Manual:$wgWikiFarmSettingsDirectory/en

Details
A directory that contains site-specific settings files. Setting this will enable multi-tenant ("Wiki family") mode, causing site-specific settings to be loaded based on information from the web request.

The  environment variable will be used to determine which wiki's settings should be loaed for the current request. The environment variable should be set by the web server based on the requested domain or path that identifies the wiki. The settings file is expected to be located in the directory specified by the  setting and use the file extension specified by , which may be   or. The file must use the YAML settings file format. Settings loaded from this file will be combined with settings found in LocalSettings.php.

Example
Assume there are three wikis with the IDs,  , and. If  is set to , then the following YAML files should exist for each wiki in the   directory: