mac上裝完boot2docker之後，想測試一下docker，結果書上的例子出錯：

$ sudo docker run hello-world           

Post http:///var/run/docker.sock/v1.19/containers/create: dial unix /var/run/docker.sock: no such file or directory. Are you trying to connect to a TLS-enabled daemon without TLS?

解決辦法：不要加sudo

$ docker run hello-world 

Hello from Docker.

This message shows that your installation appears to be working correctly.

...

原因如下：

When you use boot2docker, the docker daemon is running in a VM, essentially on a different machine. To communicate with a docker daemon on another machine, you must use the TLS connection (over HTTPS to the daemon's REST API). That's why you had to set up DOCKER_HOST

and DOCKER_CERT_PATH. Since the daemon is running on a different machine, you don't need to be root to communicate with it because outgoing http connections don't require root, unlike trying to talk with the unix:///var/run/docker.sock socket.

But when you run sudo docker, suddenly you're a different user, you're root

. The environment variables you set as your regular account are not set. So the docker CLI uses its default communication method: the unix socket. The socket isn't there, because the daemon is running on a different machine (the boot2docker vm). Hence the error message.

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