Upgrading MySQL 5.1 to 5.6 service failed to start

Operating System: CentOS 6.6 x64

error message:
2015-06-25 04:30:38 1646 [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!
2015-06-25 04:30:38 1646 [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!
2015-06-25 04:30:38 1646 [ERROR] Plugin 'InnoDB' init function returned error.
2015-06-25 04:30:38 1646 [ERROR] Plugin 'InnoDB' registration as a STORAGE ENGINE failed.
2015-06-25 04:30:38 1646 [ERROR] Unknown/unsupported storage engine: InnoDB
2015-06-25 04:30:38 1646 [ERROR] Aborting

solution:
#vi /etc/my.cnf
[mysqld]
innodb_data_file_path = ibdata1:10M:autoextend  //add this

#service mysqld restart