Comment 5 for bug 1901648

I have the same problem with a ZFS-based docker deployment.

The issue in my case seems to be, that /var/lib/dpkg/info/docker.io.postinst assumes/hard-coded, that the docker content should be located under the the /var/lib/docker directory. It then tries to migrate this off into a separate dataset.

Too bad: I already created a dedicated ZFS dataset for Docker on my own. And it's also in a different place: My /etc/docker/daemon.json has the following content

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

And this is also already a separate ZFS dataset:

   # findmnt -n -o SOURCE /srv/docker
   z4tank/docker

Looking at the docker.io.postinst file, the problem is that it hard-coded always assume /var/lib/docker and does not respect a potential diverting "data-root" setting:

https://git.launchpad.net/ubuntu/+source/docker.io/tree/debian/docker.io.postinst?h=applied/ubuntu/focal-updates#n38

@raczkow @etjohns2 : Do you both share something from my setting? i.e. a preconfigured ZFS dataset or a non-default data-root configuration?