1.用mysqldump做一个全备

mysqldump --all-databases --single-transaction --triggers --routines --events --host=127.0.0.1 --port=3306 --user=root --password=123 > dump.sql

说明
--single-transaction 参数来获得一致性备份，减少锁表。

2.在从库停止同步

-- 登陆从库mysql后执行
stop slave
reset slave
reset master

3.恢复数据

source dump.sql;

4.重新建立主从

change master to master_host='192.168.0.31',master_port=3306,master_user='repl',master_password='123',master_auto_position=1;
start slave;

5.查看同步情况

show slave status\G

*************************** 1. row ***************************
               Slave_IO_State: Waiting for master to send event
                  Master_Host: 192.168.0.31
                  Master_User: repl
                  Master_Port: 3306
                Connect_Retry: 60
              Master_Log_File: mysql-bin.000031
          Read_Master_Log_Pos: 1069264803
               Relay_Log_File: slave_relay_bin.000074
                Relay_Log_Pos: 1069265016
        Relay_Master_Log_File: mysql-bin.000031
             Slave_IO_Running: Yes    ---这两个为YES表示同步成功
            Slave_SQL_Running: Yes    ---这两个为YES表示同步成功
              Replicate_Do_DB: 
          Replicate_Ignore_DB: 
           Replicate_Do_Table: 
       Replicate_Ignore_Table: 
      Replicate_Wild_Do_Table: 
  Replicate_Wild_Ignore_Table: 
                   Last_Errno: 0
                   Last_Error: 
                 Skip_Counter: 0
          Exec_Master_Log_Pos: 1069264803
              Relay_Log_Space: 26144405550
              Until_Condition: None
               Until_Log_File: 
                Until_Log_Pos: 0
           Master_SSL_Allowed: No
           Master_SSL_CA_File: 
           Master_SSL_CA_Path: 
              Master_SSL_Cert: 
            Master_SSL_Cipher: 
               Master_SSL_Key: 
        Seconds_Behind_Master: 0     ---这个正常情况应该等于0或接近0。如果过大，或数字在不断增加，需要检查原因。
Master_SSL_Verify_Server_Cert: No
                Last_IO_Errno: 0
                Last_IO_Error: 
               Last_SQL_Errno: 0
               Last_SQL_Error: 
  Replicate_Ignore_Server_Ids: 
             Master_Server_Id: 1
                  Master_UUID: 77cc5c15-77fa-11e7-bdf4-1418774c9619
             Master_Info_File: mysql.slave_master_info
                    SQL_Delay: 0
          SQL_Remaining_Delay: NULL
      Slave_SQL_Running_State: Slave has read all relay log; waiting for more updates
           Master_Retry_Count: 86400
                  Master_Bind: 
      Last_IO_Error_Timestamp: 
     Last_SQL_Error_Timestamp: 
               Master_SSL_Crl: 
           Master_SSL_Crlpath: 
           Retrieved_Gtid_Set: 77cc5c15-77fa-11e7-bdf4-1418774c9619:229487-2282150
            Executed_Gtid_Set: 77cc5c15-77fa-11e7-bdf4-1418774c9619:1-2282150
                Auto_Position: 1
         Replicate_Rewrite_DB: 
                 Channel_Name: 
           Master_TLS_Version: 
1 row in set (0.00 sec)