Wheel user to become as root (su -) without password

1. Create a user:

useradd test
passwd test

2. Add this user in wheel group.

usermod -a -G wheel test

3. Now, Edit PAM configuration file for su. (/etc/pam.d/su)

----
 vi /etc/pam.d/su

uncomment below line

auth sufficient /lib/security/$ISA/pam_wheel.so trust use_uid

This will allow users in wheel group as a trusted users.

-----

4. Login as test user.

 #su -

It will not ask for password.

OR

If we add the test user in "visudo", we need to use "sudo su -" to become root without password.

----

1. visudo or vi /etc/sudo

2.  Add the below line 

   test    ALL=(ALL)   NOPASSWD:ALL

3. Save and exit

----

It will also grant root privilege for the user "test", but we need to use "sudo su -" to became as a root.