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Date: Tue, 4 Nov 2008 21:22:42 -0500
From: Sahil Tandon <sahil@tandon.net>
To: freebsd-questions@freebsd.org
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Subject: Re: Watching /var/log/pflog grow
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cpghost <cpghost@cordula.ws> wrote:

> How can I watch /var/log/pflog grow with tcpdump, "tail -f" style?
> 
> This won't work:
>   $ tail -f /var/log/pflog | tcpdump -n -s 116 -r -
> because tail doesn't start at the right location.

[...]

> I'm afraid that in the latter case, every packet will be
>   EITHER logged by pflogd
>   XOR    displayed by tcpdump.
> Is that so?
> 
> If yes, /var/log/pflog would be incomplete, because some packets
> would have been snatched away from pflog0 by tcpdump, before
> pflogd ever got a chance to read them out.
> 
> Is there a way to watch /var/log/pflog grow, while
> still making sure that pflogd logs EVERY packet that appears
> on the pflog0 interface? How?

According to pflogd(8):

   Display the logs in real time (this does not interfere with the
   operation of pflogd):

          # tcpdump -n -e -ttt -i pflog0

-- 
Sahil Tandon <sahil@tandon.net>