Provided by: wireshark-common_3.2.3-1_amd64 
NAME
mergecap - Merges two or more capture files into one
SYNOPSIS
mergecap [ -a ] [ -F <file format> ] [ -h ] [ -I <IDB merge mode> ] [ -s <snaplen> ] [ -v ] [ -V ]
-w <outfile>|- <infile> [<infile> ...]
DESCRIPTION
Mergecap is a program that combines multiple saved capture files into a single output file specified by
the -w argument. Mergecap knows how to read pcap and pcapng capture files, including those of tcpdump,
Wireshark and other tools that write captures in those formats.
By default, Mergecap writes the capture file in pcapng format, and writes all of the packets from the
input capture files to the output file.
Mergecap is able to detect, read and write the same capture files that are supported by Wireshark. The
input files don'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 Mergecap handles this.
Mergecap 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, mergecap -F provides a list of the available output formats.
Packets from the input files are merged in chronological order based on each frame's timestamp, unless
the -a flag is specified. Mergecap assumes that frames within a single capture file are already stored
in chronological order. When the -a flag is specified, packets are copied directly from each input file
to the output file, independent of each frame's timestamp.
The output file frame encapsulation type is set to the type of the input files if all input files have
the same type. If not all of the input files have the same frame encapsulation type, the output file
type is set to WTAP_ENCAP_PER_PACKET. Note that some capture file formats, most notably pcap, do not
currently support WTAP_ENCAP_PER_PACKET. This combination will cause the output file creation to fail.
OPTIONS
-a Causes the frame timestamps to be ignored, writing all packets from the first input file followed by
all packets from the second input file. By default, when -a is not specified, the contents of the
input files are merged in chronological order based on each frame's timestamp.
Note: when merging, mergecap assumes that packets within a capture file are already in chronological
order.
-F <file format>
Sets the file format of the output capture file. Mergecap can write the file in several formats;
mergecap -F provides a list of the available output formats. By default this is the pcapng format.
-h Prints the version and options and exits.
-I <IDB merge mode>
Sets the Interface Description Block (IDB) merge mode to use during merging. mergecap -I provides a
list of the available IDB merge modes.
Every input file has one or more IDBs, which describe the interface(s) the capture was performed on
originally. This includes encapsulation type, interface name, etc. When mergecap merges multiple
input files, it has to merge these IDBs somehow for the new merged output file. This flag controls
how that is accomplished. The currently available modes are:
* 'B<none>': no merging of IDBs is performed, and instead all IDBs are
copied to the merged output file.
* 'B<all>': IDBs are merged only if all input files have the same number
of IDBs, and each IDB matches their respective entry in the
other files. This is the default mode.
* 'B<any>': Any and all duplicate IDBs are merged into one IDB, regardless
of what file they are in.
Note that an IDB is only considered a matching duplicate if it has the same encapsulation type, name,
speed, time precision, comments, description, etc.
-s <snaplen>
Sets the snapshot length to use when writing the data. If the -s flag is used to specify a snapshot
length, frames 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
frames larger than the standard Ethernet MTU, making them incapable of handling gigabit Ethernet
captures if jumbo frames were used).
-v Causes mergecap to print a number of messages while it's working.
-V Print the version and exit.
-w <outfile>|-
Sets the output filename. If the name is '-', stdout will be used. This setting is mandatory.
EXAMPLES
To merge two capture files together, 100 seconds apart use:
capinfos -aeS a.pcap b.pcap
(Let's suppose a.pcap starts at 1009932757 and b.pcap ends at 873660281. 1009932757 - 873660281 - 100 =
136272376 seconds.)
editcap -t 136272376 b.pcap b-shifted.pcap
mergecap -w compare.pcap a.pcap b-shifted.pcap
SEE ALSO
pcap(3), wireshark(1), tshark(1), dumpcap(1), editcap(1), text2pcap(1), pcap-filter(7) or tcpdump(8)
NOTES
Mergecap is based heavily upon editcap by Richard Sharpe <sharpe[AT]ns.aus.com> and Guy Harris
<guy[AT]alum.mit.edu>.
Mergecap 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
-------- ------
Scott Renfro <scott[AT]renfro.org>
Contributors
------------
Bill Guyton <guyton[AT]bguyton.com>