On a Linux system, if you need information on how much bandwidth is being used and what type of traffic is consuming the bandwidth, two tools you can use that don't require a Graphical User Interface (GUI) are IPTraf and Linux Bandwidth Monitor (bwmon).
IPTraf description from Red Hat's IPTraf package:
IPTraf is a console-based network monitoring utility. IPTraf gathers data like TCP connection packet and byte counts, interface statistics and activity indicators, TCP/UDP traffic breakdowns, and LAN station packet and byte counts. IPTraf features include an IP traffic monitor which shows TCP flag information, packet and byte counts, ICMP details, OSPF packet types, and oversized IP packet warnings; interface statistics showing IP, TCP, UDP, ICMP, non-IP and other IP packet counts, IP checksum errors, interface activity and packet size counts; a TCP and UDP service monitor showing counts of incoming and outgoing packets for common TCP and UDP application ports, a LAN statistics module that discovers active hosts and displays statistics about their activity; TCP, UDP and other protocol display filters so you can view just the traffic you want; logging; support for Ethernet, FDDI, ISDN, SLIP, PPP, and loopback interfaces; and utilization of the built-in raw socket interface of the Linux kernel, so it can be used on a wide variety of supported network cards.
A ZDNet article, Police your network traffic with IPTraf explains how to use IPTraf to log and monitor IP traffic on your system.
The options when running bwmon are shown below:
Linux Network Bandwidth Monitor $Revision: 1.3 $ by Kimmo Nupponen (firstname.lastname@example.org) $Date: 2002/05/08 06:33:09 $ usage: bwmon [-b] [-h] [-a] [-m] [-u seconds] -a Print bandwidth utiliasation in Kbytes rather than Kbits. The default is to use Kbits -a Print also average bandwidth since last boot per interface -m Print maximum bandwidth since launch of this utility -h Print this help message -u Update timeout (integer value) Use <space-bar> to refresh the screen before update timeout expires Use 'q' or 'Q' to exit this utility Note that you have to have proc mounted to allow this software to work!