Plan: make my server into a good file server for Macs with Time Machine support.

Found this page: Howto: Make Ubuntu a Perfect Mac File Server and Time Machine Volume

Did:

sudo apt-get build-dep netatalk
sudo apt-get install cracklib2-dev fakeroot libssl-dev
sudo apt-get source netatalk
cd netatalk-2*
sudo DEB_BUILD_OPTIONS=ssl dpkg-buildpackage -rfakeroot
sudo dpkg -i ~/netatalk_2*.deb

Hm, got errors at this point. Hope it won't be a problem.

Did:

echo "netatalk hold" | sudo dpkg --set-selections

Followed the instructions modifying settings file. Left the printer service and old appletalk in, since it seems like the printer daemon was dependent on the old appletalk stuff.
Added -ipaddr to the /etc/netatalk/afpd.conf to make sure the intranet IP address was chosen.

To open up the firewall, did:

sudo ufw allow proto tcp from any to 172.16.1.21 port 548
sudo ufw allow proto udp from any to 172.16.1.21 port 5353

After a bit of 'fippling' by following the article's instructions for creating a disk image etc, it works!