Execute command upon interface initialization?

[Lowell Gilbert]

Roland Smith <rsmith at xs4all.nl> writes:

> On Tue, Apr 17, 2007 at 06:02:25PM +0300, Ido Admon wrote:
>> Hello list,
>> I couldn't find any way to execute an arbitrary command upon network
>> interface initialization. My situations is that I have and ethernet card
>> that takes DHCP from a cables provider (not a fixed IP address) and I
>> need to update a DynDNS hostname everytime it does (everytime the IP
>> changes).
>> I couldn't find a way to execute shell commands using the rc system or
>> dhclient, what did I miss?
>
> dhclient-script(8)? Maybe devd(8) will work as well.

devd won't work as well, because the timing is a bit off (even if you
only get new addresses at boot time, which isn't guaranteed.  
 
dhclient-script already has a capability ("hooks") for running scripts
at the appropriate times.  If you check the mailing list archive, I
know I have previously posted the script I used to use for exactly the
same purpose.