Manual:$wgCacheDirectory

Details
This directory stores some cache files specific for a given wiki, which means wiki farms should have one such directory per wiki.

It should not be accessible from the web. Either you can use the file .htaccess already in this directory, or you should configure it specifically (for example, if your webserver does not recognise .htaccess files). If   is set to false (or not set), the wiki will be slower.

The proposed value for single wikis is  , and for wiki farms sharing a cache folder, something along the lines of   ensures each wiki's caches remain separate from each other. This is commented in the file LocalSettings.php created during the installation and can be de-commented. In this case, you should create the directory  in your MediaWiki directory and make it writable by the web server.

Note that you should not set this directory to   else there could be conflicts with other MediaWiki installations on the same server (wiki farms or shared servers).

This folder should probably be set to  -R 775 or 755.