Witam,
Przeszukując internet znalazłem skrypt automatycznego zapisywania logów do pliku .cap przy pomocy tcpdumpa.
Może się wam przyda 
Autor : http://xnite.org/
[code]<?php
DDoS Detection & Packet Capture Script
Written by Robert ‘xnite’ Whitney
Website: http://xnite.org
Email: xnite@xnite.org
Run script as root via crontab every 5 to 10 minutes
Ensure all dependences are satisfied before running this script (ifstat, tcpdump, php)
This script will only allow a single tcpdump process to run at once
Configuration
$CONFIG = [
‘device’ => ‘eth0’, //Usually eth0, if you are unsure, you can find the device name by running ifconfig.
‘report_speed’ => ‘15’, //MBps that you want to start tracking at.
‘packets2capture’ => ‘1000’, //Number of packets to capture in pcap dump.
‘save_to’ => ‘/var/log/ddos’ //Path to save ddos pcap logs to without the trailing /.
];
Do not edit below this line!
exec("/usr/bin/ifstat .5 1 | /bin/grep -o ‘[0-9]{1,9}.[0-9]{1,9}’", $iospeed);
$report_speed = $CONFIG[‘report_speed’]*1024;
$ts = date(‘U’);
$folder = $CONFIG[‘save_to’];
$interface = $CONFIG[‘device’];
$packnum = $CONFIG[‘packets2capture’];
if($iospeed[0]+$iospeed[1] >= $CONFIG[‘report_speed’]*1024) {
echo $iospeed[0]+$iospeed[1]." is equal to or greater than $report_speed.\n";
echo “Capturing tcpdump.\nPackets: $packnum\nInterface: $interface\n Saving to: $folder/$ts.ddos.pcap\n”;
exec("/usr/bin/pkill -9 tcpdump");
exec("/usr/sbin/tcpdump -nn -i $interface -s 0 -c $packnum -w $folder/$ts.ddos.pcap");
} else {
echo $iospeed[0]+$iospeed[1]." is less than $report_speed.\n";
}
?>[/code]