I am following the tutorial at http://cloudservers.rackspacecloud.com/index.php/Basic_Cloud_Server_Security
and am trying to set up the iptables
#Now we need to ensure that the iptables rules are applied when we reboot the server. At the moment, the changes will be lost and it will go back to allowing everything from everywhere.
#Open the file /etc/network/interfaces:
#Add a single line (shown below) just after 'iface lo inet loopback':
iface lo inet loopback
pre-up iptables-restore < /etc/iptables.up.rules
# The primary network interface
However, I can't find the interfaces file?
I've done a locate and it doesn't seem to be there. Is there another file I can put this line of code?