Hi,
I find there is some customized linux with application.
When I use login account root and type the password.
It is not allow to login.
But if I login with specified user and password.
Then I use command "su - " and type root passwd.
It allow you to switch to "root" account .

Or if i use "su - root" and type password .it is not allow to login again .

It is strange I cannot login if I specified to use "root" account .


How to make this setting ..

Please advice in detailed.

Many Linux distros block direct root login as a security feature. Every hacker who knows anything will try to brute-force "root" username so it's a good idea to lock it.

So,
How to make this setting ??
Please advice in detailed.....

Which distro are you using and why do you find it inconvenient to type "su -" as a security precaution?

I want to know how can I make this setting in normal linux OS ..
I want to reproduce this .....
Please advice in detailed....

It's best to leave it this way. Its an extra layer of security. And really, it doesn't take but an extra 2 seconds to login with su -

I can't help you if you refuse to tell us which distro you are using. Have a nice day!

Might be more secure if you used sudo or chroot/fakeroot instead of using root directly.

or can edit sudo visudo and make it not to prompt for password globally or per application , but highly not recommended :

username ALL=(ALL) NOPASSWD: ALL

you still have not answered the question
What Operating System is this ?

su and su - are used as default on RHEL based systems

BUT
RHEL / CentOS /SL all allow root gui login !!! use at own RISK!!!

Now , Fedora DOSE NOT!!!!!!!

so a guess here
you are using fedora


there is a so called " pam hack"
that is NOT RECOMMENDED !!!!!!!!!!!
it causes all kinds of problems
problems that will basically turn the fedora install into a "horror story"
and a pain in the rear end to even try to use



PS
and what ever you do
DO NOT do this!!!!!!!!!!!!!!!!!
DO NOT!!!!!!!!!!!!
do not set up a normal user as root with no pasword
!!!!! a very very VERY BAD IDEA!!!!!!!!