tcpdump is a common packet analyzer that runs under the command line. It allows the user to display TCP/IP and other packets being transmitted or received over a network to which the computer is attached. Distributed under the BSD license.
tcp dump [-aAbdDefhHIJKlLnNOpqRStuUvxX] [ -B size ] [ -c count ]
[ -C file_size ] [ -E algo:secret ] [ -F file ] [ -G seconds ]
[ -i interface ] [ -j tstamptype ] [ -M secret ]
[ -P in|out|inout ]
[ -r file ] [ -s snaplen ] [ -T type ] [ -V file ] [ -w file ]
[ -W filecount ] [ -y datalinktype ] [ -z command ]
[ -Z user ] [ expression ]
cyborg@cyborg:~$ tcpdump -w out -c 16 tcp dump: listening on bluetooth0, link-type BLUETOOTH_HCI_H4_WITH_PHDR (Bluetooth HCI UART transport layer plus pseudo-header), capture size 65535 bytes 16 packets captured 1231 packets received by filter 0 packets dropped by kernel cyborg@cyborg:~$ cat out �ò������ V��re!�z Z�� V �w3�� >�� V� ʬ��,� Z�� V�� VS= ��� V���w3�� > VS��re!�z Z V� �w3�� > Vʬ��,� Z V VyF � V� ʬ��,� Z V�w3�� >�� V��re!�z Z�� V��w3�� >�� V�ʬ��,� Now, this file can previewed using chaaosreader.