Any further thoughts on this? I'm not sure where else to explore.
So, I've been stepping through this with die()'s and so forth, and eventually traced it to User::SetupSession(), which is called from Setup.php:
function SetupSession() { global $wgSessionsInMemcached, $wgCookiePath, $wgCookieDomain; if( $wgSessionsInMemcached ) { require_once( 'MemcachedSessions.php' ); } session_set_cookie_params( 0, $wgCookiePath, $wgCookieDomain ); session_cache_limiter( 'private, must-revalidate' ); @session_start(); }
And this is where the problem lies. If I remove the @ from session_start, I'll receive the following in my error log:
PHP Fatal error: session_start(): Failed to initialize storage module: user (path: /tmp) in User.php on line 159
Which at least gives me a bit more to go on now. I'll continue to poke around and report what I find, if anything, for the sake of future searchers.