Disable internet access for particular user in Ubuntu

This is very useful if you want to block internet access to your kids or particular users.First you need to edit the network interfaces file using the following command

sudo vi /etc/network/interfaces
or
sudo gedit /etc/network/interfaces 

Now you need to add the simple iptables rule to the interfaces file when the internet connection starts up. Simply add this under auto wlan0 or auto eth0 in the interfaces file
pre-up iptables -A OUTPUT -p tcp -m owner --uid-owner username -j DROP 

save and exit the file. Now you need to type in the terminal with the following command

sudo iptables -A OUTPUT -p tcp -m owner --uid-owner username -j DROP 

and switch users to the username you blocked and try to access the internet.