How to determine from a python application if X server/X forwarding is running?
pyqt4, python, ssh, xserver
Solution
Check to see that the `$DISPLAY` environment variable is set - if they didn't use `ssh -X`, it will be empty (instead of containing something like `localhost:10`).
Problem
I'm writing a linux application which uses PyQt4 for GUI and which will only be used during remote sessions (ssh -XY / vnc). So sometimes it may occur that a user will forget to run ssh with X forwarding parameters or X forwarding will be unavailable for some reason. In this case the application crashes badly (unfortunately I am force to use an old C++ library wrapped into python and it completely messes user's current session if the application crashes). I cannot use something else so my idea is to check if X forwarding is available before loading that library. However I have no idea how to do that. I usually use xclock to check if my session has X forwarding enabled, but using xclock sounds like a big workaround. ADDED If possible I would like to use another way than creating an empty PyQt window and catching an exception.