title: How do I run a script when ip-address changes (most likely using a dhclient hook) on a (Ubuntu) Linux machine?
body: <p>I have a script which contacts a few sources and tell them "the IP-address XXX.XXX.XXX.XXX is my current one". My test web server has a dynamic IP-address through DHCP and amongst other things it needs to update a DDNS entry when its IP-address changes. However it's not the only thing it does, so I will need to run my own custom script.</p>
  
  <p>I suspect that this is possible by a attaching the script to be run for a given dhclient hook. However I still need to know which hook I should use, and how.</p>