From https://forums.docker.com/t/how-do-i-change-the-docker-image-installation-directory/1169
service docker stop
# DOCKER_OPTS="-dns 8.8.8.8 -dns 8.8.4.4" DOCKER_OPTS="-g /mnt"
service docker start
https://linuxconfig.org/how-to-move-docker-s-default-var-lib-docker-to-another-directory-on-ubuntu-debian-linux