tony@localhost ~ $ beryl
**************************************************************
* Beryl system compatiblity check                            *
**************************************************************

Detected xserver                                : NVIDIA

Checking Display :0.0 ...

Checking for XComposite extension               : failed

No composite extension
134546457 screens detected.
Currently we cannot guarantee that Beryl will work correctly with multiple X screens.
Using the --no-context-share command line option can help.
Please report any success to the beryl developer mailing list. The list can be found at lists.beryl-project.org