java version "1.5.0_08" Java(TM) 2 Runtime Environment, Standard Edition (build 1.5.0_08-b03) Java HotSpot(TM) Client VM (build 1.5.0_08-b03, mixed mode, sharing) Next thing to install is Ant , its a prerequisite for building JRuby. # apt-get install ant Verify you have ant: # ant -version Apache Ant version 1.6.5 compiled on July