docker.io package fails install if docker group is pre-existing

[Charles Butler]

When installing the docker.io package, it fails during installation with a message akin to the following:

stderr: 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
Errors were encountered while processing:
 docker.io
E: Sub-process /usr/bin/dpkg returned an error code (1)

This was originally discovered during charm development where a user can switch from the canonical docker package to the docker maintained package 'lxc-docker'. With the upstream package, they are not maintaining a docker-group in the charm, and allows for installation regardless of the presence of the group. While the docker.io package will halt installation in a panic if it exists - regardless if its a system group or not. Just the presence alone appears to be the key factor in the failure.

I don't think this behavior is correct - as a user may have created a docker group themselves, and expect to install the docker.io package from the repository after removing the latest - due to a bug or any number of reasons.

I'm linking the commit to the charm and the user stack trace for additional validation/investigation if required:

https://github.com/chuckbutler/docker-charm/commit/59946a7bd6bfa3cc050de3b27e62d3207c71be47

https://gist.github.com/slatunje/735e1e5132de02a3ad1d

[Paul Tagliamonte (paultag)]

I'm marking this as Opinion.

Here's why:

The local sysadmin may have created a Docker group, but *not* intended to give the rights to use Docker to those users. Remember, the Docker group is root equivelent.

    [tag@cassiel:~][⌚ 09:02 PM] ♥ docker run -it --rm -v /./:/mnt debian:unstable chroot /mnt
    # ls /home
    tag

As such, on conflict, I'd prefer a failure to install.

Marking Opinion.

[Paul Tagliamonte (paultag)]

Honestly, this is a bug in lxc-docker for not cleaning up on postrm :)

[Charles Butler (lazypower)]

I suppose that's a fair assesment. We took this route to clean up the charm code as well - just removing the group, but having a bug here marked as opinion shows the due dilligence :)

Thanks for the rapid response Paul!

[gomex (gomex-y)]

I have the same problem. Can you please fix this package configuration?