Just like top, you can change the display options while it is running. When you have more than one, specify the interface you want to monitor: If you have just one network interface, run iftop with no options. Baud measures signal changes, which sometimes were the same as bit rates, but mostly not. We abandoned bauds a long time ago in favor of bit rates.

It is rather surprising to see how much bandwidth we use, especially for us old people who remember the days of telephone land lines, modems, screaming kilobits of speed, and real live bauds. This is a great little tool for quickly identifying hogs, measuring speed, and also to maintain a running total of your network traffic. The excellent iftop listens to the network interface that you specify, and displays connections in a top-style interface. iftop tracks network connections by process number, Nethogs quickly reveals what is hogging your bandwidth, and vnstat runs as a nice lightweight daemon to record your usage over time. You can learn an amazing amount of information about your network connections with these three glorious Linux networking commands.

Linux network usage by process