iftop is an open source and totally free command-line software designed to display network traffic usage on your Linux-based operating system. It does exactly what the top utility does for CPU usage under any GNU/Linux operating system.
This program is usually used by system administrators or end-users who want to see why their network connection is so slow. It works by listening to the network traffic on a specified interface and displays real-time bandwidth usage information, listed in a table sorted by pairs of hosts.
Various command-line options are available for iftop, which can be viewed at a glance by running the ‘iftop --help’ command in the terminal emulator. Its options are organized in three main categories: General options, Sorting orders and options that are only available in combination with the -t option.
Among the most useful ones, we can mention the ability to restrict looking up of a hostname, to prohibit the conversion of port numbers to services, to display bandwidth in bytes, to hide the bar graph of traffic, to force the program to run in promiscuous mode, to listen on named interface, as well as to display traffic only from an IPv4 or IPv6 network.
Getting started with iftop
We always recommend our users to install an application using pre-built binary packages optimized for their Linux distributions, which can be downloaded at a glance either from Softpedia or using the default package manager software of their distro.
In some case, this is not possible, so you will have to install the program using the source tarball, which also available for download on Softpedia. Save the file on your PC, unpack it and open a terminal emulator, where you must use the ‘cd’ command to navigate to the location of the extracted archive files.
Type the ‘./configure && make’ command to optimize and compile iftop’s source code for a specific architecture (32-bit or 64-bit), and then execute the ‘make install’ command as root or the the ‘sudo make install’ command to install the program system wide.
Under the hood, supported OSes and availability
The iftop program is written entirely in the C programming language, which means that it is extremely fast and can be easily compiled with GCC on any GNU/Linux distribution where the libpcap and libcurses libraries are available.
Besides the source archive, the software is also distributed as binary packages for both Linux (SuSE, Red Hat) and Solaris operating systems, which are available on the project’s homepage (see link below for details).