PHP shell_exec() script running from CPanel terminal but not from ajax POST call

Question

On my website, I have a javascript function that has a POST ajax call to a PHP file on the server (a GoDaddy VPS running CentOS 6), which executes a python script via shell_exec() and returns the output.

Javascript function:

function submitdivsheet()
{
    $.post("test.php", {}, function(data,status){
        console.log(data);
    }); 
}

PHP script: test.php

<?php
    $command = escapeshellcmd('python3.6 test.py');
    $output = shell_exec($command);
    echo $output;
?> 

Python script: test.py

import sys
print("This is the output")

When I try to run the php file from the bash terminal on CPanel, there are no issues, as shown here. However, upon running the javascript function, only an empty string is output to the console. I'm not sure why it would only run on the CPanel terminal, but I suspect it could be a permissions issue somewhere. How can I fix this issue?

NOTE: This works fine on both the server and from the POST call if shell_exec() is not present. It seems that shell_exec is causing the problem.

---

EDIT: Upon changing the PHP script to:

<?php print shell_exec('echo $PATH'); ?>

This is the output.

Answer 1

You are missing environment values when invoking python from the web server that are present in your shell. Candidates are PATH and the variables mentioned in the python man page.

Try this:

env -i python3.6 test.py

You will likely get some error messages that will hopefully point to the problem. Then try variables that are present in your shell environment, like:

env -i PYTHONHOME=$PYTHONHOME python3.6 test.py

Add all necessary environment variables. When this works, add them to the call to the script. When calling the script, you have supply the actual values for the variables, you can't refer to them as $PYTHONHOME.