Why this Debian-Linux autostart netcat script won't autostart?

Question

I placed a link to my scripts in the rc.local to autostart it on linux debian boot. It starts and then stops at the while loop. It's a netcat script that listens permantently on port 4001.

echo "Start"

while read -r line
do

    #some stuff to do

done < <(nc -l -p 4001)

When I start this script as root with command ./myscript it works 100% correctly. Need nc (netcat) root level access or something else?

EDIT:

rc.local

#!/bin/sh -e
#
# rc.local
#
# This script is executed at the end of each multiuser runlevel.
# Make sure that the script will "exit 0" on success or any other
# value on error.
#
# In order to enable or disable this script just change the execution
# bits.
#
# By default this script does nothing.
/etc/samba/SQLScripts
exit 0

rc.local starts my script "SQLScripts"

SQLScripts

#! /bin/sh

# The following part always gets executed.
echo "Starting SQL Scripts" >> /var/log/SQLScriptsStart
/etc/samba/PLCCheck >> /var/log/PLCCheck &

"SQLScripts" starts "PLCCheck" (for example only one)

PLCCheck

#!/bin/bash

echo "before SLEEP" >> /var/log/PLCCheck
sleep 5
echo "after SLEEP" >> /var/log/PLCCheck

echo "vor While" >> /var/log/PLCCheck

while read -r line
do

    echo "in While" >> /var/log/PLCCheck

done < <(netcat -u -l -p  6001)

Answer 1

In an rc script you have root level access by default. What does "it stops at the while loop" mean? It quits after a while, or so? I guess you need to run your loop in the background in order to achieve functionality usual in autostart scripts:

echo "Starting"

( while read -r line
do

    #some stuff to do

done << (nc -l -p 4001) ) &

echo "Started with pid $( jobs -p )"

Answer 2

I have tested yersterday approximatly the same things, and I have discover that you can bypass the system and execute your netcat script with the following crontask. :

(every minute, but you can ajust that as you want.)

* * * * * /home/kali/script-netcat.sh // working for me 

@reboot /home/kali/script-netcat.sh // this is blocked by the system. 

According to me, I think that by default debian (and maybe others linux distrib) block every script that try to execute a netcat command.