$ date +"%Y-%m-%d_%H-%M-%Z" | xargs -I {} bash -c "sudo tcpdump -nq -s 0 -i eth0 -w ./dump-{}.pcap"
May 17, 2013, 8:03 p.m. — kowalcj0
will dump the traffic into a file with a time-stamp in its name. Example filename:
dump-2013-05-17_15-46-UTC.pcap