How fix the issue when used the acviteadmin gem? - ruby-on-rails

Question

Use the activeadmin into the gem file. bundle install, rails g active_admin:install User, then rails s, the server will crash and give some warning.
Error Information:
rails s
WARNING: Nokogiri was built against LibXML version 2.9.4, but has dynamically loaded 2.8.0
=> Booting WEBrick
=> Rails 5.0.0 application starting in development on http://localhost:3000
=> Run `rails server -h` for more startup options
DEPRECATION WARNING: You are using the a deprecated processor interface #<Proc:0x0055902480b218#/home/guo/.rvm/gems/ruby-2.3.1/gems/autoprefixer-rails-5.2.1.3/lib/autoprefixer-rails/sprockets.rb:25>.
Please update your processor interface:
https://github.com/rails/sprockets/blob/master/guides/extending_sprockets.md#supporting-all-versions-of-sprockets-in-processors
(called from install at /home/guo/.rvm/gems/ruby-2.3.1/gems/autoprefixer-rails-5.2.1.3/lib/autoprefixer-rails/sprockets.rb:25)
Exiting
Here is my gem list.
source 'https://rubygems.org'
# Bundle edge Rails instead: gem 'rails', github: 'rails/rails'
gem 'rails', '5.0.0'
# Use postgresql as the database for Active Record
gem 'pg', '~> 0.15'
# Use SCSS for stylesheets
gem 'sass-rails', '~> 5.0'
# Use Uglifier as compressor for JavaScript assets
gem 'uglifier', '>= 1.3.0'
# Use CoffeeScript for .coffee assets and views
gem 'coffee-rails', '~> 4.1.0'
# See https://github.com/rails/execjs#readme for more supported runtimes
gem 'therubyracer', platforms: :ruby
# Use jquery as the JavaScript library
gem 'jquery-rails'
# Turbolinks makes following links in your web application faster.
# Read more: https://github.com/rails/turbolinks
gem 'turbolinks'
# Build JSON APIs with ease. Read more: https://github.com/rails/jbuilder
gem 'jbuilder', '~> 2.0'
# bundle exec rake doc:rails generates the API under doc/api.
gem 'sdoc', '~> 0.4.0', group: :doc
gem 'activeadmin'
gem 'devise'
gem 'cancancan'
gem 'rolify'
gem 'draper'
gem 'pundit'
# Use ActiveModel has_secure_password
gem 'bcrypt', '~> 3.1.7'
gem 'bootstrap-sass', '~>3.3.7'
gem 'autoprefixer-rails', '~>5.2.1'
#gem "twitter-bootstrap-rails"
gem 'carrierwave', '>= 1.0.0.beta', '< 2.0' gem 'rmagick'
gem 'grape'
gem 'doorkeeper'
gem "rack-oauth2"
#gem 'will_paginate', '~> 3.1.1' gem 'kaminari'
gem 'dalli' gem 'actionpack-page_caching' gem 'actionpack-action_caching'
gem 'delayed_job' gem 'delayed_job_active_record' #gem "sidekiq"
#gem "devise-doorkeeper"
gem 'roadie'
gem 'roadie-rails'
gem 'nokogiri', '1.6.0'
#gem 'premailer-rails'

Answer 1

If you are using rails 5, try this:
gem 'inherited_resources', git: 'https://github.com/activeadmin/inherited_resources'
gem 'activeadmin', git: 'https://github.com/activeadmin/activeadmin'
And also kill the existing server ,As suggested by #ray, and start the server. You can check the existing server
ps aux|grep puma
It prints all the puma processes like this
pragya_+ 1378 0.2 1.6 1233236 140252 tty4 Sl 10:15 0:24 puma 3.12.1 (tcp://localhost:3000)
Here 1378 is the process_id. Now kill that process by run this command:
kill -9 1378
Restart the server and check again. Hope it will work :)