📝 Script Description

This script automatically updates your DuckDNS domain with your current public IP address. It is designed to run on a Raspberry Pi (or any Linux system) and ensures your DuckDNS hostname always points to your correct external IP — useful when your home internet IP changes.

🔍 How it works

1. Fetches your public IP: The script detects your current external (WAN) IP address by using the following external service: https://api.ipify.org

2. Checks for changes: It compares the current IP with the last recorded IP (stored in a local file).

3. Updates DuckDNS only when needed: If the IP has changed, it sends an update request to DuckDNS. If the update is successful, it logs the change and saves the new IP. If the IP hasn’t changed, it does nothing (no log, no update).

4. Logs actions: It only logs events when the IP changes or if there’s an error. Logs include date, time, old IP, new IP, and the result of the update attempt.

5. Runs automatically via cron: You schedule it with cron to run every few minutes, keeping your DuckDNS address up-to-date without manual effort.

🧰 Step-by-Step Setup

1. 📁 Create a directory for the script:

mkdir -p ~/duckdns; cd ~/duckdns

2. 📝 Download the script file

wget https://raw.githubusercontent.com/honel/duckdns-updater-script/refs/heads/main/duckdns_updater.sh

3. 📂 Edit the script: In the configuration section of the script, find the following variables and replace them with your actual information: DUCKDNS_DOMAIN and DUCKDNS_TOKEN

Example:

DUCKDNS_DOMAIN="myraspberrypiexample.duckdns.org"
DUCKDNS_TOKEN="abc123def456ghi789"

If you are running the script not as root you should modify the LOG_FILE and the LAST_IP_FILE location variables in the "Configuration" section of the script:

LOG_FILE="/var/log/duckdns_updater.log"
LAST_IP_FILE="/var/tmp/last_duckdns_ip.txt"

For example, change them to:

LOG_FILE="$HOME/duckdns/duckdns_updater.log"
LAST_IP_FILE="$HOME/duckdns/last_duckdns_ip.txt"

4. ✅ Make the script executable:

chmod +x duckdns_updater.sh

5. 🔁 Set up a cron job (as your user): Open your user’s crontab:

crontab -e

Add the last line of the following block to your cron job list to run it every 5 minutes:

# ┌───────────── minute (0 - 59)
# │  ┌───────────── hour (0 - 23)
# │  │  ┌───────────── day of month (1 - 31)
# │  │  │   ┌───────────── month (1 - 12)
# │  │  │   │   ┌───────────── day of week (0 - 7) (Sunday=0 or 7)
# │  │  │   │   │
# │  │  │   │   │
# m  h dom mon dow   command
 */5 *  *   *   *    ~/duckdns/duckdns_updater.sh  # runs every 5 minutes

You can check if your crontab job is in the current crontab with:

crontab -l

6. 🔍 Check if it works After a few minutes, check the log:

cat ~/duckdns/duckdns_updater.log

You should see lines like:

2025-04-22 11:25:00 - IP changed from (none) to 203.0.113.42
2025-04-22 11:25:01 - DuckDNS update successful

🧠 Note: You can also tail the log and follow changes as they happen, e.g.:

tail -f ~/duckdns/duckdns_updater.log

The script will only log when the IP changes or something goes wrong.