# Revision history [back]

This message indicates the problem:

Error [RenderEngine.cc:608] Can't open display:
Warning [RenderEngine.cc:87] Unable to create X window. Rendering will be disabled


If a display can't be opened, then camera (and in some cases laser) sensor generation can't be done. Possible causes:

• X isn't running.
• Nobody is logged into X
• The DISPLAY environment variable isn't set correctly; it should usually be set to something like localhost:0.
• The user you're running as doesn't have permission to access the X display.

If you're trying to run gzserver remotely on a headless machine, you might find my answer to this related question useful.