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.

By default, Dumpcap uses the pcap library to capture traffic from the first available network interface and writes 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) 4.3.0 (v4.3.0rc0-87-g9c90105c365a)
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>, --interface <interface>
                           name or idx of interface (def: first non-loopback),
                           or for remote capturing, use one of these formats:
  --ifname <name>          name to use in the capture file for a pipe from which
                           we're capturing
  --ifdescr <description>
                           description to use in the capture file for a pipe
                           from which we're capturing
  -f <capture filter>      packet filter in libpcap filter syntax
  -s <snaplen>, --snapshot-length <snaplen>
                           packet snapshot length (def: appropriate maximum)
  -p, --no-promiscuous-mode
                           don't capture in promiscuous mode
  -I, --monitor-mode       capture in monitor mode, if available
  -B <buffer size>, --buffer-size <buffer size>
                           size of kernel buffer in MiB (def: 2MiB)
  -y <link type>, --linktype <link type>
                           link layer type (def: first appropriate)
  --time-stamp-type <type> timestamp method for interface
  -D, --list-interfaces    print list of interfaces and exit
  -L, --list-data-link-types
                           print list of link-layer types of iface and exit
  --list-time-stamp-types  print list of timestamp types for iface and exit
  --update-interval        interval between updates with new packets (def: 100ms)
  -d                       print generated BPF code for capture filter
  -k <freq>,[<type>],[<center_freq1>],[<center_freq2>]
                           set channel on wifi interface
  -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.> ..., --autostop <autostop cond.> ...
                           duration:NUM - stop after NUM seconds
                           filesize:NUM - stop this file after NUM kB
                              files:NUM - stop after NUM files
                            packets:NUM - stop after NUM packets
Output (files):
  -w <filename>            name of file to save (def: tempfile)
  -g                       enable group read access on the output file(s)
  -b <ringbuffer opt.> ..., --ring-buffer <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
                            packets:NUM - ringbuffer: replace after NUM packets
                           interval:NUM - switch to next file when the time is
                                          an exact multiple of NUM secs
                          printname:FILE - print filename to FILE when written
                                           (can use 'stdout' or 'stderr')
  -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)
  --temp-dir <directory>   write temporary files to this directory
                           (default: /tmp)

Diagnostic output:
  --log-level <level>      sets the active log level ("critical", "warning", etc.)
  --log-fatal <level>      sets level to abort the program ("critical" or "warning")
  --log-domains <[!]list>  comma-separated list of the active log domains
  --log-fatal-domains <list>
                           list of domains that cause the program to abort
  --log-debug <[!]list>    list of domains with "debug" level
  --log-noisy <[!]list>    list of domains with "noisy" level
  --log-file <path>        file to output messages to (in addition to stderr)

  -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, --version            print version information and exit
  -h, --help               display this help and exit

Dumpcap can benefit from an enabled BPF JIT compiler if available.
You might want to enable it by executing:
 "echo 1 > /proc/sys/net/core/bpf_jit_enable"
Note that this can make your system less secure!

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.