一、在CentOS7中普通使用者執行SU時，報如下錯誤：

[[email protected] ~]$ su -
Password: 
su: Authentication failure

解決方法：

如果root能夠正常登陸，就先使用root使用者登入系統，再執行操作

1、登陸root賬戶；
2、執行sudo -i

[[email protected] ~]# sudo -i

3、執行chmod +s /bin/su

[[email protected]53 ~]# chmod +s /bin/su

4、驗證

[[email protected] ~]$ su - root
Password: 
su: Authentication failure
[
 
[email protected] ~]$ su - root
Password: 
Last login: Tue Feb 27 18:44:34 CST 2018 on pts/0
Last failed login: Tue Feb 27 18:45:42 CST 2018 on pts/1
There was 1 failed login attempt since the last successful login.

二、在centos6中普通使用者執行su時，報錯如下：

[[email protected] ~]$ su - root
Password: 
su: incorrect password
 

解決方法：

如果root能夠正常登陸，就先使用root使用者登入系統，再執行操作

1、登陸root賬戶；
2、檢視/etc/pam.d/su配置檔案，#auth required pam_wheel.so use_uid 這句是否被啟用，如果啟用了，那麼加入了wheel組的使用者（usermod -g  wheel 使用者id）才能su，否則就會提示密碼錯誤。

[[email protected] ~]# vim /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.
 
#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

3、檢視檔案許可權，正確如下

[[email protected] ~]# ll -a /bin/su 
-rwsr-xr-x. 1 root root 34904 May 11  2016 /bin/su
[[email protected] ~]# ll -a /usr/bin/passwd 
-rwsr-xr-x. 1 root root 30768 Nov 24  2015 /usr/bin/passwd

4、驗證

[[email protected] ~]$ su - root
Password: 
su: incorrect password
[[email protected] ~]$ su - root
Password: 
[[email protected] ~]#