duckdns-systemd

Duck DNS updater script with a dedicated systemd unit and logging configuration

Why this script over the default cron entry?

This script only updates the IP if it has actually changed, instead of connecting to www.duckdns.org every X minutes.
This script logs to a file, which is useful for diagnostics.
The suggested command uses curl -k, which does not verify the server certificate, making the connection vulnerable to MiTM, see here. Probably they did this because some embedded devices like routers may not have a trust store to check the certificate against.

Installation

Install dig to query the DNS for the current IP addres, and curl to use the API

sudo apt install dnsutils curl

Clone the repository

git clone https://github.com/orazioedoardo/duckdns-systemd.git

Copy the script to some location, for example ~/

cp duckdns-systemd/duckdns ~/

Setup the systemd unit

mkdir -p ~/.config/systemd/user
cp duckdns-systemd/conf/duckdns.service ~/.config/systemd/user/
nano ~/.config/systemd/user/duckdns.service

Change the line ExecStart=... to point to the FULL PATH to the script, for example /home/user/duckdns in this case

Setup logging and log rotation

sudo cp duckdns-systemd/conf/duckdns /etc/logrotate.d/
sudo chown root:root /etc/logrotate.d/duckdns
sudo cp duckdns-systemd/conf/20-duckdns.conf /etc/rsyslog.d/
sudo chown root:root /etc/rsyslog.d/20-duckdns.conf
sudo systemctl restart rsyslog

Now create the configuration file for the script

mkdir ~/.duckdns
nano ~/.duckdns/config

Enter your token, the domain (without .duckdns.org) and the number of seconds between checks, example:

TOKEN=310eff65-bd83-4c52-b655-9d1f8d1036dc
DOMAIN=mydomain
INTERVAL=300

Start and enable the service

sudo loginctl enable-linger $(whoami)
systemctl --user daemon-reload
systemctl --user start duckdns
systemctl --user enable duckdns

Check that the service is indeed working

$ systemctl --user status duckdns
● duckdns.service - Duck DNS Updater
   Loaded: loaded (/home/user/.config/systemd/user/duckdns.service; enabled; vendor preset: enabled)
   Active: active (running) since Tue 2019-09-03 16:55:16 CEST; 8s ago
 Main PID: 711 (duckdns)
   CGroup: /user.slice/user-1000.slice/user@1000.service/duckdns.service
           ├─711 /bin/bash /home/user/duckdns
           └─722 sleep 300

set 03 16:55:16 debian systemd[499]: Started Duck DNS Updater.
set 03 16:55:16 debian duckdns[716]: Initialization succeeded, domain: mydomain.duckdns.org, IP: 0.0.0.0

You can also check out the log at /var/log/duckdns.log