vnStat is a simple console based network traffic monitoring software. It is light weight and provides detailed statistics of the network traffic. The statistics can be hourly, daily, monthly, yearly etc.
One important feature of vnStat is that it runs as a daemon and monitors the interface, so it does not matter if the interface is not up when you start vnStat, it will start collecting statistics once the interface is up. So how is this data useful? It will help me know my usage over a period of time, so in future if I need to change my internet provider, I can use the details below to decide on my plan.
You can find out more about vnStat at the site : http://humdi.net/vnstat/
The monthly and the top10 days statistics for me are detailed below:
$ vnstat -m
ppp0 / monthly
month rx | tx | total
------------------------+--------------+--------------------------------------
Jul '09 533.29 MiB | 92.18 MiB | 625.47 MiB %%%%%%%%%::
Aug '09 602.88 MiB | 123.16 MiB | 726.04 MiB %%%%%%%%%%%::
Sep '09 319.09 MiB | 87.87 MiB | 406.96 MiB %%%%%::
Oct '09 991.48 MiB | 170.32 MiB | 1.13 GiB %%%%%%%%%%%%%%%%%%%:::
Nov '09 248.32 MiB | 65.81 MiB | 314.13 MiB %%%%:
------------------------+--------------+--------------------------------------
estimated 986 MiB | 258 MiB | 1.21 GiB
$ vnstat -t
ppp0 / top 10
# day rx | tx | total
-------------------------------+-------------+---------------------------------
1 23.10.09 226.22 MiB | 8.02 MiB | 234.25 MiB %%%%%%%%%%%%%%%%%:
2 25.10.09 127.68 MiB | 10.30 MiB | 137.98 MiB %%%%%%%%%:
3 18.07.09 114.88 MiB | 8.00 MiB | 122.89 MiB %%%%%%%%:
4 19.07.09 111.19 MiB | 9.93 MiB | 121.12 MiB %%%%%%%%:
5 05.11.09 82.37 MiB | 16.67 MiB | 99.04 MiB %%%%%%:
6 07.11.09 72.35 MiB | 24.32 MiB | 96.68 MiB %%%%%::
7 24.10.09 70.41 MiB | 9.49 MiB | 79.91 MiB %%%%%:
8 08.08.09 68.50 MiB | 10.88 MiB | 79.38 MiB %%%%%:
9 21.07.09 70.15 MiB | 7.74 MiB | 77.89 MiB %%%%%
10 31.10.09 56.81 MiB | 11.86 MiB | 68.67 MiB %%%%:
-------------------------------+-------------+---------------------------------