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storageDatabase•codePHPsystem_updateUpdatelinkconnectionerrordatabase_errordangerousfatal_error•star_halfUncommon•warningModerate

Error establishing a database connection after PHP 8.2 upgrade

The upgrade to PHP 8.2 introduces stricter type handling and removes several legacy functions. When WordPress or a plugin calls a removed function such as mysql_connect or passes null where a string is required, PHP throws a fatal error before the database connection is attempted.

Additionally, PHP 8.2 changes default settings like mysqli.allow_local_infile and may alter the socket path used by MySQL. If wp-config.php contains null values or an outdated host definition, the connection fails immediately.

Symptoms

[dashicons-warning]
White screen on front end
The site shows a blank page or the standard database connection error message.
[dashicons-admin-users]
Admin login blocked
Accessing /wp-admin/ returns the same error page.
[dashicons-admin-tools]
500 Internal Server Error
Browser dev tools report a 500 status code.

Common Causes

Removed legacy functions
Plugins or custom code still call mysql_connect or each, which no longer exist in PHP 8.2.
Strict type checking in mysqli/PDO
Passing null or an empty string for host or username triggers a TypeError.
Changed default mysqli.allow_local_infile
Import‑heavy plugins fail when the setting is false.
Incorrect DB_HOST socket path
PHP upgrade may reset the socket location, leaving wp-config.php pointing to a non‑existent file.
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