最近在做mysql 多實例的時候，採用不同的方式登錄mysql數據庫，發現mysql -uroot -p -h 127.0.0.1 -P3308 ，登錄時居然不要密碼就可以登錄
，嚇得我一身汗，經過檢查終於找到原因記錄下來，給小白們參考。
[root@mysql ~]# mysql -uroot -p -S /data/3308/mysql.sock
Enter password: #需要輸入密碼
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 23
Server version: 5.5.32-log Source distribution
Copyright (c) 2000, 2013, 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> select current_user();
+----------------+
| current_user() |
+----------------+
| root@localhost |
+----------------+
1 row in set (0.00 sec)
*******************************************************************
[root@mysql ~]# mysql -uroot -p -h 127.0.0.1 -P3308
Enter password: #不需要輸入密碼，直接回車登錄
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 24
Server version: 5.5.32-log Source distribution
Copyright (c) 2000, 2013, 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>
mysql> select current_user();
+----------------+
| current_user() |
+----------------+
+----------------+
1 row in set (0.00 sec)
不要密碼登錄原因：
登錄數據庫查看密碼
mysql> select user,host,password from mysql.user;
+------+-----------+-------------------------------------------+
| user | host | password |
+------+-----------+-------------------------------------------+
| root | localhost | *FE28814B4A8B3309DAC6ED7D3237ADED6DA1E515 |
| root | mysql | |
| root | 127.0.0.1 | |
| root | ::1 | |
| | localhost | |
| | mysql | |
| tom | % | *71FF744436C7EA1B954F6276121DB5D2BF68FC07 |
| tom1 | % | *36B46F2410B8A8E6E1DC6952C5C26929FDC07421 |
| tom2 | % | *FEF6FE64F2588DC11E69F0DC5A704E231D1AAEFC |
| tom | localhost | *71FF744436C7EA1B954F6276121DB5D2BF68FC07 |
+------+-----------+-------------------------------------------+
10 rows in set (0.00 sec)
總結：第一種方式登錄後，用戶是 root@localhost，第二種方式登錄後，用戶是[email protected] 查看數據庫，發現root@localhost沒有設置密碼，所以使用第一種方式登錄不需要輸入密碼。