ddns for linux / unix in a simple cron job

edit a script:

vi /root/ddns.sh

put in ddns.sh :

#!/bin/sh USER=<USER> PASSWD=<PASSWORD> DOMAIN=<doman.dns.com> WILDCARD=<ON|OFF> WGET=/usr/bin/wget FIND=/usr/bin/find # DynDNS Update Client for linux unix # Based on http://www.nslu2-linux.org/wiki/HowTo/DynDNSupdate # Version: 08/03/2006 # Look for err.ip if [ ! -f /var/tmp/err.ip ] then # On err.ip not found. # Set up err.ip for error logging. echo "off" > /var/tmp/err.ip fi # Fetch current IP Address. ${WGET} --quiet http://checkip.dyndns.org/ --output-document=/var/tmp/now.ip; # Verify the data is good. PAT='Current IP Address: *[0-9]*\.[0-9]*\.[0-9]*\.[0-9]*' if grep -q "$PAT" /var/tmp/now.ip; then # On good IP data. # Check for IP history. if [ -f /var/tmp/old.ip ] then # On history found. if [ "`cat /var/tmp/err.ip`" = "on" ] then echo "`date +%Y%m%d.%H%M%S` - not updated: Network connection restored." >> /var/log/ip_hist.log; # Turn err.ip Off echo "off" > /var/tmp/err.ip fi # Check for IP Change if [ "`cat /var/tmp/now.ip`" = "`cat /var/tmp/old.ip`" ] then # On no IP change # Check if 28 day refresh is needed. ${FIND} /var/tmp/ -name old.ip -mtime +28 -exec rm {} \; if [ -f /var/tmp/old.ip ] then # On no refresh needed. # Check for Next day. if [ ! "`cat /var/tmp/day.ip`" = "`date +%x`" ] then # On day change # Log entry echo "`date +%Y%m%d.%H%M%S` - No update - `cat /var/tmp/upd.ip`" >> /var/log/ip_hist.log; echo "`date +%x`" > /var/tmp/day.ip; fi else # On refresh needed. # Do a 28 Day refresh and Notify user with a distinguishable beep. ${WGET} --quiet "http://${USER}:${PASSWD}@members.dyndns.org/nic/update?hostname=${DOMAIN}&wildcards=${WILDCARD}" --output-document=/var/tmp/upd.ip; echo "`date +%Y%m%d.%H%M%S` - Refresh - `cat /var/tmp/upd.ip`" >> /var/log/ip_hist.log; echo "`date +%x`" > /var/tmp/day.ip; cp /var/tmp/now.ip /var/tmp/old.ip; fi else # On IP change # Update DynDNS with new IP Address. ${WGET} --quiet "http://${USER}:${PASSWD}@members.dyndns.org/nic/update?hostname=${DOMAIN}&wildcards=${WILDCARD}" --output-document=/var/tmp/upd.ip; # Log the IP change and notify user. echo "`date +%Y%m%d.%H%M%S` - update - `cat /var/tmp/upd.ip`" >> /var/log/ip_hist.log; echo "`date +%x`" > /var/tmp/day.ip; rm -f /var/tmp/old.ip; cp /var/tmp/now.ip /var/tmp/old.ip; fi else # On No History # Initialize client and Update DynDNS. # Check err.ip status if [ "`cat /var/tmp/err.ip`" = "on" ] then # Log Service Restoral. echo "`date +%Y%m%d.%H%M%S` - not updated: Network connection restored." >> /var/log/ip_hist.log; fi # Set err.ip off echo "off" > /var/tmp/err.ip ${WGET} --quiet "http://${USER}:${PASSWD}@members.dyndns.org/nic/update?hostname=${DOMAIN}&wildcards=${WILDCARD}" --output-document=/var/tmp/upd.ip; echo "`date +%Y%m%d.%H%M%S` - initialization - `cat /var/tmp/upd.ip`" >> /var/log/ip_hist.log; echo "`date +%x`" > /var/tmp/day.ip; cp /var/tmp/now.ip /var/tmp/old.ip; fi else # On IP read error # Check err.ip status if [ ! "`cat /var/tmp/err.ip`" = "on" ] then # On err.ip = off - Log read error. echo "`date +%Y%m%d.%H%M%S` - not updated: read error on ip fetch" >> /var/log/ip_hist.log; fi # Set err.ip = On to allow only one error log on next run. echo "on" > /var/tmp/err.ip fi # end # Set the interval of the next IP check using a crontab entry. # Once every 15 minutes is good for a home server.

chmod 755 ddns.sh

then store your crontab:

crontab -l > /root/crontab.new

edit the /root/crontab.new and add the line:

*/15 * * * * /root/ddns.sh &>/dev/null

then load the new crontab:

crontab /root/crontab.new

Your done! ddns is all ready to go!