vnStat is a lightweight (command line) network traffic monitor. It monitors selectable interfaces and stores network traffic logs in a database for later analysis.
/etc/vnstat.conf with your editor and check the interface name is set right, eg.:
# Interface "enp3s0"
Start Systemd Service
After introducing the interface(s) and checking the config file. You can start the monitoring process via systemd
# systemctl start vnstat.service
To make this service permanent use
# systemctl enable vnstat.service
Query the network traffic:
# vnstat -q
Viewing live network traffic usage:
# vnstat -l
To find more options, use:
# vnstat --help