[SOLVED] network bandwith utilization bash script using only netstat

Issue

I'm having trouble calculating bandwidth usage on a network card. I am doing this on FreeBSD and I am only able to use netstat without the possibility of installing additional modules.

I just do not know how to calculate it. At this moment I came up with an idea to execute in a script the command

netstat -i -b -n -I INTERFACE write to file columns 8 and 11 that is Ibytes + Obytes

Then do this command again and read the same columns

And here I have a problem what to do with it? Is there any mathematical formula to calculate bandwidth consumption?

Solution

Processing netstat output to get the Ibytes sum and Obytes sum of a given interface with awk:

netstat -i -b -n -I IFACE |
awk 'BEGIN { getline } { i += $8; o += $11 } END { print i, o }'

Now a simple monitoring script:

#!/bin/sh

iface=$1
seconds=$2

while :
do
    read curr_Ibytes curr_Obytes < <(
        netstat -i -b -n -I "$iface" |
        awk 'BEGIN { getline } { i += $8; o += $11 } END { print i, o }'
    )

    if [ -n "$prev_Ibytes" ]
    then
        printf 'in: %d B/s\tout: %d B/s\n' \
            $(( (curr_Ibytes - prev_Ibytes) / seconds )) \
            $(( (curr_Obytes - prev_Obytes) / seconds ))
    fi

    prev_Ibytes=$curr_Ibytes
    prev_Obytes=$curr_Obytes

    sleep "$seconds"
done

Example:

./netmon.sh em0 5
in: 520 B/s out: 3040 B/s
in: 325 B/s out: 1648 B/s
in: 95 B/s  out: 130 B/s
in: 1380 B/s    out: 23629 B/s
in: 232 B/s out: 146 B/s
...

Answered By - Fravadona

Answer Checked By - Marilyn (WPSolving Volunteer)