报错：
1）
change master导致的：
              Last_IO_Error: error connecting to master 'repl1@IP:3306' - retry-time: 60  retries

2）    
在没有解锁的情况下停止slave进程：
     mysql> stop slave;
ERROR 1192 (HY000): Can't execute the given command because you have active locked tables or an active transaction

3）
change master语法错误，落下逗号
mysql> change master to
    -> master_host='IP'
    -> master_user='USER',
    -> master_password='PASSWD',
    -> master_log_file='mysql-bin.000002',
    -> master_log_pos=106;
ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'master_user='USER',
master_password='PASSWD',
master_log_file='mysql-bin.000002' at line 3

4）
在没有停止slave进程的情况下change master
mysql> change master to master_host=‘IP', master_user='USER', master_password='PASSWD', master_log_file='mysql-bin.000001',master_log_pos=106;
ERROR 1198 (HY000): This operation cannot be performed with a running slave; run STOP SLAVE first

5）
A B的server-id相同：
Last_IO_Error: Fatal error: The slave I/O thread stops because master and slave have equal MySQL server ids;
these ids must be different for replication to work (or the --replicate-same-server-id option must be used on
slave but this does not always make sense; please check the manual before using it).
查看server-id
mysql> show variables like 'server_id';
手动修改server-id
mysql> set global server_id=2; #此处的数值和my.cnf里设置的一样就行
mysql> slave start;

6）change master之后，查看slave的状态，发现slave_IO_running 为NO
需要注意的是，做完上述操作之后最后重启mysql进程