cannot accept socket

cannot accept socket

[Lee Chin]

Hi,
In my web server, when I run a stress test with many clients, after a long time I suddenly get an error on the accept system call and the error is "Too many open files".

When I do a socklist (or netstat), I see that there are only 400 sockets open (and I have 400 clients, so that is correct).

However when I "cat /proc/PID/fd" I see 1024 files.  I think accept failed because of this.  My web server is as simple as possible (it just serves up a static string compiled in with the server).  I know I am closing the sockets... what else could I be doing wrong?

Has anyone seen something similar to this before?

Thanks
Lee
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Re: cannot accept socket

[Ray Olszewski]

At 01:13 PM 3/6/2003 -0500, Lee Chin wrote:
>Hi,
>In my web server, when I run a stress test with many clients, after a long 
>time I suddenly get an error on the accept system call and the error is 
>"Too many open files".
>
>When I do a socklist (or netstat), I see that there are only 400 sockets 
>open (and I have 400 clients, so that is correct).
>
>However when I "cat /proc/PID/fd" I see 1024 files.  I think accept failed 
>because of this.

Yes. 1024 is the usual Linux limit on filehandles for a single process. I 
believe you can change this limit during kernel compilation, but offhand I 
do not remember how.

>My web server is as simple as possible (it just serves up a static string 
>compiled in with the server).  I know I am closing the sockets... what 
>else could I be doing wrong?

Depends on what the files are.

Are you really seeing them with "cat /proc/PID/fd"? (This gives me an 
error.) And not "ls -l /proc/PID/fd"? (This works here.) Whatever. Use the 
second choice to see what the filehandles listed in the pseudo-directory 
actually point to, and you (or we, if you report a meaningful subset of 
that info in a followup here) may be able to offer a suggestion.

Depending on details you haven't told us, you may be doing nothing wrong 
except underestimating the number of filehandles needed per connection 
("client").



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Re: cannot accept socket

[Ray Olszewski]

I assume you meant to send this to the list, not just to me personally, so 
I've added it back in.

/proc/sys/fs/file-max contains, according to the man page for "proc", the 
*total* number of files the kernel will open at one time. I quickly checked 
a half-dozen Linux systems I have access to, and the value for this was 
4096 on the older ones, 8192 on the newer ones ... not the 1024 the man 
page mentions for this setting.

I **think** the 1024 limit Lee is running into is on files for a *single* 
process, not for all processes together. (Full-size Web servers like apache 
handle high loads by spawning children, so each process opens only a few 
filehandles, making your solution work fine in real-world situations.)

At 08:26 PM 3/6/2003 +0000, bilbo wrote:
>On Thursday 06 March 2003 8:02 pm, Ray Olszewski wrote:
> > At 01:13 PM 3/6/2003 -0500, Lee Chin wrote:
> > >Hi,
> > >In my web server, when I run a stress test with many clients, after a long
> > >time I suddenly get an error on the accept system call and the error is
> > >"Too many open files".
> > >
> > >When I do a socklist (or netstat), I see that there are only 400 sockets
> > >open (and I have 400 clients, so that is correct).
> > >
> > >However when I "cat /proc/PID/fd" I see 1024 files.  I think accept failed
> > >because of this.
> >
> > Yes. 1024 is the usual Linux limit on filehandles for a single process. I
> > believe you can change this limit during kernel compilation, but offhand I
> > do not remember how.
> >
>
>All the webservers in my old place of work had a line in rc.local which wrote
>a value to /proc/sys/fs/file-max. eg something like:
>
>echo 8192 > /proc/sys/fs/file-max
>
>You might want to have a look at /proc/sys/fs/file-max on your machine and
>increase it if necessary.
>
>regards,
>
>John Kelly


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Re: cannot accept socket

[Carl]

See the proc.txt file in the Documentation dir that comes with the kernel source.

It says per process limits are set at compile time and are in include/linux/limits.h

Here's the relevant bit in my kernel source:


   However, there is still a per process limit of open files, which
   unfortunatly can't be changed that easily. It is set to 1024 by
   default. To change this you have to edit the files limits.h and
   fs.h in the directory /usr/src/linux/include/linux. Change the
   definition of NR_OPEN and recompile the kernel.

My limits.h has the following defined:

#define NR_OPEN         1024


Regards
Carl


At 12:02 06/03/2003 -0800, Ray Olszewski wrote:
>At 01:13 PM 3/6/2003 -0500, Lee Chin wrote:
>>Hi,
>>In my web server, when I run a stress test with many clients, after a long time I suddenly get an error on the accept system call and the error is "Too many open files".
>>
>>When I do a socklist (or netstat), I see that there are only 400 sockets open (and I have 400 clients, so that is correct).
>>
>>However when I "cat /proc/PID/fd" I see 1024 files.  I think accept failed because of this.
>
>Yes. 1024 is the usual Linux limit on filehandles for a single process. I believe you can change this limit during kernel compilation, but offhand I do not remember how.
>
>>My web server is as simple as possible (it just serves up a static string compiled in with the server).  I know I am closing the sockets... what else could I be doing wrong?
>
>Depends on what the files are.
>
>Are you really seeing them with "cat /proc/PID/fd"? (This gives me an error.) And not "ls -l /proc/PID/fd"? (This works here.) Whatever. Use the second choice to see what the filehandles listed in the pseudo-directory actually point to, and you (or we, if you report a meaningful subset of that info in a followup here) may be able to offer a suggestion.
>
>Depending on details you haven't told us, you may be doing nothing wrong except underestimating the number of filehandles needed per connection ("client").
>
>
>
>-
>To unsubscribe from this list: send the line "unsubscribe linux-newbie" in
>the body of a message to majordomo@vger.kernel.org
>More majordomo info at  http://vger.kernel.org/majordomo-info.html
>Please read the FAQ at http://www.linux-learn.org/faqs

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