IPTraf is a very useful ncurses-based application that shows the traffic passing through your machine.

One of the first things I do upon installing a Linux distribution is put the Network Monitor applet on my GNOME panel. Watching the blue lights twinkle on and off makes me aware of network traffic.

ntop is a free opensource network traffic probe that shows the network usage. ntop is based on libpcap and can run on Linux/Unix and Windows operating system. ntop provides a very easy to use a web access to navigate through ntop traffic information and get a dump of the network status.

NTM Is a network traffic monitor for Linux (ubuntu, kubuntu, ecc). Characteristics: Integrate with linux NetworkManager; Autodisconnect when a threshold is reached; Day report; Console and Gui interface (gtk); Not need root privilege;

This how-to will teach you two commands, iftop and nethogs, that you can use to monitor network traffic on a Linux machine. You can use iftop to view traffic by individual connection, port, network segment, or remote host, which gives you a detailed accounting of all packets coming in and out of your machine.

Speedometer shows a graph of your current and past network speed in your console, letting you see your network connection's up and downstream speed and history at a glance. You can also use speedometer directly on a file to monitor the download performance and history of a specific download instead of all network traffic.

A group called the Traffic Squeezer project released an open source application that accelerates WAN network traffic. The Traffic Squeezer software uses lossless compression and other procedures to accelerate traffic on Linux-based network devices, and it's said a port to an embedded hardware version is planned.

DarkStat is a simple Packet Sniffing Network Traffic/Bandwidth monitoring utility for Linux and UNIX. DarkStat presents simple webinterface with nice graphs and stats auto-refreshed. Darkstat uses a very low footprint and the memory, CPU usage and is used in pfSense, redWall opensource firewalls.

Ever since I moved to broadband I've been looking for a traffic monitor that will show me a breakdown of my usage for not just my current session, but for the entire month (as I am on a capped plan). It hasn't been easy finding one that works in Linux as most are for system administrators, not normal end-users.