Add these lines to Gemfile:

gem 'devise', github: 'plataformatec/devise'
gem 'responders', github: 'plataformatec/responders'
gem 'inherited_resources', github: 'josevalim/inherited_resources'
gem 'activeadmin', github: 'activeadmin'
gem 'polyamorous', github: 'activerecord-hackery/polyamorous'
gem 'ransack', github: 'activerecord-hackery/ransack'
gem 'formtastic', github: 'justinfrench/formtastic'

Run:

bundle install
rails g active_admin:install
rake db:migrate

in config/environments/development.rb add:

config.action_mailer.default_url_options = { host: 'localhost', port: 3000 }

And:

rails g devise:views
rails s

The default user is ‘admin@example.com’ with the password: ‘password’

If the above account doesn’t work, create one:

rails console
AdminUser.new({ :email => 'admin@example.com', :password => 'password', :password_confirmation => 'password'}).save

To register a model, run:

rails g active_admin:resource Post

This will create app/admin/post.rb, add for example:

permit_params :title, :body