即使您安装了 libyaml,libyaml 警告也不会消失
gem install bundler
/home/ec2-user/.rvm/rubies/ruby-1.9.3-p392/lib/ruby/1.9.1/yaml.rb:56:in `<top (required)>':
It seems your ruby installation is missing psych (for YAML output).
To eliminate this warning, please install libyaml and reinstall your ruby.
Fetching: bundler-1.3.4.gem (100%)
Successfully installed bundler-1.3.4