The setup seems straightforward. In /etc/ddclient.conf you find:
# Configuration file for ddclient generated by debconf # # /etc/ddclient.conf pid=/var/run/ddclient.pid daemon=3600 protocol=dyndns2 ssl=yes use=web web=checkip.dyndns.com use=web web=checkip.dyndns.com/, web-skip="IP Address" syslog=yes server=members.dyndns.org login=your-own-id-here password='make-up-your-own' hostname-at-dyndns
[Update: Something about checkip changed enough that the old line didn’t work. The web-skip made it work again. ]
But, as the comment in that file shows, that’s not where you configure ddclient in (K)Ubuntu. You actually tweak the entries in /etc/default/ddclient so the right answer pops out when ddclient gets reconfigured by something or another.
It’s not clear to me how ddclient figures out when to update the DNS entry (when an update is “necessary”), so I also force an update by putting this in /etc/rc.local:
Actually, I added that tweak when I was setting up another, slightly newer, PC for her and managed to fire off ddclient from my network. That aimed the DNS entry at my IP address and, had I not already been signed into her system, would have locked me until her ddclient grabbed it back.
I hate it when that happens.
Memo to self: make sure the defaults match the current configuration.