Watching /var/log/pflog grow

Jeremy Chadwick koitsu at
Tue Nov 4 17:16:02 PST 2008

On Tue, Nov 04, 2008 at 08:13:54PM +0100, cpghost 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.
> Using a blocksize (-b) with tail may also not be right,
> because the captured packets are not the same size.
> This seems to work:
>   $ tcpdump -n -s 116 -i pflog0
> but now, both tcpdump and pflogd are competing for the same
> interface pflog0.
> 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?

Please post this to freebsd-pf, where you can get better help.

| Jeremy Chadwick                                jdc at |
| Parodius Networking              |
| UNIX Systems Administrator                  Mountain View, CA, USA |
| Making life hard for others since 1977.              PGP: 4BD6C0CB |

More information about the freebsd-questions mailing list