问题：Cannot connect to the Docker daemon. Is the docker daemon running on this host?

问题：Cannot connect to the Docker daemon. Is the docker daemon running on this host?

从新启动 centOS 后，发现 Docker 命令会出现 Cannot connect to the Docker daemon. Is the docker daemon running on this host? 这个提示，研究了一下，发现缘由是未启动后台服务，键入下面命令后一切正常：

service docker start

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