Why Does My PHP PDO Connection Fail with 'Unknown Character Set (255)' from MySQL 8?

PDO Error: Unknown Character Set (255) from MySQL Server

When connecting to a MySQL database, developers may encounter the error: "PDO::__construct(): Server sent charset (255) unknown to the client. Please, report to the developers." This can arise in situations involving Docker containers and Symfony applications.

Cause:

MySQL version 8 introduced a change where the default character set was modified to utf8mb4. However, some clients, like certain PHP versions, do not recognize this charset. When the server communicates its default charset to the client, the client's lack of understanding leads to the error.

Solution:

The ideal solution is to upgrade the client to one that supports utf8mb4. For compatibility purposes, it is possible to adjust the server's character set to utf8, as demonstrated below:

Step 1: Edit MySQL Server Configuration

Add the following lines to /etc/my.cnf and restart MySQL:

[client]
default-character-set=utf8

[mysql]
default-character-set=utf8

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

Step 2: Restart MySQL

Restart MySQL to apply the changes:

service mysql restart

This modification will ensure compatibility with older clients that do not support utf8mb4.

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