wiki/docs/Docker/move-volume.md

Move Docker program data

Docker stores all its data in /var/lib/docker by default. This is usually fine, but this directory grows quickly, so we'll move it to /mnt/big-stuff/docker-program-data/

Edit /lib/systemd/system/docker.service and add the --data-root option to the ExecStart line:

ExecStart=/usr/bin/dockerd --data-root /mnt/big-stuff/docker-program-data/ -H fd:// $DOCKER_OPTS

If you've already done stuff with docker, you'll need to move the data:

sudo systemctl stop docker
sudo mv /var/lib/docker/ /mnt/big-stuff/docker-program-data/
sudo systemctl daemon-reload
sudo systemctl start docker

You may also need to set up some symlinks:

ln -s source_file link_file