dumpcap
(1)
Name
dumpcap - Dump network traffic
Synopsis
dumpcap [ -a <capture autostop condition> ] ...
[ -b <capture ring buffer option>] ...
[ -B <capture buffer size> ] [ -c <capture packet count> ]
[ -C <byte limit> ] [ -d ] [ -D ] [ -f <capture filter> ]
[ -g ] [ -h ]
[ -i <capture interface>|rpcap://<host>/<capture interface>|TCP@<host>:<port>|- ]
[ -I ] [ -L ] [ -M ] [ -n ] [ -N <packet limit> ] [ -p ]
[ -P ] [ -q ] [ -s <capture snaplen> ] [ -S ] [ -t ] [ -v ]
[ -w <outfile> ] [ -y <capture link type> ]
Description
The Wireshark Network Analyzer DUMPCAP(1)
NAME
dumpcap - Dump network traffic
SYNOPSIS
dumpcap [ -a <capture autostop condition> ] ...
[ -b <capture ring buffer option>] ...
[ -B <capture buffer size> ] [ -c <capture packet count> ]
[ -C <byte limit> ] [ -d ] [ -D ] [ -f <capture filter> ]
[ -g ] [ -h ]
[ -i <capture interface>|rpcap://<host>/<capture interface>|TCP@<host>:<port>|- ]
[ -I ] [ -L ] [ -M ] [ -n ] [ -N <packet limit> ] [ -p ]
[ -P ] [ -q ] [ -s <capture snaplen> ] [ -S ] [ -t ] [ -v ]
[ -w <outfile> ] [ -y <capture link type> ]
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 pcap-ng
format. When the -P option is specified, the output file is
written in the pcap format.
Without any options set it will use the libpcap/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 pcap file.
If the -w option is not specified, Dumpcap writes to a newly
created pcap 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 <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.
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 GiB.
files:value Stop writing to capture files after value
number of files were written.
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-b <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_20050604120117.pcap,
outfile_00002_20050604120523.pcap, ...
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.
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 GiB.
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 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.
Example: -b filesize:1000 -b files:5 results in a ring
buffer of five files of size one megabyte each.
-B <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
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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 systems with libpcap 1.0.0 or
later and on Windows. It is not available on UNIX
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.
-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 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 option to
specify an interface on which to capture.
This can be useful on systems that don't have a command
to list them (e.g., Windows systems, or UNIX systems
lacking ifconfig -a); the number can be useful on
Windows 2000 and later systems, where the interface name
is a somewhat complex string.
Note that "can capture" means that Dumpcap was able to
open that device to do a live capture. Depending on your
system you may need to run dumpcap from an account with
special privileges (for example, as root) to be able to
capture network traffic. If "dumpcap -D" is not run
from such an account, it will not list any interfaces.
-f <capture filter>
Set the capture filter expression.
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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.
-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 Print the version and options and exits.
interface>|TCP@<host>:<port>|-
-i <capture interface>|rpcap://<host>/<capture
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 "dumpcap -D" (described above); a number, as
reported by "dumpcap -D", can also be used. If you're
using UNIX, "netstat -i" or "ifconfig -a" might also
work to list interface names, although not all versions
of UNIX support the -a option to ifconfig.
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.
Data read from pipes must be in standard pcap format.
This option can occur multiple times. When capturing
from multiple interfaces, the capture file will be saved
in pcap-ng format.
Note: the Win32 version of Dumpcap doesn't support
capturing from pipes or stdin!
-I Put the interface in "monitor mode"; this is supported
only on IEEE 802.11 Wi-Fi interfaces, and supported only
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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.
-L 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 or -S, 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 pcap-ng. This is the default.
-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 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 pcap-ng. In
situations that require pcap-ng, such as capturing from
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multiple interfaces, this option will be overridden.
-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).
-s <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 65535, 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.
-v Print the version and exit.
-w <outfile>
Write raw packet data to outfile.
NOTE: The usage of "-" for stdout is not allowed here!
-y <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.
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The Wireshark Network Analyzer DUMPCAP(1)
CAPTURE FILTER SYNTAX
See the manual page of pcap-filter(5) or, if that doesn't
exist, tcpdump(1), or, if that doesn't exist,
<http://wiki.wireshark.org/CaptureFilters>.
ATTRIBUTES
See attributes(5) for descriptions of the following
attributes:
+---------------+---------------------------------------+
|ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+---------------+---------------------------------------+
|Availability | diagnostic/wireshark/wireshark-common |
+---------------+---------------------------------------+
|Stability | Uncommitted |
+---------------+---------------------------------------+
SEE ALSO
wireshark(1), tshark(1), editcap(1), mergecap(1),
capinfos(1), pcap(3), pcap-filter(5) or tcpdump(1)
NOTES
Dumpcap is part of the Wireshark distribution. The latest
version of Wireshark can be found at
<http://www.wireshark.org>.
HTML versions of the Wireshark project man pages are
available at: http://www.wireshark.org/docs/man-pages
<http://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.
This software was built from source available at
https://java.net/projects/solaris-userland. The original
community source was downloaded from
http://www.wireshark.org/download/src/all-
versions/wireshark-1.10.7.tar.bz2
Further information about this software can be found on the
open source community website at http://www.wireshark.org/.
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