RPi3 as access point: How to execute a bash script every time a new connection is established

Question

I use an RPI3 as a standalone access point (following this tutorial) and I would like to make it execute a bash script when a device is connected to its wireless network. What is the appropriate way to do this?

Answer 1

By searching I found a solution.

Step 1: Create a file named onHostapdChange.sh

nano onHostapdChange.sh

Step 2: In the file type or copy-paste the lines...

#!/bin/bash
if [[ $2 == "AP-STA-CONNECTED" ]]
then
  echo "someone has connected with mac id $3 on $1"
fi

if [[ $2 == "AP-STA-DISCONNECTED" ]]
then
  echo "someone has disconnected with mac id $3 on $1"
fi

... then save (Ctrl + O) and exit nano (Ctrl + X).

Step 3. Make it executable:

chmod +x onHostapdChange.sh

Step 4. Execute the command

sudo hostapd_cli -a '/onHostapdChange.sh'

If the error message 'Failed to connect to hostapd - wpa_ctrl_open: No such file or directory' appears then edit the file '/etc/hostapd/hostapd.conf'...

sudo nano /etc/hostapd/hostapd.conf 

...in the end of the file append the lines:

ctrl_interface=/var/run/hostapd
ctrl_interface_group=0

...and restart the service:

sudo systemctl stop hostapd
sudo systemctl start hostapd

Instructions (combined) from

1. https://superuser.com/questions/1071354/hostapd-execute-a-command-when-there-is-new-connection-established

2. https://www.raspberrypi.org/forums/viewtopic.php?t=63045