Enable Ctrl+Alt+F1 Virtual Consoles in GNOME (Ubuntu 17.04+)

I'm running Kubuntu v16.04 - not the version that you are - but I had to modify /etc/systemd/logind.conf, uncomment NAutoVTs=6 and restart.

Also, check /etc/default/console-setup, the line: ACTIVE_CONSOLES="/dev/tty[1-6]"