Correct way to start docker daemon listening to specific port

On Ubuntu (16.04 LTS) with docker-ce (17.03.1~ce-0~ubuntu-xenial) do the following to make docker listen to a TCP port instead of sockets.

Add a file /etc/systemd/system/docker.service.d/override.conf with the following content:

[Service]ExecStart=ExecStart=/usr/bin/dockerd

Add a file /etc/docker/daemon.json with the following content

{    "hosts": [        "tcp://127.0.0.1:2375"    ] }

Reload (systemctl daemon-reload) and restart (systemctl restart docker.service) docker.

For reference: https://github.com/moby/moby/issues/25471

EDIT:

Be careful, so the demon will only listen to that network port ignoring local requests.To make docker listen to both remote and local, edit daemon.json but keep the standard unix socket

{        "hosts" : [                "unix:///var/run/docker.sock",                "tcp://<docker-host-ip-or-localhost>:2375"        ]}

Docker daemon connection options docs

On Mac OSX you'd run the Docker Quickstart Terminal App to see:

Machine default already exists in VirtualBox.Starting machine default...Started machines may have new IP addresses. You may need to re-run the `docker-machine env` command.Setting environment variables for machine default...

...

                        ##         .                  ## ## ##        ==               ## ## ## ## ##    ===           /"""""""""""""""""\___/ ===      ~~~ {~~ ~~~~ ~~~ ~~~~ ~~~ ~ /  ===- ~~~           \______ o           __/             \    \         __/              \____\_______/docker is configured to use the default machine with IP 192.168.99.100For help getting started, check out the docs at https://docs.docker.com

now

docker ps

should work

On Linux e.g. Ubuntu prepending sudo might be necessary. E.g.

docker ps

will lead to:

Get http:///var/run/docker.sock/v1.20/containers/json: dial unix /var/run/docker.sock: permission denied.* Are you trying to connect to a TLS-enabled daemon without TLS?* Is your docker daemon up and running?

but

sudo docker ps

will work.

See https://docs.docker.com/articles/basics/

To check if your docker service is running you can call

 sudo service --status-all 2>&1 | grep docker

and it should show:

[ - ]  docker

Sometimes your docker instllation might be corrupt see: Docker daemon does not start or restart

I found a solution to my problem. I specified docker running on IP x and Port y, but docker then only listens to that socket. I had to add another -H flag with the unix socket in order to listen to local requests:

sudo /usr/bin/docker daemon -H tcp://0.0.0.0:5555 -H unix:///var/run/docker.sock