Re: Apache 2.4 DoS?

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Thank you Rainer Canavan!

Will try using 
gdb to get more information!

Thanks,

Douglas Duckworth, MSc, LFCS
HPC System Administrator
Scientific Computing Unit
Physiology and Biophysics
Weill Cornell Medicine
E: doug@xxxxxxxxxxxxxxx
O: 212-746-6305
F: 212-746-8690

On Mon, Nov 13, 2017 at 7:04 AM, Rainer Canavan <rainer.canavan@xxxxxxxxxxxx> wrote:
On Fri, Nov 10, 2017 at 6:41 PM, Douglas Duckworth
<dod2014@xxxxxxxxxxxxxxx> wrote:
> Hi
>
> I am running old PHP under Apache httpd-2.4.

[...]
> Though, ever few weeks, we see sudden increase in workers who never seem to
> retire:
>
> [Fri Nov 10 02:43:20.019924 2017] [mpm_prefork:error] [pid 13584] AH00161:
> server reached MaxRequestWorkers setting, consider raising the
> MaxRequestWorkers setting
>
> user@server[/var/www]$ ps aux | grep [h]ttpd | wc -l
> 257

If the php locks up while processing your request, no logs will be
written. You may be running
into a bug where circular, unresolvable dependencies for a lock
prevent the processes from
completing their requests. To check what's going on, install gdb, the
debug info for your php
and httpd and find the .gdbinfo that came with the httpd and php
version you're using. Then
attach gdb to any of the hanging processes (gdb `which httpd` PID),
source both .gdbinit files,
do a "zbacktrace" and a "bt full", and repeat for some other hanging
processes. Depending
on the type of lock,  you may be able to identify the first process
that has acquired that lock
that all others are waiting for, and the php code and / or php module
that causes it.

rainer

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