how to get notified for IP address changes automatically

Question

In linux is there any method like callback or signal to get notified whenever there is any change in the IP Address. I want to register a callback with with kernel or get a signal from kernel which is done automatically rather my code polling on the socket.

thanks in advance.

Answer 1

Without C programming: the command

$ ip monitor

produces output on its stdout, whenever some configuration in the IP subsystem changes. The command

# ip addr add 10.10.10.10/24 dev em1 

produces the following output

2: em1    inet 10.10.10.10/24 scope global em1
local 10.10.10.10 dev em1  table local  proto kernel  scope host  src 0.10.10.10 
10.10.10.0/24 dev em1  proto kernel  scope link  src 10.10.10.10 
broadcast 10.10.10.0 dev em1  table local  proto kernel  scope link  src 10.10.10.10 
broadcast 10.10.10.255 dev em1  table local  proto kernel  scope link  src 10.10.10.10 

deleting the 10.10.10.10 addresss with the command

# ip addr del 10.10.10.10/24 dev em1

produces the following output

Deleted 2: em1    inet 10.10.10.10/24 scope global em1
Deleted 10.10.10.0/24 dev em1  proto kernel  scope link  src 10.10.10.10 
Deleted broadcast 10.10.10.255 dev em1  table local  proto kernel  scope link  src 10.10.10.10 
Deleted broadcast 10.10.10.0 dev em1  table local  proto kernel  scope link  src 10.10.10.10 
Deleted local 10.10.10.10 dev em1  table local  proto kernel  scope host  src 10.10.10.10 

you can use either the shell and some awk or perl to process these messages, or you can use the popen() and friends C library functions and process the outpout in C.

Using C programming you can hook into the kernel via NETLINK. This is rather complicated and not very well documentd. See this Wikipedia article for a starting point into the Netlink interface.