If you're on a Red Hat-based system (Fedora/RHEL), and you've installed some of ThinLinc's dependencies via pip instead of dnf, then ThinLinc will fail to find those modules. The reason is an attempt by Red Hat at providing a more reliable python, and their heuristics seem to be a bit overzealous: https://bugzilla.redhat.com/show_bug.cgi?id=2256190