In case you are hit by https://bugs.launchpad.net/ubuntu/+source/avahi/+bug/1760128 trying to upgrade avahi-dnsconfd in 16.04, there is now a workaround (comment #4 in the above link).
Thanks for this!
Encountered this while upgrading from 16.04 to 18.04, followed these instructions posted elsewhere:
sudo systemctl disable avahi-daemon
sudo apt update && sudo apt upgrade
sudo systemctl enable avahi-daemon
            That was quite annoying as the “Software Updater” propose me each day to update “Ubuntu Base” and failed with this 15 Kb update…
Thanks a lot @maximuscore for the workaround, it worked like a charm.
- 
in terminal
sudo systemctl disable avahi-daemon - 
I used the “Software Updater” GUI (System/Administration/Software Updater) to update the Ubuntu Base, once it was done (No failure this time!)
 - 
then in the terminal again
sudo systemctl enable avahi-daemon 
Done! Thank you so much!