https://blog.csdn.net/lianjoke0/article/details/82598149
[root@java133 ~]# ll /etc/passwd
-rw-r--r-- 1 root root 1068 11月 23 17:48 /etc/passwd
[root@java133 ~]# chmod u+s /bin/su
[root@java133 ~]# ll /bin/su
-rwsr-xr-x. 1 elkuser root 32096 8月 4 2017 /bin/su #su命令应该属于root用户root组 elkuser root 改为 root root
[root@java133 ~]# chown root.root /bin/su
[root@java133 ~]# ll /bin/su
-rwxr-xr-x. 1 root root 32096 8月 4 2017 /bin/su
[root@java133 ~]# chmod u+s /bin/su
[root@java133 ~]# ll /bin/su
-rwsr-xr-x. 1 root root 32096 8月 4 2017 /bin/su