Did you ever wonder how much bandwidth your linux server is using each month, or each day? There are a number of tools that can give you this information, but many of them are packet sniffers, and can effect performance.

I recently came across a really nice lightweight tool that monitors your network bandwidth utilization on Linux (actually I just learned that it also works on BSD operating systems as well, eg. Mac OSX , so I am running it on my desktop now as well) called vnstat. It works by analyzing the /proc stats on Linux (at regular intervals using a cron job), and then stores summaries in a really small database.

You can then access these stats whenever using the vnstat command line utility.

For example if you run vnstat -m it will generate a nice plain text summary report:

   month         rx      |      tx      |   total
-------------------------+--------------+--------------------------------------
  Dec '08       1.10 GB  |    28.88 MB  |     1.13 GB   %%%%%%%%%%%%%%%%%
  Jan '09       1.35 GB  |    68.79 MB  |     1.41 GB   %%%%%%%%%%%%%%%%%%%%%:
-------------------------+--------------+--------------------------------------
 estimated      2.21 GB  |      111 MB  |     2.31 GB

That particular server is only being used for backups right now, so the numbers are kind of low.

Highly recommend this tool if you are looking for a simple and lightweight way to monitor network bandwidth.

Here's a full list of command line options:

-q,  --query          query database
-h,  --hours          show hours
-d,  --days           show days
-m,  --months         show months
-w,  --weeks          show weeks
-t,  --top10          show top10
-s,  --short          use short output
-u,  --update         update database
-i,  --iface          select interface (default: eth0)
-?,  --help           short help
-v,  --version        show version
-tr, --traffic        calculate traffic
-l,  --live           show transfer rate in real time