装了一套mysql5.6测试用，配置主从的时候，为了方便，直接拷贝的主库的mysql目录到备库的
查看slave状态的时候发现报错如下：
Last_IO_Error: Fatal error: The slave I/O thread stops because master and slave have equal MySQL server UUIDs; these UUIDs must be different for replication to work

查看文档发现mysql 5.6上新增了server_uuid
Beginning with MySQL 5.6, the server generates a true UUID in addition to the --server-id supplied by the user. This is available as the global, read-only variable server_uuid.

When starting, the MySQL server automatically obtains a UUID as follows:
1，Attempt to read and use the UUID written in the file data_dir/auto.cnf (where data_dir is the server's data directory).
2，If data_dir/auto.cnf is not found, generate a new UUID and save it to this file, creating the file if necessary.

由于我备库的data目录都是从主库直接copy过来的，所以导致主备库的uuid相同了

The auto.cnf file has a format similar to that used for my.cnf or my.ini files. In MySQL 5.6, auto.cnf has only a single [auto] section containing a single server_uuid setting and value; 
the file's contents appear similar to what is shown here:
[auto]
server_uuid=8a94f357-aab4-11df-86ab-c80aa9429562

Important
The auto.cnf file is automatically generated; do not attempt to write or modify this file.

Note
Issuing a STOP SLAVE or RESET SLAVE statement does not reset the master's UUID as used on the slave

要解决这个错误就很简单了
auto.cnf 这个文件可以直接vim修改，只要按照uuid的格式，把备库的uuid修改成跟主库的不一致就可以了
其实也可以直接删除auto.cnf这个文件，重启mysql后，会自动生成这个文件