Provided by: wireshark-common_4.4.2-1_amd64 
NAME
dumpcap - Dump network traffic
SYNOPSIS
dumpcap [ -a|--autostop <capture autostop condition> ] ...
[ -b|--ring-buffer <capture ring buffer option> ] ...
[ -B|--buffer-size <capture buffer size> ] [ -c <capture packet count> ]
[ -C <byte limit> ] [ -d ] [ -D|--list-interfaces ] [ -f <capture filter> ]
[ -F <file format> ] [ -g ]
[ -i|--interface <capture interface>|rpcap://<host>:<port>/<capture interface>|TCP@<host>:<port>|- ]
[ -I|--monitor-mode ] [ -k <freq>,[<type>],[<center_freq1>],[<center_freq2>] ]
[ -L|--list-data-link-types ] [ -M ] [ -n ] [ -N <packet limit> ]
[ -p|--no-promiscuous-mode ] [ --ifdescr <description> ] [ --ifname <name> ] [ -P ] [ -q ]
[ -Q ] [ -s|--snapshot-length <capture snaplen> ] [ -S ] [ -t ] [ --temp-dir <directory> ]
[ -w <outfile> ] [ -y|--linktype <capture link type> ] [ --capture-comment <comment> ]
[ --list-time-stamp-types ] [ --time-stamp-type <type> ] [ --update-interval <interval> ]
dumpcap -h|--help
dumpcap -v|--version
DESCRIPTION
Dumpcap is a network traffic dump tool. It lets you capture packet data from a live
network and write the packets to a file. Dumpcap's default capture file format is pcapng
format. The -F option can be specified to write the output file in the pcap format
instead.
Without any options set it will use the libpcap, Npcap, or WinPcap 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 capture file.
If the -w option is not specified, Dumpcap writes to a newly created capture file with a
randomly chosen name. If the -w option is specified, Dumpcap writes to the file specified
by that option.
Packet capturing is performed with the pcap library. The capture filter syntax follows the
rules of the pcap library.
OPTIONS
-a|--autostop <capture autostop condition>
Specify a criterion that specifies when Dumpcap is to stop writing to a capture file.
The criterion is of the form test:value, where test is one of:
duration:value Stop writing to a capture file after value seconds have elapsed.
Floating point values (e.g. 0.5) are allowed.
files:value Stop writing to capture files after value number of files were written.
filesize:value Stop writing to a capture file after it reaches a size of value kB. If
this option is used together with the -b option, dumpcap will stop writing to the
current capture file and switch to the next one if filesize is reached. Note that the
filesize is limited to a maximum value of 2 TB.
packets:value Stop writing to a capture file after value packets have been written.
Acts the same as -c <capture packet count>.
-b|--ring-buffer <capture ring buffer option>
Cause Dumpcap to run in "multiple files" mode. In "multiple files" mode, Dumpcap will
write to several capture files. When the first capture file fills up, Dumpcap will
switch writing to the next file and so on.
The created filenames are based on the filename given with the -w option, the number
of the file and on the creation date and time, e.g.
outfile_00001_20240714120117.pcapng, outfile_00002_20240714120523.pcapng, ...
With the files option it’s also possible to form a "ring buffer". This will fill up
new files until the number of files specified, at which point Dumpcap will discard the
data in the first file and start writing to that file and so on. If the files option
is not set, new files filled up until one of the capture stop conditions match (or
until the disk is full).
The criterion is of the form key:value, where key is one of:
duration:value switch to the next file after value seconds have elapsed, even if the
current file is not completely filled up. Floating point values (e.g. 0.5) are
allowed.
files:value begin again with the first file after value number of files were written
(form a ring buffer). This value must be less than 100000. Caution should be used when
using large numbers of files: some filesystems do not handle many files in a single
directory well. The files criterion requires either duration, interval or filesize to
be specified to control when to go to the next file. It should be noted that each -b
parameter takes exactly one criterion; to specify two criterion, each must be preceded
by the -b option.
filesize:value switch to the next file after it reaches a size of value kB. Note that
the filesize is limited to a maximum value of 2 TB.
interval:value switch to the next file when the time is an exact multiple of value
seconds. For example, use 3600 to switch to a new file every hour on the hour.
packets:value switch to the next file after it contains value packets.
printname:filename print the name of the most recently written file to filename after
the file is closed. filename can be stdout or - for standard output, or stderr for
standard error.
Example: -b filesize:1000 -b files:5 results in a ring buffer of five files of size
one megabyte each.
-B|--buffer-size <capture buffer size>
Set capture buffer size (in MiB, default is 2 MiB). This is used by the capture driver
to buffer packet data until that data can be written to disk. If you encounter packet
drops while capturing, try to increase this size. Note that, while Dumpcap attempts to
set the buffer size to 2 MiB by default, and can be told to set it to a larger value,
the system or interface on which you’re capturing might silently limit the capture
buffer size to a lower value or raise it to a higher value.
This is available on UNIX-compatible systems, such as Linux, macOS, \*BSD, Solaris,
and AIX, with libpcap 1.0.0 or later, and on Windows. It is not available on
UNIX-compatible systems with earlier versions of libpcap.
This option can occur multiple times. If used before the first occurrence of the -i
option, it sets the default capture buffer size. If used after an -i option, it sets
the capture buffer size for the interface specified by the last -i option occurring
before this option. If the capture buffer size is not set specifically, the default
capture buffer size is used instead.
-c <capture packet count>
Set the maximum number of packets to read when capturing live data. Acts the same as
-a packets:<capture packet count>.
-C <byte limit>
Limit the amount of memory in bytes used for storing captured packets in memory while
processing it. If used in combination with the -N option, both limits will apply.
Setting this limit will enable the usage of the separate thread per interface.
-d
Dump the code generated for the capture filter in a human-readable form, and exit.
-D|--list-interfaces
Print a list of the interfaces on which Dumpcap can capture, and exit. For each
network interface, a number and an interface name, possibly followed by a text
description of the interface, is printed. The interface name or the number can be
supplied to the -i flag to specify an interface on which to capture. The number can be
useful on Windows systems, where the interfaces have long names that usually contain a
GUID.
-f <capture filter>
Set the capture filter expression.
The entire filter expression must be specified as a single argument (which means that
if it contains spaces, it must be quoted).
This option can occur multiple times. If used before the first occurrence of the -i
option, it sets the default capture filter expression. If used after an -i option, it
sets the capture filter expression for the interface specified by the last -i option
occurring before this option. If the capture filter expression is not set
specifically, the default capture filter expression is used if provided.
-F <file format>
Set the file format of the output capture file written using the -w option. In
situations that require the pcapng format, such as capturing from multiple interfaces,
this option will be overridden. The option -F without a value will list the available
formats. The default is the pcapng format.
Fewer formats are supported than by tshark(1); this is intentional for security reasons.
Use tshark or capture and then convert the file with editcap(1) if another format is
needed.
-g
This option causes the output file(s) to be created with group-read permission
(meaning that the output file(s) can be read by other members of the calling user’s
group).
-h|--help
Print the version number and options and exit.
-i|--interface <capture interface>|rpcap://<host>:<port>/<capture
interface>|TCP@<host>:<port>|-
Set the name of the network interface or pipe to use for live packet capture.
Network interface names should match one of the names listed in "tshark -D" (described
above); a number, as reported by "dumpcap -D", can also be used.
If no interface is specified, Dumpcap searches the list of interfaces, choosing the
first non-loopback interface if there are any non-loopback interfaces, and choosing
the first loopback interface if there are no non-loopback interfaces. If there are no
interfaces at all, Dumpcap reports an error and doesn’t start the capture.
Pipe names should be either the name of a FIFO (named pipe) or "-" to read data from
the standard input. On Windows systems, pipe names must be of the form
"\\.\pipe\pipename". Data read from pipes must be in standard pcapng or pcap format.
Pcapng data must have the same endianness as the capturing host.
"TCP@<host>:<port>" causes Dumpcap to attempt to connect to the specified port on the
specified host and read pcapng or pcap data.
This option can occur multiple times. When capturing from multiple interfaces, the
capture file will be saved in pcapng format, even if -P is specified.
--ifdescr> <description>
Use description as the description in the capture file for the interface or pipe
specified before it with -i.
--ifname> <name>
Use name as the name in the capture file for the interface or pipe specified before it
with -i.
-I|--monitor-mode
Put the interface in "monitor mode"; this is supported only on IEEE 802.11 Wi-Fi
interfaces, and supported only on some operating systems.
Note that in monitor mode the adapter might disassociate from the network with which
it’s associated, so that you will not be able to use any wireless networks with that
adapter. This could prevent accessing files on a network server, or resolving host
names or network addresses, if you are capturing in monitor mode and are not connected
to another network with another adapter.
This option can occur multiple times. If used before the first occurrence of the -i
option, it enables the monitor mode for all interfaces. If used after an -i option, it
enables the monitor mode for the interface specified by the last -i option occurring
before this option.
-k <freq>,[<type>],[<center_freq1>],[<center_freq2>>
Set the channel on the interface; this is supported only on IEEE 802.11 Wi-Fi
interfaces, and supported only on some operating systems.
freq is the frequency of the channel. type is the type of the channel, for 802.11n and
802.11ac. The values for type are
NOHT
Used for non-802.11n/non-802.1ac channels
HT20
20 MHz channel
HT40-
40 MHz primary channel and a lower secondary channel
HT40+
40 MHz primary channel and a higher secondary channel
HT80
80 MHz channel, with centerfreq1 as its center frequency
VHT80+80
Two 80 MHz channels combined, with centerfreq1 and centerfreq2 as the center
frequencies of the two channels
VHT160
160 MHz channel, with centerfreq1 as its center frequency
-L|--list-data-link-types
List the data link types supported by the interface and exit. The reported link types
can be used for the -y option.
-M
When used with -D, -L, -S or --list-time-stamp-types print machine-readable output.
The machine-readable output is intended to be read by Wireshark and TShark; its format
is subject to change from release to release.
-n
Save files as pcapng. This is the default. This option is deprecated and may be
removed.
-N <packet limit>
Limit the number of packets used for storing captured packets in memory while
processing it. If used in combination with the -C option, both limits will apply.
Setting this limit will enable the usage of the separate thread per interface.
-p|--no-promiscuous-mode
Don’t put the interface into promiscuous mode. Note that the interface might be in
promiscuous mode for some other reason; hence, -p cannot be used to ensure that the
only traffic that is captured is traffic sent to or from the machine on which Dumpcap
is running, broadcast traffic, and multicast traffic to addresses received by that
machine.
This option can occur multiple times. If used before the first occurrence of the -i
option, no interface will be put into the promiscuous mode. If used after an -i
option, the interface specified by the last -i option occurring before this option
will not be put into the promiscuous mode.
-P
Save files as pcap instead of the default pcapng. In situations that require pcapng,
such as capturing from multiple interfaces, this option will be overridden. This
option is deprecated in favor of the -F option and may be removed.
-q
When capturing packets, don’t display the continuous count of packets captured that is
normally shown when saving a capture to a file; instead, just display, at the end of
the capture, a count of packets captured. On systems that support the SIGINFO signal,
such as various BSDs, you can cause the current count to be displayed by typing your
"status" character (typically control-T, although it might be set to "disabled" by
default on at least some BSDs, so you’d have to explicitly set it to use it).
-Q
When capturing packets, don’t display, on the standard error, the initial message
indicating on what interfaces the capture is being done, the messages indicating to
what file a capture is being written, the continuous count of packets captured that is
normally shown when saving a capture to a file, and the message at the end of the
capture giving a count of packets captured. This outputs less than the -q option; only
true errors are displayed on the standard error.
On systems that support the SIGINFO signal, such as various BSDs, you can cause the
current count to be displayed by typing your "status" character (typically control-T,
although it might be set to "disabled" by default on at least some BSDs, so you’d have
to explicitly set it to use it).
-s|--snapshot-length <capture snaplen>
Set the default snapshot length to use when capturing live data. No more than snaplen
bytes of each network packet will be read into memory, or saved to disk. A value of 0
specifies a snapshot length of 262144, so that the full packet is captured; this is
the default.
This option can occur multiple times. If used before the first occurrence of the -i
option, it sets the default snapshot length. If used after an -i option, it sets the
snapshot length for the interface specified by the last -i option occurring before
this option. If the snapshot length is not set specifically, the default snapshot
length is used if provided.
-S
Print statistics for each interface once every second.
-t
Use a separate thread per interface.
--temp-dir <directory>
Specifies the directory into which temporary files (including capture files) are to be
written. The default behavior on UNIX-compatible systems, such as Linux, macOS, \*BSD,
Solaris, and AIX, is to use the environment variable $TMPDIR if set, and the system
default, typically /tmp, if it is not. On Windows, the %TEMP% environment variable is
used, which typically defaults to %USERPROFILE%\AppData\Local\Temp.
-v|--version
Print the full version information and exit.
-w <outfile>
Write raw packet data to outfile. Use "-" for stdout.
-y|--linktype <capture link type>
Set the data link type to use while capturing packets. The values reported by -L are
the values that can be used.
This option can occur multiple times. If used before the first occurrence of the -i
option, it sets the default capture link type. If used after an -i option, it sets the
capture link type for the interface specified by the last -i option occurring before
this option. If the capture link type is not set specifically, the default capture
link type is used if provided.
--capture-comment <comment>
Add a capture comment to the output file, if supported by the output file format.
This option is only available if we output the captured packets to a single file.
This option may be specified multiple times. Note that Wireshark currently only
displays the first comment of a capture file.
--list-time-stamp-types
List time stamp types supported for the interface. If no time stamp type can be set,
no time stamp types are listed.
--time-stamp-type <type>
Change the interface’s timestamp method.
--update-interval <interval>
Set the length of time in milliseconds between new packet reports during a capture.
Also sets the granularity of file duration conditions. The default value is 100ms.
DIAGNOSTIC OPTIONS
--log-level <level>
Set the active log level. Supported levels in lowest to highest order are "noisy",
"debug", "info", "message", "warning", "critical", and "error". Messages at each level
and higher will be printed, for example "warning" prints "warning", "critical", and
"error" messages and "noisy" prints all messages. Levels are case insensitive.
--log-fatal <level>
Abort the program if any messages are logged at the specified level or higher. For
example, "warning" aborts on any "warning", "critical", or "error" messages.
--log-domains <list>
Only print messages for the specified log domains, e.g. "GUI,Epan,sshdump". List of
domains must be comma-separated. Can be negated with "!" as the first character
(inverts the match).
--log-debug <list>
Force the specified domains to log at the "debug" level. List of domains must be
comma-separated. Can be negated with "!" as the first character (inverts the match).
--log-noisy <list>
Force the specified domains to log at the "noisy" level. List of domains must be
comma-separated. Can be negated with "!" as the first character (inverts the match).
--log-fatal-domains <list>
Abort the program if any messages are logged for the specified log domains. List of
domains must be comma-separated.
--log-file <path>
Write log messages and stderr output to the specified file.
CAPTURE FILTER SYNTAX
See the manual page of pcap-filter(7) or, if that doesn’t exist, tcpdump(8), or, if that
doesn’t exist, https://gitlab.com/wireshark/wireshark/-/wikis/CaptureFilters.
SEE ALSO
wireshark(1), tshark(1), editcap(1), mergecap(1), capinfos(1), pcap(3), pcap-filter(7) or
tcpdump(8)
NOTES
This is the manual page for Dumpcap 4.4.2. Dumpcap is part of the Wireshark distribution.
The latest version of Wireshark can be found at https://www.wireshark.org.
HTML versions of the Wireshark project man pages are available at
https://www.wireshark.org/docs/man-pages.
AUTHORS
Dumpcap is derived from the Wireshark capturing engine code; see the list of authors in
the Wireshark man page for a list of authors of that code.
2024-11-21 DUMPCAP(1)