I have my domain name registered at OVH. To update a DNS address from a machine behind a dynamic IP, they provide a feature called DynHost. DynHost uses the same protocol as DynDNS for updating their website.

From your DNS Section of the OVH manager webapp, you can create a DynHost account: you will have to specify the DNS address you want to update, a username and password for this account.

Warning: The script that update your DynHost address sends your login and password uncrypted! Don’t use the same login/password as your main OVH Manager account.

Once created, you can configure your home server to update your DynHost.

Configure Updatedd

Updatedd is an utility recommended by OVH to update your address from Linux. You can find it here.

Get the sources:

~$ wget http://nongnu.askapache.com/updatedd/updatedd_2.6.tar.gz

Then, you will have to fix an error in a configuration file before compile it. Extract and edit the libovh file:

~$ tar xvf updatedd_2.6.tar.gz
~$ nano updatedd-2.6/src/plugins/libovh.h

And replace the host ovh.com on line 24 by www.ovh.com. You should have:

define DYNDNSHOST "www.ovh.com"

We can now compile updatedd:

~$ ./configure
~$ make
~$ sudo make install

You can now use updatedd to update your domain name with the command:

updatedd ovh -- --ipv4 yourIP dynHostUsername:dynHostPassword host

Automate the DynHost Update

To update your account, create a script and run it on a daily base with cron.

Create a Script with this content:

#!/bin/bash

## dynhost parameters
username=dynHostUser
password=dynHostPassword
host=yourmain.com

##Log (1=true,0=false)
log_change=1
log_no_change=0
log_file=/var/log/dynhost.log

#File with old IP
old_ip_file=/var/cache/ip_old

touch ${old_ip_file}
touch ${log_file}

#Get public IP
ip="`dig +short myip.opendns.com @resolver1.opendns.com`"
ip_old=`cat ${old_ip_file}`

#Compare IP
if [ "${ip}" = "${ip_old}" ]
then 
   if [ "${log_no_change}" = "1" ]
   then
      echo `date`: No IP change was found >> ${log_file}
   fi
else
   echo ${ip} > ${old_ip_file}
   if [ "${log_change}" = "1" ]
   then
      echo "`date`:IP has changed. (Old : ${ip_old}, New : ${ip})" >> ${log_file}
      updatedd ovh -- --ipv4 ${ip} ${username}:${password} ${host} >> ${log_file}
   else
      updatedd ovh -- --ipv4 ${ip} ${username}:${password} ${host}
   fi
fi

Don’t forget to change DynHost parameters with yours in the script.

Make the script executable and put both updatedd and your script in a folder in your path. For instance:

~$ chmod +x yourscript 
~$ cp updatedd yourscript /usr/local/bin

Finally, put into your cron so that it is executed on a daily base (here every 30 minutes):

sudo echo "30  *    * * *   root    your-script" >> /etc/crontab

The steps and scripts described here have been adapted from this article. This steps should work for any provider supporting DynDNS protocol.