《如何让Linux安全起来》第一篇--设置普通用户登陆、禁止超级用户登陆

[root@localhost ~]# useradd admin
[root@localhost ~]# passwd admin
更改用户 admin 的密码 。
新的 密码：
无效的密码： 密码少于 8 个字符
重新输入新的 密码：
passwd：所有的身份验证令牌已经成功更新。

[root@localhost ~]# su admin
[admin@localhost root]$ cd /
[admin@localhost /]$ ls
bin  boot  dev  etc  home  lib  lib64  media  mnt  opt  proc  root  run  sbin  srv  svn  sys  tmp  usr  var

[root@localhost ~]# ssh admin@192.168.1.80
The authenticity of host '192.168.1.80 (192.168.1.80)' can't be established.
ECDSA key fingerprint is SHA256:Fi/pk1CNtdARuy0V94CeNUQFZGHukDxXjtSkSSbaTbc.
ECDSA key fingerprint is MD5:ff:de:cd:30:70:ab:8e:d4:96:fc:0b:3c:94:38:dc:93.
Are you sure you want to continue connecting (yes/no)? yes
Warning: Permanently added '192.168.1.80' (ECDSA) to the list of known hosts.
admin@192.168.1.80's password: 
Last login: Thu Apr 15 14:25:23 2021
[admin@localhost ~]$ 

vim /etc/ssh/sshd_config
源文件内容：
#PermitRootLogin yes
修改后：#禁止登录
PermitRootLogin no

重启sshd服务
systemctl restart sshd