I used this resource:
How to install jruby on Ubuntu:
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sudo -i mdir -p ~/src/jruby/trunk cd ~/src/jruby/trunk svn svn.codehaus.org/jruby/trunk/jruby/ . ant ~/src/jruby/trunk/bin/jruby --version
The current version doesn’t work to well with rails' script/console. It is very, very, very slow. So I keep using Yarv until this is fixed. It seems really promising though. Can’t wait for Rubinius to become stable!