MySQL的SLAVE状态：Slave_IO_Running: NO和Slave_SQL_Running: No

show slave status\G;

发现:　Slave_IO_Running: NO
        　Slave_SQL_Running: No

也不能启动slave

mysql> slave start;
ERROR 1201 (HY000): Could not initialize master info structure; more error messagescan be found in the MySQL error log

打开/usr/local/mysql/datat/.err错误日志文件：

130416 14:03:54 [ERROR] Failed to open the relay log './localhost-relay-bin.000002' (relay_log_pos 253)

130416 14:03:54 [ERROR] Could not find target log during relay log initialization

130416 14:03:54 [ERROR] Failed to initialize the master info structure

解决方法：

删除所有文件名包含relay的文件，relay-log.info，relay-bin.index，relay-bin.xxxxxx文件。

1）关闭mysql, 

#/etc/init.d/mysqld stop

2）删除relay文件

#rm -f *relay*

3）登录mysql，启动slave

#mysql -uroot  -p

mysql>slave start

mysql>show slave status\G  

引起的原因：修改了centos的主机名，找不到relay-bin.index文件，导致二进制日志为空。