Why Does My Symfony 3 App Get a 'PDO::__construct(): Server sent charset (255) unknown to the client' Error When Connecting to MySQL 8?

PHP Error: Server Sent Unknown Charset (255) for PDO Connection

When attempting to establish a database connection using PDO in a Symfony 3 application, developers may encounter the following error:

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

Root Cause:

This error arises when the MySQL server, running version 8.0.1 or later, reports its default character set (utf8mb4) which is not recognized by the client, such as PHP running version 7.1.3 with PDO MySQL driver.

Solution:

The ideal remedy is to update the client. However, as a temporary workaround, one can revert the server's character set to utf8 for compatibility with older clients. This involves modifying the /etc/my.cnf file and restarting MySQL:

[client]
default-character-set=utf8

[mysql]
default-character-set=utf8


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

Additional Resources:

• [MySQL Client Bug](https://bugs.mysql.com/bug.php?id=71606)
• [Instance's Default Character Set](https://dev.mysql.com/doc/refman/8.0/en/charset-charsets.html#charset-configuration)

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