How to kill hidden process? - c

Question

I have the following script.
#!/bin/bash
if [ "$EUID" -ne 0 ]
then
echo ''
echo -e "\e[1;31m Please run the script as root \e[0m"
echo ''
exit
fi
for run in {1..11}
do
echo -e '\e[1;32m Initializing AP in backfround... \e[0m'
sudo screen -dmS hotspot
sleep 5
# start the AP in background
echo -e '\e[1;32m Starting AP in backfround... \e[0m'
sudo screen -S hotspot -X exec ./start_hostapd.sh
sleep 20
# save PIDs for dmS
ps -ef | grep "dmS" | awk '{print $2}' > dms.log
sleep 1
# save PIDs for hostapd
ps -ef | grep "hostapd" | awk '{print $2}' > process.log
sleep 1
echo -e '\e[1;33m Running data... \e[0m'
for run in {1..10}
do # send 10 times
sudo /home/ubuntu/Desktop/send_data/run_data
sleep 1
done
echo -e "\e[1;31m Stopping sending... \e[0m"
sleep 2
echo -e "\e[1;31m Quiting hotspot... \e[0m"
sudo /home/ubuntu/Desktop/kill_dms/kill_dms
sleep 5
echo -e "\e[1;31m Stopping AP... \e[0m"
sudo /home/ubuntu/Desktop/kill_hostapd/kill_hostapd
sleep 5
echo -e '\e[1;31m Wiping dead screens... \e[0m'
echo
sudo screen -wipe
sudo screen -X -S hotspot quit
sleep 5
done
I use a bash script that starts the AP (hostapd) and then it executes some another commands. Unfortunately, once the AP is started, the next lines will not be executed anymore. To avoid this problem, in the Script I start the AP using screen command that allows to run AP in background and also it allows to execute next lines.
For each iteration in the for-loop, the AP must be restarted. For this purpose I write out the PIDs of screen and hostapd and then I call my C programs, which kill these processes. At last I use screen commands again to ensure that the AP in the background has been stopped and it can be started again.
This implementation works good. However, when the script comes to the end and all processes has been already killed, the AP disappears in other devices and after some minutes it appears again and it happens several times. Only the system reboot helps to stop the AP completely.
I use htop to find out the processes which runs AP. However, I can not find the processes. The htop says that there is no processes, which I created using script from above. This is right, because the script kills the processes once it is finished.
So, I suppose that there are hidden processes for my AP and I do not see them. Is there a way to find that hidden processes and kill them to stop the AP?
When I just start the AP in another terminal and then I stop it just using CTRL+C, the AP will be stopped and my devices do not see it anymore.
That's why I suppose that the screen starts a hidden process, which can not be found by htop or by other programs like htop.

Answer 1

If you don't need any hostap process at all, I'd rather use pkill instead of trusting the management of pids. Easiest usage should look like:
pkill -f hostap
pkill -f screen
If you'd want to use another signal like 9, use:
pkill -9 -f hostap
pkill -9 -f screen
https://linux.die.net/man/1/pkill