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> ] [
--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 (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.
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>/<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 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. 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.