How to change Docker data directory in ubuntu

If you have a lot of Docker images, containers, volumes etc on your root partition and removing all unnecessary stuff with docker system prune didn’t help- you might want to move your Docker data out of the root partition to a different partition (for example, /home partition).
Here are the steps to do that.

Stop the Docker daemon if it is running

sudo service docker stop

Copy existing data to the new location

• Create the new directory if it doesn’t exist already
  mkdir -p /new/path (for example, mkdir -p /home/user/docker)
• Copy the data over from /var/lib/docker (Docker creates data there by default)
  sudo cp -a /var/lib/docker/ /new/path

Let docker know of this new location

• Create /etc/docker/daemon.json if doesn’t exist
  sudo touch /etc/docker/daemon.json

• Add/replace "data-root" to "/new/path" (for example: "data-root": "/home/username/docker").

Important: ~/ shorthand will not work. For example, you can not put "data-root": "~/docker"

For a newly created file, the file will look like this:

{ 
   "data-root": "/new/path" 
}

Remove existing data

• You may want to keep a backup first:
  sudo mv /var/lib/docker /var/lib/docker-backup
  and delete these once you confirm docker is working fine
  sudo rm -rf /var/lib/docker-backup

• OR, delete them parmanently now 🤷
  sudo rm -rf /var/lib/docker

Start docker and check if everything is running like before

sudo service docker start