1DUMPCAP(1) The Wireshark Network Analyzer DUMPCAP(1)
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6 dumpcap - Dump network traffic
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9 dumpcap [ -a <capture autostop condition> ] ...
10 [ -b <capture ring buffer option>] ... [ -B <capture buffer size> ]
11 [ -c <capture packet count> ] [ -d ] [ -D ] [ -f <capture filter> ]
12 [ -h ] [ -i <capture interface>|- ] [ -I ] [ -L ] [ -M ] [ -n ] [ -p ]
13 [ -P ] [ -q ] [ -s <capture snaplen> ] [ -S ] [ -v ] [ -w <outfile> ]
14 [ -y <capture link type> ]
15
17 Dumpcap is a network traffic dump tool. It lets you capture packet
18 data from a live network and write the packets to a file. Dumpcap's
19 default capture file format is pcap-ng format. When the -P option is
20 specified, the output file is written in the libpcap format.
21 Without any options set it will use the pcap library to capture traffic
23 from the first available network interface and writes the received raw
24 packet data, along with the packets' time stamps into a libpcap file.
25 If the -w option is not specified, Dumpcap writes to a newly created
27 libpcap file with a randomly chosen name. If the -w option is
28 specified, Dumpcap writes to the file specified by that option.
29 Packet capturing is performed with the pcap library. The capture
31 filter syntax follows the rules of the pcap library.
32
34 -a <capture autostop condition>
35 Specify a criterion that specifies when Dumpcap is to stop writing
36 to a capture file. The criterion is of the form test:value, where
37 test is one of:
38 duration:value Stop writing to a capture file after value seconds
40 have elapsed.
41 filesize:value Stop writing to a capture file after it reaches a
43 size of value kilobytes (where a kilobyte is 1024 bytes). If this
44 option is used together with the -b option, dumpcap will stop
45 writing to the current capture file and switch to the next one if
46 filesize is reached.
47 files:value Stop writing to capture files after value number of
49 files were written.
50 -b <capture ring buffer option>
52 Cause Dumpcap to run in "multiple files" mode. In "multiple files"
53 mode, Dumpcap will write to several capture files. When the first
54 capture file fills up, Dumpcap will switch writing to the next file
55 and so on.
56 The created filenames are based on the filename given with the -w
58 option, the number of the file and on the creation date and time,
59 e.g. outfile_00001_20050604120117.pcap,
60 outfile_00002_20050604120523.pcap, ...
61 With the files option it's also possible to form a "ring buffer".
63 This will fill up new files until the number of files specified, at
64 which point Dumpcap will discard the data in the first file and
65 start writing to that file and so on. If the files option is not
66 set, new files filled up until one of the capture stop conditions
67 match (or until the disk is full).
68 The criterion is of the form key:value, where key is one of:
70 duration:value switch to the next file after value seconds have
72 elapsed, even if the current file is not completely filled up.
73 filesize:value switch to the next file after it reaches a size of
75 value kilobytes (where a kilobyte is 1024 bytes).
76 files:value begin again with the first file after value number of
78 files were written (form a ring buffer). This value must be less
79 than 100000. Caution should be used when using large numbers of
80 files: some filesystems do not handle many files in a single
81 directory well. The files criterion requires either duration or
82 filesize to be specified to control when to go to the next file.
83 It should be noted that each -b parameter takes exactly one
84 criterion; to specify two criterion, each must be preceded by the
85 -b option.
86 Example: -b filesize:1024 -b files:5 results in a ring buffer of
88 five files of size one megabyte.
89 -B <capture buffer size>
91 Set capture buffer size (in MB, default is 1MB). This is used by
92 the the capture driver to buffer packet data until that data can be
93 written to disk. If you encounter packet drops while capturing,
94 try to increase this size. Note that, while Dumpcap attempts to
95 set the buffer size to 1MB by default, and can be told to set it to
96 a larger value, the system or interface on which you're capturing
97 might silently limit the capture buffer size to a lower value or
98 raise it to a higher value.
99 This is available on UNIX systems with libpcap 1.0.0 or later and
101 on Windows. It is not available on UNIX systems with earlier
102 versions of libpcap.
103 This option can occur multiple times. If used before the first
105 occurrence of the -i option, it sets the default capture buffer
106 size. If used after an -i option, it sets the capture buffer size
107 for the interface specified by the last -i option occurring before
108 this option. If the capture buffer size is not set specifically,
109 the default capture buffer size is used if provided.
110 -c <capture packet count>
112 Set the maximum number of packets to read when capturing live data.
113 -d Dump the code generated for the capture filter in a human-readable
115 form, and exit.
116 -D Print a list of the interfaces on which Dumpcap can capture, and
118 exit. For each network interface, a number and an interface name,
119 possibly followed by a text description of the interface, is
120 printed. The interface name or the number can be supplied to the
121 -i option to specify an interface on which to capture.
122 This can be useful on systems that don't have a command to list
124 them (e.g., Windows systems, or UNIX systems lacking ifconfig -a);
125 the number can be useful on Windows 2000 and later systems, where
126 the interface name is a somewhat complex string.
127 Note that "can capture" means that Dumpcap was able to open that
129 device to do a live capture. Depending on your system you may need
130 to run dumpcap from an account with special privileges (for
131 example, as root) to be able to capture network traffic. If
132 "dumpcap -D" is not run from such an account, it will not list any
133 interfaces.
134 -f <capture filter>
136 Set the capture filter expression.
137 The entire filter expression must be specified as a single argument
139 (which means that if it contains spaces, it must be quoted).
140 This option can occur multiple times. If used before the first
142 occurrence of the -i option, it sets the default capture filter
143 expression. If used after an -i option, it sets the capture filter
144 expression for the interface specified by the last -i option
145 occurring before this option. If the capture filter expression is
146 not set specifically, the default capture filter expression is used
147 if provided.
148 -h Print the version and options and exits.
150 -i <capture interface>|-
152 Set the name of the network interface or pipe to use for live
153 packet capture.
154 Network interface names should match one of the names listed in
156 "dumpcap -D" (described above); a number, as reported by "dumpcap
157 -D", can also be used. If you're using UNIX, "netstat -i" or
158 "ifconfig -a" might also work to list interface names, although not
159 all versions of UNIX support the -a option to ifconfig.
160 If no interface is specified, Dumpcap searches the list of
162 interfaces, choosing the first non-loopback interface if there are
163 any non-loopback interfaces, and choosing the first loopback
164 interface if there are no non-loopback interfaces. If there are no
165 interfaces at all, Dumpcap reports an error and doesn't start the
166 capture.
167 Pipe names should be either the name of a FIFO (named pipe) or
169 ``-'' to read data from the standard input. Data read from pipes
170 must be in standard libpcap format.
171 This option can occur multiple times. When capturing from multiple
173 interfaces, the capture file will be saved in pcap-ng format.
174 Note: the Win32 version of Dumpcap doesn't support capturing from
176 pipes or stdin!
177 -I Put the interface in "monitor mode"; this is supported only on IEEE
179 802.11 Wi-Fi interfaces, and supported only on some operating
180 systems.
181 Note that in monitor mode the adapter might disassociate from the
183 network with which it's associated, so that you will not be able to
184 use any wireless networks with that adapter. This could prevent
185 accessing files on a network server, or resolving host names or
186 network addresses, if you are capturing in monitor mode and are not
187 connected to another network with another adapter.
188 This option can occur multiple times. If used before the first
190 occurrence of the -i option, it enables the monitor mode for all
191 interfaces. If used after an -i option, it enables the monitor
192 mode for the interface specified by the last -i option occurring
193 before this option.
194 -L List the data link types supported by the interface and exit. The
196 reported link types can be used for the -y option.
197 -M When used with -D, -L or -S, print machine-readable output. The
199 machine-readable output is intended to be read by Wireshark and
200 TShark; its format is subject to change from release to release.
201 -n Save files as pcap-ng. This is the default.
203 -p Don't put the interface into promiscuous mode. Note that the
205 interface might be in promiscuous mode for some other reason;
206 hence, -p cannot be used to ensure that the only traffic that is
207 captured is traffic sent to or from the machine on which Dumpcap is
208 running, broadcast traffic, and multicast traffic to addresses
209 received by that machine.
210 This option can occur multiple times. If used before the first
212 occurrence of the -i option, no interface will be put into the
213 promiscuous mode. If used after an -i option, the interface
214 specified by the last -i option occurring before this option will
215 not be put into the promiscuous mode.
216 -P Save files as pcap instead of the default pcap-ng. In situations
218 that require pcap-ng, such as capturing from multiple interfaces,
219 this option will be overridden.
220 -q When capturing packets, don't display the continuous count of
222 packets captured that is normally shown when saving a capture to a
223 file; instead, just display, at the end of the capture, a count of
224 packets captured. On systems that support the SIGINFO signal, such
225 as various BSDs, you can cause the current count to be displayed by
226 typing your "status" character (typically control-T, although it
227 might be set to "disabled" by default on at least some BSDs, so
228 you'd have to explicitly set it to use it).
229 -s <capture snaplen>
231 Set the default snapshot length to use when capturing live data.
232 No more than snaplen bytes of each network packet will be read into
233 memory, or saved to disk. A value of 0 specifies a snapshot length
234 of 65535, so that the full packet is captured; this is the default.
235 This option can occur multiple times. If used before the first
237 occurrence of the -i option, it sets the default snapshot length.
238 If used after an -i option, it sets the snapshot length for the
239 interface specified by the last -i option occurring before this
240 option. If the snapshot length is not set specifically, the default
241 snapshot length is used if provided.
242 -S Print statistics for each interface once every second.
244 -v Print the version and exit.
246 -w <outfile>
248 Write raw packet data to outfile.
249 NOTE: The usage of "-" for stdout is not allowed here!
251 -y <capture link type>
253 Set the data link type to use while capturing packets. The values
254 reported by -L are the values that can be used.
255 This option can occur multiple times. If used before the first
257 occurrence of the -i option, it sets the default capture link type.
258 If used after an -i option, it sets the capture link type for the
259 interface specified by the last -i option occurring before this
260 option. If the capture link type is not set specifically, the
261 default capture link type is used if provided.
262
264 See the manual page of pcap-filter(7) or, if that doesn't exist,
265 tcpdump(8), or, if that doesn't exist,
266 <http://wiki.wireshark.org/CaptureFilters>.
267
269 wireshark(1), tshark(1), editcap(1), mergecap(1), capinfos(1), pcap(3),
270 pcap-filter(7) or tcpdump(8) if it doesn't exist.
271
273 Dumpcap is part of the Wireshark distribution. The latest version of
274 Wireshark can be found at <http://www.wireshark.org>.
275 HTML versions of the Wireshark project man pages are available at:
277 <http://www.wireshark.org/docs/man-pages>.
278
280 Dumpcap is derived from the Wireshark capturing engine code; see the
281 list of authors in the Wireshark man page for a list of authors of that
282 code.
2831.8.10 2012-06-05 DUMPCAP(1)