I believe something fucked up the permissions for the session dir, and the session table crashed at some point. I couldn't access phpMyAdmin to fix the crashed table until the permissions for the session dir were fixed. Perfect storm and all that. It also didn't help that it happened at the start of a work day (GMT+10, remember?), so the problem couldn't be addressed for 8 hours at least, and it took hours to track down and fix.
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andwhyisit
Mint
yet another reason to hate PHP
andwhyisit
How is php related to any of that? It's only faults were that it tried to access a table in mysql that had crashed, and it tried to access a directory that the OS said it couldn't for whatever reason.