Comment 4 for bug 806559

Michael,

does update-manager set something that /var/lib/dpkg/info/lightdm.config can read to see whether this is a dist-upgrade instead of a normal package installation? Or can it be changed to export something which indicates that? Or can lightdm.config just check if update-manager is in its parental chain?

Then the db_input could be guarded:

 if [ dist_upgrade running ];
    # set default to lightdm
else
    db_input
fi