遇到以下错误：

[root@dba ~]# mysql -uroot -p
Enter password:
ERROR 1045 (28000): Access denied for user 'root'@'localhost' (using password: YES)

解决方案：

1、关闭原有的数据库：

[root@dba ~]# /etc/init.d/mysql stop
Shutting down MySQL.... SUCCESS

2、以特殊的模式启动数据库：

[root@dba ~]#  mysqld_safe --user=mysql --skip-grant-tables --skip-networking &
[1] 3196
[root@dba ~]# 150714 11:52:19 mysqld_safe Logging to '/var/lib/mysql/dba.fei.com.err'.
150714 11:52:19 mysqld_safe Starting mysqld daemon with databases from /var/lib/mysql

3、不使用密码登录数据库：
[root@dba ~]#  mysql -u root mysql
Reading table information for completion of table and column names
You can turn off this feature to get a quicker startup with -A

Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 1
Server version: 5.6.23 MySQL Community Server (GPL)

Copyright (c) 2000, 2015, 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>

4、更新用户密码：

mysql> UPDATE user SET Password=PASSWORD('123456') where USER='root' and host='root' or host='localhost' or host='dba.fei.com';
Query OK, 2 rows affected (0.00 sec)
Rows matched: 2  Changed: 2  Warnings: 0

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

mysql> quit
Bye

5、使用新密码登录数据库：

[root@dba ~]# mysql -uroot -p
Enter password:
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 3
Server version: 5.6.23

Copyright (c) 2000, 2015, 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> SET PASSWORD = PASSWORD('123456');
Query OK, 0 rows affected (0.00 sec)

mysql>  show databases;
+--------------------+
| Database           |
+--------------------+
| information_schema |
| mysql              |
| performance_schema |
| test               |
+--------------------+
4 rows in set (0.00 sec)

mysql> use mysql
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
mysql> show tables;
+---------------------------+
| Tables_in_mysql           |
+---------------------------+
| columns_priv              |
| db                        |
| event                     |
| func                      |
| general_log               |
| help_category             |
| help_keyword              |
| help_relation             |
| help_topic                |
| innodb_index_stats        |
| innodb_table_stats        |
| ndb_binlog_index          |
| plugin                    |
| proc                      |
| procs_priv                |
| proxies_priv              |
| servers                   |
| slave_master_info         |
| slave_relay_log_info      |
| slave_worker_info         |
| slow_log                  |
| tables_priv               |
| time_zone                 |
| time_zone_leap_second     |
| time_zone_name            |
| time_zone_transition      |
| time_zone_transition_type |
| user                      |
+---------------------------+
28 rows in set (0.00 sec)

mysql> grant all  on *.* to 'root'@'%' identified by '123' with grant option;
Query OK, 0 rows affected (0.00 sec)

mysql> FLUSH   PRIVILEGES;
Query OK, 0 rows affected (0.00 sec)