Ubuntu Manpage: editcap - Edit and/or translate the format of capture files

Provided by: wireshark-common_4.4.7-1_amd64

NAME

       editcap - Edit and/or translate the format of capture files

SYNOPSIS

       editcap [ -a <frame:comment> ] [ -A <start time> ] [ -B <stop time> ] [ -c <packets per file> ]
       [ -C [offset:]<choplen> ] [ -E <error probability> ] [ -F <file format> ] [ -i <seconds per file> ]
       [ -o <change offset> ] [ -L ] [ -r ] [ -s <snaplen> ] [ -S <strict time adjustment> ]
       [ -t <time adjustment> ] [ -T <encapsulation type> ] [ -V ] [ --inject-secrets <secrets type>,<file> ]
       [ --discard-all-secrets ] [ --capture-comment <comment> ] [ --discard-capture-comment ]
       [ --discard-packet-comments ] infile outfile [ packet#[-packet#] ... ]

       editcap -d -D <dup window> -w <dup time window> [ -V ] [ -I <bytes to ignore> ]
       [ --skip-radiotap-header ] [ --set-unused ] infile outfile

       editcap --extract-secrets [ -V ] infile outfile

       editcap -h|--help

       editcap -v|--version

DESCRIPTION

Editcap is a program that reads some or all of the captured packets from the infile, optionally converts
them in various ways and writes the resulting packets to the capture outfile (or outfiles).

By default, it reads all packets from the infile and writes them to the outfile in pcapng file format.
Use '-' for infile or outfile to read from standard input or write to standard output, respectively.

The -A and -B option allow you to limit the time range from which packets are read from the infile.

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, zstd or lz4
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. Editcap can
also compress the output file. The --compress option can specify the compression type. If that option is
not given, then the desired compression method, if any, is deduced from the extension of outfile; e.g.,
if the output filename has the .gz extension, then the gzip format is used.

Editcap can also be used to extract embedded decryption secrets from file formats like pcapng that
contain them, in lieu of writing a capture file.

OPTIONS

-a <framenum:comment>

For the specified frame number, assign the given comment string. Can be repeated for multiple frames.
Quotes should be used with comment strings that include spaces.

-A <start time>

Reads only the packets whose timestamp is on or after <start time>. The time may be given either in
ISO 8601 format or in Unix epoch timestamp format.

ISO 8601 format is either

YYYY-MM-DD HH:MM:SS[.nnnnnnnnn][Z|±hh:mm]

YYYY-MM-DDTHH:MM:SS[.nnnnnnnnn][Z|±hh:mm]

The fractional seconds are optional, as is the time zone offset from UTC (in which case local time is
assumed).

Unix epoch format is in seconds since the Unix epoch and nanoseconds, with either a period or a comma
separating the seconds and nanoseconds. The nanoseconds are optional. The Unix epoch is 1970-01-01
00:00:00 UTC, so this format is not local time.

-B <stop time>

Reads only the packets whose timestamp is before <stop time>. The time may be given either in ISO
8601 format or in Unix epoch timestamp format.

ISO 8601 format is either

YYYY-MM-DD HH:MM:SS[.nnnnnnnnn][Z|±hh:mm]

YYYY-MM-DDTHH:MM:SS[.nnnnnnnnn][Z|±hh:mm]

The fractional seconds are optional, as is the time zone offset from UTC (in which case local time is
assumed).

-c <packets per file>

Splits the packet output to different files based on uniform packet counts with a maximum of <packets
per file> each.

Each output file will be created with an infix _nnnnn[_YYYYmmddHHMMSS] inserted before the file
extension (which may be null) of outfile. The infix consists of the ordinal number of the output
file, starting with 00000, followed by the timestamp of its first packet. The timestamp is omitted if
the input file does not contain timestamp information.

After the specified number of packets is written to the output file, the next output file is opened.
The default is to use a single output file. This option conflicts with -i.

-C [offset:]<choplen>

Sets the chop length to use when writing the packet data. Each packet is chopped by <choplen> bytes
of data. Positive values chop at the packet beginning while negative values chop at the packet end.

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.

-d

Attempts to remove duplicate packets. The length and MD5 hash of the current packet are compared to
the previous four (4) packets. If a match is found, the current packet is skipped. This option is
equivalent to using the option -D 5.

-D <dup window>

Attempts to remove duplicate packets. The length and MD5 hash of the current packet are compared to
the previous <dup window> - 1 packets. If a match is found, the current packet is skipped.

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 error. 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.

-E <error probability>

Sets the probability that bytes in the output file are randomly changed. Editcap uses that
probability (between 0.0 and 1.0 inclusive) to apply errors to each data byte in the file. For
instance, a probability of 0.02 means that each byte has a 2% chance of having an error.

This option is meant to be used for fuzz-testing protocol dissectors.

-F <file format>

Sets the file format of the output capture file. Editcap can write the file in several formats,
editcap -F provides a list of the available output formats. The default is the pcapng format.

-h|--help
Print the version number and options and exit.

-i <seconds per file>

Splits the packet output to different files based on uniform time intervals using a maximum interval
of <seconds per file> each. Floating point values (e.g. 0.5) are allowed.

After packets for the specified time interval are written to the output file, the next output file is
opened. The default is to use a single output file. This option conflicts with -c.

-I <bytes to ignore>

Ignore the specified number of bytes at the beginning of the frame during MD5 hash calculation,
unless the frame is too short, then the full frame is used. Useful to remove duplicated packets taken
on several routers (different mac addresses for example) e.g. -I 26 in case of Ether/IP will ignore
ether(14) and IP header(20 - 4(src ip) - 4(dst ip)). The default value is 0.

-L

Adjust the original frame length accordingly when chopping and/or snapping (in addition to the
captured length, which is always adjusted regardless of whether -L is specified or not). See also -C
<choplen> and -s <snaplen>.

-o <change offset>

When used in conjunction with -E, skip some bytes from the beginning of the packet from being
changed. In this way some headers don’t get changed, and the fuzzer is more focused on a smaller part
of the packet. Keeping a part of the packet fixed the same dissector is triggered, that make the
fuzzing more precise.

-r

Reverse the packet selection. Causes the packets whose packet numbers are specified on the command
line to be written to the output capture file, instead of discarding them.

-s <snaplen>

Sets the snapshot length to use when writing the data. If the -s flag is used to specify a snapshot
length, packets in the input file with more captured data than the specified snapshot length will
have only the amount of data specified by the snapshot length written to the output file.

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).

--seed <seed>

When used in conjunction with -E, set the seed for the pseudo-random number generator. This is useful
for recreating a particular sequence of errors.

--skip-radiotap-header

Skip the radiotap header of each frame when checking for packet duplicates. This is useful when
processing a capture created by combining outputs of multiple capture devices on the same channel in
the vicinity of each other.

-S <strict time adjustment>

Time adjust selected packets to ensure strict chronological order.

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 <strict time adjustment> 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.

-t <time adjustment>

Sets the time adjustment to use on selected packets. If the -t flag is used to specify a time
adjustment, the specified adjustment will be applied to all selected packets in the capture file. The
adjustment is specified as seconds[.fractional seconds]. For example, -t 3600 advances the timestamp
on selected packets by one hour while -t -0.5 reduces the timestamp on selected packets by one-half
second.

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.

-T <encapsulation type>

Sets the packet encapsulation type of the output capture file. If the -T flag is used to specify an
encapsulation type, the encapsulation type of the output capture file will be forced to the specified
type. editcap -T provides a list of the available types. The default type is the one appropriate to
the encapsulation type of the input capture file.

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).

-v|--version
Print the full version information and exit.

-V

Causes editcap to print verbose messages while it’s working.

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.

-w <dup time window>

Attempts to remove duplicate packets. The current packet’s arrival time is compared with up to
1000000 previous packets. If the packet’s relative arrival time is less than or equal to the <dup
time window> of a previous packet and the packet length and MD5 hash of the current packet are the
same then the packet to skipped. The duplicate comparison test stops when the current packet’s
relative arrival time is greater than <dup time window>.

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.

--inject-secrets <secrets type>,<file>

Inserts the contents of <file> into a Decryption Secrets Block (DSB) within the pcapng output file.
This enables decryption without requiring additional configuration in protocol preferences.

The file format is described by <secrets type> which can be one of:

opcua OPC UA Key Log, see
https://ietf-opsawg-wg.github.io/draft-ietf-opsawg-pcap/draft-ietf-opsawg-pcapng.html#name-decryption-secrets-block
ssh SSH Key Log, see https://wiki.wireshark.org/SSH#key-log-format
tls TLS Key Log, see https://tlswg.org/sslkeylogfile/draft-ietf-tls-keylogfile.html
wg WireGuard Key Log, see https://wiki.wireshark.org/WireGuard#key-log-format

This option may be specified multiple times. The available options for <secrets type> can be listed
with --inject-secrets help.

--extract-secrets

Extracts each Decryption Secrets Block (DSB) contained within infile. If there is only one, it is
written to outfile instead of a capture file. If there is more than one, they are each written to
unique output files named with an infix _nnnnn before the file extension of outfile in a manner
similar to the -c flag (unless writing to standard output.)

Incompatible with other options except for -V.

--discard-all-secrets

Discard all decryption secrets from the input file when writing the output file. Does not discard
secrets added by --inject-secrets in the same command line.

--capture-comment <comment>

Adds the given comment to the output file, if supported by the output file format. New comments will
be added after any comments present in the input file unless --discard-capture-comment is also
specified.

This option may be specified multiple times. Note that Wireshark currently only displays the first
comment of a capture file.

--discard-capture-comment

Discard all capture file comments from the input file when writing the output file. Does not discard
comments added by --capture-comment in the same command line.

--set-unused

Set the unused bytes (if any) to zero in SLL link type. Useful when when checking for duplicates. As
the unused bytes can be anything. When the packet traverses the device stack for bonded interfaces on
Linux for example.

--discard-packet-comments

Discard all packet comments from the input file when writing the output file. Does not discard
comments added by -a in the same command line.

--compress <type>

Compress the output file using the type compression format. --compress with no argument provides a
list of the compression formats supported for writing. The type given takes precedence over the
extension of outfile.

DIAGNOSTIC OPTIONS

--log-level <level>
Set the active log level. Supported levels in lowest to highest order are "noisy", "debug", "info",
"message", "warning", "critical", and "error". Messages at each level and higher will be printed, for
example "warning" prints "warning", "critical", and "error" messages and "noisy" prints all messages.
Levels are case insensitive.

--log-fatal <level>
Abort the program if any messages are logged at the specified level or higher. For example, "warning"
aborts on any "warning", "critical", or "error" messages.

--log-domains <list>
Only print messages for the specified log domains, e.g. "GUI,Epan,sshdump". List of domains must be
comma-separated. Can be negated with "!" as the first character (inverts the match).

--log-debug <list>
Force the specified domains to log at the "debug" level. List of domains must be comma-separated. Can
be negated with "!" as the first character (inverts the match).

--log-noisy <list>
Force the specified domains to log at the "noisy" level. List of domains must be comma-separated. Can
be negated with "!" as the first character (inverts the match).

--log-fatal-domains <list>
Abort the program if any messages are logged for the specified log domains. List of domains must be
comma-separated.

--log-file <path>
Write log messages and stderr output to the specified file.

EXAMPLES

       To see more detailed description of the options use:

           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

NOTES

       This is the manual page for Editcap 4.4.7. Editcap is part of the Wireshark distribution. The latest
       version of Wireshark can be found at https://www.wireshark.org.

       HTML versions of the Wireshark project man pages are available at
       https://www.wireshark.org/docs/man-pages.

AUTHORS

       Original Author
       Richard Sharpe <sharpe[AT]ns.aus.com>

       Contributors
       Guy Harris <guy[AT]alum.mit.edu>
       Ulf Lamping <ulf.lamping[AT]web.de>

                                                   2025-06-10                                         EDITCAP(1)

NAME

SYNOPSIS

DESCRIPTION

OPTIONS

DIAGNOSTIC OPTIONS

EXAMPLES

SEE ALSO

NOTES

AUTHORS