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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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NAME | SYNOPSIS | DESCRIPTION | OPTIONS | DIAGNOSTIC OPTIONS | EXAMPLES | SEE ALSO | NOTES | AUTHORS |
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EDITCAP(1) EDITCAP(1)
editcap - Edit and/or translate the format of capture files
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 ] [ -R <frame:timestamp> ] [
-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 ] [ --preserve-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
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.
-a <framenum:comment>
For the specified frame number, assign the given comment
string. Can be repeated for multiple frames. Only the last
comment string for each unique frame number specified in the
command line will be saved. Quotes should be used with comment
strings that include spaces.
By default the -a option will replace any and all packet
comments for the given frame number. Add the
--preserve-packet-comment option to the command line to
preserve any pre-existing packet comments.
-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]
or
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]
or
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.
-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.
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 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.
-R <framenum:timestamp>
For the specified frame number, assign the given timestamp.
Can be repeated for multiple frames.
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]
or
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.
-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.
This option takes precedence over the
--preserve-packet-comments option.
--preserve-packet-comments
When adding a new packet comment with the -a option preserve
from the input file any packet comments for the specified
frame when writing the output file. Without this option, any
-a options will replace any and all pre-existing packet
comments for the given frame number.
This option does not allow for the -a option to add multiple
packet comments for same frame number in the same command
line`.
The --discard-packet-comments option takes precedence over
this option.
--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.
--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.
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
To add an additional comment to the first frame, use:
editcap --preserve-packet-comments -a "1:This is another comment" \
capture-comments.pcapng more-capture-comments.pcapng
pcap(3), wireshark(1), tshark(1), mergecap(1), dumpcap(1),
capinfos(1), text2pcap(1), reordercap(1), od(1), pcap-filter(7) or
tcpdump(8)
This is the manual page for Editcap 4.5.0. 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.
Original Author
Richard Sharpe <sharpe[AT]ns.aus.com>
Contributors
Guy Harris <guy[AT]alum.mit.edu>
Ulf Lamping <ulf.lamping[AT]web.de>.SH COLOPHON This page is part
of the wireshark (Interactively dump and analyze network traffic)
project. Information about the project can be found at
⟨https://www.wireshark.org/⟩. If you have a bug report for this
manual page, see
⟨https://gitlab.com/wireshark/wireshark/-/issues⟩. This page was
obtained from the project's upstream Git repository
⟨https://gitlab.com/wireshark/wireshark.git⟩ on 2025-08-11. (At
that time, the date of the most recent commit that was found in
the repository was 2025-08-11.) If you discover any rendering
problems in this HTML version of the page, or you believe there is
a better or more up-to-date source for the page, or you have
corrections or improvements to the information in this COLOPHON
(which is not part of the original manual page), send a mail to
[email protected]
2025-04-29 EDITCAP(1)
Pages that refer to this page: capinfos(1), captype(1), dumpcap(1), mergecap(1), rawshark(1), reordercap(1), stratoshark(1), text2pcap(1), tshark(1), wireshark(1), wireshark-filter(4)
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