I have been able to remove the /etc/init.d/ddclient sh script with the appropriate /etc/rc*.d/*ddclient files and use the attached ddclient.service file in the /lib/systemd/system directory.
I have been able to remove the /etc/init. d/ddclient sh script with the appropriate /etc/rc* .d/*ddclient files and use the attached ddclient.service file in the /lib/systemd/system directory.