shell_exec doesn't work on Linux server - php

Question

I'm using youtube-dl.exe on my Windows WAMP server and shell_exec() is working great on Windows, I get the right info from youtube-dl (returns a string).
Once the same PHP script is uploaded on my real Linux server it just stops working, even though I upload the Linux version of youtube-dl.
for the Linux version file that I've obtained from a sudo curl command on a Linux machine on VirtualBox, I'm trying to do this:
$var = shell_exec("youtube-dl -g https://www.youtube.com/watch?v=97Eagwlt-ZA");
And for the same version I've got on my WAMP server (exe):
$var = shell_exec("youtube-dl.exe -g https://www.youtube.com/watch?v=97Eagwlt-ZA");
Both of the commands returns absolutely nothing, the two different version of files are in the same root (/) folder and
$var = exec("youtube-dl -g https://www.youtube.com/watch?v=97Eagwlt-ZA", $errors);
$errors returns an empty Array()
But
$var = shell_exec("echo test > test.txt");
Works like a charm (creates the test file with "test" inside of it).
The PHP & youtube-dl files' CHMOD is set to 755. PHP Version 5.6.
I'm really stuck here.. Any ideas?

Answer 1

A few things to check:
Check to make sure youtube-dl has execute permissions for the webserver user. On Linux systems scripts have to be flagged executable in order to be run directly. Setting 755 permissions should do the trick.
Either add ./ to the path (e.g. ./youtube-dl) or make sure youtube-dl is on the web server's $PATH. Unlike Windows the current directory isn't automatically included on the path.
If your Linux server is running SELinux or AppArmor these applications may be preventing your web server from running commands. You can generally find out about items getting blocked in your syslog.