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 ] [ -f <capture filter> ] [ -h ]
12 [ -i <capture interface>|- ] [ -I ] [ -L ] [ -n ] [ -M ] [ -p ] [ -q ]
13 [ -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 native capture file format is libpcap format, which is also the format
20 used by Wireshark, tcpdump and various other tools. When the -n option
21 is specified, the output file is written in the new pcapng format.
22 Without any options set it will use the pcap library to capture traffic
24 from the first available network interface and writes the received raw
25 packet data, along with the packets' time stamps into a libpcap file.
26 If the -w option is not specified, Dumpcap writes to a newly created
28 libpcap file with a randomly chosen name. If the -w option is
29 specified, Dumpcap writes to the file specified by that option.
30 Packet capturing is performed with the pcap library. The capture
32 filter syntax follows the rules of the pcap library.
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35 -a <capture autostop condition>
36 Specify a criterion that specifies when Dumpcap is to stop writing
37 to a capture file. The criterion is of the form test:value, where
38 test is one of:
39 duration:value Stop writing to a capture file after value seconds
41 have elapsed.
42 filesize:value Stop writing to a capture file after it reaches a
44 size of value kilobytes (where a kilobyte is 1024 bytes). If this
45 option is used together with the -b option, dumpcap will stop
46 writing to the current capture file and switch to the next one if
47 filesize is reached.
48 files:value Stop writing to capture files after value number of
50 files were written.
51 -b <capture ring buffer option>
53 Cause Dumpcap to run in "multiple files" mode. In "multiple files"
54 mode, Dumpcap will write to several capture files. When the first
55 capture file fills up, Dumpcap will switch writing to the next file
56 and so on.
57 The created filenames are based on the filename given with the -w
59 option, the number of the file and on the creation date and time,
60 e.g. outfile_00001_20050604120117.pcap,
61 outfile_00002_20050604120523.pcap, ...
62 With the files option it's also possible to form a "ring buffer".
64 This will fill up new files until the number of files specified, at
65 which point Dumpcap will discard the data in the first file and
66 start writing to that file and so on. If the files option is not
67 set, new files filled up until one of the capture stop conditions
68 match (or until the disk is full).
69 The criterion is of the form key:value, where key is one of:
71 duration:value switch to the next file after value seconds have
73 elapsed, even if the current file is not completely filled up.
74 filesize:value switch to the next file after it reaches a size of
76 value kilobytes (where a kilobyte is 1024 bytes).
77 files:value begin again with the first file after value number of
79 files were written (form a ring buffer). This value must be less
80 than 100000. Caution should be used when using large numbers of
81 files: some filesystems do not handle many files in a single
82 directory well. The files criterion requires either duration or
83 filesize to be specified to control when to go to the next file.
84 It should be noted that each -b parameter takes exactly one
85 criterion; to specify two criterion, each must be preceded by the
86 -b option.
87 Example: -b filesize:1024 -b files:5 results in a ring buffer of
89 five files of size one megabyte.
90 -B <capture buffer size>
92 Set capture buffer size (in MB, default is 1MB). This is used by
93 the the capture driver to buffer packet data until that data can be
94 written to disk. If you encounter packet drops while capturing,
95 try to increase this size. Note that, while Dumpcap attempts to
96 set the buffer size to 1MB by default, and can be told to set it to
97 a larger value, the system or interface on which you're capturing
98 might silently limit the capture buffer size to a lower value or
99 raise it to a higher value.
100 This is available on on UNIX systems with libpcap 1.0.0 or later
102 and on Windows. It is not available on UNIX systems with earlier
103 versions of libpcap.
104 -c <capture packet count>
106 Set the maximum number of packets to read when capturing live data.
107 -D Print a list of the interfaces on which Dumpcap can capture, and
109 exit. For each network interface, a number and an interface name,
110 possibly followed by a text description of the interface, is
111 printed. The interface name or the number can be supplied to the
112 -i option to specify an interface on which to capture.
113 This can be useful on systems that don't have a command to list
115 them (e.g., Windows systems, or UNIX systems lacking ifconfig -a);
116 the number can be useful on Windows 2000 and later systems, where
117 the interface name is a somewhat complex string.
118 Note that "can capture" means that Dumpcap was able to open that
120 device to do a live capture. Depending on your system you may need
121 to run dumpcap from an account with special privileges (for
122 example, as root) to be able to capture network traffic. If
123 "dumpcap -D" is not run from such an account, it will not list any
124 interfaces.
125 -f <capture filter>
127 Set the capture filter expression.
128 The entire filter expression must be specified as a single argument
130 (which means that if it contains spaces, it must be quoted).
131 -h Print the version and options and exits.
133 -i <capture interface>|-
135 Set the name of the network interface or pipe to use for live
136 packet capture.
137 Network interface names should match one of the names listed in
139 "dumpcap -D" (described above); a number, as reported by "dumpcap
140 -D", can also be used. If you're using UNIX, "netstat -i" or
141 "ifconfig -a" might also work to list interface names, although not
142 all versions of UNIX support the -a option to ifconfig.
143 If no interface is specified, Dumpcap searches the list of
145 interfaces, choosing the first non-loopback interface if there are
146 any non-loopback interfaces, and choosing the first loopback
147 interface if there are no non-loopback interfaces. If there are no
148 interfaces at all, Dumpcap reports an error and doesn't start the
149 capture.
150 Pipe names should be either the name of a FIFO (named pipe) or
152 ``-'' to read data from the standard input. Data read from pipes
153 must be in standard libpcap format.
154 Note: the Win32 version of Dumpcap doesn't support capturing from
156 pipes or stdin!
157 -I Put the interface in "monitor mode"; this is supported only on IEEE
159 802.11 Wi-Fi interfaces, and supported only on some operating
160 systems.
161 Note that in monitor mode the adapter might disassociate from the
163 network with which it's associated, so that you will not be able to
164 use any wireless networks with that adapter. This could prevent
165 accessing files on a network server, or resolving host names or
166 network addresses, if you are capturing in monitor mode and are not
167 connected to another network with another adapter.
168 -L List the data link types supported by the interface and exit. The
170 reported link types can be used for the -y option.
171 -M When used with -D, -L and -S, print machine-readable output. The
173 machine-readable output is intended to be read by Wireshark and
174 TShark; its format is subject to change from release to release.
175 -n Write the output file in the pcap-ng format instead of the default
177 pcap format.
178 -p Don't put the interface into promiscuous mode. Note that the
180 interface might be in promiscuous mode for some other reason;
181 hence, -p cannot be used to ensure that the only traffic that is
182 captured is traffic sent to or from the machine on which Dumpcap is
183 running, broadcast traffic, and multicast traffic to addresses
184 received by that machine.
185 -q When capturing packets, don't display the continuous count of
187 packets captured that is normally shown when saving a capture to a
188 file; instead, just display, at the end of the capture, a count of
189 packets captured. On systems that support the SIGINFO signal, such
190 as various BSDs, you can cause the current count to be displayed by
191 typing your "status" character (typically control-T, although it
192 might be set to "disabled" by default on at least some BSDs, so
193 you'd have to explicitly set it to use it).
194 -s <capture snaplen>
196 Set the default snapshot length to use when capturing live data.
197 No more than snaplen bytes of each network packet will be read into
198 memory, or saved to disk. A value of 0 specifies a snapshot length
199 of 65535, so that the full packet is captured; this is the default.
200 -S Print statistics for each interface once every second.
202 -v Print the version and exit.
204 -w <outfile>
206 Write raw packet data to outfile.
207 NOTE: The usage of "-" for stdout is not allowed here!
209 -y <capture link type>
211 Set the data link type to use while capturing packets. The values
212 reported by -L are the values that can be used.
213
215 See the manual page of pcap-filter(4) or, if that doesn't exist,
216 tcpdump(8), or, if that doesn't exist,
217 <http://wiki.wireshark.org/CaptureFilters>.
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220 wireshark(1), tshark(1), editcap(1), mergecap(1), capinfos(1),
221 pcap-filter(4), tcpdump(8), pcap(3)
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224 Dumpcap is part of the Wireshark distribution. The latest version of
225 Wireshark can be found at <http://www.wireshark.org>.
226 HTML versions of the Wireshark project man pages are available at:
228 http://www.wireshark.org/docs/man-pages
229 <http://www.wireshark.org/docs/man-pages>.
230
232 Dumpcap is derived from the Wireshark capturing engine code; see the
233 list of authors in the Wireshark man page for a list of authors of that
234 code.
2351.4.10 2011-11-01 DUMPCAP(1)