I followed these instructions and it all seems to work quite well.
I have installed Ubuntu 64 bit so selected jdk and jre x64. The version was also 1.7.0_10
I also installed the rxtx per your instructions but in mango under the modbus serial data source I get: "no rxtxSerial in java.library.path"
Because of the x64 java there is no usr/local/java/jdk1.7.0_09/jre/lib/i386 so i used usr/local/java/jdk1.7.0_09/jre/lib/amd64
Any other thoughts on the rxtx?