Editcap is a program that reads a saved capture file and writes some
or all of the packets in that capture file to another capture file.
Editcap knows how to read libpcap capture files, including those
of tcpdump, Ethereal, and other tools that write captures in that
format.
Editcap can read / import the following file formats:
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There is no need to tell Editcap what type of
file you are reading; it will determine the file type by itself.
Editcap is also capable of reading any of these file formats if they
are compressed using gzip. Editcap recognizes this directly from the
file; the '.gz' extension is not required for this purpose.
By default, it writes the capture file in libpcap format, and writes
all of the packets in the capture file to the output file. The -F
flag can be used to specify the format in which to write the capture
file; it can write the file in libpcap format (standard libpcap
format, a modified format used by some patched versions of libpcap,
the format used by Red Hat Linux 6.1, or the format used by SuSE Linux
6.3), snoop format, uncompressed Sniffer format, Microsoft
Network Monitor 1.x format, the format used by Windows-based versions
of the Sniffer software, and the format used by Visual Networks'
software.
A list of packet numbers can be specified on the command line; the
packets with those numbers will not be written to the capture file,
unless the -r flag is specified, in which case only those packets
will be written to the capture file. Ranges of packet numbers can be
specified as start-end, referring to all packets from start to
end (removing them all if -r isn't specified, including them all
if -r is specified).
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).
If the -t flag is used to specify a time adjustment, the specified
adjustment will be applied to all selected frames in the capture file.
The adjustment is specified as [-]seconds[.fractional seconds].
For example, -t 3600 advances the timestamp on selected frames by one
hour while -t -0.5 reduces the timestamp on selected frames by
one-half second. This feature is useful when synchronizing dumps
collected on different machines where the time difference between the
two machines is known or can be estimated.
If the -T flag is used to specify an encapsulation type, the
encapsulation type of the output capture file will be forced to the
specified type, rather than being the type appropriate to the
encapsulation type of the input capture file. Note that this merely
forces the encapsulation type of the output file to be the specified
type; the packet headers of the packets will not be translated from the
encapsulation type of the input capture file to the specified
encapsulation type (for example, it will not translate an Ethernet
capture to an FDDI capture if an Ethernet capture is read and '-T
fddi' is specified).
If the -E flag is used to specify a probability (between 0.0 and
1.0 inclusive), Editcap uses that probability to apply errors to each
data byte in the file. For instance, a probability of 0.02 means that
each byte has a 2% chance of having an error. This option is meant to
be used for fuzz-testing protocol dissectors.
OPTIONS
"-F"
Sets the file format of the output capture file.
"-T"
Sets the packet encapsulation type of the output capture file.
"-r"
Causes the packets whose packet numbers are specified on the command
line to be written to the output capture file, and no other packets to
be written to the output capture file.
"-v"
Causes editcap to print a number of messages while it's working.
"-s"
Sets the snapshot length to use when writing the data.
"-t"
Sets the time adjustment to use on selected frames.
