3.新创建wangwu用户，并查看密码有效期为30天。

[root@localhost ~]# useradd wangwu && echo "000000" | passwd --stdin wangwu
Changing password for user wangwu.
passwd: all authentication tokens updated successfully.
[root@localhost ~]# cat /etc/shadow | grep wangwu
wangwu:$6$qTt8ruAd$PbgMJlgjO6.Bp4YpQwN60oTyZyPloMxTjOUBJ0aYEBAjzg/opw4Ci6LZG5/RtBJW/YJ7QbJaMUEFbkLl9XTG8/:18136:0:30:7:::

4.更改已存在的用户lisi密码有效期为30天。

[root@localhost ~]# chage -M 30 lisi
[root@localhost ~]# cat /etc/shadow | grep lisi
lisi:$6$VLsvfMkO$aNnVeB1wWspXnD.4QErik1iLRw80jI7qqosbn9RgtGA9di5QFYh5ZWe3sUtLyshADukCH9vdZ55DZghDu4c.K.:18136:0:30:7:::

5.强制zhangsan用户下次登录必须修改密码。

[root@localhost ~]# chage -d 0 zhangsan
[root@localhost ~]# cat /etc/shadow | grep zhangsan
zhangsan:$6$MWTXL8Jt$rEFwO.UoAmoKmxczVgiJtOWCHtdYwRbW1G.drbEFrWuKYCAvfEByRN7eohVxonsVZCtqJ.oV3c1sLaVGUVIk9.:0:0:99999:7:::

6.使用zhangsan用户登录发现必须要修改密码，注意密码复杂性要求，示例密码：asdf1928。

login as: zhangsan
zhangsan@192.168.128.133's password:

You are required to change your password immediately (root enforced)
WARNING: Your password has expired.
You must change your password now and login again!
Changing password for user zhangsan.
Changing password for zhangsan.
(current) UNIX password:
New password:
Retype new password:
passwd: all authentication tokens updated successfully.

history 命令历史

命令历史记录在带来便利的同时，也存在着潜在的风险，比如曾经输入的明文密码等。

• 对所有用户生效，修改系统环境变量，可修改能查看最近历史记录的条数。

# vi /etc/profile
HISTSIZE=1000

• ~/.bash_logout在用户注销时会自动执行，可实现自动清除命令记录，下次登录将无法查看以前的命令记录。

# vi ~/.bash_logout
history -c
clear

Demo：

1.查看命令历史记录。

[root@localhost ~]# history
    1  grep "/bin/bash$" /etc/passwd
    2  useradd zhangsan && echo "000000" | passwd --stdin zhangsan
    3  grep "/bin/bash$" /etc/passwd
    4  lsattr /etc/passwd /etc/shadow
    5  chattr +i /etc/passwd /etc/shadow
    6  lsattr /etc/passwd /etc/shadow
    7  useradd lisi && echo "000000" | passwd --stdin lisi
    8  grep "/bin/bash$" /etc/passwd
    9  lsattr /etc/passwd /etc/shadow
   10  chattr -i /etc/passwd /etc/shadow
   11  lsattr /etc/passwd /etc/shadow
   12  useradd lisi && echo "000000" | passwd --stdin lisi
   13  grep "/bin/bash$" /etc/passwd
   14  cat /etc/shadow
   15  yum install vim -y
   16  vim /etc/login.defs
   17  useradd wangwu && echo "000000" | passwd --stdin wangwu
   18  cat /etc/shadow | grep wangwu
   19  chage -M 30 lisi
   20  cat /etc/shadow | grep lisi
   21  chage -d 0 zhangsan
   22  cat /etc/shadow | grep zhangsan
   23  history

2.修改配置文件记录的历史为20条，并立即生效。

[root@localhost ~]# vim /etc/profile
#HISTSIZE=1000
HISTSIZE=20
[root@localhost ~]# source /etc/profile

3.再次查看命令历史记录。