Erro Could not find a JavaScript runtime – rails

se este erro ocorrer quando estiver executando “rails server” ou rails s
/usr/lib/ruby/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 /usr/lib/ruby/gems/1.8/gems/execjs-1.4.0/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-3.2.2/lib/coffee-rails.rb:1:in `require’
from /usr/lib/ruby/gems/1.8/gems/coffee-rails-3.2.2/lib/coffee-rails.rb:1
from /usr/lib/ruby/gems/1.8/gems/bundler-1.1.5/lib/bundler/runtime.rb:68:in `require’
from /usr/lib/ruby/gems/1.8/gems/bundler-1.1.5/lib/bundler/runtime.rb:68:in `require’
from /usr/lib/ruby/gems/1.8/gems/bundler-1.1.5/lib/bundler/runtime.rb:66:in `each’
from /usr/lib/ruby/gems/1.8/gems/bundler-1.1.5/lib/bundler/runtime.rb:66:in `require’
from /usr/lib/ruby/gems/1.8/gems/bundler-1.1.5/lib/bundler/runtime.rb:55:in `each’
from /usr/lib/ruby/gems/1.8/gems/bundler-1.1.5/lib/bundler/runtime.rb:55:in `require’
from /usr/lib/ruby/gems/1.8/gems/bundler-1.1.5/lib/bundler.rb:119:in `require’
from /Ruby/projeto/college/config/application.rb:7
from /usr/lib/ruby/gems/1.8/gems/railties-3.2.7/lib/rails/commands.rb:53:in `require’
from /usr/lib/ruby/gems/1.8/gems/railties-3.2.7/lib/rails/commands.rb:53
from /usr/lib/ruby/gems/1.8/gems/railties-3.2.7/lib/rails/commands.rb:50:in `tap’
from /usr/lib/ruby/gems/1.8/gems/railties-3.2.7/lib/rails/commands.rb:50
from script/rails:6:in `require’
from script/rails:6
instale o gem ‘therubyracer’ para javascript
no linux

gem install therubyracer

e depois execute

echo "gem 'therubyracer'" >> Gemfile

dentro do projeto.