If you have a server and you wish to get the actual bandwidth usage on real time basis, you may simply install iftop from your server to track the information time by time.
iftop is a good network monitoring tool to check real time network bandwidth usage and CPU usage.
To download iftop,
# cd /usr/src # wget http://www.ex-parrot.com/~pdw/iftop/download/iftop-0.17.tar.gz
To install iftop,
# cd /usr/src # tar zxf iftop-0.17.tar.gz # cd iftop-0.17 # ./configure # make # make install
To use iftop, you may simply type in iftop,
iftop
Or specify the network interface,
iftop -i eth0