久しぶりにアプリケーションを作って rails server したらエラーが出た

Ruby Rails

Ruby のバージョンを 1.9.3p392、rails のバージョンを 4.0.0 にした後、しばらく放置していたので久しぶりにアプリケーションを作って起動しようとしたらエラーが出た。

$ rails server
/usr/local/lib/ruby/gems/1.9.1/gems/execjs-2.0.1/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/local/lib/ruby/gems/1.9.1/gems/execjs-2.0.1/lib/execjs.rb:5:in `<module:ExecJS>'
     from /usr/local/lib/ruby/gems/1.9.1/gems/execjs-2.0.1/lib/execjs.rb:4:in `<top (required)>'
     from /usr/local/lib/ruby/gems/1.9.1/gems/uglifier-2.2.1/lib/uglifier.rb:3:in `require'
     from /usr/local/lib/ruby/gems/1.9.1/gems/uglifier-2.2.1/lib/uglifier.rb:3:in `<top (required)>'
     from /usr/local/lib/ruby/gems/1.9.1/gems/bundler-1.3.5/lib/bundler/runtime.rb:72:in `require'
     from /usr/local/lib/ruby/gems/1.9.1/gems/bundler-1.3.5/lib/bundler/runtime.rb:72:in `block (2 levels) in require'
     from /usr/local/lib/ruby/gems/1.9.1/gems/bundler-1.3.5/lib/bundler/runtime.rb:70:in `each'
     from /usr/local/lib/ruby/gems/1.9.1/gems/bundler-1.3.5/lib/bundler/runtime.rb:70:in `block in require'
     from /usr/local/lib/ruby/gems/1.9.1/gems/bundler-1.3.5/lib/bundler/runtime.rb:59:in `each'
     from /usr/local/lib/ruby/gems/1.9.1/gems/bundler-1.3.5/lib/bundler/runtime.rb:59:in `require'
     from /usr/local/lib/ruby/gems/1.9.1/gems/bundler-1.3.5/lib/bundler.rb:132:in `require'
     from /home/iishun/rails/iishun/config/application.rb:7:in `<top (required)>'
     from /usr/local/lib/ruby/gems/1.9.1/gems/railties-4.0.0/lib/rails/commands.rb:76:in `require'
     from /usr/local/lib/ruby/gems/1.9.1/gems/railties-4.0.0/lib/rails/commands.rb:76:in `block in <top (required)>'
     from /usr/local/lib/ruby/gems/1.9.1/gems/railties-4.0.0/lib/rails/commands.rb:73:in `tap'
     from /usr/local/lib/ruby/gems/1.9.1/gems/railties-4.0.0/lib/rails/commands.rb:73:in `<top (required)>'
     from bin/rails:4:in `require'
     from bin/rails:4:in `<main>'

どうやら下記の記述を Gemfile に書き加えると解消するようなので、

gem 'execjs'
gem 'therubyracer'

もう一度 bundle install をしてあげたら無事立ち上がった。