ubuntu10.04にrvmで入れたruby1.8.7, 1.9.2でirbを使ったら Readline was unable to be required, if you need completion or history install readline then reinstall the ruby. You may follow 'rvm notes' for dependencies and/or read the docs page http://rvm.beginrescueend.com/packages/readline/ . Be sure you 'rvm remove X ; rvm install X' to re-compile your ruby with readline support after obtaining the readline libr