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NAMEmergecap - Merges two or more capture files into one
SYNOPSISmergecap [ -a ] [ -F <file format> ] [ -h ] [ -I <
DESCRIPTIONMergecap 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 capture files, including those of tcpdump, Wireshark, and other tools that write captures in that format.
By default, Mergecap writes the capture file in pcap 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
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
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. The default is to use the file format of the first input file.
- Prints the version and options and exits.
- -I <IDBmerge mode>
Sets the Interface Description Block (IDB) merge mode to use during merging. mergecap -I provides a list of the availableIDBmerge 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 anIDBis 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).
- Causes mergecap to print a number of messages while it's working.
- Print the version and exit.
- -w <outfile>|-
- Sets the output filename. If the name is '-', stdout will be used. This setting is mandatory.
EXAMPLESTo 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 ALSOpcap(3), wireshark(1), tshark(1), dumpcap(1), editcap(1), text2pcap(1), pcap-filter(7) or tcpdump(8)
NOTESMergecap is based heavily upon editcap by Richard Sharpe <sharpe[
Mergecap is part of the Wireshark distribution. The latest version of Wireshark can be found at <www.wireshark.org>.
Original Author -------- ------ Scott Renfro <scott[AT]renfro.org> Contributors ------------ Bill Guyton <guyton[AT]bguyton.com>