There are situations where you need to expose docker cli via a tcp port. For example when you use management tools like portainer.

On debian with systemd (stretch for example)

You need to add to ExecStart in /lib/systemd/system/docker.service: -H IP:2375:

root@uranus:/docker# ps -ef|grep -i dockerd
root     17570     1  1 02:28 ?        00:00:26 /usr/bin/dockerd -H fd:// --containerd=/run/containerd/containerd.sock
root     20778  2216  0 02:55 pts/0    00:00:00 grep -i dockerd
root@uranus:/docker# netstat -tlnp | grep -i dockerd
root@uranus:/docker# nano /lib/systemd/system/docker.service
root@uranus:/docker# grep ExecStart /lib/systemd/system/docker.service
ExecStart=/usr/bin/dockerd -H fd:// -H 192.168.11.10:2375 --containerd=/run/containerd/containerd.sock
root@uranus:/docker# systemctl daemon-reload
root@uranus:/docker# /etc/init.d/docker restart
Restarting docker (via systemctl): docker.service.
root@uranus:/docker# netstat -tlnp | grep -i dockerd
tcp        0      0 192.168.11.10:2375      0.0.0.0:*               LISTEN      21021/dockerd       
root@uranus:/docker# ps -ef|grep -i dockerd
root     21021     1  1 02:55 ?        00:00:00 /usr/bin/dockerd -H fd:// -H 192.168.11.10:2375 --containerd=/run/containerd/containerd.sock
root     21157  2216  0 02:55 pts/0    00:00:00 grep -i dockerd

On debian without systemd(wheezy for example)

You need to add to DOCKER_OPTS in /etc/default/docker: -H IP:2375:

00:27:31 root@jupiter:~# ps -ef|grep -i dockerd|grep -v grep
root      4868     1  0 00:23 ?        00:00:00 /usr/bin/dockerd -p /var/run/docker.pid
00:29:46 root@jupiter:~# grep ^DOCKER_OPTS /etc/default/docker 
DOCKER_OPTS="-H 192.168.11.7:2375"

The docker process should now look like this:

00:29:54 root@jupiter:~# ps -ef|grep -i dockerd|grep -v grep
root      5747     1  0 00:28 ?        00:00:00 /usr/bin/dockerd -p /var/run/docker.pid -H 192.168.11.7:2375

On wheezy you may have by default another problem. Unix socket may not be setup by default and docker command will not work:

00:41:44 root@jupiter:~# docker container ls
Cannot connect to the Docker daemon at unix:///var/run/docker.sock. Is the docker daemon running?

You must configure unix socket too, in the same file. The modified like would be:

00:42:34 root@jupiter:~# grep ^DOCKER_OPTS /etc/default/docker
DOCKER_OPTS="-H unix:///var/run/docker.sock -H 192.168.11.7:2375"

The docker process should now look like this:

00:43:38 root@jupiter:~# ps -ef|grep -i dockerd|grep -v grep
root      5747     1  0 00:28 ?        00:00:00 /usr/bin/dockerd -p /var/run/docker.pid -H unix:///var/run/docker.sock -H 192.168.11.7:2375

And now docker command works (no running containers, ignore that):

00:43:44 root@jupiter:~# docker container ls
CONTAINER ID        IMAGE               COMMAND             CREATED             STATUS              PORTS               NAMES