Shutting down my Pi safely

Question

I was looking at How to shut down RPi when running headless and really happy to see the awesomeness!

So, is it possible to use udev rule to shutdown my Pi when I switch off the router that connects my Pi with the eth cable?

Answer 1

You could write a script that checks the content of the file /sys/class/net/eth0/operstate in a loop. When the state shows down execute the halt command on your RPi.

Something like:

while true
    grep 'down' /sys/class/net/eth0/operstate && halt
    sleep 5
done

Or, even better with a cron job run, say, every 2 minutes:

*/2 * * * * root /bin/grep 'down' /sys/class/net/eth0/operstate && halt -p