这几天在MySQL新建用户后,出现访问拒绝的问题,错误码为ERROR 1045(28000)。在网上搜索了很久,找到了很多解决办法,但很遗憾的是这么多办法没有一个能解决该问题。虽然出现的错误码28000很多人都遇到过,但原因也有所不同,有的是mysql.user表中没有信息,有的是root用户没有密码(那就不用密码登录),而使用mysql-5.6.19时,mysql.user有用户信息,root用户没有密码,采用的方法是root用户登录时输入空密码,登录成功。使用root用户创建测试用test,密码为test,语句如下:
grant all onlogdb.* to test identified by ‘test’;
在命令行输入mysql -u test –p,输入密码test,出现下面的错误信息,详细该错误信息很多人在使用MySQL时都遇到过。
ERROR 1045 (28000):Access denied for user 'test'@'localhost' (using password: YES)
解决方法是用root用户再创建用户test,密码test,唯一不同的是指定test登录的主机为localhost,如下:
grant all onlogdb.* to test@'localhost' identified by 'test';
再次使用test用户登录MySQL,成功,如下所示:
使用root用户登录MySQL,查看user表中的用户信息如下,可以发现存在两个test用户,host的字段分别为%和localhost,就是前面创建的两个用户。
在MySQL中%表示可以在任何主机上登录MySQL数据库,那为什么还需要明确创建登录主机为localhost的用户呢?这涉及到MySQL安装时的初始化用户,匿名用户以及连接验证策略等,下面进行深入的分析。
在安装MySQL时,会默认初始化一些用户,比如root用户,以及host字段为localhost,user字段为空的用户。User字段为空的用户即为匿名用户,该用户的密码也为空,任何人都可以使用匿名用户登录MySQL数据库,但可以做的事情却是有限的,比如在命令行直接输入mysql登录,可以查看匿名用户对哪些数据库有权限:

/
通过上面的图片可以发现,匿名用户仅对information_schema和test数据库有权限。而匿名用户又是如何影响其他用户登录,进而出现28000错误的呢?当试图连接MySQL数据库时,数据库根据提供的身份和密码决定是否接受连接请求,身份由两部分组成:用户名和客户端主机(即输入mysql命令的主机)。由于host字段中的%匹配任何主机或者host字段包含通配符,就可能出现多个匹配行,服务器必须决定匹配哪一个,解决方案如下:
服务器将user表中的数据读入内存中,按照host和user字段对行进行排序。
当客户端试图连接时,服务器查找已排序的行并使用第一个匹配客户端主机和用户名的行,user字段为空表示可以匹配任何用户。
找到匹配行后,在验证密码是否一致,如果一致则登录成功。
根据上面描述的规则,通过示例来演示为什么必须要创建test@localhost用户,才能在本地登录成功。对user表进行排序的结果如下图所示:
当未创建test@localhost时,该表不包含第一行的记录。用户test登录时,则会匹配到第四行的记录:host为localhost,user为空,因为user为空可以匹配任何用户,再去验证密码不成功登录失败。或者不使用密码登录,还是匹配到第四行,但验证密码成功,然而匿名用户只对information_schema和test数据库有权限,使用其它数据库时也会失败,如下所示:
总结一下,当出现28000错误时,首先查看user中是否有数据,是否存在匿名用户。若存在匿名用户则创建userName@localhost,或者也可以删除匿名用户。

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