解决方法：
查看是否存在进程：
$ ps aux |grep docker停止进程
$sudo service docker stop重启docker：
$dockerd或者:
If you see an error such as the following, your Docker client may be configured to connect to a Docker daemon on a different host, and that host may not be reachable.
Cannot connect to the Docker daemon. Is ‘docker daemon’ running on this host? To see which host your client is configured to connect to, check the value of the DOCKER_HOST variable in your environment.
$ env | grep DOCKER_HOST If this command returns a value, the Docker client is set to connect to a Docker daemon running on that host. If it is unset, the Docker client is set to connect to the Docker daemon running on the local host. If it is set in error, use the following command to unset it:
$ unset DOCKER_HOST You may need to edit your environment in files such as ~/.bashrc or ~/.profile to prevent the DOCKER_HOST variable from being set erroneously.
If DOCKER_HOST is set as intended, verify that the Docker daemon is running on the remote host and that a firewall or network outage is not preventing you from connecting.
