Here is a simple shell script to calculate the bandwidth usage on the external interface of a bsd or linux box. Netstat bandwidth summary works well on OpenBSD v4.4, but colleagues have mentioned 3.9 may not work. Linux should work without issue. Also, remember that the netstat stats will reset on reboot of the box.
One could use this script to keep track of Internet bandwidth in case their ISP accused them of using to much bandwidth. Comcast for example will call foul if you use more than 250 gigabytes of combined upload and download bandwidth per month. Comcast's policy is to work with the abusive customer, but more than likely they are already on the list to be terminated. Verizon says they do not have a limit, but they will contact bandwidth abusers if the need arises. Your ISP and in fact the same ISP in different parts of the country might have different rules so check with them. Then use this simple tool to make sure you know what you are using.
This is what the summary of your system might look like...
External interface bandwidth usage: uptime 16 days ExtIf in total 13 GBytes ExtIf out total 16 GBytes ExtIf in/day 831 MBytes/day ExtIf out/day 986 MBytes/day ExtIf in/30day 24 GBytes/month ExtIf out/30day 29 GBytes/month ExtIf in+out/30day 53 GBytes/month
Here is the script called "calomel_interface_stats.sh". You will need to edit the name of your external interface card. In this example we are using "em0" in the netstat lines starting with "netstat -I em0".
NOTE: The variable "$SECS" expects to see the uptime in days, hours and minutes. For this reason the box must be up for at least one day (24 hours) before this script will work properly.
#!/usr/local/bin/bash
#
## moneyslow.com calomel_interface_stats.sh
#
SECS=`uptime | awk '{ if ($3 ~ /:/) { split($3,a,":"); print (a[1]*60+a[2])*60} else { split($3,b,":"); split($5,a,":"); print b[1]*86400+(a[1]*60+a[2])*60} }'`
EXT_IN=`netstat -b -n -I em0 | grep em0 | tail -1 | awk '{print $5}'`
EXT_OUT=`netstat -b -n -I em0 | grep em0 | tail -1 | awk '{print $6}'`
echo " "
echo "External interface bandwidth usage:"
echo " uptime " $(($SECS/86400)) "days"
echo " ExtIf in total " $(($EXT_IN/1000000000)) "GBytes"
echo " ExtIf out total " $(($EXT_OUT/1000000000)) "GBytes"
echo " ExtIf in/day " $(($EXT_IN*86400/$SECS/1000000)) "MBytes/day"
echo " ExtIf out/day " $(($EXT_OUT*86400/$SECS/1000000)) "MBytes/day"
echo " ExtIf in/30day " $(($EXT_IN*86400*30/$SECS/1000000000)) "GBytes/month"
echo " ExtIf out/30day " $(($EXT_OUT*86400*30/$SECS/1000000000)) "GBytes/month"
echo " ExtIf in+out/30day " $((($EXT_OUT+$EXT_IN)*86400*30/$SECS/1000000000)) "GBytes/month"
You could put the script's executable line into /etc/daily on the 13th line after the commands "sysctl -n kern.version" and "uptime". This way you will receive the summary in the "daily output" email the bsd box sends and includes the above stats.