You need to start the daemon with a separate command:
I got this from https://www.upcloud.com/support/how-to-configure-docker-swarm :
After the installation finishes, Docker usually starts up on its own, but for the next part to work you will need to stop it.
sudo service docker stop
Then run the daemon with the following command:
sudo nohup docker daemon -H tcp://0.0.0.0:2375 -H unix:///var/run/docker.sock &
The script leaves the daemon running in the background, and with the Docker ready you can test that it is accepting commands.
sudo docker info
To make working with Docker easier, you should add your username to
the Docker users group. Adding a user to the group can be done with the
command underneath by replacing the with your username.
sudo usermod -aG docker