Docker saves it’s images, volumes, networks etc in /var/lib/docker. Sometimes it is useful to move this directory to another location. For example a separate disk mounted under /opt.
This can be done by specifying the data-root in the /etc/docker/daemon.json configuration-file.

/etc/docker/daemon.json

{
	"data-root": "/opt/docker"
}

For these changes to take affect, you need to restart the Docker-service.

Warning! This will restart your containers as well. That means a short downtime for your services.

If you want to migrate an existing installation, you should copy the present data into the new directory before restarting the service.
If you have a new Docker installation, you can skip this step.

[tux@server]$ sudo cp -r /var/lib/docker /opt/docker

Now restart the service.

[tux@server]$ sudo systemctl restart docker

From now on all data will be saved in the new directory.