ipac is a package which is designed to gather, summarize and nicely output the IP accounting data. ipac make summaries and graphs as ascii text and/or gif images with graphs.
Note: linux kernel 2.2 used ipchains, 2.4 uses iptables.
ipac consists of two scripts (shell and perl) and one C program:
If you're running debian, the config file format is slightly different to newer versions. You don't have ipacin/out/fwin etc, you just have 'in' and 'out', and both in and out get called on the forward chain.
If you're running ipac on a machine that is a gateway between two networks, you will find that your totals are largely irrelevant because if I download 2Mb of stuff, I will get 2Mb in on the external interface and then 2Mb out on the internal interface.
The easiest way around this is to simply monitor your external interface. You really don't care about internal traffic because it's all free.
Edit /etc/ipac-ng/ipac.conf and replace the +'s with 'eth1' or 'ppp0' etc.
The manual page for ipacsum(8).
Perhaps you'd rather use MRTG? See http://www.saas.nsw.edu.au/solutions/ipac-2-mrtg.html.