EDITCAP(1) EDITCAP(1)
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]
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.
-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
SEE ALSO
pcap(3), wireshark(1), tshark(1), mergecap(1), dumpcap(1), capinfos(1),
text2pcap(1), reordercap(1), od(1), pcap-filter(7) or tcpdump(8)
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)
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