Why Isn't My PHP exec() Function Working?

Troubleshooting exec() Function in PHP

Facing issues with the exec() function can be frustrating, especially when it does not yield any obvious results. This article provides a comprehensive guide to help you debug and resolve such problems.

Problem:
The exec() function fails to execute commands on a server, despite having disabled safe_mode and verifying the functionality of console commands. Permissions for applications have been set correctly.

Code Snippets:
The following code snippets have been attempted:

echo exec('/usr/bin/whoami');

echo exec('whoami');

exec('whoami 2>&1',$output,$return_val);
if($return_val !== 0) {
    echo 'Error<br>';
    print_r($output);   
}

exec('/usr/bin/whoami 2>&1',$output,$return_val);
if($return_val !== 0) {
    echo 'Error<br>';
    print_r($output);   
}

The last two code snippets display an error and an empty array. Server support has been unable to assist.

Solution:

1. Check disable_functions:

   • Navigate to /etc/php.ini and check if exec is listed under disable_functions.
   • If present, remove it and restart Apache.

2. Enable Debug Mode:

   • For easier debugging, use the following code:

     #!/usr/bin/php
     ini_set("display_errors", 1);
     ini_set("track_errors", 1);
     ini_set("html_errors", 1);
     error_reporting(E_ALL);

   • Execute the script manually: chmod x myscript.php and ./myscript.php.

3. Permission Issues:

   • Create a bash script that executes a simple command, e.g., echo "hello world."
   • Set permissions for the file and folder using chmod 755.
   • Attempt to run the script.

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