I am not sure, but I think there is no simple way how to do that. Try to find something like "how to spawn a df command in Rhino". If it were me, I would create a separate PHP script (because I am PHP junky ) which would run df command via exec() or system() or any other function. and return its output as a JSON or XML upon GET request (simple REST API). Simpler way might by using Java Extension SDK though to create a widget which would invoke system command. I would prefer to use JAVA, but I am not that far.
Tomas
