Isso foi resolvido usando o xcape ( sudo apt-get install xcape
ou do github - link )
e seguindo o script no README:
# Map an unused modifier's keysym to the spacebar's keycode and make it a
# control modifier. It needs to be an existing key so that emacs won't
# spazz out when you press it. Hyper_L is a good candidate.
spare_modifier="Hyper_L"
xmodmap -e "keycode 65 = $spare_modifier"
xmodmap -e "remove mod4 = $spare_modifier" # hyper_l is mod4 by default
xmodmap -e "add Control = $spare_modifier"
# Map space to an unused keycode (to keep it around for xcape to
# use).
xmodmap -e "keycode any = space"
# Finally use xcape to cause the space bar to generate a space when tapped.
xcape -e "$spare_modifier=space"
Isso funcionou para mim, independentemente da distro - trabalhei no Fedora 23 e no Debian9 além do Ubuntu 17.04, pois é uma solução genérica. Obrigado