ruby-on-rails – 在“rails s”中获取错误,服务器未运行

我做了什么：

rails new site
cd site
rails s

我收到的消息：

/home/user1/.rvm/gems/ruby-1.9.2-p180/gems/execjs-1.2.9/lib/execjs/runtimes.rb:47:in `autodetect': Could not find a JavaScript runtime. See https://github.com/sstephenson/execjs for a list of available runtimes. (ExecJS::RuntimeUnavailable)
    from /home/user1/.rvm/gems/ruby-1.9.2-p180/gems/execjs-1.2.9/lib/execjs.rb:5:in `<module:ExecJS>'
    from /home/user1/.rvm/gems/ruby-1.9.2-p180/gems/execjs-1.2.9/lib/execjs.rb:4:in `<top (required)>'
    from /home/user1/.rvm/gems/ruby-1.9.2-p180/gems/coffee-script-2.2.0/lib/coffee_script.rb:1:in `require'
    from /home/user1/.rvm/gems/ruby-1.9.2-p180/gems/coffee-script-2.2.0/lib/coffee_script.rb:1:in `<top (required)>'
    from /home/user1/.rvm/gems/ruby-1.9.2-p180/gems/coffee-script-2.2.0/lib/coffee-script.rb:1:in `require'
    from /home/user1/.rvm/gems/ruby-1.9.2-p180/gems/coffee-script-2.2.0/lib/coffee-script.rb:1:in `<top (required)>'
    from /home/user1/.rvm/gems/ruby-1.9.2-p180/gems/coffee-rails-3.1.1/lib/coffee-rails.rb:1:in `require'
    from /home/user1/.rvm/gems/ruby-1.9.2-p180/gems/coffee-rails-3.1.1/lib/coffee-rails.rb:1:in `<top (required)>'
    from /home/user1/.rvm/gems/ruby-1.9.2-p180/gems/bundler-1.0.21/lib/bundler/runtime.rb:68:in `require'
    from /home/user1/.rvm/gems/ruby-1.9.2-p180/gems/bundler-1.0.21/lib/bundler/runtime.rb:68:in `block (2 levels) in require'
    from /home/user1/.rvm/gems/ruby-1.9.2-p180/gems/bundler-1.0.21/lib/bundler/runtime.rb:66:in `each'
    from /home/user1/.rvm/gems/ruby-1.9.2-p180/gems/bundler-1.0.21/lib/bundler/runtime.rb:66:in `block in require'
    from /home/user1/.rvm/gems/ruby-1.9.2-p180/gems/bundler-1.0.21/lib/bundler/runtime.rb:55:in `each'
    from /home/user1/.rvm/gems/ruby-1.9.2-p180/gems/bundler-1.0.21/lib/bundler/runtime.rb:55:in `require'
    from /home/user1/.rvm/gems/ruby-1.9.2-p180/gems/bundler-1.0.21/lib/bundler.rb:122:in `require'
    from /home/user1/social/config/application.rb:7:in `<top (required)>'
    from /home/user1/.rvm/gems/ruby-1.9.2-p180/gems/railties-3.1.0/lib/rails/commands.rb:52:in `require'
    from /home/user1/.rvm/gems/ruby-1.9.2-p180/gems/railties-3.1.0/lib/rails/commands.rb:52:in `block in <top (required)>'
    from /home/user1/.rvm/gems/ruby-1.9.2-p180/gems/railties-3.1.0/lib/rails/commands.rb:49:in `tap'
    from /home/user1/.rvm/gems/ruby-1.9.2-p180/gems/railties-3.1.0/lib/rails/commands.rb:49:in `<top (required)>'
    from script/rails:6:in `require'
    from script/rails:6:in `<main>'

为什么我会收到此错误？

任何人都可以提示修复它吗？