How can PHP users determine under which user Apache is running and how does this information impact script execution?

PHP users can determine under which user Apache is running by using the `posix_getuid()` function in PHP. This information can impact script execution because the user running Apache might have different permissions than the user running the PHP script, leading to potential permission issues when accessing files or directories.

$user = posix_getpwuid(posix_geteuid());
echo 'Apache is running under user: ' . $user['name'];