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> ...
11
13 Mergecap is a program that combines multiple saved capture files into a
14 single output file specified by the -w argument. Mergecap knows how to
15 read libpcap capture files, including those of tcpdump, Wireshark, and
16 other tools that write captures in that format.
17 By default, Mergecap writes the capture file in libpcap format, and
19 writes all of the packets from the input capture files to the output
20 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
28 <http://www.wireshark.org/docs/man-pages/wireshark.html> is a detailed
29 description of the way Wireshark handles this, which is the same way
30 Mergecap handles this.
31 Mergecap can write the file in several output formats. The -F flag can
33 be used to specify the format in which to write the capture file,
34 mergecap -F provides a list of the available output formats.
35 Packets from the input files are merged in chronological order based on
37 each frame's timestamp, unless the -a flag is specified. Mergecap
38 assumes that frames within a single capture file are already stored in
39 chronological order. When the -a flag is specified, packets are copied
40 directly from each input file to the output file, independent of each
41 frame's timestamp.
42 The output file frame encapsulation type is set to the type of the
44 input files if all input files have the same type. If not all of the
45 input files have the same frame encapsulation type, the output file
46 type is set to WTAP_ENCAP_PER_PACKET. Note that some capture file
47 formats, most notably libpcap, do not currently support
48 WTAP_ENCAP_PER_PACKET. This combination will cause the output file
49 creation to fail.
50
52 -a Causes the frame timestamps to be ignored, writing all packets from
53 the first input file followed by all packets from the second input
54 file. By default, when -a is not specified, the contents of the
55 input files are merged in chronological order based on each frame's
56 timestamp.
57 Note: when merging, mergecap assumes that packets within a capture
59 file are already in chronological order.
60 -F <file format>
62 Sets the file format of the output capture file. Mergecap can write
63 the file in several formats; mergecap -F provides a list of the
64 available output formats. The default is to use the file format of
65 the first input file.
66 -h Prints the version and options and exits.
68 -s <snaplen>
70 Sets the snapshot length to use when writing the data. If the -s
71 flag is used to specify a snapshot length, frames in the input file
72 with more captured data than the specified snapshot length will
73 have only the amount of data specified by the snapshot length
74 written to the output file. This may be useful if the program that
75 is to read the output file cannot handle packets larger than a
76 certain size (for example, the versions of snoop in Solaris 2.5.1
77 and Solaris 2.6 appear to reject Ethernet frames larger than the
78 standard Ethernet MTU, making them incapable of handling gigabit
79 Ethernet captures if jumbo frames were used).
80 -v Causes mergecap to print a number of messages while it's working.
82 -w <outfile>|-
84 Sets the output filename. If the name is '-', stdout will be used.
85 This setting is mandatory.
86 -T <encapsulation type>
88 Sets the packet encapsulation type of the output capture file. If
89 the -T flag is used to specify a frame encapsulation type, the
90 encapsulation type of the output capture file will be forced to the
91 specified type, rather than being the type appropriate to the
92 encapsulation type of the input capture files.
93 Note that this merely forces the encapsulation type of the output
95 file to be the specified type; the packet headers of the packets
96 will not be translated from the encapsulation type of the input
97 capture file to the specified encapsulation type (for example, it
98 will not translate an Ethernet capture to an FDDI capture if an
99 Ethernet capture is read and '-T fddi' is specified).
100
102 To merge two capture files together, 100 seconds apart use:
103 capinfos -aeS a.pcap b.pcap
105 (Let's suppose a.pcap starts at 1009932757 and b.pcap ends at
107 873660281. 1009932757 - 873660281 - 100 = 136272376 seconds.)
108 editcap -t 136272376 b.pcap b-shifted.pcap
110 mergecap -w compare.pcap a.pcap b-shifted.pcap
111
113 tcpdump(8), pcap(3), wireshark(1), tshark(1), dumpcap(1), editcap(1),
114 text2pcap(1)
115
117 Mergecap is based heavily upon editcap by Richard Sharpe
118 <sharpe[AT]ns.aus.com> and Guy Harris <guy[AT]alum.mit.edu>.
119 Mergecap is part of the Wireshark distribution. The latest version of
121 Wireshark can be found at <http://www.wireshark.org>.
122 HTML versions of the Wireshark project man pages are available at:
124 http://www.wireshark.org/docs/man-pages
125 <http://www.wireshark.org/docs/man-pages>.
126
128 Original Author
129 -------- ------
130 Scott Renfro <scott[AT]renfro.org>
131 Contributors
134 ------------
135 Bill Guyton <guyton[AT]bguyton.com>
1361.4.10 2011-11-01 MERGECAP(1)