MySQL 5.6启动后，其日志文件存在如下错误：
......
2015-10-28 13:27:05 25054 [ERROR] Function 'innodb' already exists
2015-10-28 13:27:05 25054 [Warning] Couldn't load plugin named 'innodb' with soname 'ha_innodb.so'.
2015-10-28 13:27:05 25054 [ERROR] Function 'federated' already exists
2015-10-28 13:27:05 25054 [Warning] Couldn't load plugin named 'federated' with soname 'ha_federated.so'.
2015-10-28 13:27:05 25054 [ERROR] Function 'blackhole' already exists
2015-10-28 13:27:05 25054 [Warning] Couldn't load plugin named 'blackhole' with soname 'ha_blackhole.so'.
2015-10-28 13:27:05 25054 [ERROR] Function 'archive' already exists
2015-10-28 13:27:05 25054 [Warning] Couldn't load plugin named 'archive' with soname 'ha_archive.so'.
......
分析原因，是MySQL 5.6没有以下四个插件所致。
MySQL 5.6服务器初始化脚本添加了以下的插件表，而实际上MySQL 5.6不依赖于任何插件。
mysql> select * from mysql.plugin;
+-----------+-----------------+
| name | dl |
+-----------+-----------------+
| innodb | ha_innodb.so |
| federated | ha_federated.so |
| blackhole | ha_blackhole.so |
| archive | ha_archive.so |
+-----------+-----------------+
4 rows in set (0.00 sec)
解决它很简单，执行命令：
mysql> delete from mysql.plugin;
Query OK, 4 rows affected (0.00 sec)
删掉这4个插件，清除日志，重启MySQL服务，可以看到，MySQL无错运行。
MySQL在Ubuntu系统的三种自启动方法：http://www.linuxdiyf.com/linux/15274.html
ubuntu15.04 mysql字符集修改：http://www.linuxdiyf.com/linux/15226.html
ubuntu 15.04开放mysql远程3306端口：http://www.linuxdiyf.com/linux/15206.html
Linux下查看MySQL的安装路径：http://www.linuxdiyf.com/linux/14760.html
ubuntu15.04手动安装MySQL5.6.27数据库：http://www.linuxdiyf.com/linux/14699.html