Why Does My PHP PDO Connection Fail with 'Server sent charset (255) unknown to the client'?

PDO Connection Error with Unknown Charset (255)

When attempting to establish a database connection using PHP Data Objects (PDO), you may encounter the following error:

PDO::__construct(): Server sent charset (255) unknown to the client. Please, report to the developers

Explanation

MySQL 8.0.1 introduced a change where the default character set was updated to utf8mb4. However, some client applications, including older versions of PHP, may not recognize this charset, leading to this error.

Possible Solution

The recommended solution is to upgrade your client application to a version that supports utf8mb4. This will ensure compatibility with the server's default charset.

Alternative Solution

If upgrading the client is not feasible, you can adjust the server's character set to utf8, which is more widely recognized by clients. This can be achieved by adding the following lines to your /etc/my.cnf file:

[client]
default-character-set=utf8

[mysql]
default-character-set=utf8


[mysqld]
collation-server = utf8_unicode_ci
character-set-server = utf8

Restart MySQL after making these changes. This will allow your client to connect without encountering the charset unknown error.

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