editcap -d | -D <dup window> | -w <dup time window> [ -v ] [ -I <bytes to ignore> ] [ --skip-radiotap-header ] infile outfile
By default, it reads all packets from the infile and writes them to the outfile in pcapng file format.
An optional list of packet numbers can be specified on the command tail; individual packet numbers separated by whitespace and/or ranges of packet numbers can be specified as start-end, referring to all packets from start to end. By default the selected packets with those numbers will not be written to the capture file. If the -r flag is specified, the whole packet selection is reversed; in that case only the selected packets will be written to the capture file.
Editcap can also be used to remove duplicate packets. Several different options (-d, -D and -w) are used to control the packet window or relative time window to be used for duplicate comparison.
Editcap can be used to assign comment strings to frame numbers.
Editcap is able to detect, read and write the same capture files that are supported by Wireshark. The input file doesn't need a specific filename extension; the file format and an optional gzip compression will be automatically detected. Near the beginning of the DESCRIPTION section of wireshark(1) or <https://www.wireshark.org/docs/man-pages/wireshark.html> is a detailed description of the way Wireshark handles this, which is the same way Editcap handles this.
Editcap can write the file in several output formats. The -F flag can be used to specify the format in which to write the capture file; editcap -F provides a list of the available output formats.
If an optional offset precedes the <choplen>, then the bytes chopped will be offset from that value. Positive offsets are from the packet beginning, while negative offsets are from the packet end.
This is useful for chopping headers for decapsulation of an entire capture, removing tunneling headers, or in the rare case that the conversion between two file formats leaves some random bytes at the end of each packet. Another use is for removing vlan tags.
NOTE: This option can be used more than once, effectively allowing you to chop bytes from up to two different areas of a packet in a single pass provided that you specify at least one chop length as a positive value and at least one as a negative value. All positive chop lengths are added together as are all negative chop lengths.
The use of the option -D 0 combined with the -v option is useful in that each packet's Packet number, Len and MD5 Hash will be printed to standard out. This verbose output (specifically the MD5 hash strings) can be useful in scripts to identify duplicate packets across trace files.
The <dup window> is specified as an integer value between 0 and 1000000 (inclusive).
NOTE: Specifying large <dup window> values with large tracefiles can result in very long processing times for editcap.
This option is meant to be used for fuzz-testing protocol dissectors.
This may be useful if the program that is to read the output file cannot handle packets larger than a certain size (for example, the versions of snoop in Solaris 2.5.1 and Solaris 2.6 appear to reject Ethernet packets larger than the standard Ethernet MTU, making them incapable of handling gigabit Ethernet captures if jumbo packets were used).
The <strict time adjustment> value represents relative seconds specified as [-]seconds[.fractional seconds].
As the capture file is processed each packet's absolute time is possibly adjusted to be equal to or greater than the previous packet's absolute timestamp depending on the <strict time adjustment> value.
If <strict time adjustment> value is 0 or greater (e.g. 0.000001) then only packets with a timestamp less than the previous packet will adjusted. The adjusted timestamp value will be set to be equal to the timestamp value of the previous packet plus the value of the <strict time adjustment> value. A <strict time adjustment> value of 0 will adjust the minimum number of timestamp values necessary to ensure that the resulting capture file is in strict chronological order.
If <strict time adjustment> value is specified as a negative value, then the timestamp values of all packets will be adjusted to be equal to the timestamp value of the previous packet plus the absolute value of the <lt>strict time adjustment<gt> value. A <strict time adjustment> value of -0 will result in all packets having the timestamp value of the first packet.
This feature is useful when the trace file has an occasional packet with a negative delta time relative to the previous packet.
This feature is useful when synchronizing dumps collected on different machines where the time difference between the two machines is known or can be estimated.
Note: this merely forces the encapsulation type of the output file to be the specified type; the packet headers of the packets will not be translated from the encapsulation type of the input capture file to the specified encapsulation type (for example, it will not translate an Ethernet capture to an FDDI capture if an Ethernet capture is read and '-T fddi' is specified). If you need to remove/add headers from/to a packet, you will need od(1)/text2pcap(1).
Use of -v with the de-duplication switches of -d, -D or -w will cause all MD5 hashes to be printed whether the packet is skipped or not.
The <dup time window> is specified as seconds[.fractional seconds].
The [.fractional seconds] component can be specified to nine (9) decimal places (billionths of a second) but most typical trace files have resolution to six (6) decimal places (millionths of a second).
NOTE: Specifying large <dup time window> values with large tracefiles can result in very long processing times for editcap.
NOTE: The -w option assumes that the packets are in chronological order. If the packets are NOT in chronological order then the -w duplication removal option may not identify some duplicates.
The file format is described by <secrets type> which can be one of:
tls TLS Key Log as described at <https://developer.mozilla.org/NSS_Key_Log_Format> wg WireGuard Key Log, see <https://gitlab.com/wireshark/wireshark/-/wikis/WireGuard#key-log-format>
This option may be specified multiple times. The available options for <secrets type> can be listed with --inject-secrets help.
This option may be specified multiple times. Note that Wireshark currently only recognizes the first comment of a capture file.
editcap -h
To shrink the capture file by truncating the packets at 64 bytes and writing it as Sun snoop file use:
editcap -s 64 -F snoop capture.pcapng shortcapture.snoop
To delete packet 1000 from the capture file use:
editcap capture.pcapng sans1000.pcapng 1000
To limit a capture file to packets from number 200 to 750 (inclusive) use:
editcap -r capture.pcapng small.pcapng 200-750
To get all packets from number 1-500 (inclusive) use:
editcap -r capture.pcapng first500.pcapng 1-500
or
editcap capture.pcapng first500.pcapng 501-9999999
To exclude packets 1, 5, 10 to 20 and 30 to 40 from the new file use:
editcap capture.pcapng exclude.pcapng 1 5 10-20 30-40
To select just packets 1, 5, 10 to 20 and 30 to 40 for the new file use:
editcap -r capture.pcapng select.pcapng 1 5 10-20 30-40
To remove duplicate packets seen within the prior four frames use:
editcap -d capture.pcapng dedup.pcapng
To remove duplicate packets seen within the prior four frames while skipping radiotap headers use:
editcap -d --skip-radiotap-header capture.pcapng dedup.pcapng
To remove duplicate packets seen within the prior 100 frames use:
editcap -D 101 capture.pcapng dedup.pcapng
To remove duplicate packets seen equal to or less than 1/10th of a second:
editcap -w 0.1 capture.pcapng dedup.pcapng
To display the MD5 hash for all of the packets (and NOT generate any real output file):
editcap -v -D 0 capture.pcapng /dev/null
or on Windows systems
editcap -v -D 0 capture.pcapng NUL
To advance the timestamps of each packet forward by 3.0827 seconds:
editcap -t 3.0827 capture.pcapng adjusted.pcapng
To ensure all timestamps are in strict chronological order:
editcap -S 0 capture.pcapng adjusted.pcapng
To introduce 5% random errors in a capture file use:
editcap -E 0.05 capture.pcapng capture_error.pcapng
To remove vlan tags from all packets within an Ethernet-encapsulated capture file, use:
editcap -L -C 12:4 capture_vlan.pcapng capture_no_vlan.pcapng
To chop both the 10 byte and 20 byte regions from the following 75 byte packet in a single pass, use any of the 8 possible methods provided below:
<--------------------------- 75 ---------------------------->
+---+-------+-----------+---------------+-------------------+
| 5 | 10 | 15 | 20 | 25 |
+---+-------+-----------+---------------+-------------------+
1) editcap -C 5:10 -C -25:-20 capture.pcapng chopped.pcapng
2) editcap -C 5:10 -C 50:-20 capture.pcapng chopped.pcapng
3) editcap -C -70:10 -C -25:-20 capture.pcapng chopped.pcapng
4) editcap -C -70:10 -C 50:-20 capture.pcapng chopped.pcapng
5) editcap -C 30:20 -C -60:-10 capture.pcapng chopped.pcapng
6) editcap -C 30:20 -C 15:-10 capture.pcapng chopped.pcapng
7) editcap -C -45:20 -C -60:-10 capture.pcapng chopped.pcapng
8) editcap -C -45:20 -C 15:-10 capture.pcapng chopped.pcapng
To add comment strings to the first 2 input frames, use:
editcap -a "1:1st frame" -a 2:Second capture.pcapng capture-comments.pcapng
HTML versions of the Wireshark project man pages are available at: <https://www.wireshark.org/docs/man-pages>.
Original Author -------- ------ Richard Sharpe <sharpe[AT]ns.aus.com> Contributors ------------ Guy Harris <guy[AT]alum.mit.edu> Ulf Lamping <ulf.lamping[AT]web.de>