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From Michael B Allen <iop...@gmail.com>
Subject Re: Debugging: child process 14446 still did not exit, sending a SIGTERM
Date Fri, 16 Oct 2009 19:23:37 GMT
On Fri, Oct 16, 2009 at 2:42 PM, Joe Lewis <joe@joe-lewis.com> wrote:
> Michael B Allen wrote:
>>
>> On Fri, Oct 16, 2009 at 1:10 PM, Joe Lewis <joe@joe-lewis.com> wrote:
>>
>>>
>>> Michael B Allen wrote:
>>>
>>>>
>>>> I have a customer who very occasionally sees apache workers hang. I'm
>>>> pretty sure this is caused by an errant module but I don't know which
>>>> one.
>>>>
>>>> Is there any way to determine which module is causing Apache workers to
>>>> hang?
>>>>
>>>> Can I temporarily disable that SIGTERM so that I can have enough time
>>>> to attach GDB to the hanging processes?
>>>>
>>>> Mike
>>>>
>>>>
>>>
>>> Perhaps run it in a non-forking mode (httpd -X -k start) inside of gdb
>>> and
>>> see what it hangs on?
>>>
>>
>> If I run it in gdb like you suggest:
>>
>>  # gdb httpd
>>  (gdb) run -X -k start
>>
>> I cannot get httpd to run module deinitialization. Meaning if I do
>> apachectl stop or httpd -X -k stop or graceful-stop in another
>> terminal, it just kills the whole process group. Since the problem is
>> hanging during module deinitialization I don't think this is going to
>> help me. How do I shutdown httpd so that it runs the module
>> deinitialization routines?
>>
>> Otherwise does anyone have a web-svn pointer to the code that's
>> calling the SIGTERM? Maybe I can find a way to disable it.
>>
>> Mike
>>
>
> Disabling SIGTERM for apache would be akin to leaving the landing gear of
> your airplane on the ground when you take off.  How are you going to
> properly shutdown apache if you completely kill the SIGTERM signals?

SIGTERM should not be used to stop processes. A process should
complete gracefully and call exit(2). Normally, this is what httpd
does. However if a child process takes too long, something is sending
a SIGTERM to *kill* the process. I assume this is Apache since it's
writing a message in error_log to that effect. This is what I want to
disable. Meaning, if a child process hangs, I want it to just sit
there stuck forever until an operator can login and attach gdb to it.

If I could find that part of the code, I might find a directive that
controls how long Apache waits before it sends the SIGTERM.

> The "deinitialization" - are you just not seeing the messages you'd normally
> see?  Or did apache just terminate (which is normal in gdb, which causes the
> gdb session to terminate as well).

Right. I have an Apache module that writes to a separate log. When the
module is deinitialized, information is written to the log. Without
gdb, that information is correctly written to the log. When running in
gdb, nothing is written to the log. It seems the entire process group
is simply being killed. And thus the part of interest is not
accessible.

Mike

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