Basically, any time I access the standard http://fedora:3000/rails/info/properties, I get the exception with the following stacktrace: /opt/work/jruby/lib/ruby/gems/1.8/gems/activerecord-2.0.1/lib/active_record/vendor/mysql.rb:111:in `real_connect' /opt/work/jruby/lib/ruby/gems/1.8/gems/activerecord-2.0.1/lib/active_record/connection_adapters/mysql_adapter.rb:471:in `connect' /opt/work/jruby/lib/ruby/gems/1.8/gems/activerecord-2.0.1/lib/active_record/connection_adapters/mysql_adapter.rb:165:in `initialize' /opt/work/jruby/lib/ruby/gems/1.8/gems/activerecord-2.0.1/lib/active_record/connection_adapters/mysql_adapter.rb:88:in `new' /opt/work/jruby/lib/ruby/gems/1.8/gems/activerecord-2.0.1/lib/active_record/connection_adapters/mysql_adapter.rb:88:in `mysql_connection' /opt/work/jruby/lib/ruby/gems/1.8/gems/activerecord-2.0.1/lib/active_record/connection_adapters/abstract/connection_specification.rb:291:in `connection=' /opt/work/jruby/lib/ruby/gems/1.8/gems/activerecord-2.0.1/lib/active_record/connection_adapters/abstract/connection_specification.rb:259:in `retrieve_connection' /opt/work/jruby/lib/ruby/gems/1.8/gems/activerecord-2.0.1/lib/active_record/connection_adapters/abstract/connection_specification.rb:78:in `connection' /opt/work/jruby/lib/ruby/gems/1.8/gems/activerecord-2.0.1/lib/active_record/query_cache.rb:8:in `cache' /opt/work/jruby/lib/ruby/gems/1.8/gems/actionpack-2.0.1/lib/action_controller/caching.rb:677:in `perform_action_with_caching' /opt/work/jruby/lib/ruby/gems/1.8/gems/actionpack-2.0.1/lib/action_controller/caching.rb:677:in `process' /opt/work/jruby/lib/ruby/gems/1.8/gems/actionpack-2.0.1/lib/action_controller/filters.rb:685:in `process_with_filters' /opt/work/jruby/lib/ruby/gems/1.8/gems/actionpack-2.0.1/lib/action_controller/session_management.rb:123:in `process_with_session_management_support' /opt/work/jruby/lib/ruby/gems/1.8/gems/actionpack-2.0.1/lib/action_controller/base.rb:388:in `process' /opt/work/jruby/lib/ruby/gems/1.8/gems/actionpack-2.0.1/lib/action_controller/dispatcher.rb:171:in `handle_request' /opt/work/jruby/lib/ruby/gems/1.8/gems/actionpack-2.0.1/lib/action_controller/dispatcher.rb:115:in `dispatch' /opt/work/jruby/lib/ruby/gems/1.8/gems/actionpack-2.0.1/lib/action_controller/dispatcher.rb:126:in `dispatch_cgi' /opt/work/jruby/lib/ruby/gems/1.8/gems/actionpack-2.0.1/lib/action_controller/dispatcher.rb:9:in `dispatch' /opt/work/jruby/lib/ruby/gems/1.8/gems/mongrel-1.1.1-jruby/lib/mongrel/rails.rb:76:in `process' /opt/work/jruby/lib/ruby/gems/1.8/gems/mongrel-1.1.1-jruby/lib/mongrel/rails.rb:74:in `synchronize' /opt/work/jruby/lib/ruby/gems/1.8/gems/mongrel-1.1.1-jruby/lib/mongrel/rails.rb:74:in `process' /opt/work/jruby/lib/ruby/gems/1.8/gems/mongrel-1.1.1-jruby/lib/mongrel/rails.rb:74:in `process_client' /opt/work/jruby/lib/ruby/gems/1.8/gems/mongrel-1.1.1-jruby/lib/mongrel.rb:154:in `each' /opt/work/jruby/lib/ruby/gems/1.8/gems/mongrel-1.1.1-jruby/lib/mongrel.rb:154:in `process_client' /opt/work/jruby/lib/ruby/gems/1.8/gems/mongrel-1.1.1-jruby/lib/mongrel.rb:154:in `run' /opt/work/jruby/lib/ruby/gems/1.8/gems/mongrel-1.1.1-jruby/lib/mongrel.rb:281:in `initialize' This is due to fact that JRuby's TCPSocket can't handle nil as a host parameter, while MRI can. The proposed patch fixes the porblem