Calculate Linux (Gentoo) using terminal dd comman to make a bootable ISO to USB stick.
I hope this will help anyone struggling to make a bootable USB stick from a ISO file.
Having said this, Absolute Linux ISO files are coming back as none bootable images (Etcher reported that)
check if sdd is your USB stick
replace /home/dirk/iso/cldx-17.6-x86_64.iso
with your own path and iso file
sudo dd status=progress if=/home/dirk/iso/cldx-17.6-x86_64.iso of=/dev/sdd