How to Monitor and Log Network Traffic on Linux Using vnStat

“vnstat without any argument will give you a quick summary with
the following info:

• The last time when the vnStat datbase located under
  /var/lib/vnstat/ was updated
• From when it started collecting the statistics for a specific
  interface
• The network statistic data (bytes transmitted, bytes received)
  for the last two months, and last two days.

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