A.2.3.  Client does not support authentication protocol

MySQL 4.1 and up uses an authentication protocol based on a password hashing algorithm that is incompatible with that used by older clients. If you upgrade the server from 4.0, attempts to connect to it with an older client may fail with the following message:

To solve this problem, you should use one of the following approaches:

• Upgrade all client programs to use a 4.1.1 or newer client library.

• When connecting to the server with a pre-4.1 client program, use an account that still has a pre-4.1-style password.

• Reset 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.

• Tell the server to use the older password hashing algorithm:

  1. Start mysqld with the --old-passwords option.

  2. Assign 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.

Note : In PHP, the standard mysql extension does not support the new authentication protocol in MySQL 4.1.1 and higher. This is true regardless of the PHP version being used. If you wish to use the mysql extension with MySQL 4.1 or newer, you will need to follow one of the options discussed above for configuring MySQL to work with old clients. The mysqli extension (stands for "MySQL, Improved"; new in PHP 5) is compatible with the improved password hashing employed in MySQL 4.1 and higher, and no special configuration of MySQL need be done to use this newer MySQL client library for PHP. For more information about the mysqli extension, see http://php.net/mysqli .

It may also be possible to compile the older mysql extension against the new MySQL client library. This is beyond the scope of this Manual; consult the PHP documentation for more information. You also be able to obtain assistance with these issues in our MySQL with PHP forum .

For additional background on password hashing and authentication, see Section 5.7.9, “Password Hashing as of MySQL 4.1” .