Apache gives empty reply

Question

It happens randomly, and only on moodle installations. Apache don't add a line in the logs when this happens, and I don't know where to look.

koke@escher:~/Code/eboxhq/moodle[master]$ curl -I http://training.ebox-technologies.com/login/signup.php?course=WNA001 
curl: (52) Empty reply from server
koke@escher:~/Code/eboxhq/moodle[master]$ curl -I http://training.ebox-technologies.com/login/signup.php?course=WNA001 
HTTP/1.1 200 OK

The apache conf is quite straightforward and works perfectly in the other vhosts

<VirtualHost *:80>
    ServerAdmin [email protected]
    DocumentRoot /srv/apache/training.ebox-technologies.com/htdocs
    ServerName training.eboxhq.com
    ErrorLog /var/log/apache2/training.ebox-technologies.com-error.log
    CustomLog /var/log/apache2/training.ebox-technologies.com-access.log combined

        <FilesMatch "\.(ico|gif|jpe?g|png|js|css)$">
                ExpiresActive On
                ExpiresDefault "access plus 1 week"
                Header add Cache-Control public
        </FilesMatch>
</VirtualHost>

Using apache 2.2.9 php 5.2.6 and moodle 1.9.5+ (Build: 20090722)

Any ideas welcome :)

Solution 1

Finally solved by adding to /etc/apache2/envvars:

export USE_ZEND_ALLOC=0

Solution 2

Look at the main server error log, it should have some Child Segfault Error (11).

This is probably given by a PHP engine fault, often given by a buggy php module, unicode chars handling, gettext corrupted DB, and so on.

It is very difficult to debug.

You can enable xdebug tracing and look at what line it is segfaulting:

pecl install xdebug

php.ini:

[xdebug]
xdebug.profiler_enable=1
xdebug.profiler_output_dir="/tmp/xdebug"
xdebug.auto_trace=1            ; enable tracing
xdebug.trace_format=0
xdebug.show_mem_delta=1        ; memory difference
xdebug.show_local_vars=1
xdebug.max_nesting_level=100

Comments

[Jorge Bernal]

Found this on error log: zend_mm_heap corrupted [Fri Sep 18 16:47:08 2009] [notice] child pid 7361 exit signal Segmentation fault (11) [Fri Sep 18 16:47:09 2009] [notice] child pid 7368 exit signal Segmentation fault (11) [Fri Sep 18 16:47:10 2009] [notice] child pid 7375 exit signal Segmentation fault (11) Will try xdebug and see if it helps

[Jorge Bernal]

Only see the segmentation fault and xdebug is not leaving anything useful in /tmp/xdebug

[Sandokas]

it should print a trace of every php function called. So when the trace stops is when the segfault happened. This should suffice to argue what php function is faulting.

[sglessard]

If you leave that as is for a couple of weeks it will full your hard drive.

[Sandokas]

It looks like you forgot them as is for 11 years, not weeks 😬😉

[Artefacto]

Very bad idea. This will cause PHP to leak memory when a request finishes with an error.