Ruby, yaml, and gem in Fedora Linux

If you're trying to use gem to install something, and you're getting the following error message:

It seems your ruby installation is missing psych (for YAML output)....

You could try to install libyaml like this:

yum install libyaml

If that still doesn't work, it might be because the libyaml library is not new enough.  If that's the case, install libyaml from source from here:

http://pyyaml.org/download/libyaml/

Then, uninstall ruby, and then re-install ruby.  Hopefully you'll have success after that.