不使用-h参数来指定登录host，默认会连接localhost，仅当mysql.user表中有一条对应的localhost访问授权(username@%不对任何主机做限制也不行)时登录才成功，否则登录会被拒绝。
虚拟机VMUest上安装两个MySQL实例，两个实例搭建了Master(端口3306)-Slave(端口3307)，主从数据完全一致。
mysql> select Host,User,Password from mysql.user; +-----------------------+--------+-------------------------------------------+ | Host | User | Password | +-----------------------+--------+-------------------------------------------+ | localhost | root | *6B4F89A54E2D27ECD7E8DA05B4AB8FD9D1D8B119 | | localhost.localdomain | root | | | 127.0.0.1 | root | | | ::1 | root | | | localhost | | | | localhost.localdomain | | | | % | mydba | *80BF8C1F4008F25267DB194E29D2E8BC20C836ED | | % | backup | *975B2CD4FF9AE554FE8AD33168FBFC326D2021DD | | 192.168.85.% | repl | *A424E797037BF97C19A2E88CF7891C5C2038C039 | +-----------------------+--------+-------------------------------------------+ 9 rows in set