title: docker: Couldn't connect to Docker daemon
body: <p>I am running Ubuntu with the following docker software installed:</p>
  
  <pre><code>$ docker version
  Client:
   Version:      1.9.1
   API version:  1.21
   Go version:   go1.4.3
   Git commit:   a34a1d5
   Built:        Fri Nov 20 17:56:04 UTC 2015
   OS/Arch:      linux/amd64
  Cannot connect to the Docker daemon. Is the docker daemon running on this host?
  
  $ docker-compose -v
  docker-compose version 1.7.0, build 0d7bf73
  </code></pre>
  
  <p>When trying to run docker-compose I am getting the following error:</p>
  
  <pre><code>$ sudo docker-compose up
  ERROR: Couldn't connect to Docker daemon at http+docker://localunixsocket - is it running?
  
  If it's at a non-standard location, specify the URL with the DOCKER_HOST environment variable.
  </code></pre>
  
  <p>I have tried the following:</p>
  
  <pre><code>systemctl unmask docker.service
  systemctl unmask docker.socket
  systemctl start docker.service
  
  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 Fri 2016-04-29 13:36:57 CEST; 4min 3s ago
       Docs: https://docs.docker.com
   Main PID: 6394 (docker)
     Memory: 13.3M
        CPU: 119ms
     CGroup: /system.slice/docker.service
             └─6394 /usr/bin/docker daemon -H fd://
  
  Apr 29 13:36:57 Charles docker[6394]: time="2016-04-29T13:36:57.722083467+02:00" level=info msg="Default bridge (docker0) is assigned with an IP address 172.17.0.0/16. Daemon opt...d IP address"
  Apr 29 13:36:57 Charles docker[6394]: time="2016-04-29T13:36:57.805189862+02:00" level=warning msg="Your kernel does not support swap memory limit."
  Apr 29 13:36:57 Charles docker[6394]: time="2016-04-29T13:36:57.827955299+02:00" level=info msg="Loading containers: start."
  Apr 29 13:36:57 Charles docker[6394]: time="2016-04-29T13:36:57.828083895+02:00" level=info msg="Loading containers: done."
  Apr 29 13:36:57 Charles docker[6394]: time="2016-04-29T13:36:57.828095512+02:00" level=info msg="Daemon has completed initialization"
  Apr 29 13:36:57 Charles docker[6394]: time="2016-04-29T13:36:57.828125198+02:00" level=info msg="Docker daemon" commit=a34a1d5 execdriver=native-0.2 graphdriver=aufs version=1.9.1
  Apr 29 13:36:57 Charles systemd[1]: Started Docker Application Container Engine.
  Apr 29 13:37:10 Charles systemd[1]: Started Docker Application Container Engine.
  Apr 29 13:37:34 Charles systemd[1]: Started Docker Application Container Engine.
  Apr 29 13:38:01 Charles systemd[1]: Started Docker Application Container Engine.
  Hint: Some lines were ellipsized, use -l to show in full.
  anton@Charles:~/Documents/software/deliverable$ docker ps
  Cannot connect to the Docker daemon. Is the docker daemon running on this host?
  </code></pre>
  
  <p>Sudo?</p>
  
  <p>When I run using sudo docker seems to be running:</p>
  
  <pre><code>$ sudo docker ps
  CONTAINER ID        IMAGE               COMMAND             CREATED             STATUS              PORTS               NAMES
  $ docker ps
  Cannot connect to the Docker daemon. Is the docker daemon running on this host?
  </code></pre>
  
  <p>How can I fix this?</p>