Ruby on Rails: Could not find a JavaScript runtime

Un error al intentar levanta el servidor de RoR para las versiones:

Rails 3.1.0.rc5

ruby 1.9.2p290 (2011-07-09 revision 32553) [i686-linux]

El error completo al ejecutar rails s:

/home/user/.rvm/gems/ruby-1.9.2-p290/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)
	from /home/user/.rvm/gems/ruby-1.9.2-p290/gems/execjs-1.2.4/lib/execjs.rb:5:in `<module:ExecJS>'
	from /home/user/.rvm/gems/ruby-1.9.2-p290/gems/execjs-1.2.4/lib/execjs.rb:4:in `<top (required)>'
	from /home/user/.rvm/gems/ruby-1.9.2-p290/gems/coffee-script-2.2.0/lib/coffee_script.rb:1:in `require'
	from /home/user/.rvm/gems/ruby-1.9.2-p290/gems/coffee-script-2.2.0/lib/coffee_script.rb:1:in `<top (required)>'
	from /home/user/.rvm/gems/ruby-1.9.2-p290/gems/coffee-script-2.2.0/lib/coffee-script.rb:1:in `require'
	from /home/user/.rvm/gems/ruby-1.9.2-p290/gems/coffee-script-2.2.0/lib/coffee-script.rb:1:in `<top (required)>'
	from /home/user/.rvm/gems/ruby-1.9.2-p290/gems/coffee-rails-3.1.0.rc.5/lib/coffee-rails.rb:1:in `require'
	from /home/user/.rvm/gems/ruby-1.9.2-p290/gems/coffee-rails-3.1.0.rc.5/lib/coffee-rails.rb:1:in `<top (required)>'
	from /home/user/.rvm/gems/ruby-1.9.2-p290/gems/bundler-1.0.17/lib/bundler/runtime.rb:68:in `require'
	from /home/user/.rvm/gems/ruby-1.9.2-p290/gems/bundler-1.0.17/lib/bundler/runtime.rb:68:in `block (2 levels) in require'
	from /home/user/.rvm/gems/ruby-1.9.2-p290/gems/bundler-1.0.17/lib/bundler/runtime.rb:66:in `each'
	from /home/user/.rvm/gems/ruby-1.9.2-p290/gems/bundler-1.0.17/lib/bundler/runtime.rb:66:in `block in require'
	from /home/user/.rvm/gems/ruby-1.9.2-p290/gems/bundler-1.0.17/lib/bundler/runtime.rb:55:in `each'
	from /home/user/.rvm/gems/ruby-1.9.2-p290/gems/bundler-1.0.17/lib/bundler/runtime.rb:55:in `require'
	from /home/user/.rvm/gems/ruby-1.9.2-p290/gems/bundler-1.0.17/lib/bundler.rb:120:in `require'
	from /home/user/Proyectos/Ruby/dldla/config/application.rb:8:in `<top (required)>'
	from /home/user/.rvm/gems/ruby-1.9.2-p290/gems/railties-3.1.0.rc5/lib/rails/commands.rb:52:in `require'
	from /home/user/.rvm/gems/ruby-1.9.2-p290/gems/railties-3.1.0.rc5/lib/rails/commands.rb:52:in `block in <top (required)>'
	from /home/user/.rvm/gems/ruby-1.9.2-p290/gems/railties-3.1.0.rc5/lib/rails/commands.rb:49:in `tap'
	from /home/user/.rvm/gems/ruby-1.9.2-p290/gems/railties-3.1.0.rc5/lib/rails/commands.rb:49:in `<top (required)>'
	from script/rails:6:in `require'
	from script/rails:6:in `<main>'

La solución es editar el archivo Gemfile y añadir las siguientes líneas: