MySQL 4.1以后, 采用了一种新的用户认证协议, 对于老的客户端会出现不支持认证协议的错误, 以下是官方网站的解决方法﹔
１Upgrade all client programs to use a 4.1.1 or newer client library.
更新客户端库，这需要更新PHP的扩展库，对于老的api PHP已经不提供了这样的扩展库了
２When connecting to the server with a pre-4.1 client program, use an account that still has a pre-4.1-style password.
使用以前建立的账号连接，对于在新的认证协议下建立的账户就不行了
３Reset the password to pre-4.1 style for each user that needs to use a pre-4.1 client program. This can be done using the SET PASSWORD statement and the OLD_PASSWORD() function: MySQL> SET PASSWORD FOR
-> 'some_user'@'some_host' = OLD_PASSword('newpwd');
Alternatively, use UPDATE and FLUSH PRIVILEGES: MySQL> UPDATE mysql.user SET Password = OLD_PASSWORD('newpwd') -> WHERE Host = 'some_host' AND User = 'some_user';
MySQL> FLUSH PRIVILEGES;
Substitute the password you want to use for ``newpwd'' in the preceding examples. MySQL cannot tell you what the original password was, so you'll need to pick a new one.
这是一个不错的办法，新建立的账号采用老式的加密协议
４Tell the server to use the older password hashing algorithm:
Start MySQLd with the --old-passwords option.
这样新认证协议的优点就没法使用了
５Assign an old-format password to each account that has had its password updated to the longer 4.1 format. You can identify these accounts with the following query: MySQL> SELECT Host, User, Password FROM mysql.user
-> WHERE LENGTH(Password) > 16;
For each account record displayed by the query, use the Host and User values and assign a password using the OLD_PASSWORD() function and either SET PASSWORD or UPDATE, as described earlier.
恢复已经升级了口令到老样式