Iniciando estudos no Rails

Boa tarde....

Comecei meus estudos no Ruby on Rails (e pra falar a verdade tá mais dificil botar ele pra funcionar do que usar ele de fato) e preciso da ajuda de voces....

Eu estava tentando fazer um blog usando alguns tutoriais que tenho aqui. No entanto eu esbarrei nesse comando...

$sudo rails generate scaffold post titulo:string conteudo:text

Pelo que entendi este comando atribui o nome do autor do blog, titulo, etc....

No entanto ao tentar executar ele aparece essa mensagem abaixo:

/var/lib/gems/1.8/gems/execjs-1.4.0/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 /var/lib/gems/1.8/gems/execjs-1.4.0/lib/execjs.rb:5
from /var/lib/gems/1.8/gems/coffee-script-2.2.0/lib/coffee_script.rb:1:in `require'
from /var/lib/gems/1.8/gems/coffee-script-2.2.0/lib/coffee_script.rb:1
from /var/lib/gems/1.8/gems/coffee-script-2.2.0/lib/coffee-script.rb:1:in `require'
from /var/lib/gems/1.8/gems/coffee-script-2.2.0/lib/coffee-script.rb:1
from /var/lib/gems/1.8/gems/coffee-rails-3.2.2/lib/coffee-rails.rb:1:in `require'
from /var/lib/gems/1.8/gems/coffee-rails-3.2.2/lib/coffee-rails.rb:1
from /var/lib/gems/1.8/gems/bundler-1.2.3/lib/bundler/runtime.rb:68:in `require'
from /var/lib/gems/1.8/gems/bundler-1.2.3/lib/bundler/runtime.rb:68:in `require'
from /var/lib/gems/1.8/gems/bundler-1.2.3/lib/bundler/runtime.rb:66:in `each'
from /var/lib/gems/1.8/gems/bundler-1.2.3/lib/bundler/runtime.rb:66:in `require'
from /var/lib/gems/1.8/gems/bundler-1.2.3/lib/bundler/runtime.rb:55:in `each'
from /var/lib/gems/1.8/gems/bundler-1.2.3/lib/bundler/runtime.rb:55:in `require'
from /var/lib/gems/1.8/gems/bundler-1.2.3/lib/bundler.rb:128:in `require'
from /home/guilherme/blog/config/application.rb:7
from /var/lib/gems/1.8/gems/railties-3.2.11/lib/rails/commands.rb:24:in `require'
from /var/lib/gems/1.8/gems/railties-3.2.11/lib/rails/commands.rb:24
from script/rails:6:in `require'
from script/rails:6

Como vi ali, pensei que fosse alguma dependencia relacionada com ExecJS aí eu executei o comando:

$gem install execJS

No entanto não houve mudança nenhuma.....

O que voces acham que pode ser?????

Desde já agradeço.......