I tried all of this, still would not work.  If anyone does not believe me, I
challenge thee to get qmail working under linux with a conf-spawn greater
than 509 without crashing.

The limitation is something to do with FD_SET(), which I guess is different
that ulimit type stuff.


> -----Original Message-----
> From: Troy.A Johnson [mailto:troy.johnson at health.state.mn.us]
> Sent: Thursday, July 17, 2003 1:44 PM
> To: tclug-list at mn-linux.org
> Subject: RE: [TCLUG] mail server
> 
> 
> I found some info about this on this page:
> 
> http://www.cs.wisc.edu/~adesmet/linux_scalability.html
> 
> It looks like you can do it, but it isn't just echoing 
> 1 or 0 to a /proc/ filesystem location. I have not tested 
> it.
> 
> >>> JAustad at temgweb.com 07/17/03 11:54AM >>>
> > That's simply untrue, there are many IRC servers out there 
> that handle
> > thousands of clients running on Linux, and have done so since 
> > the 2.2.x
> > kernels.
> I've argued this before on this list.  :)  With FreeBSD, you just add
> -DFD_SETSIZE when you compile, and this works.  However, with 
> linux, you
> cannot do this.  There is a hard limit of 1024 descriptors in 
> FD_SET().
> Apparently, you can't just change it and recompile as it will break a
> bunch
> of things.  I would assume that these IRC servers are forking multiple
> copies or using poll() instead of select() (qmail uses select()).  
> If you can get qmail running on linux with a conf-spawn of 
> more than 509,
> I'd like to see it.  I spent weeks trying to get this to work, I tried
> recompiling the kernel, using ulimit, changing things in 
> /proc, and there
> is
> still a hard set limit for FD_SET of 1024.  Anyway, if I remember
> correctly,
> it's qmail-queue that actually dies when you go over the limit.  It
> communicates with every qmail-send process that's running, 
> and has a file
> descriptor open for each one, rather than qmail-send opening the
> descriptor
> itself.  
> 
> 
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