Can't trigger GPIO control via executable run through php's exec function

Question

/var/www/html/index.php

<?php

exec("./on");
shell_exec("/var/www/html/on");

on.cpp

#include <string>
#include <getopt.h>
#include <cstdlib>
#include <sstream>
#include <iostream>
#include <unistd.h>
#include <wiringPi.h>

using namespace std;

void light_1_on() {
  digitalWrite(0, HIGH);
}

int main( int argc, char ** argv){

  cout << "Setting up wiringPi" << endl;
  wiringPiSetup();
  pinMode(0, OUTPUT);

  light_1_on();

}

Built using: g++ on.cpp -o on -lwiringPi

Permissions changed with: chmod 777 on

Access changed with: chown www-data:www-data on

When run ./on via the terminal, the light that's connected to this GPIO output turns on. But when run via my exec or shell_exec via php, the light does not turn on.

Any ideas why I might not be able to turn the light on via execution in php? Any fixes or workarounds for this?

Thanks!

Answer 1

It turns out I had to add gpio to the group for www-data. I had to use this:

sudo usermod -a -G gpio www-data

Took me quite a while to figure this out. Hope it helps someone!