vnStat is a console-based network traffic monitor for Linux/BSD/UNIX, logging usage hourly, daily, and monthly on the server or router
* Linux installation
https://www.cyberciti.biz/faq/ubuntu-install-vnstat-console-network-traffic-monitor/ or https://www.cyberciti.biz/faq/centos-redhat-fedora-linux-install-vnstat-bandwidth-monitor/
* FreeBSD installation https://www.cyberciti.biz/faq/freebsd-install-vnstat-network-traffic-monitor-software/