su - or su - root in centos linux

You reference link is not my case .

My case is :

In non-root account , I can use " su - " to switch to root account.
But the command "su - root " is needed to disabled...

I search you reference link but it is not my case ..
Please suggest another way .....

Extraction of "man su" on CentOS: and most important, I don't understand why you use "su -" but want to disable "su - root" at the same time.

$ sudo -i
$ sudo su - -s /bin/bash root

I do not understand what do you mean ...

I want to know how I can make in normal centos linux .
Only allow "su - " to switch to root .
But it is not allow use "su - root" to switch to root.

How I can make this in normal centos OS ...not need to ask the purpose .....It just want to reproduce ...