vnStat is a console-based network traffic monitor for Linux and BSD that keeps a
log of network traffic for the selected interface(s). It uses the network
interface statistics provided by the kernel as information source. This means
that vnStat won't actually be sniffing any traffic and also ensures light use of
system resources regardless of network traffic rate.

WWW: https://humdi.net/vnstat/
WWW: https://github.com/vergoh/vnstat