how to solve “ruby installation is missing psych” error?

Question

I used rvm to install ruby 1.9.3. even though it was successfully installed, it complained about libyaml. and now every time i wanna install a gem (say rails) this warning s

Answer 1

I had the same problem (Cent OS 5.7), none of the above solutions worked to me.

// My console warning
/usr/local/rvm/rubies/ruby-1.9.3-p286/lib/ruby/1.9.1/yaml.rb:56:in `':
It seems your ruby installation is missing psych (for YAML output).
To eliminate this warning, please install libyaml and reinstall your ruby.

After doing several re-installs, I realized it's looking for yaml in ruby version of 1.9.1 instead of 1.9.3. So i downgraded

// obviously after installing `libyaml`
rvm remove all
rvm install 1.9.1
rvm use 1.9.1 --default

And it worked 8D!