Network monitoring with ntop

Install ntop

sudo apt-get install ntop

Create the directories that for some reason are not created by the installer

sudo mkdir /var/lib/ntop/rrd
sudo mkdir /var/lib/ntop/rrd/graphics
sudo mkdir /var/lib/ntop/rrd/flows
sudo mkdir /var/lib/ntop/rrd/interfaces
sudo mkdir /var/lib/ntop/rrd/interfaces/eth0
sudo mkdir /var/lib/ntop/rrd/interfaces/ppp0
sudo chmod -R 775 /var/lib/ntop

Start ntop on selected interface ppp0 (you will be asked to create an admin password, don't forget it!)

sudo ntop -i ppp0

browse to the ntop web interface at

http://router.example.com:3000

To manually start as a daemon, use

sudo ntop -i ppp0 --daemon

You can use the usual init scripts to start ntop;

sudo /etc/init.d/ntop start

In my case I need to monitor ppp0 so I need to edit /var/lib/ntop/init.cfg

vi /var/lib/ntop/init.cfg

and change the interface to ppp0.