#!/bin/bash

rm -rf target.rrd

# Init timestamp.
timestamp=$(date +%s)

# Align timestamp to multiple of 5 seconds.
timestamp=$(($timestamp/5*5))
init_timestamp=$timestamp

rrdtool create target.rrd \
         --start $timestamp \
         --step 5 \
         DS:speedIn:COUNTER:10:U:U \
         DS:speedOut:COUNTER:10:U:U \
         RRA:AVERAGE:0.5:2:60 \
         RRA:AVERAGE:0.5:60:12

for i in $(seq 1 24); do
   sleep 5
   timestamp=$(($timestamp + 5))

   outOctets=$(...)
   inOctets=$(...)

   rrdtool update target.rrd  $timestamp:$inOctets:$outOctets
done

echo --start $init_timestamp --end $timestamp