Re: TCP Connections, Am I Running Out?

[Chuck Mead <chuck moongroup com>]

On Fri, 30 Apr 1999, Daniel Parker wrote:

> OK,
> 
> Here's the deal:
> 
> I'm running RedHat 5.0 as a sendmail server.  I've got almost 9000 users on
> it (pretty close anyway), lately in the evenings I have been running into a
> problem where users can't connect to the POP3 service to pick up their
> messages.  It's intermittent and the problem usually doesn't last more than
> a few seconds.  sendmail is never affected by this (at least not that I can
> see), just popper.

Have a look at this section of "man inetd"

The wait/nowait entry is applicable to datagram sockets only (other
sockets should have a ``nowait'' entry in this space).  If a datagram
server connects to its peer, freeing the socket so inetd can received
further messages on the socket, it is said to be a ``multi-threaded''
server, and should use the ``nowait'' entry.  For datagram servers which
process all incoming datagrams on a socket and eventually time out, the
server is said to be ``single-threaded'' and should use a ``wait'' entry.  
Comsat(8)  (biff(1))  and talkd(8) are both examples of the latter type of
datagram server.  Tftpd(8) is an exception; it is a datagram server that
establishes pseudo-connections.  It must be listed as ``wait'' in order to
avoid a race; the server reads the first packet, creates a new socket, and
then forks and exits to allow inetd to check for new service requests to
spawn new servers.  The optional ``max'' suffix (separated from ``wait''
or ``nowait'' by a dot) specifies the maximum number of server instances
that may be spawned from inetd within an interval of 60 seconds. When
omitted, ``max'' defaults to 40.

I ran into this recently when dealing specifically with a popper install
that was falling over under load adding a number higher than 40 to the
hollowing line fixed it:

pop-3   stream  tcp     nowait.xx  root    /usr/sbin/tcpd  ipop3d

where xx= some number higher than 40... you'll have to play with it to
tune it for your requirements.  It also applies to qpopper and just about
all of the inet daemons.

Cheers!
--                         
Chuck Mead, CTO - Moongroup Consulting, Inc. <chuck moongroup com>
http://www.moongroup.com/

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