title: Redis raises "NOAUTH Authentication required" error but there is no password setting
body: <p>I got error <strong>NOAUTH Authentication required</strong> when I connect to Redis server via command: <code>redis-cli</code> and run <code>ping</code> to check if Redis is working.</p>
  
  <p>I found <a href="https://stackoverflow.com/questions/23396336/shutdown-redis-server-from-command-line%20and">answer for NOAUTH Authentication required error</a> which describes that this error only happens when Redis is set a password, but I checked Redis config file at <code>etc/redis/redis.conf</code> and there is no password setting.</p>
  
  <p><a href="https://i.stack.imgur.com/pjv6z.png" rel="noreferrer"><img src="https://i.stack.imgur.com/pjv6z.png" alt="Redis config"></a></p>
  
  <p>Does anyone know that if there are other settings which can cause this error? Thanks for any help.</p>
  
  <p>p/s: I am using Ruby on Rails web framework, Redis database is used for Sidekiq.</p>
  
  <p>Edited: Redis version is 2.8.4. Server is hosted on AWS.</p>
  
  <p>Currently, I decided to set a password for Redis server so that it can not be set password when it is running.</p>
  
  <p>(When Redis server is restarted, it will work normal. You can run <code>sudo service redis-server restart</code> to restart Redis server.)</p>