>rails server
error message:
/usr/local/ruby1.9.2/lib/ruby/gems/1.9.1/gems/execjs-1.2.4/lib/execjs/runtimes.rb:45:in `autodetect': Could not find a JavaScript runtime. See https://github.com/sstephenson/execjs for a list of available runtimes. (ExecJS::RuntimeUnavailable)

>sudo gem install rake
>sudo gem install rack
>sudo gem install fastthread
>sudo gem install execjs
>sudo gem install therubyracer
>sudo gem install --no-ri --no-rdoc therubyracer

>sudo gem install libv8

install node