CentOS / RHEL: Install vnStat Network Traffic Monitor To Keep a Log Of Daily Traffic

How do I install vnstat software – a console-based network traffic monitor under CentOS or RHEL or Fedora Linux operating system to keep a log of hourly, daily and monthly network traffic? vnstat command is a console-based network traffic monitor. It keeps a log of hourly, daily and monthly network traffic for the selected interface(s). However, it isn’t a packet sniffer. The traffic information is analyzed from the proc filesystem. That way vnStat can be used even without root permissions.