Couldn't connect to Docker daemon at http+unix://var/run/docker.sock - is it running?

Docker Compose raise error below.

$ docker-compose up Couldn't connect to Docker daemon at http+unix://var/run/docker.sock - is it running? If it's at a non-standard location, specify the URL with the DOCKER_HOST environment variable.

$(docker-machine env MACHINE NAME) solved the problem.

$(docker-machine env dev)