Python file called by PHP script in apache server unable to get RPi.GPIO

Question

I've been trying to use a site on my local network to activate the GPIO pins on my Raspberry Pi 4. I installed apache and wrote a quick PHP script which executes a python file in /var/www/html.I have a script called LED-on.py, that, when I run directly through the terminal, works with no errors and turns on the LED which I connected through that pin, but if I run it through a PHP shell_exec function and echo the result, I get the error Not running on a RPi!.

echo shell_exec('python /var/www/LED-on.py');

try:
 import RPi.GPIO as GPIO
 GPIO.setwarnings(False)
 GPIO.setmode(GPIO.BCM)
 GPIO.setup(4, GPIO.OUT)
 GPIO.output(4, True)
except Exception as e: print(e)

Answer 1

It's possible that this might mirror something I was doing a couple of years ago and I preface this with the observation that I don't believe that it was good practice, but I didn't find a way around it, so I welcome any correction.

The issue (in my case) was that running a python program that accessed the GPIO pins required root access. If you are going to execute a python file from PHP, then the user that calles the PHP file will require root (sudo permission) access.

For my part that involved (and here I am paraphrasing to reflect your example) creating a php file that executes the python script similar to;

<?php
echo exec( 'sudo python /var/www/LED-on.py' );
?>

Change the permissions for the python file so that the web user 'www-data' has permissions for the files

sudo chown www-data:pi /var/www/LED-on.py

give the www-data user the ability to run python scripts as root (this is the ugly part)

sudo visudo

Then add www-data ALL=(ALL) NOPASSWD: /usr/bin/python under the # User privilege specification area

It's not secure, but it worked. I would appreciate any advice that would make it better for myself or the OP.

To try and make myself feel better about it I added password protection using 'Web Page Password Protect' by downloading the script from 'http://www.zubrag.com/scripts/password-protect.php', putting it in the same directory as the php file and adding the following line to the top of the .php file;

include("password_protect.php");

Answer 2

A little poking with Google suggests this is a permissions problem. I don't have an instance of Apache running on a Pi, but it runs as user www-data on Debian. If that's the case, try sudo adduser www-data gpio, reboot or restart Apache, and test.

• Bob Brown: There is a discussion of the problem, or something similar, here: sourceforge.net/p/raspberry-gpio-python/tickets/171 but as yet no resolution.