccessful solution
I did not manage to install unetbootin in Debian 8.1. Also, copying byte-wisely did not work. I made Windows 10 disk and opened the .iso image there. This way, I managed to install Ubuntu 14.04 but it required also ruining the Windows 10 installation; meaning two times work, since using other system to start the system. However, it is frustrating that I could not create easily Ubuntu USB where the system would boot.
I get now this after an unsuccessful try
There has to really be better options installing Ubuntu 14.04.
Solution which works
Reject USB and burn the image to DVD. However, this is not an answer to the question.
How can you make a bootable USB of Ubuntu 14.04 in Debian 8.1?