title: Cannot connect to the Docker daemon. Is the docker daemon running on this host?
body: <p>I have installed docker on ubuntu 14.04, it told me installed successfully. Then I entered <code>sudo docker version</code>, it returned</p>
  
  <pre><code>Client:
   Version:      1.9.1
   API version:  1.21
   Go version:   go1.4.2
   Git commit:   a34a1d5
   Built:        Fri Nov 20 13:12:04 UTC 2015
   OS/Arch:      linux/amd64
  Cannot connect to the Docker daemon. Is the docker daemon running on this host?
  </code></pre>
  
  <p>I entered <code>sudo service docker status</code>, I got </p>
  
  <pre><code>docker start/running, process 8063
  </code></pre>
  
  <p>I tried <code>sudo docker images</code> and <code>sudo docker info</code>, I got the same reply:</p>
  
  <pre><code>Cannot connect to the Docker daemon. Is the docker daemon running on this host?
  </code></pre>
  
  <p>I do not know why it returned this, I tried to pull ubuntu using <code>sudo docker pull ubuntu</code>, and got </p>
  
  <pre><code>Using default tag: latest
  Cannot connect to the Docker daemon. Is the docker daemon running on this host?
  </code></pre>
  
  <p>Please tell me how can I solve this problem, how can I pull and run docker image. And is <code>docker -d</code> the same as <code>docker deamon</code>?</p>