1DUMPCAP(1) DUMPCAP(1)
2
6 dumpcap - Dump network traffic
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9 dumpcap [ -a|--autostop <capture autostop condition> ] ...
10 [ -b|--ring-buffer <capture ring buffer option> ] ...
11 [ -B|--buffer-size <capture buffer size> ]
12 [ -c <capture packet count> ] [ -C <byte limit> ] [ -d ]
13 [ -D|--list-interfaces ] [ -f <capture filter> ] [ -g ] [ -h|--help ]
14 [ -i|--interface <capture interface>|rpcap://<host>:<port>/<capture interface>|TCP@<host>:<port>|- ]
15 [ -I|--monitor-mode ]
16 [ -k <freq>,[<type>],[<center_freq1>],[<center_freq2>] ]
17 [ -L|--list-data-link-types ] [ -M ] [ -n ] [ -N <packet limit> ]
18 [ -p|--no-promiscuous-mode ] [ --ifdescr <description> ]
19 [ --ifname <name> ] [ -P ] [ -q ]
20 [ -s|--snapshot-length <capture snaplen> ] [ -S ] [ -t ]
21 [ -v|--version ] [ -w <outfile> ] [ -y|--linktype <capture link type> ]
22 [ --capture-comment <comment> ] [ --list-time-stamp-types ]
23 [ --time-stamp-type <type> ]
24
26 Dumpcap is a network traffic dump tool. It lets you capture packet data
27 from a live network and write the packets to a file. Dumpcap's default
28 capture file format is pcapng format. When the -P option is specified,
29 the output file is written in the pcap format.
30 Without any options set it will use the libpcap, Npcap, or WinPcap
32 library to capture traffic from the first available network interface
33 and writes the received raw packet data, along with the packets' time
34 stamps into a pcap file.
35 If the -w option is not specified, Dumpcap writes to a newly created
37 pcap file with a randomly chosen name. If the -w option is specified,
38 Dumpcap writes to the file specified by that option.
39 Packet capturing is performed with the pcap library. The capture filter
41 syntax follows the rules of the pcap library.
42
44 -a|--autostop <capture autostop condition>
45 Specify a criterion that specifies when Dumpcap is to stop writing
47 to a capture file. The criterion is of the form test:value, where
48 test is one of:
49 duration:value Stop writing to a capture file after value seconds
51 have elapsed. Floating point values (e.g. 0.5) are allowed.
52 files:value Stop writing to capture files after value number of
54 files were written.
55 filesize:value Stop writing to a capture file after it reaches a
57 size of value kB. If this option is used together with the -b
58 option, dumpcap will stop writing to the current capture file and
59 switch to the next one if filesize is reached. Note that the
60 filesize is limited to a maximum value of 2 GiB.
61 packets:value Stop writing to a capture file after value packets
63 have been written. Same as -c <capture packet count>.
64 -b|--ring-buffer <capture ring buffer option>
66 Cause Dumpcap to run in "multiple files" mode. In "multiple files"
68 mode, Dumpcap will write to several capture files. When the first
69 capture file fills up, Dumpcap will switch writing to the next file
70 and so on.
71 The created filenames are based on the filename given with the -w
73 option, the number of the file and on the creation date and time,
74 e.g. outfile_00001_20210714120117.pcap,
75 outfile_00002_20210714120523.pcap, ...
76 With the files option it’s also possible to form a "ring buffer".
78 This will fill up new files until the number of files specified, at
79 which point Dumpcap will discard the data in the first file and
80 start writing to that file and so on. If the files option is not
81 set, new files filled up until one of the capture stop conditions
82 match (or until the disk is full).
83 The criterion is of the form key:value, where key is one of:
85 duration:value switch to the next file after value seconds have
87 elapsed, even if the current file is not completely filled up.
88 Floating point values (e.g. 0.5) are allowed.
89 files:value begin again with the first file after value number of
91 files were written (form a ring buffer). This value must be less
92 than 100000. Caution should be used when using large numbers of
93 files: some filesystems do not handle many files in a single
94 directory well. The files criterion requires either duration,
95 interval or filesize to be specified to control when to go to the
96 next file. It should be noted that each -b parameter takes exactly
97 one criterion; to specify two criterion, each must be preceded by
98 the -b option.
99 filesize:value switch to the next file after it reaches a size of
101 value kB. Note that the filesize is limited to a maximum value of 2
102 GiB.
103 interval:value switch to the next file when the time is an exact
105 multiple of value seconds. For example, use 3600 to switch to a new
106 file every hour on the hour.
107 packets:value switch to the next file after it contains value
109 packets.
110 printname:filename print the name of the most recently written file
112 to filename after the file is closed. filename can be stdout or -
113 for standard output, or stderr for standard error.
114 Example: -b filesize:1000 -b files:5 results in a ring buffer of
116 five files of size one megabyte each.
117 -B|--buffer-size <capture buffer size>
119 Set capture buffer size (in MiB, default is 2 MiB). This is used by
121 the capture driver to buffer packet data until that data can be
122 written to disk. If you encounter packet drops while capturing, try
123 to increase this size. Note that, while Dumpcap attempts to set the
124 buffer size to 2 MiB by default, and can be told to set it to a
125 larger value, the system or interface on which you’re capturing
126 might silently limit the capture buffer size to a lower value or
127 raise it to a higher value.
128 This is available on UNIX systems with libpcap 1.0.0 or later and
130 on Windows. It is not available on UNIX systems with earlier
131 versions of libpcap.
132 This option can occur multiple times. If used before the first
134 occurrence of the -i option, it sets the default capture buffer
135 size. If used after an -i option, it sets the capture buffer size
136 for the interface specified by the last -i option occurring before
137 this option. If the capture buffer size is not set specifically,
138 the default capture buffer size is used instead.
139 -c <capture packet count>
141 Set the maximum number of packets to read when capturing live data.
143 Same as -a packets:<capture packet count>.
144 -C <byte limit>
146 Limit the amount of memory in bytes used for storing captured
148 packets in memory while processing it. If used in combination with
149 the -N option, both limits will apply. Setting this limit will
150 enable the usage of the separate thread per interface.
151 -d
153 Dump the code generated for the capture filter in a human-readable
155 form, and exit.
156 -D|--list-interfaces
158 Print a list of the interfaces on which Dumpcap can capture, and
160 exit. For each network interface, a number and an interface name,
161 possibly followed by a text description of the interface, is
162 printed. The interface name or the number can be supplied to the -i
163 option to specify an interface on which to capture.
164 This can be useful on systems that don’t have a command to list
166 them (UNIX systems lacking ifconfig -a or Linux systems lacking ip
167 link show). The number can be useful on Windows systems, where the
168 interface name might be a long name or a GUID.
169 Note that "can capture" means that Dumpcap was able to open that
171 device to do a live capture. Depending on your system you may need
172 to run dumpcap from an account with special privileges (for
173 example, as root) to be able to capture network traffic. If
174 "dumpcap -D" is not run from such an account, it will not list any
175 interfaces.
176 -f <capture filter>
178 Set the capture filter expression.
180 The entire filter expression must be specified as a single argument
182 (which means that if it contains spaces, it must be quoted).
183 This option can occur multiple times. If used before the first
185 occurrence of the -i option, it sets the default capture filter
186 expression. If used after an -i option, it sets the capture filter
187 expression for the interface specified by the last -i option
188 occurring before this option. If the capture filter expression is
189 not set specifically, the default capture filter expression is used
190 if provided.
191 Pre-defined capture filter names, as shown in the GUI menu item
193 Capture→Capture Filters, can be used by prefixing the argument with
194 "predef:". Example: -f "predef:MyPredefinedHostOnlyFilter"
195 -g
197 This option causes the output file(s) to be created with group-read
199 permission (meaning that the output file(s) can be read by other
200 members of the calling user’s group).
201 -h|--help
203 Print the version and options and exits.
205 -i|--interface <capture interface>|rpcap://<host>:<port>/<capture
207 interface>|TCP@<host>:<port>|-
208 Set the name of the network interface or pipe to use for live
210 packet capture.
211 Network interface names should match one of the names listed in
213 "dumpcap -D" (described above); a number, as reported by "dumpcap
214 -D", can also be used. If you’re using UNIX, "netstat -i",
215 "ifconfig -a" or "ip link" might also work to list interface names,
216 although not all versions of UNIX support the -a option to
217 ifconfig.
218 If no interface is specified, Dumpcap searches the list of
220 interfaces, choosing the first non-loopback interface if there are
221 any non-loopback interfaces, and choosing the first loopback
222 interface if there are no non-loopback interfaces. If there are no
223 interfaces at all, Dumpcap reports an error and doesn’t start the
224 capture.
225 Pipe names should be either the name of a FIFO (named pipe) or "-"
227 to read data from the standard input. On Windows systems, pipe
228 names must be of the form "\\pipe\.*pipename*". Data read from
229 pipes must be in standard pcapng or pcap format. Pcapng data must
230 have the same endianness as the capturing host.
231 This option can occur multiple times. When capturing from multiple
233 interfaces, the capture file will be saved in pcapng format.
234 --ifdescr> <description>
236 Use description as the description in the capture file for the
238 interface or pipe specified before it with -i.
239 --ifname> <name>
241 Use name as the name in the capture file for the the interface or
243 pipe specified before it with -i.
244 -I|--monitor-mode
246 Put the interface in "monitor mode"; this is supported only on IEEE
248 802.11 Wi-Fi interfaces, and supported only on some operating
249 systems.
250 Note that in monitor mode the adapter might disassociate from the
252 network with which it’s associated, so that you will not be able to
253 use any wireless networks with that adapter. This could prevent
254 accessing files on a network server, or resolving host names or
255 network addresses, if you are capturing in monitor mode and are not
256 connected to another network with another adapter.
257 This option can occur multiple times. If used before the first
259 occurrence of the -i option, it enables the monitor mode for all
260 interfaces. If used after an -i option, it enables the monitor mode
261 for the interface specified by the last -i option occurring before
262 this option.
263 -k <freq>,[<type>],[<center_freq1>],[<center_freq2>>
265 Set the channel on the interface; this is supported only on IEEE
267 802.11 Wi-Fi interfaces, and supported only on some operating
268 systems.
269 freq is the frequency of the channel. type is the type of the
271 channel, for 802.11n and 802.11ac. The values for type are
272 NOHT
274 Used for non-802.11n/non-802.1ac channels
276 HT20
278 20 MHz channel
280 HT40-
282 40 MHz primary channel and a lower secondary channel
284 HT40+
286 40 MHz primary channel and a higher secondary channel
288 HT80
290 80 MHz channel, with centerfreq1 as its center frequency
292 VHT80+80
294 two 80 MHz channels combined, with centerfreq1 and centerfreq2 as
296 the center frequencies of the two channels
297 VHT160
299 160 MHz channel, with centerfreq1 as its center frequency
301 -L|--list-data-link-types
303 List the data link types supported by the interface and exit. The
305 reported link types can be used for the -y option.
306 -M
308 When used with -D, -L, -S or --list-time-stamp-types print
310 machine-readable output. The machine-readable output is intended to
311 be read by Wireshark and TShark; its format is subject to change
312 from release to release.
313 -n
315 Save files as pcapng. This is the default.
317 -N <packet limit>
319 Limit the number of packets used for storing captured packets in
321 memory while processing it. If used in combination with the -C
322 option, both limits will apply. Setting this limit will enable the
323 usage of the separate thread per interface.
324 -p|--no-promiscuous-mode
326 Don’t put the interface into promiscuous mode. Note that the
328 interface might be in promiscuous mode for some other reason;
329 hence, -p cannot be used to ensure that the only traffic that is
330 captured is traffic sent to or from the machine on which Dumpcap is
331 running, broadcast traffic, and multicast traffic to addresses
332 received by that machine.
333 This option can occur multiple times. If used before the first
335 occurrence of the -i option, no interface will be put into the
336 promiscuous mode. If used after an -i option, the interface
337 specified by the last -i option occurring before this option will
338 not be put into the promiscuous mode.
339 -P
341 Save files as pcap instead of the default pcapng. In situations
343 that require pcapng, such as capturing from multiple interfaces,
344 this option will be overridden.
345 -q
347 When capturing packets, don’t display the continuous count of
349 packets captured that is normally shown when saving a capture to a
350 file; instead, just display, at the end of the capture, a count of
351 packets captured. On systems that support the SIGINFO signal, such
352 as various BSDs, you can cause the current count to be displayed by
353 typing your "status" character (typically control-T, although it
354 might be set to "disabled" by default on at least some BSDs, so
355 you’d have to explicitly set it to use it).
356 -s|--snapshot-length <capture snaplen>
358 Set the default snapshot length to use when capturing live data. No
360 more than snaplen bytes of each network packet will be read into
361 memory, or saved to disk. A value of 0 specifies a snapshot length
362 of 262144, so that the full packet is captured; this is the
363 default.
364 This option can occur multiple times. If used before the first
366 occurrence of the -i option, it sets the default snapshot length.
367 If used after an -i option, it sets the snapshot length for the
368 interface specified by the last -i option occurring before this
369 option. If the snapshot length is not set specifically, the default
370 snapshot length is used if provided.
371 -S
373 Print statistics for each interface once every second.
375 -t
377 Use a separate thread per interface.
379 -v|--version
381 Print the version and exit.
383 -w <outfile>
385 Write raw packet data to outfile. Use "-" for stdout.
387 -y|--linktype <capture link type>
389 Set the data link type to use while capturing packets. The values
391 reported by -L are the values that can be used.
392 This option can occur multiple times. If used before the first
394 occurrence of the -i option, it sets the default capture link type.
395 If used after an -i option, it sets the capture link type for the
396 interface specified by the last -i option occurring before this
397 option. If the capture link type is not set specifically, the
398 default capture link type is used if provided.
399 --capture-comment <comment>
401 Add a capture comment to the output file, if supported by the
403 output file format.
404 This option is only available if we output the captured packets to
406 a single file.
407 This option may be specified multiple times. Note that Wireshark
409 currently only displays the first comment of a capture file.
410 --list-time-stamp-types
412 List time stamp types supported for the interface. If no time stamp
414 type can be set, no time stamp types are listed.
415 --time-stamp-type <type>
417 Change the interface’s timestamp method.
419
421 See the manual page of pcap-filter(7) or, if that doesn’t exist,
422 tcpdump(8), or, if that doesn’t exist,
423 https://gitlab.com/wireshark/wireshark/-/wikis/CaptureFilters.
424
426 wireshark(1), tshark(1), editcap(1), mergecap(1), capinfos(1), pcap(3),
427 pcap-filter(7) or tcpdump(8)
428
430 This is the manual page for Dumpcap 3.6.0. Dumpcap is part of the
431 Wireshark distribution. The latest version of Wireshark can be found at
432 https://www.wireshark.org.
433 HTML versions of the Wireshark project man pages are available at
435 https://www.wireshark.org/docs/man-pages.
436
438 Dumpcap is derived from the Wireshark capturing engine code; see the
439 list of authors in the Wireshark man page for a list of authors of that
440 code.
441 2021-11-25 DUMPCAP(1)