set password=password("password");

flush privileges;

#设置用户密码永不过期
ALTER USER 'root'@'localhost' PASSWORD EXPIRE NEVER;

查看用户密码默认过期时间设置，默认360天
mysql> show global variables like "default_password_lifetime";
+---------------------------+-------+
| Variable_name             | Value |
+---------------------------+-------+
| default_password_lifetime | 360   |
+---------------------------+-------+
1 row in set (0.00 sec)

设置用户密码永不过期（临时生效）
mysql> SET GLOBAL default_password_lifetime = 0;
Query OK, 0 rows affected (0.00 sec)

mysql> show global variables like "default_password_lifetime";
+---------------------------+-------+
| Variable_name             | Value |
+---------------------------+-------+
| default_password_lifetime | 0     |
+---------------------------+-------+
1 row in set (0.00 sec)

如果要设置密码永不过期，设置my.cnf
vi /etc/my.cnf
添加
#设置用户密码永不过期
default_password_lifetime=0

这样重启后也是没问题的

查看用户密码设置
mysql> select user,host,password_expired,password_last_changed,password_lifetime from mysql.user;
+----------------+-----------+------------------+-----------------------+-------------------+
| user           | host      | password_expired | password_last_changed | password_lifetime |
+----------------+-----------+------------------+-----------------------+-------------------+
| root           | localhost | N                | 2018-01-05 16:54:02   |                 0 |
| mysql.sys      | localhost | N                | 2017-01-07 16:49:55   |              NULL |
| root           | %         | N                | 2017-01-12 17:21:08   |              NULL |
| zabbix_monitor | localhost | N                | 2017-05-08 09:45:40   |              NULL |
+----------------+-----------+------------------+-----------------------+-------------------+
6 rows in set (0.00 sec)

创建一个有效期30天的用户
create user tt@'%' identified by '123456' password expire interval 30 day;

mysql> select user,host,password_expired,password_last_changed,password_lifetime from mysql.user;
+-----------+------------+------------------+-----------------------+-------------------+
| user      | host       | password_expired | password_last_changed | password_lifetime |
+-----------+------------+------------------+-----------------------+-------------------+
| root      | localhost  | N                | 2017-12-28 15:59:39   |              NULL |
| mysql.sys | localhost  | N                | 2017-12-28 11:42:12   |              NULL |
| mysync    | 10.73.86.% | N                | 2017-12-28 16:11:49   |              NULL |
| tt        | %          | N                | 2018-01-08 12:59:08   |                30 |
+-----------+------------+------------------+-----------------------+-------------------+