php-fpm backend, sigsegv and limit_conn

Grégory Pakosz gpakosz at
Thu Apr 19 13:45:11 UTC 2012

On Thu, Apr 19, 2012 at 3:35 PM, Maxim Dounin <mdounin at> wrote:

> You mean nginx worker process crash, right?
errors get logged into /var/log/nginx/error.log:
2012/04/19 15:34:41 [alert] 5712#0: worker process 9234 exited on signal 11
2012/04/19 15:34:48 [alert] 5712#0: worker process 9252 exited on signal 11
2012/04/19 15:34:57 [alert] 5712#0: worker process 9253 exited on signal 11
2012/04/19 15:35:06 [alert] 5712#0: worker process 9272 exited on signal 11
2012/04/19 15:36:11 [alert] 5712#0: worker process 9277 exited on signal 11

debian squeeze
nginx-full  1.1.19-1~bpo60+1  from squeeze-backports
php5-fpm 5.3.10-1~dotdeb.1 from dotdeb

The context: I'm experimenting with Piwik's new log analytics import
script. It's a Python script that parses server logs and does POST requests
to a Piwik instance.
I wouldn't say it's hammering much as it's able to post only around 10 log
lines per second.

It's those POST requests that randomly cause the SIGSEGV errors that got
logged into /var/log/nginx/error.log. After many worker process crashes, I
eventually hit a connection limit I set with limit_conn (of 10 simultaneous
connections per IP). I could disable limit_conn as a workaround until I
find out the root cause of those crashes.

About the crashes themselves, I really don't know what's going on so far.
PHP-FPM logs remain empty (or I wasn't able to enable them correctly).
Piwik's wiki states it's impossible Piwik itself is the root cause for
SIGSEGV; instead they say bugs in PHP itself, MySQL or accelerators like
APC are to blame. (note I disabled APC without much luck).

> The limit_conn numbers are kept in a shared memory and will not be
> decremented on nginx worker process crash, leading to a limit
> hits eventually.  To clear the numbers you may do an online
> upgrade, see
> Or, better, you may want to debug crashes, see here for basic
> instructions:
> Note well that crashes might lead to much more severe
> consequences, e.g. if the crash happens during shared memory
> update it may be left in an inconsistent state, leading to
> unpredictable behaviour (usually more crashes).
I'll try to give it a go. thank you for the reply

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