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dumpcap(1)              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>:<port>/<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> ] [ --capture-comment <comment> ]


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.

       -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 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 (UNIX systems lacking ifconfig -a or Linux systems lacking ip
           link show). The number can be useful on Windows systems, where the
           interface name might be a long name or a GUID.

           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.

           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.

           Pre-defined capture filter names, as shown in the GUI menu item
           Capture->Capture Filters, can be used by prefixing the argument
           with "predef:".  Example: -f "predef:MyPredefinedHostOnlyFilter"

       -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.

       -i  <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
           "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 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 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 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.

       -v  Print the version and exit.

       -w  <outfile>
           Write raw packet data to outfile. Use "-" for stdout.

       -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.

       --capture-comment <comment>
           Add a capture comment to the output file.

           This option is only available if we output the captured packets to
           a single file in pcap-ng format. Only one capture comment may be
           set per output 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://wiki.wireshark.org/CaptureFilters>.


SEE ALSO

       wireshark(1), tshark(1), editcap(1), mergecap(1), capinfos(1), pcap(3),
       pcap-filter(7) or tcpdump(8)


NOTES

       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.



2.4.1                             2017-08-29                        dumpcap(1)

wireshark 2.4.1 - Generated Wed Aug 30 15:10:28 CDT 2017
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