1MERGECAP(1) The Wireshark Network Analyzer MERGECAP(1)
2
6 mergecap - Merges two or more capture files into one
7
9 mergecap [ -a ] [ -F <file format> ] [ -h ] [ -s <snaplen> ]
10 [ -T <encapsulation type> ] [ -v ] -w <outfile>|- <infile> [<infile>
11 ...]
12
14 Mergecap is a program that combines multiple saved capture files into a
15 single output file specified by the -w argument. Mergecap knows how to
16 read pcap capture files, including those of tcpdump, Wireshark, and
17 other tools that write captures in that format.
18 By default, Mergecap writes the capture file in pcap format, and writes
20 all of the packets from the input capture files to the output file.
21 Mergecap is able to detect, read and write the same capture files that
23 are supported by Wireshark. The input files don't need a specific
24 filename extension; the file format and an optional gzip compression
25 will be automatically detected. Near the beginning of the DESCRIPTION
26 section of wireshark(1) or
27 <http://www.wireshark.org/docs/man-pages/wireshark.html> is a detailed
28 description of the way Wireshark handles this, which is the same way
29 Mergecap handles this.
30 Mergecap can write the file in several output formats. The -F flag can
32 be used to specify the format in which to write the capture file,
33 mergecap -F provides a list of the available output formats.
34 Packets from the input files are merged in chronological order based on
36 each frame's timestamp, unless the -a flag is specified. Mergecap
37 assumes that frames within a single capture file are already stored in
38 chronological order. When the -a flag is specified, packets are copied
39 directly from each input file to the output file, independent of each
40 frame's timestamp.
41 The output file frame encapsulation type is set to the type of the
43 input files if all input files have the same type. If not all of the
44 input files have the same frame encapsulation type, the output file
45 type is set to WTAP_ENCAP_PER_PACKET. Note that some capture file
46 formats, most notably pcap, do not currently support
47 WTAP_ENCAP_PER_PACKET. This combination will cause the output file
48 creation to fail.
49
51 -a Causes the frame timestamps to be ignored, writing all packets from
52 the first input file followed by all packets from the second input
53 file. By default, when -a is not specified, the contents of the
54 input files are merged in chronological order based on each frame's
55 timestamp.
56 Note: when merging, mergecap assumes that packets within a capture
58 file are already in chronological order.
59 -F <file format>
61 Sets the file format of the output capture file. Mergecap can write
62 the file in several formats; mergecap -F provides a list of the
63 available output formats. The default is to use the file format of
64 the first input file.
65 -h Prints the version and options and exits.
67 -s <snaplen>
69 Sets the snapshot length to use when writing the data. If the -s
70 flag is used to specify a snapshot length, frames in the input file
71 with more captured data than the specified snapshot length will
72 have only the amount of data specified by the snapshot length
73 written to the output file. This may be useful if the program that
74 is to read the output file cannot handle packets larger than a
75 certain size (for example, the versions of snoop in Solaris 2.5.1
76 and Solaris 2.6 appear to reject Ethernet frames larger than the
77 standard Ethernet MTU, making them incapable of handling gigabit
78 Ethernet captures if jumbo frames were used).
79 -T <encapsulation type>
81 Sets the packet encapsulation type of the output capture file. If
82 the -T flag is used to specify a frame encapsulation type, the
83 encapsulation type of the output capture file will be forced to the
84 specified type, rather than being the type appropriate to the
85 encapsulation type of the input capture files.
86 Note that this merely forces the encapsulation type of the output
88 file to be the specified type; the packet headers of the packets
89 will not be translated from the encapsulation type of the input
90 capture file to the specified encapsulation type (for example, it
91 will not translate an Ethernet capture to an FDDI capture if an
92 Ethernet capture is read and '-T fddi' is specified).
93 -v Causes mergecap to print a number of messages while it's working.
95 -w <outfile>|-
97 Sets the output filename. If the name is '-', stdout will be used.
98 This setting is mandatory.
99
101 To merge two capture files together, 100 seconds apart use:
102 capinfos -aeS a.pcap b.pcap
104 (Let's suppose a.pcap starts at 1009932757 and b.pcap ends at
106 873660281. 1009932757 - 873660281 - 100 = 136272376 seconds.)
107 editcap -t 136272376 b.pcap b-shifted.pcap
109 mergecap -w compare.pcap a.pcap b-shifted.pcap
110
112 pcap(3), wireshark(1), tshark(1), dumpcap(1), editcap(1), text2pcap(1),
113 pcap-filter(7) or tcpdump(8)
114
116 Mergecap is based heavily upon editcap by Richard Sharpe
117 <sharpe[AT]ns.aus.com> and Guy Harris <guy[AT]alum.mit.edu>.
118 Mergecap is part of the Wireshark distribution. The latest version of
120 Wireshark can be found at <http://www.wireshark.org>.
121 HTML versions of the Wireshark project man pages are available at:
123 <http://www.wireshark.org/docs/man-pages>.
124
126 Original Author
127 -------- ------
128 Scott Renfro <scott[AT]renfro.org>
129 Contributors
132 ------------
133 Bill Guyton <guyton[AT]bguyton.com>
1341.10.14 2015-05-12 MERGECAP(1)