Readline was unable to be required, if you need completion or history install readline then reinstall the ruby.

This happens on Ubuntu 12 when installing Ruby 2.0 using RVM. To fix this follow the instructions below:

If you're using Ubuntu 12.04, DO NOT pkg install readline, with or without --skip-autoreconf. After you've done that, either readline or zlib will be broken no matter what combination of switches you give to rvm install ruby-2.0.0-p0 . To get it to work, do the apt-get install that rvm requirements tells you to do, do a rvm pkg uninstall readline and then do a simple rvm remove ruby-2.0.0-p0; rvm install ruby-2.0.0-p0 Now the irb should work fine without any warnings.   http://stackoverflow.com/questions/8176076/how-to-get-readline-support-in-irb-using-rvm-on-ubuntu-11-10