What does this error log mean?

[Maxim Dounin]

Hello!

On Sun, Jan 20, 2008 at 09:03:27PM +0800, Joe wrote:

> Hi all
> I installed Nginx 0.5.34 on FreeBSD 6.2 (AMD) as a load balance, and I 
> defined the error log like:
>
> error_log  /home/nginx/logs/crit_error.log  crit;
>
> Today, I find the following error info from this error log file:
>
> 2008/01/20 20:46:46 [error] 2233#0: accept() failed (53: Software caused 
> connection abort) while accepting new connection on 0.0.0.0:80
> 2008/01/20 20:47:39 [error] 2233#0: accept() failed (53: Software caused 
> connection abort) while accepting new connection on 0.0.0.0:80
> 2008/01/20 20:53:15 [error] 2219#0: accept() failed (53: Software caused 
> connection abort) while accepting new connection on 0.0.0.0:80
> 2008/01/20 20:54:33 [error] 2219#0: accept() failed (53: Software caused 
> connection abort) while accepting new connection on 0.0.0.0:80
> 2008/01/20 20:54:56 [error] 2219#0: accept() failed (53: Software caused 
> connection abort) while accepting new connection on 0.0.0.0:80
> 2008/01/20 20:55:35 [error] 2219#0: accept() failed (53: Software caused 
> connection abort) while accepting new connection on 0.0.0.0:80
> 2008/01/20 20:56:11 [error] 2215#0: accept() failed (53: Software caused 
> connection abort) while accepting new connection on 0.0.0.0:80
>
> The number 2233,2219 should be the PIDs, what does the number 53 mean here? 
> and what's the root cause which will trigger this kind of error?

http://www.sysoev.ru/nginx/docs/faq.html (in russian)

This is non-critical error caused by client closed connection 
befor nginx accept()'ed it. Number 53 here is error number, see 
errno(2) manpage for details.

Maxim Dounin