In the setup of series 13, I receive too many email telling my IP address of both diskstations. I think I should receive email alert ONLY when public IP address is changed.
The simple script I written here is running non-stop for a year, it is working just fine on my DS
So I wrote another bash script and have it run on my diskstations. Since it generate email only when IP address is changed, I can have the diskstations run the script like every 15 minutes.
Noted: the script need wget, bash and nail to work.
You need to edit /etc/crontab and restart cron daemon in order to have Diskstation to execute the scripts periodically.
Following /etc/crontab executes the script per 15 minutes.
*/15 * * * * root /bin/sh /opt/bin/checkip.sh
To restart cron daemon:
DiskStation> /usr/syno/etc/rc.d/S04crond.sh stop
DiskStation> /usr/syno/etc/rc.d/S04crond.sh start
Update Jul 26 2009
After over 12 hours testing, the script is working and I’m receiving email alert only when IP is changed now. 
The script is in page 2.
[...] The disadvantage for this solution is that you will receive email alert even your public IP is remains unchanged. Another script is written to detect and send email alert only when public IP is changed. [...]