I'm not exactly a newbie, I have used Squeak for several months.  I have just converted an old P90 to Linux, and started fresh with Squeak by installing a new 2.8 image on that computer.  I am looking at doing some FFI work for the first time.  However, I can't get the X11 FFI examples  to work.  The error I keep getting is in XOpenDisplay: at the first FFI call.  The ExternalFunction error string is "Callout Mechanism not available."  


I have downloaded and installed SqueakFFIPrims.so and libffi.so.1.
I can't see anything obviously missing.  What else do I need to do?

Thanks