ntop and RRD

"ntop" conveniently displays web pages with charts and plots of your local network traffic. To record historical traffic, it uses Round Robin Database (rrd). The default ntop package enables the RRD plugin, but doesn't give itself permission to write out its data. Here's how to get the two to work:

sudo apt-get install ntop
sudo install -d /var/lib/ntop
sudo install -o nobody -d /var/lib/ntop/interfaces
sudo install -o nobody -d /var/lib/ntop/rrd

To test, start "sudo ntop" (probably in "screen"), then open the web page http://localhost:3000

To activate the RRD plugin, select Plugins / Round Robin / Describe, then click the red "no" to become a blue "yes." You'll see messages in the terminal where you started ntop.

After a few moments, you can view RRD graphs. One is in Summary / Network Load.