[root]# gem --version
/usr/local/rubygems/lib/rubygems.rb:267:in `config_file': undefined method `user_home' for Gem:Module (NoMethodError)
        from /usr/local/rubygems/lib/rubygems/config_file.rb:157:in `config_file_name'
        from /usr/local/rubygems/lib/rubygems/config_file.rb:121:in `initialize'
        from /usr/local/rubygems/lib/rubygems/gem_runner.rb:51:in `new'
        from /usr/local/rubygems/lib/rubygems/gem_runner.rb:51:in `do_configuration'
        from /usr/local/rubygems/lib/rubygems/gem_runner.rb:27:in `run'
        from /usr/local/rubygems/bin/gem:24:in `<main>'