Custom Linux Hosting Control Panel in PHP - running commands as root

I want to work on a custom linux hosting control panel based on my experience in managing LEMP/LAMP stack. This is just a pet project. I believe I have ran into some hurdle.

The CP is being written in PHP and server by NginX as default server on port 8000. I am not using any framework, just vanilla PHP.

In putty, logged in as root, I can get the system uuid like this:

[root@localhost ~]# dmidecode -s system-uuid
997C4DE8-213B-4ACC-8E23-01E79D6CC12F

When I try this in PHP with the following script:

var_dump(shell_exec('dmidecode -s system-uuid 2>&1'));

I get the following:

sh: dmidecode: command not found

How can I execute that above command get the output in PHP?

Nginx/PHP-FPM is running as user nginx. Do i need to add nginx user to root group?

I want to be able to execute very specific commands like: /etc/init.d/php-fpm restart from my control panel (to restart php-fpm gateway).

How can I achieve this? What are my options? How does control panel like cPanel, DirectAdmin, etc... do it?

I have tried the following method also. Installed sudo and used the sudo visudo command and added the following lines at the end:

nginx    ALL=(ALL)    NOPASSWD:/path/to/php_shell.sh
Defaults:nginx        !requiretty

and the content of php_shell.sh is:

#!/bin/bash
dmidecode -s system-uuid

Now, I tried to execute it like this:

var_dump(shell_exec('sudo sh /path/to/php_shell.sh 2>&1'));

I get: sudo: no tty present and no askpass program specified