title: ruby tutorial to launch my app
body: <p>i'm just starting with an Unix based OS 
  i installed RVM to do the same basic tutorial like windows(dos), but i get
  an error, i tried to do the same work in root/user shell but is the same
  when i run <code>rails server</code> i get this message:</p>
  
  <pre><code>/usr/local/rvm/gems/ruby-2.0.0-p247/gems/execjs-2.0.1/lib/execjs/runtimes.rb:51:in `autodetect': Could not find a JavaScript runtime. See https://github.com/sstephenson/execjs for a list of available runtimes. (ExecJS::RuntimeUnavailable)
      from /usr/local/rvm/gems/ruby-2.0.0-p247/gems/execjs-2.0.1/lib/execjs.rb:5:in `&lt;module:ExecJS&gt;'
      from /usr/local/rvm/gems/ruby-2.0.0-p247/gems/execjs-2.0.1/lib/execjs.rb:4:in `&lt;top (required)&gt;'
      from /usr/local/rvm/gems/ruby-2.0.0-p247/gems/uglifier-2.2.1/lib/uglifier.rb:3:in `require'
      from /usr/local/rvm/gems/ruby-2.0.0-p247/gems/uglifier-2.2.1/lib/uglifier.rb:3:in `&lt;top (required)&gt;'
      from /usr/local/rvm/gems/ruby-2.0.0-p247/gems/bundler-1.3.5/lib/bundler/runtime.rb:72:in `require'
      from /usr/local/rvm/gems/ruby-2.0.0-p247/gems/bundler-1.3.5/lib/bundler/runtime.rb:72:in `block (2 levels) in require'
      from /usr/local/rvm/gems/ruby-2.0.0-p247/gems/bundler-1.3.5/lib/bundler/runtime.rb:70:in `each'
      from /usr/local/rvm/gems/ruby-2.0.0-p247/gems/bundler-1.3.5/lib/bundler/runtime.rb:70:in `block in require'
      from /usr/local/rvm/gems/ruby-2.0.0-p247/gems/bundler-1.3.5/lib/bundler/runtime.rb:59:in `each'
      from /usr/local/rvm/gems/ruby-2.0.0-p247/gems/bundler-1.3.5/lib/bundler/runtime.rb:59:in `require'
      from /usr/local/rvm/gems/ruby-2.0.0-p247/gems/bundler-1.3.5/lib/bundler.rb:132:in `require'
      from /home/raul/blog/config/application.rb:7:in `&lt;top (required)&gt;'
      from /usr/local/rvm/gems/ruby-2.0.0-p247/gems/railties-4.0.0/lib/rails/commands.rb:76:in `require'
      from /usr/local/rvm/gems/ruby-2.0.0-p247/gems/railties-4.0.0/lib/rails/commands.rb:76:in `block in &lt;top (required)&gt;'
      from /usr/local/rvm/gems/ruby-2.0.0-p247/gems/railties-4.0.0/lib/rails/commands.rb:73:in `tap'
      from /usr/local/rvm/gems/ruby-2.0.0-p247/gems/railties-4.0.0/lib/rails/commands.rb:73:in `&lt;top (required)&gt;'
      from bin/rails:4:in `require'
      from bin/rails:4:in `&lt;main&gt;'
  </code></pre>
  
  <p>i reviwed the gem command and dome problems was founded too. Execjs is installed several times in my machine, <code>root-&gt;user</code>. This is what i get with <code>gem check</code>:</p>
  
  <pre><code>json-1.8.0.gem has 12 problems
    ext/json/ext/generator/.RUBYARCHDIR.time:
      Extra file
    ext/json/ext/generator/Makefile:
      Extra file
    ext/json/ext/generator/generator.o:
      Extra file
    ext/json/ext/generator/generator.so:
      Extra file
    ext/json/ext/generator/siteconf20130920-14093-1b8hzo9.rb:
      Extra file
    ext/json/ext/parser/.RUBYARCHDIR.time:
      Extra file
    ext/json/ext/parser/Makefile:
      Extra file
    ext/json/ext/parser/parser.o:
      Extra file
    ext/json/ext/parser/parser.so:
      Extra file
    ext/json/ext/parser/siteconf20130920-14093-zefm93.rb:
      Extra file
    lib/json/ext/generator.so:
      Extra file
    lib/json/ext/parser.so:
      Extra file
  </code></pre>