Why is Apache2 doing exec() strangely?

Question

PHP

Good evening gentlemen!
The point is this: for myself I write a Web-control panel for the laptop. It has Apache2, mod_python. I don’t look into the external network - I don’t bother with security. As a result, I got something like this :
Commands are executed by PHP by GET key, via system(). For example:

<?php

  if ($_GET["bright"] == "increace") { 
    exec('SBLM -up');

And now, in fact, the problem: some commands are not executed. system() does not return anything. For example, here it is:

if ($_GET["mocp"] == "prev") { 
   system('mocp -G');
    echo "Comlete";

in response - silence. At the same time right there through Geany - everything works. Tell me, in which direction to dig?
Thanks in advance
PS on board Ubuntu 14.04 with gnome.

Answer 1

If apache is running from www-data, then most likely it does not have enough rights to access devices / sockets or something like that. Try to run as your user. To do this, in /etc/apache2/envvars you need to change the values

export APACHE_RUN_USER=www-data
export APACHE_RUN_GROUP=www-data

and restart apache