In recent work, Ian Selby came across something odd - a setup where PHP was segfaulting without any real indication of where the error might be:

Starting to get a little frustrated, I took a peek at my error logs (/var/log/httpd/error_log for the unitiated), and discovered a wonderful message [about the segfault]. As any person scratching their head would do, I hit up google.. to no real avail. Just a bunch of php bug reports. So, what happened, and how did I fix it?

After searching through the code and narrowing down where it could be, the culprit looked like a custom session handler he was using. It uses MySQL to store the sesion information and, unfortunately, when Ian had compiled the server he didn't let PHP know about his unique setup.

His default installation was trying to use the default MySQL information (including the socket) to reach the database. Obviously failing, the server simply gave up and segfaulted. Thankfully, all it takes it a recompile with a few extra parameters and you're back in business.