Detect IP-Address change on an interface

Question

I would like to trigger a service when a change of an ip address on a specific interface occurs. Is there a target for this or some other method I am not aware of to achieve this using systemd on Linux (Kernel 3.19)?

The service would be used to send a SIGNAL to a defined process. The Linux is running on an embedded system.

Thanks!

score 1 · Answer 1 · edited May 23 '17 at 12:31

There is an solution in other question of StackOverflow. Just here: Detecting a change of IP address in Linux

I like this code, it's easy, you onli need a cron job with frecuency as you need (I made a little change):

#!/bin/bash
OLD_IP=`cat ip.txt`
NEW_IP=`/sbin/ifconfig  | awk -F "[: ]+'{ print $4}'`
if [ $NEW_IP != OLD_IP ]; then
    YOU_COMMAND <commands> 
    echo $NEW_IP > ip.txt
fi
exit 0

score 1 · Accepted Answer · edited May 23 '17 at 12:24

1

Because you use Systemd you might already use systemd-networkd for managing your devices instead of relying on 3rd party code.

You could use the structured journal output to get the last 2 ADDRESS field of the current BOOD_ID.(sadly, there is no notification mechanism for address changes in systemd-networkd):

→ sudo journalctl -F ADDRESS -u systemd-networkd -n 2
192.168.178.29

So, if there is only one line output, there was no address change.

edited May 23 '17 at 12:24

Community

1
1

answered Jun 15 '16 at 07:47

Jürgen Hötzel

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Not exactly what I was looking for, but I can work with that, thanks! – user3482407 Jun 16 '16 at 06:18
Btw, how do you know the name of the ADDRESS field? I was not able to find it in the docs anywhere... – user3482407 Jun 16 '16 at 06:22
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I used `sudo journalctl -u systemd-networkd -o json-pretty` to jeck the logging output of this service. – Jürgen Hötzel Jun 16 '16 at 07:30

Detect IP-Address change on an interface

2 Answers2