iftop or Interface TOP is a free and open source terminal based bandwidth usage and monitoring application for Linux. Using this iftop, you can view real time network bandwidth usage and monitor your system. It is based on libpcap and libcurses and released under GNU General Public License.
NetHogs is a free and open source real time command-line network bandwidth and statistics application for Linux. It groups and shows bandwidth by per process. So you can easily view, identify and monitor network heavy programs via PID. In this article we will see how to install and use NetHogs on your Ubuntu system. It is released under GNU General Public License v2.0.
IPTraf is a free and open source interactive real time command-line based network monitoring and statistics application for Linux. it supports IP, TCP, UDP, ICMP, IGMP, IGP, IGRP, OSPF, ARP and RARP protocols and Local loopback, Ethernet interfaces, FDDI interfaces, SLIP, Asynchronous PPP, Synchronous PPP over ISDN, ISDN with Raw IP encapsulation, ISDN with Cisco HDLC encapsulation and Parallel Line IP network interfaces.
It comes with IP traffic monitor module, interface statistics module, TCP and UDP service monitor module and LAN statistics module.
