RoR を学習していますが、コントローラーの生成時にエラーが発生します
mitchell@ubuntu:~/Ruby/Website/blog$ rails generate controller posts
/home/mitchell/.rvm/gems/ruby-1.9.3-p327/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 /home/mitchell/.rvm/gems/ruby-1.9.3-p327/gems/execjs-1.4.0/lib/execjs.rb:5:in `<module:ExecJS>'
from /home/mitchell/.rvm/gems/ruby-1.9.3-p327/gems/execjs-1.4.0/lib/execjs.rb:4:in `<top (required)>'
from /home/mitchell/.rvm/gems/ruby-1.9.3-p327/gems/coffee-script-2.2.0/lib/coffee_script.rb:1:in `require'
from /home/mitchell/.rvm/gems/ruby-1.9.3-p327/gems/coffee-script-2.2.0/lib/coffee_script.rb:1:in `<top (required)>'
from /home/mitchell/.rvm/gems/ruby-1.9.3-p327/gems/coffee-script-2.2.0/lib/coffee-script.rb:1:in `require'
from /home/mitchell/.rvm/gems/ruby-1.9.3-p327/gems/coffee-script-2.2.0/lib/coffee-script.rb:1:in `<top (required)>'
from /home/mitchell/.rvm/gems/ruby-1.9.3-p327/gems/coffee-rails-3.2.2/lib/coffee-rails.rb:1:in `require'
from /home/mitchell/.rvm/gems/ruby-1.9.3-p327/gems/coffee-rails-3.2.2/lib/coffee-rails.rb:1:in `<top (required)>'
from /home/mitchell/.rvm/gems/ruby-1.9.3-p327@global/gems/bundler-1.2.1/lib/bundler/runtime.rb:68:in `require'
from /home/mitchell/.rvm/gems/ruby-1.9.3-p327@global/gems/bundler-1.2.1/lib/bundler/runtime.rb:68:in `block (2 levels) in require'
from /home/mitchell/.rvm/gems/ruby-1.9.3-p327@global/gems/bundler-1.2.1/lib/bundler/runtime.rb:66:in `each'
from /home/mitchell/.rvm/gems/ruby-1.9.3-p327@global/gems/bundler-1.2.1/lib/bundler/runtime.rb:66:in `block in require'
from /home/mitchell/.rvm/gems/ruby-1.9.3-p327@global/gems/bundler-1.2.1/lib/bundler/runtime.rb:55:in `each'
from /home/mitchell/.rvm/gems/ruby-1.9.3-p327@global/gems/bundler-1.2.1/lib/bundler/runtime.rb:55:in `require'
from /home/mitchell/.rvm/gems/ruby-1.9.3-p327@global/gems/bundler-1.2.1/lib/bundler.rb:128:in `require'
from /home/mitchell/Ruby/Website/blog/config/application.rb:7:in `<top (required)>'
from /home/mitchell/.rvm/gems/ruby-1.9.3-p327/gems/railties-3.2.9/lib/rails/commands.rb:24:in `require'
from /home/mitchell/.rvm/gems/ruby-1.9.3-p327/gems/railties-3.2.9/lib/rails/commands.rb:24:in `<top (required)>'
from script/rails:6:in `require'
from script/rails:6:in `<main>'
Ubuntu で Rails 3.2.9 と Ruby 1.9.3 を実行しています。