why would I get a segmentation fault on one system but not the other?

[cpet]

On 2015-02-21 16:40, David Benfell wrote:
> Hi all,
> 
> I am running into a segmentation fault that I don't know how to track
> down. It appears on one system but not the other. It seems to afflict
> both apache24 and php-fpm.
> 
> apache logs lots of segementation faults but I don't have any idea
> where they're coming from.
> 
> When I try to start php-fpm it dies instantly with a segmentation
> fault. I think it's one of the modules, but I don't know which one.
> 
> And I'm absolutely baffled that this occurs on one system and not the
> other. Both are fairly recent FreeBSD Stable.
> 
> I do not see the segmentation faults (or at least not in such a dire
> way) on:
> 
> 10.1-STABLE
> FreeBSD home.parts-unknown.org 10.1-STABLE FreeBSD 10.1-STABLE #0
> r278923: Tue Feb 17 15:27:20 PST 2015
> root at home.parts-unknown.org:/usr/obj/usr/src/sys/GENERIC  amd64
> 
> I do see them on:
> 
> 10.1-STABLE
> FreeBSD vegan.parts-unknown.org 10.1-STABLE FreeBSD 10.1-STABLE #0
> r278934: Wed Feb 18 09:11:24 UTC 2015
> root at home.parts-unknown.org:/usr/obj/usr/src/sys/GENERIC  amd64

You have 2 systems one running a different svn rev than the other, first 
I would suggest before suggesting bad ram is to sync both to be equal, 
meaning the one that is failing to either upgrade or downgrade it. if 
it's seg faulting I would mem test that and replace failing module.