I am trying to follow this tutorial http://doc.silverstripe.org/framework/en/reference/siteconfig
to extend the SiteConfig, but I get this error when I visit "dev/build?flush=all":

[Sat Dec  1 20:47:00 2012] [notice] child pid 4036 exit signal Segmentation fault (11)

The access that caused this error was logged some thirty seconds later when I was served a blank page:

xxx.xxx.xxx.xxx - - [01/Dec/2012:20:47:33 -0800] "GET /xxxxxxxxx/dev/build?flush=all HTTP/1.1" 200 1724

top shows heavy cpu use by the httpd process in the meantime. It's curious that the time elapsed coincides with php's default max_execution_time, but I'm at a loss to what's going on here.

This is most likely a bug with your version of PHP. I used to get this when accessing some of the automagic functions SilverStripe added to objects for relationships ie: $this->Relation()

What version of PHP do you have? Some googling might find the problem...

OpenBSD 5.2 with 5.3.14+suhosin. No idea if it's the exact same problem, but sure enough, there's a segfaulter in this version: https://bugs.php.net/bug.php?id=62384

Update: php 5.3.17 same problem, so that wasn't the bug.