Since many articles with the same purpose have already been posted, I have the regret of building a rooftop, but I think I have added some new knowledge and ingenuity, so I will post it as a memo for myself.
It is a CentOS 8 environment.
/root/ddnscheck.sh
ddnscheck.sh
#!/usr/bin/bash
# This script checks and updates ddns connection for this server.
# TARGET
TARGET="myserver.xxx.xx"
# Operating limit in seconds (default 16 hours : 4am to 8pm)
LIMIT=57600
if [ $# -ge 1 ]; then
let LIMIT=$1
fi
# Sleep seconds between pings
SLEEP=15
# Forced update limit in seconds (1 hour)
UPDATE_LIMIT=3600
# Overall loop counter
I=0
# Updating loop counter
J=0
echo "Going to check ddns for $LIMIT seconds ..." 1>&2
while [ $I -lt $LIMIT ];
do
echo -n "`date +"%m-%d %H:%M:%S"` " 1>&2
ping -4 -c1 -w5 $TARGET >> /dev/null
if [ $? == 0 ]; then
echo " OK." 1>&2
else
echo " Not Connected."
let J=$UPDATE_LIMIT
fi
if [ $J -ge $UPDATE_LIMIT ]; then
echo " Going to update DDNS ..."
wget -4 -O - https://mydns******:[email protected]/login.html 1>&2
wget -6 -O - https://mydns******:[email protected]/login.html 1>&2
let J=0
fi
sleep $SLEEP
let I=$I+$SLEEP
let J=$J+$SLEEP
done
echo "Operation finished." 1>&2
/etc/cron.d/ddnscheck
55 3 * * * root /root/ddnscheck.sh &> /var/log/nginx/ddnscheck.log
ddnscheck.sh runs for 57600 seconds (16 hours) by default. Every 15 seconds I type ping on my home server (or myself) with his DDNS server name, and if I don't get a response, I think my home server's global address has changed and MyDNS. Hit the JP address notification URL. Even if the address has not changed, notify MyDNS.JP of the address every hour. Start this script with cron daily at 3:55 AM.
The -4 and -6 used in ping and wget are switches that force operation on ipv4 or ipv6, respectively. When I accessed the address notification URL of MyDNS.JP with wget without these switches, only the ipv6 address was updated in my environment. That's not the case, so I'm doing the above.
Instead of changing the wget switch, you may change the URL of MyDNS.JP to a dedicated address as follows.
wget -O - https://mydns******:[email protected]/login.html 1>&2
wget -O - https://mydns******:[email protected]/login.html 1>&2
It is good to refer to the document of MyDNS.JP.