安装MySQL后，root用户可设置密码登录，其他新建的用户不能通过密码登录，只能不输入密码登录，而且对新建用户的授权均无效。

--创建一个库和用户mysql> create database fire;Query OK, 1 row affected (0.00 sec)
mysql> create user neo identified by 'Mysql#2015';Query OK, 0 rows affected (0.00 sec)
mysql> grant select,create,update,delete on fire.* to neo;Query OK, 0 rows affected (0.00 sec)
mysql> flush privileges;Query OK, 0 rows affected (0.00 sec)

--使用新用户登录报错

[root@localhost data]# ./bin/mysql -u neo -p"Mysql#2015"
ERROR 1045 (28000): Access denied for user 'neo'@'localhost' (using password: YES)

--但是不输入密码却可以登录

[root@localhost software]# ./bin/mysql -uneo
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 11
Server version: 5.5.48-log production environment

Copyright (c) 2000, 2016, Oracle and/or its affiliates. All rights reserved.

Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

mysql> show grants;
+--------------------------------------+
| Grants for @localhost |
+--------------------------------------+
| GRANT USAGE ON *.* TO ''@'localhost' |
+--------------------------------------+
1 row in set (0.00 sec)

报错原因：Mysql使用源码安装后，数据库中存在匿名用户，可以通过任意用户名不输入密码即可登录数据库。

mysql> select host,user,password from mysql.user where (user) not in ('root');
+-----------------------+------+-------------------------------------------+
| host | user | password |
+-----------------------+------+-------------------------------------------+
| localhost | | |
| localhost.localdomain | | |
| % | neo | *CC4C777F1511C297751B78287D6E05345D227819 |
| % | test | *443EF031E558E317B19BAD70BDF4E25FA73A89A7 |
+-----------------------+------+-------------------------------------------+
4 rows in set (0.00 sec)

mysql> select host,user,password from mysql.user where (user) not in ('root','neo','test');
+-----------------------+------+----------+
| host | user | password |
+-----------------------+------+----------+
| localhost | | |
| localhost.localdomain | | |
+-----------------------+------+----------+
2 rows in set (0.00 sec)

解决方法：删除匿名用户。

mysql> delete from mysql.user where (user) not in ('root','neo','test');
Query OK, 2 rows affected (0.00 sec)

mysql> flush privileges;
Query OK, 0 rows affected (0.00 sec)

之后新创建的用户即可正常登录到数据库

[root@localhost software]# ./bin/mysql -uneo -p'Mysql#2015'
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 1
Server version: 5.5.48-log production environment

Copyright (c) 2000, 2016, Oracle and/or its affiliates. All rights reserved.

Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

mysql> show grants;
+-----------------------------------------------------------------+
| Grants for neo@% |
+-----------------------------------------------------------------+
| GRANT USAGE ON *.* TO 'neo'@'%' IDENTIFIED BY PASSWORD <secret> |
| GRANT SELECT, INSERT, DELETE, CREATE ON `fire`.* TO 'neo'@'%' |
+-----------------------------------------------------------------+
2 rows in set (0.00 sec)