why is my rails server logging everything twice? - ruby-on-rails

Question

my rails server seems like it is logging everything twice, not sure what is going on here, what should I do to investigate this ?
my gemfile
source 'https://rubygems.org'
ruby '2.1.0'
gem 'rails', '4.0.1'
gem 'haml-rails'
gem 'pg', '~> 0.17.1'
gem 'redis'
gem 'redis-namespace'
gem 'thin', '~> 1.6.1'
gem 'rabl'
gem 'underscore-rails'
#assets
gem 'sass-rails', '~> 4.0.0'
gem 'uglifier', '>= 1.3.0'
gem 'foundation-rails'
gem 'font-awesome-rails'
#javascript
gem 'coffee-rails', '~> 4.0.0'
gem 'jquery-rails'
gem 'jbuilder', '~> 1.2'
gem 'angularjs-rails', '~> 1.2.7'
gem 'ngmin-rails', '~> 0.4.0'
#user auth
gem 'devise', '3.0.0'
gem 'omniauth'
gem 'omniauth-twitter'
gem 'uuidtools'
#misc tools
gem 'twitter'
#heroku
gem 'rails_12factor'
group :development, :test do
gem 'capybara-webkit', github: 'thoughtbot/capybara-webkit', branch: 'master'
gem 'rspec-rails', '~> 2.14.1'
gem 'factory_girl_rails', '4.2.1'
gem 'mocha', '~> 1.0.0'
gem 'pry'
gem 'pry-debugger'
gem 'quiet_assets'
gem 'parallel_tests'
gem 'zeus-parallel_tests'
gem 'guard-rspec'
gem 'rb-fsevent'
end
group :development do
gem 'guard-livereload'
gem 'rack-livereload'
gem 'better_errors'
gem 'terminal-notifier-guard'
end
group :test do
gem 'launchy', '>= 2.1.2'
gem 'capybara', '>= 1.1.3'
gem 'database_cleaner', '~> 1.2.0'
gem 'zeus', :require => false
gem 'shoulda-matchers'
gem 'pdf-inspector'
gem 'selenium-webdriver'
gem "mock_redis", "~> 0.11.0"
end

Answer 1

In my case this was caused by the rails_12factor gem. This gem adds the rails_stdout_logging gem which sends the logs to standard output. This can be useful in a production environment but not in development when Rails already does it by default.
https://github.com/heroku/rails_12factor#rails-4-logging
The solution is to only add this gem in production:
gem 'rails_12factor', group: :production

Answer 2

Have a look at this issue
Try adding the following code to you config/application.rb
if Rails.env.development?
# Don't log to STDOUT, by default rails s will handle it
config.logger = Logger.new('/dev/null')
else
# Don't log to file, sending everything to unicorn file.
config.logger = Logger.new(STDOUT)
end

Answer 3

Do you have your logger set to anything in either config/application.rb or config/environments/development.rb?
If nothing, try adding this line to config/environments/development.rb:
config.logger = Logger.new('/dev/null')

Answer 4

I had success with this in development.rb:
config.logger = ActiveSupport::Logger.new('/dev/null')