D.4. dumpcap: Capturing with dumpcap for viewing with Wireshark
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## D.4. dumpcap: Capturing with dumpcap for viewing with Wireshark

Dumpcap is a network traffic dump tool. It captures packet data from a live network and writes the packets to a file. Dumpcap's native capture file format is libpcap format, which is also the format used by Wireshark, tcpdump and various other tools.

Without any options set it will use the pcap library to capture traffic from the first available network interface and write the received raw packet data, along with the packets' time stamps into a libpcap file.

Packet capturing is performed with the pcap library. The capture filter syntax follows the rules of the pcap library.

Example D.1. Help information available from dumpcap

    Dumpcap 0.99.6
    Capture network packets and dump them into a libpcap file.
    See http://www.wireshark.org for more information.

    Usage: dumpcap [options] ...

    Capture interface:
      -i <interface>           name or idx of interface (def: first none loopback)
      -f <capture filter>      packet filter in libpcap filter syntax
      -s <snaplen>             packet snapshot length (def: 65535)
      -p                       don't capture in promiscuous mode
      -B <buffer size>         size of kernel buffer (def: 1MB)
      -y <link type>           link layer type (def: first appropriate)
      -D                       print list of interfaces and exit
      -L                       print list of link-layer types of iface and exit

    Stop conditions:
      -c <packet count>        stop after n packets (def: infinite)
      -a <autostop cond.> ...  duration:NUM - stop after NUM seconds
                               filesize:NUM - stop this file after NUM KB
                                  files:NUM - stop after NUM files
    Output (files):
      -w <filename>            name of file to save (def: tempfile)
      -b <ringbuffer opt.> ... duration:NUM - switch to next file after NUM secs
                               filesize:NUM - switch to next file after NUM KB
                                  files:NUM - ringbuffer: replace after NUM files
    Miscellaneous:
      -v                       print version information and exit
      -h                       display this help and exit

    Example: dumpcap -i eth0 -a duration:60 -w output.pcap
    "Capture network packets from interface eth0 until 60s passed into output.pcap"

    Use Ctrl-C to stop capturing at any time.

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