Hi,
Centos 4 is currently unsupported. We have an old version server binary compiled for it, but it won't have the newer features and it might not work well with modern browsers:
http://download.fop2.com/fop2_server_centos4
That is the server binary only, you have to install the regular centos tarball and then replace the fop2_server binary with the above. I am not sure but that is probably version 2.10 or so of FOP2, with no websocket support, etc.
Best regards,
