Annoying problem with apache22 / php5 - how to investigate?

[Bruce Ferrell]

Per olof Ljungmark wrote:
> Bruce Ferrell wrote:
>>
>> Per olof Ljungmark wrote:
>>> Hi,
>>>
>>> We run 7-STABLE and apache22 with php5 serving pages from a webmail app
>>> (Horde).
>>>
>>> Randomly (as it seems at least), there is a 500 (Internal server error)
>>> and a blank page is presented to the user like
>>>
>>> [04/Jul/2009:15:19:37 +0200] "GET
>>> /services/portal/sidebar.php?httpclient=1 HTTP/1.1" 500 -
>>>
>>> There are no other messages in the logs, not even with LogLevel debug.
>>> The problem has survived several both OS and port upgrades and I really
>>> need to track this down now.
>>>
>>> Question: What OS tools would be the best to further analyze this?
>>> Someone with more exparience running this combo perhaps would know?
>>>
>>> Thanks a lot!
>>>
>>> -- 
>>> per
>>
>> I'd look in the Apache error_log
>>
> 
> I've looked, as stated above. Even with LogLevel debug there is not a
> trace. Likewise, I have E_ALL set in php.ini.
> 
> So, I need to dig deeper inte the workings of Apache with the aid of the
> right tools.


You're not looking at an Apache problem, but a PHP problem. 500 is the
error code for a failed CGI script/program. Try executing the php from
the command line.  i.e. Go to where ever
/services/portal/sidebar.php is and execute:

 ./sidebar.php httpclient=1

See what, if any, errors are thrown that way.

PHP is notorious for not sending good errors into the logs or to STDERR.