Am I trying to connect to a TLS-enabled daemon without TLS?

Question

I\'m trying to learn about Docker, but I keep getting cryptic (to me) error messages.

Possibly the simplest example of this is trying to print the version of Docker

Answer 1

The underlining problem is simple – lack of permission to /var/run/docker.sock unix domain socket.

From Daemon socket option chapter of Docker Command Line reference for Docker 1.6.0:

By default, a unix domain socket (or IPC socket) is created at /var/run/docker.sock, requiring either root permission, or docker group membership.

Steps necessary to grant rights to users are nicely described in Docker installation instructions for Fedora:

Granting rights to users to use Docker

The docker command line tool contacts the docker daemon process via a socket file /var/run/docker.sock owned by root:root. Though it's recommended to use sudo for docker commands, if users wish to avoid it, an administrator can create a docker group, have it own /var/run/docker.sock, and add users to this group.

$ sudo groupadd docker
$ sudo chown root:docker /var/run/docker.sock
$ sudo usermod -a -G docker $USERNAME

Log out and log back in for above changes to take effect. Please note that Docker packages of some Linux distributions (Ubuntu) do already place /var/run/docker.sock in the docker group making the first two of above steps unnecessary.

In case of OS X and boot2docker the situation is different; the Docker daemon runs inside a VM so the DOCKER_HOST environment variable must be set to this VM so that the Docker client could find the Docker daemon. This is done by running $(boot2docker shellinit) in the shell.