vnStat is a command line utility which helps users in monitoring, logging and viewing network statistics over various time periods for various network interfaces.
##How to install?
For Arch and its derivatives:

pacman -S vnstat

For Debian and its derivatives:

apt install vnstat

##How to setup?
vnStat monitors data usage on a network interface basis so first you'll need to know the name of the network interface you want to monitor.
For that, run below command in terminal:

ip link

To initialize monitoring on any network interface, run following command:

vnstat -u -i wlp0s20u2

Here wlp0s20u2 is name of my netw