editcap - Edit and/or translate the format of capture files
<start time> ] [
<stop time> ] [
<packets per file> ] [
[offset:]<choplen> ] [
<error probability> ] [
<file format> ] [
<seconds per file> ] [
<change offset> ] [
] [ -r
<snaplen> ] [
<strict time adjustment> ]
<time adjustment> ] [
<encapsulation type> ] [
] infile outfile
] ... ]
<dup window> |
<dup time window> [
<bytes to ignore> ] infile
is a program that reads some or all of the captured packets from
, optionally converts them in various ways and writes the
resulting packets to the capture outfile
By default, it reads all packets from the infile
and writes them to the
in pcap 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
, referring to all packets
. By default the selected packets with those
numbers will not
be written to the capture file. If the -r
is specified, the whole packet selection is reversed; in that case only
the selected packets will be written to the capture file.
can also be used to remove duplicate packets. Several different
options ( -d
) are used to control the packet
window or relative time window to be used for duplicate comparison.
can be used to assign comment strings to frame numbers.
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
<https://www.wireshark.org/docs/man-pages/wireshark.html> is a detailed
description of the way Wireshark
handles this, which is the same way
can write the file in several output formats. The -F
can be used to specify the format in which to write the capture file;
provides a list of the available output formats.
- -a <framenum:comment>
- For the specificed 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>
- Saves only the packets whose timestamp is on or after start time. The time
is given in the following format YYYY-MM-DD HH:MM:SS
- -B <stop time>
- Saves only the packets whose timestamp is before stop time. The time is
given in the following format YYYY-MM-DD HH:MM:SS
- -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 a suffix -nnnnn, starting with 00000. If 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.
- -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.
- 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 out. This verbose output (specifically the MD5 hash
strings) can be useful in scripts to identify duplicate packets across
The <dup window> is specified as an integer value between 0 and
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 pcap format.
- Prints the version and options and exits.
- -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. Each
output file will be created with a suffix -nnnnn, starting with 00000. If
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
- -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.
- 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.
- 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
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).
- -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
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.
- -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
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
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).
- 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.
- Print the version and exit.
- -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
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.
To see more detailed description of the options use:
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.pcap shortcapture.snoop
To delete packet 1000 from the capture file use:
editcap capture.pcap sans1000.pcap 1000
To limit a capture file to packets from number 200 to 750 (inclusive) use:
editcap -r capture.pcap small.pcap 200-750
To get all packets from number 1-500 (inclusive) use:
editcap -r capture.pcap first500.pcap 1-500
editcap capture.pcap first500.pcap 501-9999999
To exclude packets 1, 5, 10 to 20 and 30 to 40 from the new file use:
editcap capture.pcap exclude.pcap 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.pcap select.pcap 1 5 10-20 30-40
To remove duplicate packets seen within the prior four frames use:
editcap -d capture.pcap dedup.pcap
To remove duplicate packets seen within the prior 100 frames use:
editcap -D 101 capture.pcap dedup.pcap
To remove duplicate packets seen equal to or less than
1/10th of a
editcap -w 0.1 capture.pcap dedup.pcap
To display the MD5 hash for all of the packets (and NOT generate any real output
editcap -v -D 0 capture.pcap /dev/null
or on Windows systems
editcap -v -D 0 capture.pcap NUL
To advance the timestamps of each packet forward by 3.0827 seconds:
editcap -t 3.0827 capture.pcap adjusted.pcap
To ensure all timestamps are in strict chronological order:
editcap -S 0 capture.pcap adjusted.pcap
To introduce 5% random errors in a capture file use:
editcap -E 0.05 capture.pcap capture_error.pcap
To remove vlan tags from all packets within an Ethernet-encapsulated capture
editcap -L -C 12:4 capture_vlan.pcap capture_no_vlan.pcap
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.pcap chopped.pcap
2) editcap -C 5:10 -C 50:-20 capture.pcap chopped.pcap
3) editcap -C -70:10 -C -25:-20 capture.pcap chopped.pcap
4) editcap -C -70:10 -C 50:-20 capture.pcap chopped.pcap
5) editcap -C 30:20 -C -60:-10 capture.pcap chopped.pcap
6) editcap -C 30:20 -C 15:-10 capture.pcap chopped.pcap
7) editcap -C -45:20 -C -60:-10 capture.pcap chopped.pcap
8) editcap -C -45:20 -C 15:-10 capture.pcap chopped.pcap
To add comment strings to the first 2 input frames, use:
editcap -a "1:1st frame" -a 2:Second capture.pcap capture-comments.pcap
(7) or tcpdump
is part of the Wireshark
distribution. The latest version
can be found at <https://www.wireshark.org>.
HTML versions of the Wireshark project man pages are available at:
Richard Sharpe <sharpe[AT]ns.aus.com>
Guy Harris <guy[AT]alum.mit.edu>
Ulf Lamping <ulf.lamping[AT]web.de>