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 pcapng, which is also the format used by Wireshark.

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 pcapng file. The capture filter syntax follows the rules of the pcap library. For more information on dumpcap consult your local manual page (man dumpcap) or the online version.

Help information available from dumpcap

Dumpcap (Wireshark) 2.5.0 (v2.5.0rc0-1220-g23e2b1f9)
Capture network packets and dump them into a pcapng or pcap file.
See https://www.wireshark.org for more information.

Usage: dumpcap [options] ...

Capture interface:
  -i <interface>           name or idx of interface (def: first non-loopback),
                           or for remote capturing, use one of these formats:
                               rpcap://<host>/<interface>
                               [email protected]<host>:<port>
  -f <capture filter>      packet filter in libpcap filter syntax
  -s <snaplen>             packet snapshot length (def: appropriate maximum)
  -p                       don't capture in promiscuous mode
  -I                       capture in monitor mode, if available
  -B <buffer size>         size of kernel buffer in MiB (def: 2MiB)
  -y <link type>           link layer type (def: first appropriate)
  --time-stamp-type <type> timestamp method for interface
  -D                       print list of interfaces and exit
  -L                       print list of link-layer types of iface and exit
  --list-time-stamp-types  print list of timestamp types for iface and exit
  -d                       print generated BPF code for capture filter
  -k                       set channel on wifi interface:
                           <freq>,[<type>],[<center_freq1>],[<center_freq2>]
  -S                       print statistics for each interface once per second
  -M                       for -D, -L, and -S, produce machine-readable output

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)
  -g                       enable group read access on the output file(s)
  -b <ringbuffer opt.> ... duration:NUM - switch to next file after NUM secs
                           interval:NUM - create time intervals of NUM secs
                           filesize:NUM - switch to next file after NUM KB
                              files:NUM - ringbuffer: replace after NUM files
  -n                       use pcapng format instead of pcap (default)
  -P                       use libpcap format instead of pcapng
  --capture-comment <comment>
                           add a capture comment to the output file
                           (only for pcapng)

Miscellaneous:
  -N <packet_limit>        maximum number of packets buffered within dumpcap
  -C <byte_limit>          maximum number of bytes used for buffering packets
                           within dumpcap
  -t                       use a separate thread per interface
  -q                       don't report packet capture counts
  -v                       print version information and exit
  -h                       display this help and exit

WARNING: dumpcap will enable kernel BPF JIT compiler if available.
You might want to reset it
By doing "echo 0 > /proc/sys/net/core/bpf_jit_enable"

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

Use Ctrl-C to stop capturing at any time.