vnStat
vnStat is a lightweight (command line) network traffic monitor. It monitors selectable interfaces and stores network traffic logs in a database for later analysis.
Configuration
Start/enable the vnstat.service daemon.
Pick a preferred network interface and edit the Interface variable in the /etc/vnstat.conf accordingly. To list all interfaces available to vnstat, use vnstat --iflist.
To start monitoring a particular interface that was not referred to in the configuration file when the daemon was started, you must initialize a database first. Each interface needs its own database. The command to initialize one for the eth0 interface is:
# vnstat --add -i eth0
Remember to restart the vnstat.service daemon after you have added a new interface.
Usage
Query the network traffic:
# vnstat --query
Viewing live network traffic usage:
# vnstat --live
To find more options, use:
# vnstat --help
or to see all options use:
# vnstat --longhelp
Eye candy presentation of the data can also be achieved by vnstati(1), which is part of the vnstat package.