Why Does My Symfony 3 App Get a 'PDO::__construct(): Server sent charset (255) unknown to the client' Error When Connecting to MySQL 8.0.1?

Unknown Server Charset Error in PDO MySQL Connection

When attempting to establish a MySQL database connection from a Symfony 3 application, an error message arises: "PDO::__construct(): Server sent charset (255) unknown to the client. Please, report to the developers." This signifies an issue where the MySQL server is transmitting a character set (255) that the PHP client is unfamiliar with.

Background:

The error stems from MySQL 8.0.1's default character set transformation to utf8mb4. However, not all clients may recognize this new character set. As a result, the server's transmission triggers this error.

Solution:

The optimal solution is to upgrade the client software. However, an interim workaround is available:

1. Alter the MySQL server's character set to utf8 to ensure compatibility with older clients.
2. Add the following settings to the MySQL configuration file (/etc/my.cnf):

[client]
default-character-set=utf8

[mysql]
default-character-set=utf8


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

3. Restart the MySQL server (mysqld) to apply these changes.

Additional Considerations:

• The error may persist even if the PHP client version is 7.1.33 or higher.
• Ensure that the PDO driver is updated to the latest version.
• Verify that the database character set is set to UTF8.

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