Comment 9 for bug 1769911

reverified on xenial:

root@xenial:~# apt-get purge -y docker.io
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following packages were automatically installed and are no longer required:
  bridge-utils cgroupfs-mount libfreetype6 libltdl7 pigz ubuntu-fan
Use 'apt autoremove' to remove them.
The following packages will be REMOVED:
  docker.io*
0 upgraded, 0 newly installed, 1 to remove and 0 not upgraded.
After this operation, 197 MB disk space will be freed.
(Reading database ... 39634 files and directories currently installed.)
Removing docker.io (18.06.1-0ubuntu1~16.04.2) ...
'/usr/share/docker.io/contrib/nuke-graph-directory.sh' -> '/var/lib/docker/nuke-graph-directory.sh'
Purging configuration files for docker.io (18.06.1-0ubuntu1~16.04.2) ...

Nuking /var/lib/docker ...
  (if this is wrong, press Ctrl+C NOW!)

+ sleep 10

+ rm -rf /var/lib/docker/builder /var/lib/docker/buildkit /var/lib/docker/containerd /var/lib/docker/containers /var/lib/docker/image /var/lib/docker/network /var/lib/docker/nuke-graph-directory.sh /var/lib/docker/plugins /var/lib/docker/runtimes /var/lib/docker/swarm /var/lib/docker/tmp /var/lib/docker/trust /var/lib/docker/vfs /var/lib/docker/volumes
dpkg: warning: while removing docker.io, directory '/etc/docker' not empty so not removed
Processing triggers for man-db (2.7.5-1) ...
root@xenial:~# delgroup docker
Removing group `docker' ...
Done.
root@xenial:~# addgroup docker
Adding group `docker' (GID 1001) ...
Done.
root@xenial:~# apt-get install docker.io/xenial-updates
Reading package lists... Done
Building dependency tree
Reading state information... Done
Selected version '17.03.2-0ubuntu2~16.04.1' (Ubuntu:16.04/xenial-updates [amd64]) for 'docker.io'
The following packages were automatically installed and are no longer required:
  libfreetype6 libltdl7 pigz
Use 'apt autoremove' to remove them.
Suggested packages:
  aufs-tools debootstrap docker-doc rinse zfs-fuse | zfsutils
The following NEW packages will be installed:
  docker.io
0 upgraded, 1 newly installed, 0 to remove and 0 not upgraded.
Need to get 0 B/17.1 MB of archives.
After this operation, 90.2 MB of additional disk space will be used.
Preconfiguring packages ...
Selecting previously unselected package docker.io.
(Reading database ... 39432 files and directories currently installed.)
Preparing to unpack .../docker.io_17.03.2-0ubuntu2~16.04.1_amd64.deb ...
Unpacking docker.io (17.03.2-0ubuntu2~16.04.1) ...
Processing triggers for man-db (2.7.5-1) ...
Processing triggers for ureadahead (0.100.0-19) ...
Processing triggers for systemd (229-4ubuntu21.10) ...
Setting up docker.io (17.03.2-0ubuntu2~16.04.1) ...
addgroup: The group `docker' already exists and is not a system group. Exiting.
dpkg: error processing package docker.io (--configure):
 subprocess installed post-installation script returned error exit status 1
Processing triggers for systemd (229-4ubuntu21.10) ...
Processing triggers for ureadahead (0.100.0-19) ...
Errors were encountered while processing:
 docker.io
E: Sub-process /usr/bin/dpkg returned an error code (1)
root@xenial:~# apt-get purge -y docker.io
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following packages were automatically installed and are no longer required:
  bridge-utils cgroupfs-mount libfreetype6 libltdl7 pigz ubuntu-fan
Use 'apt autoremove' to remove them.
The following packages will be REMOVED:
  docker.io*
0 upgraded, 0 newly installed, 1 to remove and 0 not upgraded.
1 not fully installed or removed.
After this operation, 90.2 MB disk space will be freed.
(Reading database ... 39533 files and directories currently installed.)
Removing docker.io (17.03.2-0ubuntu2~16.04.1) ...
'/usr/share/docker.io/contrib/nuke-graph-directory.sh' -> '/var/lib/docker/nuke-graph-directory.sh'
Purging configuration files for docker.io (17.03.2-0ubuntu2~16.04.1) ...

Nuking /var/lib/docker ...
  (if this is wrong, press Ctrl+C NOW!)

+ sleep 10

+ rm -rf /var/lib/docker/nuke-graph-directory.sh
dpkg: warning: while removing docker.io, directory '/etc/docker' not empty so not removed
Processing triggers for man-db (2.7.5-1) ...
root@xenial:~# apt-get install docker.io/xenial-proposed
Reading package lists... Done
Building dependency tree
Reading state information... Done
Selected version '18.06.1-0ubuntu1~16.04.2' (Ubuntu:16.04/xenial-proposed [amd64]) for 'docker.io'
The following package was automatically installed and is no longer required:
  libfreetype6
Use 'apt autoremove' to remove it.
Suggested packages:
  aufs-tools debootstrap docker-doc rinse zfs-fuse | zfsutils
The following NEW packages will be installed:
  docker.io
0 upgraded, 1 newly installed, 0 to remove and 0 not upgraded.
Need to get 0 B/40.3 MB of archives.
After this operation, 197 MB of additional disk space will be used.
Preconfiguring packages ...
Selecting previously unselected package docker.io.
(Reading database ... 39432 files and directories currently installed.)
Preparing to unpack .../docker.io_18.06.1-0ubuntu1~16.04.2_amd64.deb ...
Unpacking docker.io (18.06.1-0ubuntu1~16.04.2) ...
Processing triggers for ureadahead (0.100.0-19) ...
Processing triggers for systemd (229-4ubuntu21.10) ...
Processing triggers for man-db (2.7.5-1) ...
Setting up docker.io (18.06.1-0ubuntu1~16.04.2) ...
Processing triggers for systemd (229-4ubuntu21.10) ...
Processing triggers for ureadahead (0.100.0-19) ...
root@xenial:~#