Allow the user in wheel group to be able to login system

1. Add the following line in /etc/pam.d/login

Account required pam_access.so

2. Add the following line in /etc/security/access.conf

# Disallow logins to all but wheel
-:ALL EXCEPT wheel:ALL

3. Modify /etc/group as follow

wheel:x:10:user1,user2,user3,user4