Проблема установки и запуска Ruby on Rails

Я установил Ruby + Rails и его зависимости на новую установку Ubuntu 14.04, используя следующие команды:

Предустановочный контрольный список

sudo apt-get update sudo apt-get upgrade

Добавьте apt-репозитории с сайта Brightbox.

sudo apt-get install software-properties-common
sudo apt-add-repository ppa:brightbox/ruby-ng
sudo apt-get update

sudo apt-get install ruby2.2 ruby2.2-dev
sudo apt-get install ruby-switch
sudo apt-get install bundler
sudo ruby-switch --set ruby2.2

ruby -v

Установить другие зависимости

sudo apt-get update
sudo apt-get install git-core curl zlib1g-dev build-essential libssl-dev 
libreadline-dev libyaml-dev libsqlite3-dev sqlite3 libxml2-dev libxslt1-dev 
libcurl4-openssl-dev python-software-properties libffi-dev

Установить MySQL

sudo apt-get install mysql-server mysql-client libmysqlclient-dev

Установить ImageMagick

sudo apt-get install imagemagick

Установить Rails

gem install rails --no-rdoc --no-ri

Установить SublimeText

sudo add-apt-repository ppa:webupd8team/sublime-text-3
sudo apt-get update
sudo apt-get install sublime-text-installer

Создать новое приложение

mkdir projects
cd projects
rails new testapp
cd testapp

Открыть проект в возвышенном тексте

subl -n .

Запустить сервер rails

bin/rails server

Я не получил никакой ошибки во время установки, но когда я выполнил команду bin/rails server, она выдала мне следующую ошибку

Ignoring json-1.8.3 because its extensions are not built.  Try: gem pristine json --version 1.8.3
Warning: Running `gem pristine --all` to regenerate your installed gemspecs (and deleting then reinstalling your bundle if you use bundle --path) will improve the startup performance of Spring.
/var/lib/gems/2.2.0/gems/execjs-2.5.2/lib/execjs/runtimes.rb:48:in `autodetect': Could not find a JavaScript runtime. See https://github.com/rails/execjs for a list of available runtimes. (ExecJS::RuntimeUnavailable)
    from /var/lib/gems/2.2.0/gems/execjs-2.5.2/lib/execjs.rb:5:in `<module:ExecJS>'
    from /var/lib/gems/2.2.0/gems/execjs-2.5.2/lib/execjs.rb:4:in `<top (required)>'
    from /var/lib/gems/2.2.0/gems/uglifier-2.7.1/lib/uglifier.rb:3:in `require'
    from /var/lib/gems/2.2.0/gems/uglifier-2.7.1/lib/uglifier.rb:3:in `<top (required)>'
    from /usr/lib/ruby/vendor_ruby/bundler/runtime.rb:72:in `require'
    from /usr/lib/ruby/vendor_ruby/bundler/runtime.rb:72:in `block (2 levels) in require'
    from /usr/lib/ruby/vendor_ruby/bundler/runtime.rb:70:in `each'
    from /usr/lib/ruby/vendor_ruby/bundler/runtime.rb:70:in `block in require'
    from /usr/lib/ruby/vendor_ruby/bundler/runtime.rb:59:in `each'
    from /usr/lib/ruby/vendor_ruby/bundler/runtime.rb:59:in `require'
    from /usr/lib/ruby/vendor_ruby/bundler.rb:132:in `require'
    from /home/arif/projects/testapp/config/application.rb:7:in `<top (required)>'
    from /var/lib/gems/2.2.0/gems/railties-4.2.1/lib/rails/commands/commands_tasks.rb:78:in `require'
    from /var/lib/gems/2.2.0/gems/railties-4.2.1/lib/rails/commands/commands_tasks.rb:78:in `block in server'
    from /var/lib/gems/2.2.0/gems/railties-4.2.1/lib/rails/commands/commands_tasks.rb:75:in `tap'
    from /var/lib/gems/2.2.0/gems/railties-4.2.1/lib/rails/commands/commands_tasks.rb:75:in `server'
    from /var/lib/gems/2.2.0/gems/railties-4.2.1/lib/rails/commands/commands_tasks.rb:39:in `run_command!'
    from /var/lib/gems/2.2.0/gems/railties-4.2.1/lib/rails/commands.rb:17:in `<top (required)>'
    from /home/arif/projects/testapp/bin/rails:8:in `require'
    from /home/arif/projects/testapp/bin/rails:8:in `<top (required)>'
    from /var/lib/gems/2.2.0/gems/spring-1.3.6/lib/spring/client/rails.rb:28:in `load'
    from /var/lib/gems/2.2.0/gems/spring-1.3.6/lib/spring/client/rails.rb:28:in `call'
    from /var/lib/gems/2.2.0/gems/spring-1.3.6/lib/spring/client/command.rb:7:in `call'
    from /var/lib/gems/2.2.0/gems/spring-1.3.6/lib/spring/client.rb:26:in `run'
    from /var/lib/gems/2.2.0/gems/spring-1.3.6/bin/spring:48:in `<top (required)>'
    from /var/lib/gems/2.2.0/gems/spring-1.3.6/lib/spring/binstub.rb:11:in `load'
    from /var/lib/gems/2.2.0/gems/spring-1.3.6/lib/spring/binstub.rb:11:in `<top (required)>'
    from /usr/lib/ruby/2.2.0/rubygems/core_ext/kernel_require.rb:54:in `require'
    from /usr/lib/ruby/2.2.0/rubygems/core_ext/kernel_require.rb:54:in `require'
    from /home/arif/projects/testapp/bin/spring:13:in `<top (required)>'
    from bin/rails:3:in `load'
    from bin/rails:3:in `<main>'

Я сильно застрял, пожалуйста, помогите мне!