安装ruby运行环境的时候出现异常！

以下是错误提示！！
Ruby on Rails application could not be started
Phusion Passenger has listen more information about the error below

These are the possible causes:

    *
      There may be a syntax error in the application's code. Please check for such errors and fix them.
    *
      A required library may not installed. Please install all libraries that this application requires.
    *
      The application may not be properly configured. Please check whether all configuration files are written correctly, fix any incorrect configurations, and restart this application.
    *
      A service that the application relies on (such as the database server or the Ferret search engine server) may not have been started. Please start that service.

Further information about the error may have been written to the application's log file. Please check it in order to analyse the problem.

Error message:
    uninitialized constant Rails
Exception class:
    NameError
Application root:
    /var/www/vpn 
Backtrace:
    #     File     Line     Location
    0     /var/www/vpn/config/environment.rb     13     
    1     /usr/local/lib/site_ruby/1.8/rubygems/custom_require.rb     31     in `gem_original_require'
    2     /usr/local/lib/site_ruby/1.8/rubygems/custom_require.rb     31     in `require'
    3     /usr/lib/ruby/gems/1.8/gems/passenger-2.2.15/lib/phusion_passenger/railz/application_spawner.rb     318     in `preload_application'
    4     /usr/lib/ruby/gems/1.8/gems/passenger-2.2.15/lib/phusion_passenger/railz/application_spawner.rb     267     in `initialize_server'
    5     /usr/lib/ruby/gems/1.8/gems/passenger-2.2.15/lib/phusion_passenger/utils.rb     323     in `report_app_init_status'
    6     /usr/lib/ruby/gems/1.8/gems/passenger-2.2.15/lib/phusion_passenger/railz/application_spawner.rb     246     in `initialize_server'
    7     /usr/lib/ruby/gems/1.8/gems/passenger-2.2.15/lib/phusion_passenger/abstract_server.rb     194     in `start_synchronously'
    8     /usr/lib/ruby/gems/1.8/gems/passenger-2.2.15/lib/phusion_passenger/abstract_server.rb     163     in `start'
    9     /usr/lib/ruby/gems/1.8/gems/passenger-2.2.15/lib/phusion_passenger/railz/application_spawner.rb     222     in `start'
    10     /usr/lib/ruby/gems/1.8/gems/passenger-2.2.15/lib/phusion_passenger/spawn_manager.rb     253     in `spawn_rails_application'
    11     /usr/lib/ruby/gems/1.8/gems/passenger-2.2.15/lib/phusion_passenger/abstract_server_collection.rb     126     in `lookup_or_add'
    12     /usr/lib/ruby/gems/1.8/gems/passenger-2.2.15/lib/phusion_passenger/spawn_manager.rb     247     in `spawn_rails_application'
    13     /usr/lib/ruby/gems/1.8/gems/passenger-2.2.15/lib/phusion_passenger/abstract_server_collection.rb     80     in `synchronize'
    14     /usr/lib/ruby/gems/1.8/gems/passenger-2.2.15/lib/phusion_passenger/abstract_server_collection.rb     79     in `synchronize'
    15     /usr/lib/ruby/gems/1.8/gems/passenger-2.2.15/lib/phusion_passenger/spawn_manager.rb     246     in `spawn_rails_application'
    16     /usr/lib/ruby/gems/1.8/gems/passenger-2.2.15/lib/phusion_passenger/spawn_manager.rb     145     in `spawn_application'
    17     /usr/lib/ruby/gems/1.8/gems/passenger-2.2.15/lib/phusion_passenger/spawn_manager.rb     278     in `handle_spawn_application'
    18     /usr/lib/ruby/gems/1.8/gems/passenger-2.2.15/lib/phusion_passenger/abstract_server.rb     352     in `__send__'
    19     /usr/lib/ruby/gems/1.8/gems/passenger-2.2.15/lib/phusion_passenger/abstract_server.rb     352     in `main_loop'
    20     /usr/lib/ruby/gems/1.8/gems/passenger-2.2.15/lib/phusion_passenger/abstract_server.rb     196     in `start_synchronously'
    21     /usr/lib/ruby/gems/1.8/gems/passenger-2.2.15/bin/passenger-spawn-server     61 

然后我在 系统下  gem install rails 

Successfully installed rails-3.0.0
1 gem installed
Installing ri documentation for rails-3.0.0...
File not found: li