How to Fix the 'PDO::__construct(): Server Sent Charset (255) Unknown to the Client' Error in Symfony 3?

Troubleshooting "PDO::__construct(): Server Sent Charset (255) Unknown to the Client" Error

When attempting to establish a MySQL database connection within a Symfony 3 application, users may encounter the following error:

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

This issue arises due to a change in MySQL's default charset in version 8.0.1 to utf8mb4. Some clients, such as PHP 7.1.3, may not recognize this charset.

Symptoms

The error occurs when the MySQL server communicates its default charset to the client, but the client fails to recognize it. This issue affects clients using the pdo_mysql driver, including PHP.

Background

Prior to MySQL 8.0.1, the default charset was utf8. However, MySQL 8.0.1 introduced utf8mb4 as the new default, which provides wider character support and better handling of Unicode characters.

Solution

The ideal resolution is to upgrade the client to a version that recognizes utf8mb4. However, as a temporary workaround, users can manually configure the server's character set to utf8, which is compatible with non-upgraded clients.

[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 ensure compatibility with the older client version.

It's important to note that upgrading the client remains the preferred long-term solution for resolving this issue.

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