If you receive the following error message while running a CircleCI 2.0 build:
Cannot connect to the Docker daemon at unix:///var/run/docker.sock.
Is the docker daemon running?
You may also encounter the following error:
Exception message: /home/circleci/.docker/config.json (No such file or directory)
This typically indicates that you are running a docker command without using remote docker.
In order to run any docker command on CircleCI 2.0 you need to add the setup_remote_docker step as described in the following documentation. You can also use the machine executor.