1EDITCAP(1) The Wireshark Network Analyzer EDITCAP(1)
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6 editcap - Edit and/or translate the format of capture files
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9 editcap [ -a <frame:comment> ] [ -A <start time> ] [ -B <stop time> ]
10 [ -c <packets per file> ] [ -C [offset:]<choplen> ]
11 [ -E <error probability> ] [ -F <file format> ] [ -h ]
12 [ -i <seconds per file> ] [ -o <change offset> ] [ -L ] [ -r ]
13 [ -s <snaplen> ] [ -S <strict time adjustment> ]
14 [ -t <time adjustment> ] [ -T <encapsulation type> ] [ -v ]
15 [ --inject-secrets <secrets type>,<file> ] [ --discard-all-secrets ]
16 infile outfile [ packet#[-packet#] ... ]
17
18 editcap -d | -D <dup window> | -w <dup time window> [ -v ]
19 [ -I <bytes to ignore> ] [ --skip-radiotap-header ] infile outfile
20
21 editcap [ -V ]
22
24 Editcap is a program that reads some or all of the captured packets
25 from the infile, optionally converts them in various ways and writes
26 the resulting packets to the capture outfile (or outfiles).
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28 By default, it reads all packets from the infile and writes them to the
29 outfile in pcapng file format.
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31 An optional list of packet numbers can be specified on the command
32 tail; individual packet numbers separated by whitespace and/or ranges
33 of packet numbers can be specified as start-end, referring to all
34 packets from start to end. By default the selected packets with those
35 numbers will not be written to the capture file. If the -r flag is
36 specified, the whole packet selection is reversed; in that case only
37 the selected packets will be written to the capture file.
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39 Editcap can also be used to remove duplicate packets. Several
40 different options (-d, -D and -w) are used to control the packet window
41 or relative time window to be used for duplicate comparison.
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43 Editcap can be used to assign comment strings to frame numbers.
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45 Editcap is able to detect, read and write the same capture files that
46 are supported by Wireshark. The input file doesn't need a specific
47 filename extension; the file format and an optional gzip compression
48 will be automatically detected. Near the beginning of the DESCRIPTION
49 section of wireshark(1) or
50 <https://www.wireshark.org/docs/man-pages/wireshark.html> is a detailed
51 description of the way Wireshark handles this, which is the same way
52 Editcap handles this.
53
54 Editcap can write the file in several output formats. The -F flag can
55 be used to specify the format in which to write the capture file;
56 editcap -F provides a list of the available output formats.
57
59 -a <framenum:comment>
60 For the specificed frame number, assign the given comment string.
61 Can be repeated for multiple frames. Quotes should be used with
62 comment strings that include spaces.
63
64 -A <start time>
65 Saves only the packets whose timestamp is on or after start time.
66 The time is given in the following format YYYY-MM-DD HH:MM:SS
67
68 -B <stop time>
69 Saves only the packets whose timestamp is before stop time. The
70 time is given in the following format YYYY-MM-DD HH:MM:SS
71
72 -c <packets per file>
73 Splits the packet output to different files based on uniform packet
74 counts with a maximum of <packets per file> each. Each output file
75 will be created with a suffix -nnnnn, starting with 00000. If the
76 specified number of packets is written to the output file, the next
77 output file is opened. The default is to use a single output file.
78
79 -C [offset:]<choplen>
80 Sets the chop length to use when writing the packet data. Each
81 packet is chopped by <choplen> bytes of data. Positive values chop
82 at the packet beginning while negative values chop at the packet
83 end.
84
85 If an optional offset precedes the <choplen>, then the bytes
86 chopped will be offset from that value. Positive offsets are from
87 the packet beginning, while negative offsets are from the packet
88 end.
89
90 This is useful for chopping headers for decapsulation of an entire
91 capture, removing tunneling headers, or in the rare case that the
92 conversion between two file formats leaves some random bytes at the
93 end of each packet. Another use is for removing vlan tags.
94
95 NOTE: This option can be used more than once, effectively allowing
96 you to chop bytes from up to two different areas of a packet in a
97 single pass provided that you specify at least one chop length as a
98 positive value and at least one as a negative value. All positive
99 chop lengths are added together as are all negative chop lengths.
100
101 -d Attempts to remove duplicate packets. The length and MD5 hash of
102 the current packet are compared to the previous four (4) packets.
103 If a match is found, the current packet is skipped. This option is
104 equivalent to using the option -D 5.
105
106 -D <dup window>
107 Attempts to remove duplicate packets. The length and MD5 hash of
108 the current packet are compared to the previous <dup window> - 1
109 packets. If a match is found, the current packet is skipped.
110
111 The use of the option -D 0 combined with the -v option is useful in
112 that each packet's Packet number, Len and MD5 Hash will be printed
113 to standard out. This verbose output (specifically the MD5 hash
114 strings) can be useful in scripts to identify duplicate packets
115 across trace files.
116
117 The <dup window> is specified as an integer value between 0 and
118 1000000 (inclusive).
119
120 NOTE: Specifying large <dup window> values with large tracefiles
121 can result in very long processing times for editcap.
122
123 -E <error probability>
124 Sets the probability that bytes in the output file are randomly
125 changed. Editcap uses that probability (between 0.0 and 1.0
126 inclusive) to apply errors to each data byte in the file. For
127 instance, a probability of 0.02 means that each byte has a 2%
128 chance of having an error.
129
130 This option is meant to be used for fuzz-testing protocol
131 dissectors.
132
133 -F <file format>
134 Sets the file format of the output capture file. Editcap can write
135 the file in several formats, editcap -F provides a list of the
136 available output formats. The default is the pcapng format.
137
138 -h Prints the version and options and exits.
139
140 -i <seconds per file>
141 Splits the packet output to different files based on uniform time
142 intervals using a maximum interval of <seconds per file> each.
143 Floating point values (e.g. 0.5) are allowed. Each output file will
144 be created with a suffix -nnnnn, starting with 00000. If packets
145 for the specified time interval are written to the output file, the
146 next output file is opened. The default is to use a single output
147 file.
148
149 -I <bytes to ignore>
150 Ignore the specified number of bytes at the beginning of the frame
151 during MD5 hash calculation, unless the frame is too short, then
152 the full frame is used. Useful to remove duplicated packets taken
153 on several routers (different mac addresses for example) e.g. -I 26
154 in case of Ether/IP will ignore ether(14) and IP header(20 - 4(src
155 ip) - 4(dst ip)). The default value is 0.
156
157 -L Adjust the original frame length accordingly when chopping and/or
158 snapping (in addition to the captured length, which is always
159 adjusted regardless of whether -L is specified or not). See also
160 -C <choplen> and -s <snaplen>.
161
162 -o <change offset>
163 When used in conjunction with -E, skip some bytes from the
164 beginning of the packet from being changed. In this way some
165 headers don't get changed, and the fuzzer is more focused on a
166 smaller part of the packet. Keeping a part of the packet fixed the
167 same dissector is triggered, that make the fuzzing more precise.
168
169 -r Reverse the packet selection. Causes the packets whose packet
170 numbers are specified on the command line to be written to the
171 output capture file, instead of discarding them.
172
173 -s <snaplen>
174 Sets the snapshot length to use when writing the data. If the -s
175 flag is used to specify a snapshot length, packets in the input
176 file with more captured data than the specified snapshot length
177 will have only the amount of data specified by the snapshot length
178 written to the output file.
179
180 This may be useful if the program that is to read the output file
181 cannot handle packets larger than a certain size (for example, the
182 versions of snoop in Solaris 2.5.1 and Solaris 2.6 appear to reject
183 Ethernet packets larger than the standard Ethernet MTU, making them
184 incapable of handling gigabit Ethernet captures if jumbo packets
185 were used).
186
187 --seed <seed>
188 When used in conjunction with -E, set the seed for the pseudo-
189 random number generator. This is useful for recreating a
190 particular sequence of errors.
191
192 --skip-radiotap-header
193 Skip the readiotap header of each frame when checking for packet
194 duplicates. This is useful when processing a caputure created by
195 combining outputs of multiple capture devices on the same channel
196 in the vicinity of each other.
197
198 -S <strict time adjustment>
199 Time adjust selected packets to ensure strict chronological order.
200
201 The <strict time adjustment> value represents relative seconds
202 specified as [-]seconds[.fractional seconds].
203
204 As the capture file is processed each packet's absolute time is
205 possibly adjusted to be equal to or greater than the previous
206 packet's absolute timestamp depending on the <strict time
207 adjustment> value.
208
209 If <strict time adjustment> value is 0 or greater (e.g. 0.000001)
210 then only packets with a timestamp less than the previous packet
211 will adjusted. The adjusted timestamp value will be set to be
212 equal to the timestamp value of the previous packet plus the value
213 of the <strict time adjustment> value. A <strict time adjustment>
214 value of 0 will adjust the minimum number of timestamp values
215 necessary to ensure that the resulting capture file is in strict
216 chronological order.
217
218 If <strict time adjustment> value is specified as a negative value,
219 then the timestamp values of all packets will be adjusted to be
220 equal to the timestamp value of the previous packet plus the
221 absolute value of the <lt>strict time adjustment<gt> value. A
222 <strict time adjustment> value of -0 will result in all packets
223 having the timestamp value of the first packet.
224
225 This feature is useful when the trace file has an occasional packet
226 with a negative delta time relative to the previous packet.
227
228 -t <time adjustment>
229 Sets the time adjustment to use on selected packets. If the -t
230 flag is used to specify a time adjustment, the specified adjustment
231 will be applied to all selected packets in the capture file. The
232 adjustment is specified as [-]seconds[.fractional seconds]. For
233 example, -t 3600 advances the timestamp on selected packets by one
234 hour while -t -0.5 reduces the timestamp on selected packets by
235 one-half second.
236
237 This feature is useful when synchronizing dumps collected on
238 different machines where the time difference between the two
239 machines is known or can be estimated.
240
241 -T <encapsulation type>
242 Sets the packet encapsulation type of the output capture file. If
243 the -T flag is used to specify an encapsulation type, the
244 encapsulation type of the output capture file will be forced to the
245 specified type. editcap -T provides a list of the available types.
246 The default type is the one appropriate to the encapsulation type
247 of the input capture file.
248
249 Note: this merely forces the encapsulation type of the output file
250 to be the specified type; the packet headers of the packets will
251 not be translated from the encapsulation type of the input capture
252 file to the specified encapsulation type (for example, it will not
253 translate an Ethernet capture to an FDDI capture if an Ethernet
254 capture is read and '-T fddi' is specified). If you need to
255 remove/add headers from/to a packet, you will need
256 od(1)/text2pcap(1).
257
258 -v Causes editcap to print verbose messages while it's working.
259
260 Use of -v with the de-duplication switches of -d, -D or -w will
261 cause all MD5 hashes to be printed whether the packet is skipped or
262 not.
263
264 -V Print the version and exit.
265
266 -w <dup time window>
267 Attempts to remove duplicate packets. The current packet's arrival
268 time is compared with up to 1000000 previous packets. If the
269 packet's relative arrival time is less than or equal to the <dup
270 time window> of a previous packet and the packet length and MD5
271 hash of the current packet are the same then the packet to skipped.
272 The duplicate comparison test stops when the current packet's
273 relative arrival time is greater than <dup time window>.
274
275 The <dup time window> is specified as seconds[.fractional seconds].
276
277 The [.fractional seconds] component can be specified to nine (9)
278 decimal places (billionths of a second) but most typical trace
279 files have resolution to six (6) decimal places (millionths of a
280 second).
281
282 NOTE: Specifying large <dup time window> values with large
283 tracefiles can result in very long processing times for editcap.
284
285 NOTE: The -w option assumes that the packets are in chronological
286 order. If the packets are NOT in chronological order then the -w
287 duplication removal option may not identify some duplicates.
288
289 --inject-secrets <secrets type>,<file>
290 Inserts the contents of <file> into a Decryption Secrets Block
291 (DSB) within the pcapng output file. This enables decryption
292 without requiring additional configuration in protocol preferences.
293
294 The file format is described by <secrets type> which can be one of:
295
296 tls TLS Key Log as described at
297 <https://developer.mozilla.org/NSS_Key_Log_Format> wg WireGuard
298 Key Log, see <https://wiki.wireshark.org/WireGuard#Key_Log_Format>
299
300 This option may be specified multiple times. The available options
301 for <secrets type> can be listed with --inject-secrets help.
302
303 --discard-all-secrets
304 Discard all decryption secrets from the input file when writing the
305 output file. Does not discard secrets added by --inject-secrets in
306 the same command line.
307
309 To see more detailed description of the options use:
310
311 editcap -h
312
313 To shrink the capture file by truncating the packets at 64 bytes and
314 writing it as Sun snoop file use:
315
316 editcap -s 64 -F snoop capture.pcapng shortcapture.snoop
317
318 To delete packet 1000 from the capture file use:
319
320 editcap capture.pcapng sans1000.pcapng 1000
321
322 To limit a capture file to packets from number 200 to 750 (inclusive)
323 use:
324
325 editcap -r capture.pcapng small.pcapng 200-750
326
327 To get all packets from number 1-500 (inclusive) use:
328
329 editcap -r capture.pcapng first500.pcapng 1-500
330
331 or
332
333 editcap capture.pcapng first500.pcapng 501-9999999
334
335 To exclude packets 1, 5, 10 to 20 and 30 to 40 from the new file use:
336
337 editcap capture.pcapng exclude.pcapng 1 5 10-20 30-40
338
339 To select just packets 1, 5, 10 to 20 and 30 to 40 for the new file
340 use:
341
342 editcap -r capture.pcapng select.pcapng 1 5 10-20 30-40
343
344 To remove duplicate packets seen within the prior four frames use:
345
346 editcap -d capture.pcapng dedup.pcapng
347
348 To remove duplicate packets seen within the prior four frames while
349 skipping radiotap headers use:
350
351 editcap -d --skip-radiotap-header capture.pcapng dedup.pcapng
352
353 To remove duplicate packets seen within the prior 100 frames use:
354
355 editcap -D 101 capture.pcapng dedup.pcapng
356
357 To remove duplicate packets seen equal to or less than 1/10th of a
358 second:
359
360 editcap -w 0.1 capture.pcapng dedup.pcapng
361
362 To display the MD5 hash for all of the packets (and NOT generate any
363 real output file):
364
365 editcap -v -D 0 capture.pcapng /dev/null
366
367 or on Windows systems
368
369 editcap -v -D 0 capture.pcapng NUL
370
371 To advance the timestamps of each packet forward by 3.0827 seconds:
372
373 editcap -t 3.0827 capture.pcapng adjusted.pcapng
374
375 To ensure all timestamps are in strict chronological order:
376
377 editcap -S 0 capture.pcapng adjusted.pcapng
378
379 To introduce 5% random errors in a capture file use:
380
381 editcap -E 0.05 capture.pcapng capture_error.pcapng
382
383 To remove vlan tags from all packets within an Ethernet-encapsulated
384 capture file, use:
385
386 editcap -L -C 12:4 capture_vlan.pcapng capture_no_vlan.pcapng
387
388 To chop both the 10 byte and 20 byte regions from the following 75 byte
389 packet in a single pass, use any of the 8 possible methods provided
390 below:
391
392 <--------------------------- 75 ---------------------------->
393
394 +---+-------+-----------+---------------+-------------------+
395 | 5 | 10 | 15 | 20 | 25 |
396 +---+-------+-----------+---------------+-------------------+
397
398 1) editcap -C 5:10 -C -25:-20 capture.pcapng chopped.pcapng
399 2) editcap -C 5:10 -C 50:-20 capture.pcapng chopped.pcapng
400 3) editcap -C -70:10 -C -25:-20 capture.pcapng chopped.pcapng
401 4) editcap -C -70:10 -C 50:-20 capture.pcapng chopped.pcapng
402 5) editcap -C 30:20 -C -60:-10 capture.pcapng chopped.pcapng
403 6) editcap -C 30:20 -C 15:-10 capture.pcapng chopped.pcapng
404 7) editcap -C -45:20 -C -60:-10 capture.pcapng chopped.pcapng
405 8) editcap -C -45:20 -C 15:-10 capture.pcapng chopped.pcapng
406
407 To add comment strings to the first 2 input frames, use:
408
409 editcap -a "1:1st frame" -a 2:Second capture.pcapng capture-comments.pcapng
410
412 pcap(3), wireshark(1), tshark(1), mergecap(1), dumpcap(1), capinfos(1),
413 text2pcap(1), od(1), pcap-filter(7) or tcpdump(8)
414
416 Editcap is part of the Wireshark distribution. The latest version of
417 Wireshark can be found at <https://www.wireshark.org>.
418
419 HTML versions of the Wireshark project man pages are available at:
420 <https://www.wireshark.org/docs/man-pages>.
421
423 Original Author
424 -------- ------
425 Richard Sharpe <sharpe[AT]ns.aus.com>
426
427
428 Contributors
429 ------------
430 Guy Harris <guy[AT]alum.mit.edu>
431 Ulf Lamping <ulf.lamping[AT]web.de>
432
433
434
4353.2.3 2020-04-13 EDITCAP(1)