Assuming, your script has the name sound_notifier and it's placed in /usr/bin:

sudo chmod +x /usr/bin/sound_notifier


Create a script /etc/network/if-up.d/start_sound_notifier

sudo nano /etc/network/if-up.d/start_sound_notifier


add the code below

#!/bin/sh
if [ "$METHOD" = loopback ]; then
    exit 0
fi

# Only run from ifup.
# if [ "$MODE" != start ]; then
#    exit 0
# fi

sound_notifier


Make the script executable. 

sudo chmod +x /etc/network/if-up.d/start_sound_notifier


That's all

;)

How to execute a custom script when Internet reconnects?
In a previous question I asked how to add a column to the Posts page in the Administration section, and got a working answer. But now I need to know how to delete an existing column (e.g. the Date column) so that my customized Date column replaces it.
