参考：http://www.jb51.net/article/66951.htm
用5.7版本启动原5.5实例后，再用5.5启动出现以下报错
InnoDB: Error: checksum mismatch in data file /data/mysql/ibdata1 160627 10:42:11 InnoDB: Could not open or create data files. 160627 10:42:11 InnoDB: If you tried to add new data files, and it failed here, 160627 10:42:11 InnoDB: you should now edit innodb_data_file_path in my.cnf back 160627 10:42:11 InnoDB: to what it was, and remove the new ibdata files InnoDB created 160627 10:42:11 InnoDB: in this failed attempt. InnoDB only wrote those files full of 160627 10:42:11 InnoDB: zeros, but did not yet use them in any way. But be careful: do not 160627 10:42:11 InnoDB: remove old data files which contain your precious data! 160627 10:42:11 [ERROR] Plugin 'InnoDB' init function returned error. 160627 10:42:11 [ERROR] Plugin 'InnoDB' registration as a STORAGE ENGINE failed. 160627 10:42:11 [ERROR] Unknown/unsupported storage engine: InnoDB 160627 10:42:11 [ERROR] Aborting 160627 10:42:11 [Note] /usr/local/mysql/bin/mysqld: Shutdown complete
通过参数可以跳过错误启动，导出数据
innodb_force_recovery=6
innodb_purge_thread=0