While upgrading docker you may get the following error:

Preparing to unpack .../0-docker.io_20.10.7-0ubuntu1~20.04.1_amd64.deb ...
The aufs storage-driver is no longer supported.
Please ensure that none of your containers are
using the aufs storage driver, remove the directory
/var/lib/docker/aufs and try again.
dpkg: error processing archive /tmp/apt-dpkg-install-qrebPX/0-docker.io_20.10.7-0ubuntu1~20.04.1_amd64.deb (--unpack):
 new docker.io package pre-installation script subprocess returned error exit status 1

The issue here is that docker has deprecated the AUFS storage driver, previously the default.

You can read about the details here.

To fix this do the following:

  1. Stop running containers

    From where you have your docker-compose.yml file, run the following command:

     sudo docker-compose down
  2. Stop docker

    Run the following command to stop the docker service:

     sudo systemctl stop docker
  3. Back up the current aufs location

     sudo cp -au /var/lib/docker /var/lib/docker.bak
  4. Clear the current aufs location

     sudo rm -rf /var/lib/docker/aufs/

    If you get the following error:

     rm: cannot remove 'aufs/mnt/7d07dfe17fda8a61bc2b90ec6bd02ba43166394dd2c91ed171864e5389ab8103': Is a directory
     rm: cannot remove 'aufs/mnt/98e8c98dabd63b3ebc36911416c808966b24fcb0367d66c294f0b4a4da273bed': Is a directory

    This means that your containers are probably still running, or docker has an active handle to one of more of your containers.

  5. Create / Update /etc/docker/daemon.json

    It should have the following contents:

         "storage-driver": "overlay2"
  6. Restart docker

    Run the following command

     sudo systemctl start docker

To verify that it worked, run the following command:

docker info

If you see the following, it was a success.

You can now restart your containers.

sudo docker-compose up -d

Note that this will re-download and recreate the images and volumes.

You can now upgrade your docker.

If everything runs OK after upgrading and restarting your containers, you can delete the backups.

Happy hacking!