glxinfo -V (return code: 255)
Error: unable to open display
glxinfo -h (return code: 0)
Usage: glxinfo [-v] [-t] [-h] [-b] [-l] [-s] [-i] [-display <dname>]
-display <dname>: Print GLX visuals on specified server.
-i: Force an indirect rendering context.
-B: brief output, print only the basics.
-v: Print visuals info in verbose form.
-t: Print verbose table.
-h: This information.
-b: Find the 'best' visual and print its number.
-l: Print interesting OpenGL limits.
-s: Print a single extension per line.