mysql主從同步：
有三臺mysql A B C
其中A 和 B 已經做了主從，又把B做成了C的主，然後問題是，B上說什麼也不記錄bin-log，所以C就一直不能從B上同步到數據，B能從A上順利同步到數據。
解決辦法：
在B的配置文件my.cnf 加上一句
log-slave-updates
AB主從已設置好，問題出在BC之間
B上：
mysql>grant replication slave on *.* to 'repl2'@'192.168.1.118' identified by 'mysqlslave'
mysql> flush table with read clock;
mysql> show master status;
+-----------------+----------+--------------+------------------+
| File | Position | Binlog_Do_DB | Binlog_Ignore_DB |
+-----------------+----------+--------------+------------------+
| B_Master.000002 | 524565 | db1,db2 | mysql,db1 |
+-----------------+----------+--------------+------------------+
1 row in set (0.00 sec)C上：
vim /usr/local/mysql_slave/my.cnf
修改如下：
server-id = 2 //區別於主的id相同
在主上已經配置過，註釋下面的配置
#指定要同步的庫
#replicate-do-db=db2
#忽略不同步的庫
#replicate-ignore-db=mysql重啓生效：/etc/init.d/mysqldslave restart
mysql> change master to master_host='192.168.1.119',master_port=3307,master_user='repl2',master_password='mysqlslave',master_log_file='B_Master.000002',master_log_pos=524565;C連接B時報錯：
這樣配置了之後，B能同步A，但是C連接不到B，提示：
Last_IO_Error: error connecting to master '[email protected]:3307' - retry-time: 60 retries: 86400查看C錯誤日誌：
Version: '5.1.73' socket: '/tmp/mysql.sock' port: 3306 MySQL Community Server (GPL)
160512 8:40:29 [ERROR] Slave I/O: error connecting to master '[email protected]:3307' - retry-time: 60 retries: 86400, Error_code: 1130
160512 8:40:53 [Note] Error reading relay log event: slave SQL thread was killed
160512 8:40:53 [Note] Slave I/O thread killed while connecting to master
160512 8:40:53 [Note] Slave I/O thread exiting, read up to log 'B_Master.000003', position 340
160512 8:42:14 [Note] 'CHANGE MASTER TO executed'. Previous state master_host='192.168.1.119', master_port='3307', master_log_file='B_Master.000003', master_log_pos='340'. New state master_host='192.168.1.119', master_port='3307', master_log_file='B_Master.000004', master_log_pos='338'.
160512 8:42:29 [Note] Slave SQL thread initialized, starting replication in log 'B_Master.000004' at position 338, relay log './localCoohx-relay-bin.000001' position: 4
160512 8:42:29 [ERROR] Slave I/O: error connecting to master '[email protected]:3307' - retry-time: 60 retries: 86400, Error_code: 1130
160512 8:48:09 [Note] /usr/local/mysql/bin/mysqld: Normal shutdownC連接不到B，再試着直接C登錄B：
[root@localCoohx ~]# mysql -u repl2 -h192.168.1.119 -P 3307 -pmysqlslave
ERROR 1130 (HY000): Host '192.168.1.118' is not allowed to connect to this MySQL server問題就出在這了，突然想起來B沒有給C授權遠程登錄，於是在B上：
mysql> grant all on *.* to 'repl2'@'192.168.1.118' identified by 'mysqlslave';
Query OK, 0 rows affected (0.01 sec)
mysql> flush privileges;
Query OK, 0 rows affected (0.00 sec)之後就連接成功了。
————————————————–
由於之前mysql 從機的IP發生變化，所以需要BC之間從新設置主從：
B 192.168.1.112 C:192.168.1.118
B上： 重新給作爲Slave的C授權
mysql> grant replication slave on *.* to 'repl2'@192.168.1.118 identified by 'mysqlslave';
Query OK, 0 rows affected (0.00 sec)
mysql> flush privileges;
mysql> flush tables with read lock; //讓事務show master status鎖死表的讀
mysql> show master status;
+--------------+----------+--------------+------------------+
| File | Position | Binlog_Do_DB | Binlog_Ignore_DB |
+--------------+----------+--------------+------------------+
| coohx.000002 | 333 | db1 | mysql |
+--------------+----------+--------------+------------------+
1 row in set (0.00 sec)C上：
mysql> slave stop;
Query OK, 0 rows affected, 1 warning (0.00 sec)
mysql> change master to master_host='192.168.1.112',master_port=3307,master_user='repl2',master_password='mysqlslave',master_log_file='B_Master.000028',master_log_pos=106;
ERROR 1201 (HY000): Could not initialize master info structure; more error messages can be found in the MySQL error log
C上重新設置主信息失敗.
查看錯誤日誌：
160529 13:15:52 [Note] /usr/local/mysql/bin/mysqld: ready for connections.
Version: '5.1.73' socket: '/tmp/mysql.sock' port: 3306 MySQL Community Server (GPL)
160529 13:40:50 [ERROR] Failed to open the relay log './localCoohx-relay-bin.000004' (relay_log_pos 549)
160529 13:40:50 [ERROR] Could not find target log during relay log initialization
160529 13:45:38 [ERROR] Failed to open the relay log './localCoohx-relay-bin.000004' (relay_log_pos 549)
160529 13:45:38 [ERROR] Could not find target log during relay log initialization
160529 13:52:06 [ERROR] Failed to open the relay log './localCoohx-relay-bin.000004' (relay_log_pos 549)
160529 13:52:06 [ERROR] Could not find target log during relay log initialization
160529 13:52:18 [ERROR] Failed to open the relay log './localCoohx-relay-bin.000004' (relay_log_pos 549)
160529 13:52:18 [ERROR] Could not find target log during relay log initialization
160529 14:00:21 [ERROR] Failed to open the relay log './localCoohx-relay-bin.000004' (relay_log_pos 549)
160529 14:00:21 [ERROR] Could not find target log during relay log initializationlocalCoohx-relay-bin.000004 這是上一次C同步B後生成的relay重演文件，後來由於改過主機名，所以作廢，於是刪掉這些同步文件，繼續執行：
mysql> change master to master_host='192.168.1.112',master_port=3307,master_user='repl2',master_password='mysqlslave',master_log_file='B_Master.000028',master_log_pos=106;
ERROR 1201 (HY000): Could not initialize master info structure; more error messages can be found in the MySQL error log還是出錯，查看slave狀態：
mysql> show slave status\G;
*************************** 1. row ***************************
Slave_IO_State:
Master_Host: 192.168.1.119
Master_User: repl2
Master_Port: 3307
Connect_Retry: 60
Master_Log_File: B_Master.000005
Read_Master_Log_Pos: 405
Relay_Log_File: localCoohx-relay-bin.000004
Relay_Log_Pos: 549
Relay_Master_Log_File: B_Master.000005
Slave_IO_Running: No
Slave_SQL_Running: No
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: 405
Relay_Log_Space: 0
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: NULL
Master_SSL_Verify_Server_Cert: No
Last_IO_Errno: 0
Last_IO_Error:
Last_SQL_Errno: 0
Last_SQL_Error:
1 row in set (0.00 sec)顯示爲上一次主從同步時主的信息，主B的IP已經改變，所以重新設置slave-C，但是失敗，
解決辦法：
mysql> slave stop;
Query OK, 0 rows affected, 1 warning (0.00 sec)
mysql> reset slave; //這是關鍵一步！！！
Query OK, 0 rows affected (0.03 sec)mysql> change master to master_host='192.168.1.112',master_port=3307,master_user='repl2',master_password='mysqlslave',master_log_file='B_Master.000028',master_log_pos=106;
Query OK, 0 rows affected (0.09 sec)
mysql> slave start;
Query OK, 0 rows affected (0.05 sec)mysql> show slave status\G;
*************************** 1. row ***************************
Slave_IO_State: Waiting for master to send event
Master_Host: 192.168.1.112
Master_User: repl2
Master_Port: 3307
Connect_Retry: 60
Master_Log_File: B_Master.000028
Read_Master_Log_Pos: 106
Relay_Log_File: Coohx_slave-relay-bin.000002
Relay_Log_Pos: 250
Relay_Master_Log_File: B_Master.000028
Slave_IO_Running: Yes
Slave_SQL_Running: Yes
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: 106
Relay_Log_Space: 411
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
Master_SSL_Verify_Server_Cert: No
Last_IO_Errno: 0
Last_IO_Error:
Last_SQL_Errno: 0
Last_SQL_Error:
1 row in set (0.00 sec)成功連接到主，進行同步。
補充：
查看某一賬戶權限
mysql> show grants for ‘repl2’@’192.168.1.119’;
+——————————————————————————————————————————+
| Grants for [email protected] |
+——————————————————————————————————————————+
| GRANT REPLICATION SLAVE ON . TO ‘repl2’@’192.168.1.119’ IDENTIFIED BY PASSWORD ‘*EBB378AC232302FF0D4565FFF9F42577B1C04625’ |
+——————————————————————————————————————————+
1 row in set (0.00 sec)
總結：在同一臺mysql服務器上第二次設置從服務器時，應先關掉上一次的主從連接，reset清空以前的master信息，然後重新設置新的slave。
即：
stop
reset
change master