Error in Creating a rubyonrails application

when i try to run the rails server after successfully creating a rails
application i get following error...
can you please suggest some solutions to fix this.

sward@master:~/work/myapp$ rails server
/usr/lib/ruby/gems/1.8/gems/execjs-1.2.13/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 /usr/lib/ruby/gems/1.8/gems/execjs-1.2.13/lib/execjs.rb:5
  from /usr/lib/ruby/gems/1.8/gems/coffee-script-2.2.0/lib/
coffee_script.rb:1:in `require'
  from /usr/lib/ruby/gems/1.8/gems/coffee-script-2.2.0/lib/
coffee_script.rb:1
  from /usr/lib/ruby/gems/1.8/gems/coffee-script-2.2.0/lib/coffee-
script.rb:1:in `require'
  from /usr/lib/ruby/gems/1.8/gems/coffee-script-2.2.0/lib/coffee-
script.rb:1
  from /usr/lib/ruby/gems/1.8/gems/coffee-rails-3.1.1/lib/coffee-
rails.rb:1:in `require'
  from /usr/lib/ruby/gems/1.8/gems/coffee-rails-3.1.1/lib/coffee-
rails.rb:1
  from /usr/lib/ruby/gems/1.8/gems/bundler-1.0.21/lib/bundler/
runtime.rb:68:in `require'
  from /usr/lib/ruby/gems/1.8/gems/bundler-1.0.21/lib/bundler/
runtime.rb:68:in `require'
  from /usr/lib/ruby/gems/1.8/gems/bundler-1.0.21/lib/bundler/
runtime.rb:66:in `each'
  from /usr/lib/ruby/gems/1.8/gems/bundler-1.0.21/lib/bundler/
runtime.rb:66:in `require'
  from /usr/lib/ruby/gems/1.8/gems/bundler-1.0.21/lib/bundler/
runtime.rb:55:in `each'
  from /usr/lib/ruby/gems/1.8/gems/bundler-1.0.21/lib/bundler/
runtime.rb:55:in `require'
  from /usr/lib/ruby/gems/1.8/gems/bundler-1.0.21/lib/bundler.rb:122:in
`require'
  from /home/sward/work/myapp/config/application.rb:7
  from /usr/lib/ruby/gems/1.8/gems/railties-3.1.3/lib/rails/commands.rb:
52:in `require'
  from /usr/lib/ruby/gems/1.8/gems/railties-3.1.3/lib/rails/commands.rb:
52
  from /usr/lib/ruby/gems/1.8/gems/railties-3.1.3/lib/rails/commands.rb:
49:in `tap'
  from /usr/lib/ruby/gems/1.8/gems/railties-3.1.3/lib/rails/commands.rb:
49
  from script/rails:6:in `require'
  from script/rails:6

It is a pity this is not covered in the Getting Started guide, though
I would have thought Google might have helped you out. Add

gem 'execjs'
gem 'therubyracer'

to Gemfile then run bundle install and try again.

Colin