PHP: How to detect if user is root/sudo?

I have a command line PHP script that needs to be run with root-level permissions on Linux systems.

On our old, old Redhat Enterprise 2 Linux distro, this code worked:

// If we are linux, make sure we're root
if ($bIsLinux && $_ENV['USER'] != 'root')
    die("This script must be run as root.\n");

However, we've upgraded servers and are now on a modern version of linux (Amazon Linux). Which is great, but the above no longer works. On AML, you don't actually have the root password, but you can sudo from ec2-user. I've even tried sudo -i but that doesn't change the environment variable - and thus the above code fails.

So I need a new way to ensure root-level privileges before continuing.

Anyone have any ideas?

Thanks!