DO NOT EDIT - MOVED TO HERE => <a href="http://wiki.jruby.org/JRubyOnUbuntu">JRubyOnUbuntu</a> [[Home|&raquo; JRuby Project Home Page]] &nbsp;&nbsp; [[Getting Started|&raquo; Getting Started with JRuby]] ==JRuby With Wrong Java== [''ed: This page needs revision because some other Linux distros have the same problem as Ubuntu. What we might want to add is proper instructions for getting a hotspot-based JVM on those Linux versions, either as OpenJDK (like RedHat's "icedtea" builds) or a Sun build.''] You may find that even though you have an up-to-date JDK installed, JRuby does not work on Ubuntu. When running <tt>jruby -v</tt>, you might get exceptions from Java. The reason for these errors might be that, even though you have an up-to-date JDK installed, Ubuntu is not using it by default. You need to update your configuration to use the proper JDK. See [https://help.ubuntu.com/community/Java] for more information on this issue. On Ubuntu 7.10, I ran java -version which said that I was running Java version 1.5.0 when I knew I had Java version 1.6 installed. I then ran: sudo update-alternatives --config java I picked the option <tt>/usr/lib/jvm/java-6-sun/jre/bin/java</tt>. Following that, running <tt>java -version</tt> gave me java version "1.6.0_03" Java(TM) SE Runtime Environment (build 1.6.0_03-b05) Java HotSpot(TM) Server VM (build 1.6.0_03-b05, mixed mode) And JRuby then worked fine.