- Monitor bandwidth consumption per process - NetHogs

NetHogs is a small 'net top' tool. Instead of breaking the traffic down per protocol or per subnet, like most tools do, it groups bandwidth by process. NetHogs does not rely on a special kernel module to be loaded. If there's suddenly a lot of network traffic, you can fire up NetHogs and immediately see which PID is causing this. This makes it easy to indentify programs that have gone wild and are suddenly taking up your bandwidth.

NetHogs Installation:
Fedora user can install NetHogs using command: yum install nethogs
Ubuntu user can install NetHogs using command: sudo apt-get install nethogs

Using NetHogs:
The default device to monitor is eth0. If you wish to use other device, simply type the argument after nethog, open the terminal and run the following command: nethogs eth0

When nethogs is running, press:
 q: quit
 m: switch between total and kb/s mode

usage: nethogs [-V] [-b] [-d seconds] [-t] [-p] [device [device [device ...]]]
-V : prints version.
-d : delay for update refresh rate in seconds. default is 1.
-t : tracemode.
-b : bughunt mode - implies tracemode.
-p : sniff in promiscious mode (not recommended).

source:http://linuxpoison.blogspot.com/2010/09/1357816775545.html