I'm trying to identify trouble users on our network. ntop identifies high traffic and high connection users, but malware doesn't always need high bandwidth to really mess things up. So I am trying to do offline analysis with snort (don't want to burden the router with inline analysis of 20 Mbps traffic). Apparently snort provides a -r option for this purpose, but I can't get the analysis to run.

The analysis system is gentoo, amd64, in case that makes any difference. I've already used oinkmaster to download the latest IDS signatures. But when I try to run snort, I keep getting the following error:

% snort -V

   ,,_     -*> Snort! <*-
  o"  )~   Version 2.9.0.3 IPv6 GRE (Build 98) x86_64-linux
   ''''    By Martin Roesch & The Snort Team: http://www.snort.org/snort/snort-team
           Copyright (C) 1998-2010 Sourcefire, Inc., et al.
           Using libpcap version 1.1.1
           Using PCRE version: 8.11 2010-12-10
           Using ZLIB version: 1.2.5

%> snort -v -r jan21-for-snort.cap -c /etc/snort/snort.conf -l ~/snortlog/

(snip)

273 out of 1024 flowbits in use.

[ Port Based Pattern Matching Memory ]
+- [ Aho-Corasick Summary ] -------------------------------------
| Storage Format    : Full-Q
| Finite Automaton  : DFA
| Alphabet Size     : 256 Chars
| Sizeof State      : Variable (1,2,4 bytes)
| Instances         : 314
|     1 byte states : 304
|     2 byte states : 10
|     4 byte states : 0
| Characters        : 69371
| States            : 58631
| Transitions       : 3471623
| State Density     : 23.1%
| Patterns          : 3020
| Match States      : 2934
| Memory (MB)       : 29.66
|   Patterns        : 0.36
|   Match Lists     : 0.77
|   DFA
|     1 byte states : 1.37
|     2 byte states : 26.59
|     4 byte states : 0.00
+----------------------------------------------------------------
[ Number of patterns truncated to 20 bytes: 563 ]
ERROR: Can't find pcap DAQ!
Fatal Error, Quitting..

net-libs/daq is installed, but I don't even want to capture traffic, I just want to process the capture file.

What configuration options should I be setting/unsetting in order to do offline analysis instead of real-time capture?