centos 升级mysql 5.1 到5.6（及rpm安装可能启动不了问题）

备份数据库，升级MySQL通常不会丢失数据，但保险起见，我们需要做这一步。输入命令：

mysqldump -u xxx -h xxx -P 3306 -p --all-databases > databases.sql

停止MySQL服务，输入命令：

service mysqld stop

yum remove mysql mysql-*

执行过程中会询问你是否移除，此时输入“Y”

移除命令执行后，可再看看是否有残余的mysql，输入命令：

yum list installed | grep mysql

如果有，可输入命令删除：

rum remove mysql－libs

下载安装最新的rpm文件

rpm -Uvh http://repo.mysql.com/mysql-community-release-el6-5.noarch.rpm

安装MySQL，输入命令：

yum install mysql-community-server

安装完成后，输入命令查看MySQL版本号：

mysql -V

启动MySQL，输入命令：

service mysqld start

有可能发生如下错误

$yum install mysql-server
　　安装之后执行命令mysql

　　报错：

　　查看mysql的启动日志：

$tail -f /var/log/mysqld.log 

[ERROR] InnoDB: auto-extending data file ./ibdata1 is of a different size 640 pages (rounded down to MB) than specified in the .cnf file: initial 768 pages, max 0 (relevant if non-zero) pages!
2016-02-22 23:02:55 29830 [ERROR] InnoDB: Could not open or create the system tablespace. If you tried to add new data files to the system tablespace, and it failed here, you should now edit innodb_data_file_path in my.cnf back to what it was, and remove the new ibdata files InnoDB created in this failed attempt. InnoDB only wrote those files full of zeros, but did not yet use them in any way. But be careful: do not remove old data files which contain your precious data!
2016-02-22 23:02:55 29830 [ERROR] Plugin 'InnoDB' init function returned error.
2016-02-22 23:02:55 29830 [ERROR] Plugin 'InnoDB' registration as a STORAGE ENGINE failed.
2016-02-22 23:02:55 29830 [ERROR] Unknown/unsupported storage engine: InnoDB
2016-02-22 23:02:55 29830 [ERROR] Aborting
解决方法：

　执行删除命令：rm -rf /var/lib/mysql/ib*

删除：ibdata1、ib_logfile0、ib_logfile1文件

重新启动：service mysqld start