Manual talk:$wgFileCacheDirectory

You have to create the directory
Thankyou to netninja.com for pointing out that you have to create the directory (which I will clarify on here) -- Harry Wood 00:04, 8 November 2007 (UTC)
 * Looks like that isn't a problem (at least in 1.15). Looks like that was fixed in r40418 maybe? Dunno, there was mkdir in the code since at least r1519.  Either way, I'm going to update the note. --Little Filament 17:53, 9 September 2009 (UTC)

Default value for versions 1.16.0+ is wrong.
This page currently states that the default value for this variable since 1.16.0 is "{$wgCacheDirectory}/html".

However, in the include/Setup.php file for versions 1.16.0 and 1.17.0 the default is clearly still being set as "{$wgUploadDirectory}/cache".

I am editing the default value to "{$wgUploadDirectory}/cache" for all versions to reflect the defaults set in the code.