For dynamic updating of dns, don't use ddclient or cron scripts on the server. Instead use inadyn.

Ddclient is more or less just dead/maintenance mode.

also using cron scripts kinda sucks and is ugly.

just use inadyn and spare yourself headache.

You'd basically just add something like this to the inadyn.conf file

provider duckdns.org {
    username         = YOUR_TOKEN
    password         = noPasswordForDuckdns
    hostname         = YOUR_DOMAIN.duckdns.org
}