反复提示您在每次ssh登录时更改密码

我有一个装有Ubuntu 18.04的VPS。

在每次成功登录user时root，系统都会提示我：

Changing password for root.
(current) UNIX password: 
Enter new UNIX password: 
Retype new UNIX password: 
root@ubuntu...*:~#

当我检查密码的到期日期时：

root@ubuntu...*:~# chage -l root
Last password change                    : Jan 30, 2019
Password expires                    : never
Password inactive                   : never
Account expires                     : never
Minimum number of days between password change      : 0
Maximum number of days between password change      : 14600
Number of days of warning before password expires   : 14

怎么了？我想选择一个永久密码。