docker: Cannot connect to the Docker daemon at unix:///var/run/docker.sock. Is the docker daemon running?

 Issue:

docker: Cannot connect to the Docker daemon at unix:///var/run/docker.sock. Is the docker daemon running?

Fix:

• sudo update-alternatives --config iptables
• choose 1 : "/usr/sbin/iptables-legacy"
• sudo service docker start
• sudo service docker status