Tạo user trên Linux

[1]Add a new user. I used user name as 'cent' on following examples, but Set any names you like to use.
[root@ns ~]# useradd cent
[root@ns ~]# passwd cent
Changing password for user cent.
New UNIX password:# // input password you want to set
Retype new UNIX password:# verify
passwd: all authentication tokens updated successfully.
[root@ns ~]# exit

[2]Try to switch by user that was added in section [1].
ns login: cent# input user name
password: # input password
[cent@ns ~]$ su -# switch to root
Password:# input password for root
[root@ns ~]## done to switching to root

[3]Make 'cent' user that was added in section [1] be only a user who can switch to root.
[root@ns ~]# vi /etc/group

# line 11: add a user
wheel:x:10:root,cent

[root@ns ~]# vi /etc/pam.d/su

#%PAM-1.0
auth sufficient pam_rootok.so
# Uncomment the following line to implicitly trust users in the "wheel" group.
#auth sufficient pam_wheel.so trust use_uid
# Uncomment the following line to require a user to be in the "wheel" group.
#↓ remove '#' that was on the head of lin
auth required pam_wheel.so use_uid
auth include system-auth
account sufficient pam_succeed_if.so uid = 0 use_uid quiet
account include system-auth
password include system-auth
session include system-auth
session optional pam_xauth.so
Forwarding email for root

[4] Set config to forward mails for root to a user who is a system administrator you set as.
[root@ns ~]# vi /etc/aliases

# Person who should get root's mail
# bottom: remove '#' and change your user name
root: cent

[root@ns ~]# newaliases# set new aliases
/etc/aliases: 77 aliases, longest 10 bytes, 776 bytes total