vnstat is a console-based network traffic monitor. It keeps a log of hourly, daily and monthly network traffic for the selected interface(s). The traffic information is analyzed from the proc filesystem. That way vnStat can be used even without root permissions.

First you will need to install the epel repository
You can then install the tool with

yum install vnstat

You will then need to create a database for the tool:
Create the user first:

chsh -s /bin/bash vnstat

Create the database:

runuser -l vnstat -g vnstat -c '/usr/bin/vnstat -u -i eth0'

Once this has been done we will remove shell access for the user:

chsh -s /sbin/nologin vnstat

vnstat -i eth0

vnstat -i eth0 -d

Example output:

         day         rx      |     tx      |    total    |   avg. rate
     ------------------------+-------------+-------------+---------------
      02/26/16      1.12 GiB |    1.14 GiB |    2.26 GiB |  219.79 kbit/s
      02/27/16      1.37 GiB |    1.39 GiB |    2.76 GiB |  267.79 kbit/s
      02/28/16      7.09 MiB |   12.27 MiB |   19.36 MiB |    1.84 kbit/s
      02/29/16     17.41 MiB |   10.16 MiB |   27.57 MiB |    5.08 kbit/s
     ------------------------+-------------+-------------+---------------
     estimated        33 MiB |      19 MiB |      52 MiB |

vnstat -i eth0 -l