How to Enable Root Login on RHEL6

If You want to login as a root from GUI in RHEL6  then you have
to edit something like some files which are located to /etc/pam.d/
Open your Terminal from Applications -> System Tools -> Terminal

Now Login as a root  from your terminal

Step 1 :- [sham@rhel6]$ su – root
Password:-

Step 2:- Now go to your /etc/pam.d/ directory.

[root@rhel6]# cd /etc/pam.d/
Then first take a backup of gdm file
cp gdm gdm.bkp ( always take backup if anything goes wrong you can correct it by original file)

Step 3 :- Now Open gdm file in your favourite editor. I am using vi as my editor.
[root@rhel6]#  vi gdm
Find and Comment or remove this line into your gdm file
auth required pam_succeed_if.so user != root quiet

Step 4 :- Save & Exit From that File.

Step 5 :- Here is the additional file that you need to edit and that
file name is gdm-password. Open gdm-password file in your favourite
editor. I am using vi as my editor.
Then first take a backup of gdm-password file
cp gdm-password gdm-password.bkp ( always take backup if anything goes wrong you can correct it by original file)
[root@rhel6]# vi gdm-password
Find and Comment or remove this line into your gdm file
auth required pam_succeed_if.so user != root quiet

Step 6 :- Save & Exit from File. Now Logout and Try to Login as a
root user. Now you are able to Login as a root user from GUI in RHEL6.