=== Installing vnstat ===
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.
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First you will need to install the epel repository
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You can then install the tool with 
<sxh bash>
yum install vnstat
</sxh>
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You will then need to create a database for the tool:
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Create the user first:
<sxh bash>
chsh -s /bin/bash vnstat
</sxh>
Create the database:
<sxh bash>
runuser -l vnstat -g vnstat -c '/usr/bin/vnstat -u -i eth0'
</sxh>
Once this has been done we will remove shell access for the user:
<sxh bash>
chsh -s /sbin/nologin vnstat
</sxh>
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===Stats overview===
^ Value ^ Description ^
| rx | Total Received |
| tx | Total Transmitted |
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<sxh bash>
vnstat -i eth0
</sxh>
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Example:
<sxh bash>
Database updated: Mon Feb 29 12:31:07 2016

   eth0 since 02/26/16

          rx:  2.52 GiB      tx:  2.55 GiB      total:  5.07 GiB

   monthly
                     rx      |     tx      |    total    |   avg. rate
     ------------------------+-------------+-------------+---------------
       Feb '16      2.52 GiB |    2.55 GiB |    5.07 GiB |   17.25 kbit/s
     ------------------------+-------------+-------------+---------------
     estimated      2.56 GiB |    2.59 GiB |    5.15 GiB |

   daily
                     rx      |     tx      |    total    |   avg. rate
     ------------------------+-------------+-------------+---------------
     yesterday      7.09 MiB |   12.27 MiB |   19.36 MiB |    1.84 kbit/s
         today     17.47 MiB |   10.33 MiB |   27.81 MiB |    5.05 kbit/s
     ------------------------+-------------+-------------+---------------
     estimated        32 MiB |      19 MiB |      51 MiB |

</sxh>
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===Daily Stats===
<sxh bash>
vnstat -i eth0 -d
</sxh>
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Example output:
<sxh bash>
         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 |
</sxh>
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===Real time view===
<sxh bash>
vnstat -i eth0 -l
</sxh>