I've run into a problem with apache giving a segmentation fault, and I've found a possible solution. I am creating this post to share what I've found in case anyone else runs into the same problem.
Setup:
Turnkey LAMP server from OVA file (turnkey-lamp-14.0-jessie-amd64.ova) running a VirtualBox on a Windows 7 host (Just trying dokuwiki out for the first time, hence the relatively temporary setup)
DokuWiki 2015-08-10a (I think that's how the version is displayed, not sure how to check this from inside dokuwiki, I've only been playing with it for a few hours)
root@lamp ~# apache2 -v
Server version: Apache/2.4.10 (Debian)
Server built: Aug 28 2015 16:28:08
root@lamp ~# php --version
PHP 5.6.14-0+deb8u1 (cli) (built: Oct 4 2015 16:13:10)
...
Symptom:
After freshly installing DokuWiki I had a problem when trying to open the extension manager from the admin panel. It simply would not load (I think my browser said error 500 no data). I started to tail the apache error log and this is what I found:
[Fri Nov 20 04:14:28.536146 2015] [:error] [pid 1580] [client 192.168.1.141:49898] PHP Fatal error: Cannot redeclare class DokuHTTPClient in /var/www/inc/HTTPClient.php on line 18, referer: http://192.168.1.104/doku.php?id=maintenance&do=admin
[Fri Nov 20 04:14:28.536174 2015] [:error] [pid 1580] [client 192.168.1.141:49898] PHP Stack trace:, referer: http://192.168.1.104/doku.php?id=maintenance&do=admin
[Fri Nov 20 04:14:28.536227 2015] [:error] [pid 1580] [client 192.168.1.141:49898] PHP 1. {main}() /var/www/doku.php:0, referer: http://192.168.1.104/doku.php?id=maintenance&do=admin
[Fri Nov 20 04:14:28.536238 2015] [:error] [pid 1580] [client 192.168.1.141:49898] PHP 2. act_dispatch() /var/www/doku.php:124, referer: http://192.168.1.104/doku.php?id=maintenance&do=admin
[Fri Nov 20 04:14:28.536246 2015] [:error] [pid 1580] [client 192.168.1.141:49898] PHP 3. admin_plugin_extension->handle() /var/www/inc/actions.php:167, referer: http://192.168.1.104/doku.php?id=maintenance&do=admin
[Fri Nov 20 04:14:28.536254 2015] [:error] [pid 1580] [client 192.168.1.141:49898] PHP 4. helper_plugin_extension_repository->hasAccess() /var/www/lib/plugins/extension/admin.php:52, referer: http://192.168.1.104/doku.php?id=maintenance&do=admin
[Fri Nov 20 04:14:28.536261 2015] [:error] [pid 1580] [client 192.168.1.141:49898] PHP 5. spl_autoload_call() /var/www/lib/plugins/extension/admin.php:69, referer: http://192.168.1.104/doku.php?id=maintenance&do=admin
[Fri Nov 20 04:14:28.536268 2015] [:error] [pid 1580] [client 192.168.1.141:49898] PHP 6. load_autoload() /var/www/lib/plugins/extension/admin.php:0, referer: http://192.168.1.104/doku.php?id=maintenance&do=admin
[Fri Nov 20 04:14:28.536275 2015] [:error] [pid 1580] [client 192.168.1.141:49898] PHP 7. require_once() /var/www/inc/load.php:110, referer: http://192.168.1.104/doku.php?id=maintenance&do=admin
[Fri Nov 20 04:14:32.282470 2015] [core:notice] [pid 676] AH00052: child pid 1581 exit signal Segmentation fault (11)
[Fri Nov 20 04:14:32.282563 2015] [core:notice] [pid 676] AH00052: child pid 1611 exit signal Segmentation fault (11)
[Fri Nov 20 04:14:34.284985 2015] [core:notice] [pid 676] AH00052: child pid 1012 exit signal Segmentation fault (11)
[Fri Nov 20 04:14:34.285084 2015] [core:notice] [pid 676] AH00052: child pid 1609 exit signal Segmentation fault (11)
[Fri Nov 20 04:14:35.287094 2015] [core:notice] [pid 676] AH00052: child pid 1010 exit signal Segmentation fault (11)
[Fri Nov 20 04:14:35.287120 2015] [core:notice] [pid 676] AH00052: child pid 1610 exit signal Segmentation fault (11)
[Fri Nov 20 04:14:37.292114 2015] [core:notice] [pid 676] AH00052: child pid 1579 exit signal Segmentation fault (11)
[Fri Nov 20 04:14:37.292208 2015] [core:notice] [pid 676] AH00052: child pid 1580 exit signal Segmentation fault (11)
[Fri Nov 20 04:14:39.298258 2015] [core:notice] [pid 676] AH00052: child pid 1011 exit signal Segmentation fault (11)
[Fri Nov 20 04:15:29.370367 2015] [core:notice] [pid 676] AH00052: child pid 1670 exit signal Segmentation fault (11)
[Fri Nov 20 04:15:29.370462 2015] [core:notice] [pid 676] AH00052: child pid 1776 exit signal Segmentation fault (11)
[Fri Nov 20 04:16:44.475139 2015] [core:notice] [pid 676] AH00052: child pid 1753 exit signal Segmentation fault (11)
[Fri Nov 20 04:16:44.475240 2015] [core:notice] [pid 676] AH00052: child pid 1780 exit signal Segmentation fault (11)
[Fri Nov 20 04:17:28.535776 2015] [core:notice] [pid 676] AH00052: child pid 1778 exit signal Segmentation fault (11)
The first attempt created the "PHP Fatal error: ..." and all subsequent attempts created the segmentation faults. After googling around and unsuccessfully trying to get apache to do a coredump, I finally settled on disabling xcache (per another thread:
https://forum.dokuwiki.org/thread/10783). I admit, no real problem solving or troubleshooting going on, simply a patch that seemed to have worked. I have no idea if the problem is with dokuwiki or xcache.
If anyone wants anymore details just let me know.
Cheers,
Matt