Doug Dalton: ddns for linux / unix in a simple cron job

Here is a script to update your dynamic dns for linux / unix...

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!

Doug Dalton

CTO :: Unix, PHP, Mysql, WebDAV and Random other topics

ddns for linux / unix in a simple cron job

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