linux-kernel - Multiple invocations of cron-job AT THE SAME MINUTE on Raspbian

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Date:   Wed, 14 Sep 2016 15:45:10 +0530
From:   Ajay Garg <ajaygargnsit@...il.com>
To:     linux-kernel@...r.kernel.org
Subject: Multiple invocations of cron-job AT THE SAME MINUTE on Raspbian

Hi All.

I have a raspbian-pi-3, and following is the first-level information ::

########################################
uname -a
Linux raspberrypi 4.4.11-v7+ #888 SMP Mon May 23 20:10:33 BST 2016
armv7l GNU/Linux
########################################

Following is the script that is run by the every-minute cron ::

########################################
PID=`ps -aux | grep instamsg | grep -v grep | grep -v tail`

if [ -z "${PID}" ]
then
    echo "Binary not running"
    cd /home/sensegrow
    chmod 777 instamsg

    sleep 3
    ./instamsg &
else
    echo "Binary running fine"
fi
########################################

Now, things are mostly fine, but very spuriously, I see that multiple
instances of "instamsg" are spawned, sometimes upto 5, ALL IN THE SAME
MINUTE.
The occurrence of such phenomena is like once in a day.

I know there are multiple posts about this on the internet, but all of
those point to faulty-script(s) that are run as part of cron.
However, I guess the script I am using is pretty simple, and can never
be "long-running, longer than a minute".

The same script runs without any issues for days on Maestro-Wireless
routers, and Lanner-systems running Ubuntu.
The issue seems to be only on Raspberry-Pi.

Who/what might be the culprit here?

Thanks and Regards,
Ajay