[root@localhost ~]# mysql -u root 
[root@localhost ~]# mysql -uroot -p

MariaDB [mysql]> use mysql;回车，会显示以下内容
Reading table information for completion of table and column names You can turn off this feature to get a quicker startup with -A
Database changed

MariaDB [mysql]> update user set password=password('新密码') where user='要更新密码的用户名';回车
　　-> ;
Query OK, 0 rows affected (0.00 sec)
Rows matched: 5 Changed: 0 Warnings: 0

MariaDB [mysql]> flush privileges;回车
Query OK, 0 rows affected (0.00 sec)

MariaDB [mysql]> quit
Bye

[root@localhost ~]# service mysqld restart(重启mysql)
[root@localhost ~]# service mariadb restart(重启mariadb)