title: Docker command can't connect to Docker daemon
body: <p>I want to make a move to Docker, so I've just started to mess around with it. I've installed Docker on a VirtualBox Ubuntu 15.10 (Wily Werewolf) installation and as <a href="https://blog.docker.com/2015/04/tips-for-deploying-nginx-official-image-with-docker/" rel="noreferrer">suggested here</a> I then tried running a basic <a href="http://en.wikipedia.org/wiki/Nginx" rel="noreferrer">nginx</a> Docker image:</p>
  
  <pre><code>$ docker run --name mynginx1 -P -d nginx
  Cannot connect to the Docker daemon. Is the docker daemon running on this host?
  </code></pre>
  
  <p>So I checked out whether Docker was running:</p>
  
  <pre><code>$ sudo service docker status
  ● docker.service - Docker Application Container Engine
     Loaded: loaded (/lib/systemd/system/docker.service; enabled; vendor preset: enabled)
     Active: active (running) since vr 2015-11-06 08:41:48 CET; 15min ago
       Docs: https://docs.docker.com
   Main PID: 7542 (docker)
     CGroup: /system.slice/docker.service
             └─7542 /usr/bin/docker daemon -H fd://
  
  nov 06 08:41:47 kramer65-VirtualBox systemd[1]: Starting Docker Application Container Engine...
  nov 06 08:41:47 kramer65-VirtualBox docker[7542]: time="2015-11-06T08:41:47.900410966+01:00" level=info msg="API ...ock"
  nov 06 08:41:48 kramer65-VirtualBox docker[7542]: time="2015-11-06T08:41:48.033514149+01:00" level=info msg="Fire...lse"
  nov 06 08:41:48 kramer65-VirtualBox docker[7542]: time="2015-11-06T08:41:48.141594321+01:00" level=info msg="Defa...ess"
  nov 06 08:41:48 kramer65-VirtualBox docker[7542]: time="2015-11-06T08:41:48.416294436+01:00" level=warning msg="Y...it."
  nov 06 08:41:48 kramer65-VirtualBox docker[7542]: time="2015-11-06T08:41:48.565507576+01:00" level=info msg="Load...rt."
  nov 06 08:41:48 kramer65-VirtualBox docker[7542]: time="2015-11-06T08:41:48.567907022+01:00" level=info msg="Load...ne."
  nov 06 08:41:48 kramer65-VirtualBox docker[7542]: time="2015-11-06T08:41:48.567945214+01:00" level=info msg="Daem...ion"
  nov 06 08:41:48 kramer65-VirtualBox docker[7542]: time="2015-11-06T08:41:48.567969891+01:00" level=info msg="Dock....9.0
  nov 06 08:41:48 kramer65-VirtualBox systemd[1]: Started Docker Application Container Engine.
  Hint: Some lines were ellipsized, use -l to show in full.
  </code></pre>
  
  <p>This suggests that the Docker daemon is actually already running, but to be sure I just started the Docker daemon manually:</p>
  
  <pre><code>$ sudo docker daemon
  INFO[0000] API listen on /var/run/docker.sock           
  INFO[0000] [graphdriver] using prior storage driver "aufs" 
  INFO[0000] Firewalld running: false                     
  INFO[0000] Default bridge (docker0) is assigned with an IP address XXX.XX.X.X/XX. Daemon option --bip can be used to set a preferred IP address 
  WARN[0000] Your kernel does not support swap memory limit. 
  INFO[0000] Loading containers: start.                   
  
  INFO[0000] Loading containers: done.                    
  INFO[0000] Daemon has completed initialization          
  INFO[0000] Docker daemon                                 commit=76d6bc9 execdriver=native-0.2 graphdriver=aufs version=1.9.0
  </code></pre>
  
  <p>I then tried running the image again, but with the same result:</p>
  
  <pre><code>$ docker run --name mynginx1 -P -d nginx
  Cannot connect to the Docker daemon. Is the docker daemon running on this host?
  </code></pre>
  
  <p>I tried sudo'ing the command, but to no avail. What am I doing wrong here? </p>