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2 =head1 NAME
3  
4 mergecap - Merges two or more capture files into one
5  
6 =head1 SYNOPSIS
7  
8 B<mergecap>
9 S<[ B<-a> ]>
10 S<[ B<-F> E<lt>I<file format>E<gt> ]>
11 S<[ B<-h> ]>
12 S<[ B<-I> E<lt>I<IDB merge mode>E<gt> ]>
13 S<[ B<-s> E<lt>I<snaplen>E<gt> ]>
14 S<[ B<-v> ]>
15 S<[ B<-V> ]>
16 S<B<-w> E<lt>I<outfile>E<gt>|->
17 E<lt>I<infile>E<gt> [E<lt>I<infile>E<gt> I<...>]
18  
19 =head1 DESCRIPTION
20  
21 B<Mergecap> is a program that combines multiple saved capture files into
22 a single output file specified by the B<-w> argument. B<Mergecap> knows
23 how to read B<pcap> capture files, including those of B<tcpdump>,
24 B<Wireshark>, and other tools that write captures in that format.
25  
26 By default, B<Mergecap> writes the capture file in B<pcap> format, and writes
27 all of the packets from the input capture files to the output file.
28  
29 B<Mergecap> is able to detect, read and write the same capture files that
30 are supported by B<Wireshark>.
31 The input files don't need a specific filename extension; the file
32 format and an optional gzip compression will be automatically detected.
33 Near the beginning of the DESCRIPTION section of wireshark(1) or
34 L<https://www.wireshark.org/docs/man-pages/wireshark.html>
35 is a detailed description of the way B<Wireshark> handles this, which is
36 the same way B<Mergecap> handles this.
37  
38 B<Mergecap> can write the file in several output formats.
39 The B<-F> flag can be used to specify the format in which to write the
40 capture file, B<mergecap -F> provides a list of the available output
41 formats.
42  
43 Packets from the input files are merged in chronological order based on
44 each frame's timestamp, unless the B<-a> flag is specified. B<Mergecap>
45 assumes that frames within a single capture file are already stored in
46 chronological order. When the B<-a> flag is specified, packets are
47 copied directly from each input file to the output file, independent of
48 each frame's timestamp.
49  
50 The output file frame encapsulation type is set to the type of the input
51 files if all input files have the same type. If not all of the input
52 files have the same frame encapsulation type, the output file type is
53 set to WTAP_ENCAP_PER_PACKET. Note that some capture file formats, most
54 notably B<pcap>, do not currently support WTAP_ENCAP_PER_PACKET.
55 This combination will cause the output file creation to fail.
56  
57 =head1 OPTIONS
58  
59 =over 4
60  
61 =item -a
62  
63 Causes the frame timestamps to be ignored, writing all packets from the
64 first input file followed by all packets from the second input file. By
65 default, when B<-a> is not specified, the contents of the input files
66 are merged in chronological order based on each frame's timestamp.
67  
68 Note: when merging, B<mergecap> assumes that packets within a capture
69 file are already in chronological order.
70  
71 =item -F E<lt>file formatE<gt>
72  
73 Sets the file format of the output capture file. B<Mergecap> can write
74 the file in several formats; B<mergecap -F> provides a list of the
75 available output formats. The default is to use the file format of the
76 first input file.
77  
78 =item -h
79  
80 Prints the version and options and exits.
81  
82 =item -I E<lt>IDB merge modeE<gt>
83  
84 Sets the Interface Description Block (IDB) merge mode to use during merging.
85 B<mergecap -I> provides a list of the available IDB merge modes.
86  
87 Every input file has one or more IDBs, which describe the interface(s) the
88 capture was performed on originally. This includes encapsulation type,
89 interface name, etc. When mergecap merges multiple input files, it has to
90 merge these IDBs somehow for the new merged output file. This flag controls
91 how that is accomplished. The currently available modes are:
92  
93 * 'B<none>': no merging of IDBs is performed, and instead all IDBs are
94 copied to the merged output file.
95 * 'B<all>': IDBs are merged only if all input files have the same number
96 of IDBs, and each IDB matches their respective entry in the
97 other files. This is the default mode.
98 * 'B<any>': Any and all duplicate IDBs are merged into one IDB, regardless
99 of what file they are in.
100  
101 Note that an IDB is only considered a matching duplicate if it has the same
102 encapsulation type, name, speed, time precision, comments, description, etc.
103  
104 =item -s E<lt>snaplenE<gt>
105  
106 Sets the snapshot length to use when writing the data.
107 If the B<-s> flag is used to specify a snapshot length, frames in the
108 input file with more captured data than the specified snapshot length
109 will have only the amount of data specified by the snapshot length
110 written to the output file. This may be useful if the program that is
111 to read the output file cannot handle packets larger than a certain size
112 (for example, the versions of snoop in Solaris 2.5.1 and Solaris 2.6
113 appear to reject Ethernet frames larger than the standard Ethernet MTU,
114 making them incapable of handling gigabit Ethernet captures if jumbo
115 frames were used).
116  
117 =item -v
118  
119 Causes B<mergecap> to print a number of messages while it's working.
120  
121 =item -V
122  
123 Print the version and exit.
124  
125 =item -w E<lt>outfileE<gt>|-
126  
127 Sets the output filename. If the name is 'B<->', stdout will be used.
128 This setting is mandatory.
129  
130 =back
131  
132 =head1 EXAMPLES
133  
134 To merge two capture files together, 100 seconds apart use:
135  
136 capinfos -aeS a.pcap b.pcap
137  
138 (Let's suppose a.pcap starts at 1009932757 and b.pcap ends
139 at 873660281. 1009932757 - 873660281 - 100 = 136272376
140 seconds.)
141  
142 editcap -t 136272376 b.pcap b-shifted.pcap
143 mergecap -w compare.pcap a.pcap b-shifted.pcap
144  
145 =head1 SEE ALSO
146  
147 pcap(3), wireshark(1), tshark(1), dumpcap(1), editcap(1), text2pcap(1),
148 pcap-filter(7) or tcpdump(8)
149  
150 =head1 NOTES
151  
152 B<Mergecap> is based heavily upon B<editcap> by Richard Sharpe
153 <sharpe[AT]ns.aus.com> and Guy Harris <guy[AT]alum.mit.edu>.
154  
155 B<Mergecap> is part of the B<Wireshark> distribution. The latest version
156 of B<Wireshark> can be found at L<https://www.wireshark.org>.
157  
158 HTML versions of the Wireshark project man pages are available at:
159 L<https://www.wireshark.org/docs/man-pages>.
160  
161 =head1 AUTHORS
162  
163 Original Author
164 -------- ------
165 Scott Renfro <scott[AT]renfro.org>
166  
167  
168 Contributors
169 ------------
170 Bill Guyton <guyton[AT]bguyton.com>