glxheads [display ...]
The glxheads program will try to open GLX connections on multiple X displays as specified on the command-line. If a connection can be made it will try to create a direct GLX context (and fallback to using indirect contexts if that fails) and open a window displaying a spinning green triangle.
If no display names are specified, glxheads will default to opening a single local connection on display 0.
To open a local connection on display 0 and two remote connections to the hosts mars (display 0) and venus (display 1), run glxheads with the following command-line:
$ glxheads :0 mars:0 venus:1
glxheads was written by Brian Paul <firstname.lastname@example.org>.
This manual page was written by Thierry Reding <email@example.com> for the Debian project (but may be used by others).