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Re: Problems with stability of networking / pfinet

From: Thomas Schwinge
Subject: Re: Problems with stability of networking / pfinet
Date: Tue, 16 Dec 2008 23:13:04 +0100
User-agent: Mutt/1.5.11


Nothing fundamentally new; just noting down what we know so far.

On Sat, Jul 12, 2008 at 10:06:54AM +0200, I wrote:
> For a few weeks now, I seem to notice more and more problems w.r.t.
> networking.  Olaf confirmed this.
>     $ ssh flubber
>     Warning: Permanently added '[flubber.bddebian.com]:2250' (RSA) to the 
> list of known hosts.
>     Connection closed by
> The connection is first established, but then closed.
>     $ ssh root@flubber
>     Warning: Permanently added '[flubber.bddebian.com]:2250' (RSA) to the 
> list of known hosts.
>     root@flubber.bddebian.com's password: 
>     Connection closed by
> The remote site is even asking for the password before then closing the
> connection again.

This difference is because the non-root case is using public key

The underlying problem is that sshd hangs when it tries to syslog the new
successful login attempt.  (Samuel told about this already some time
ago.)  At this time everything using syslog will hang: be it a ``logger
foo'' command manually run, or be it using sudo which roughly does the
same logging sshd does.

This situation can easily be induced like this:

    $ while logger .; do echo -n .; done

This will usually hang after a few hundred invokations.

Killing the system's pflocal server will ``fix'' this situation.  If you,
however, after that restart the system's syslogd, the looping command
will again hang after another few hundred invokations.

> A problem with the TCP/IP stack?  But nothing has been changed
> there, recently.  Michael also assured me that he's still using GCC 4.2
> for building pfinet (using GCC 4.3 indeed yields a dysfunctional one).
> Or a problem with the SSH packages?

Killing pfinet and restarting sshd indeed also does ``fix'' this
situation (why?), but neither pfinet nor sshd seem to be originally
involved in the underlying problem.


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