I’ve got a list of tools I think are cool or useful, so I’m going to start sharing my thoughts of them here….isn’t that the point? So today’s tool is iftop. It can be used to display bandwidth usage on an interface. If you can’t figure out what it does based on the name, their description of the tool lays it out well:
iftop does for network usage what top(1) does for CPU usage. It listens to network traffic on a named interface and displays a table of current bandwidth usage by pairs of hosts. Handy for answering the question “why is our ADSL link so slow?”.
Small and simple tool, what’s not to like. Real good for those times that you know something is eating traffic but don’t know what. Check out screenshots of iftop at http://www.ex-parrot.com/~pdw/iftop/.
Update: While perusing through logs it is clear that people find this page because they are looking for information on how to read iftop output. Looking back at this post I clearly stiffed everybody on that aspect of things, and have wanted to post an update on how to interpret what’s going on in iftop. Luckily Techthrob.com took care of that far better than I would be able to do, so go check out his article How to Monitor Network Traffic in Linux.