dumpcap - Dump network traffic
S<[ B<-a> E<lt>capture autostop conditionE<gt> ] ...>
S<[ B<-b> E<lt>capture ring buffer optionE<gt>] ...>
S<[ B<-B> E<lt>capture buffer size (Win32 only)E<gt> ] >
S<[ B<-c> E<lt>capture packet countE<gt> ]>
S<[ B<-D> ]>
S<[ B<-f> E<lt>capture filterE<gt> ]>
S<[ B<-h> ]>
S<[ B<-i> E<lt>capture interfaceE<gt>|- ]>
S<[ B<-L> ]>
S<[ B<-p> ]>
S<[ B<-s> E<lt>capture snaplenE<gt> ]>
S<[ B<-v> ]>
S<[ B<-w> E<lt>outfileE<gt> ]>
S<[ B<-y> E<lt>capture link typeE<gt> ]>
B<Dumpcap> is a network traffic dump tool. It lets you capture packet
data from a live network and write the packets to a file. B<Dumpcap>'s
native capture file format is B<libpcap> format, which is also the format
used by B<Ethereal>, B<tcpdump> and various other tools.
Without any options set it will
use the pcap library to capture traffic from the first available network
interface and writes the received raw packet data, along with the packets'
time stamps into a libpcap file.
If the B<-w> option is not specified, B<Dumpcap> writes to a newly
created libpcap file with a randomly chosen name.
If the B<-w> option is specified, B<Dumpcap> writes to the file
specified by that option.
Packet capturing is performed with the pcap library. The capture filter
syntax follows the rules of the pcap library.
=item -a E<lt>capture autostop conditionE<gt>
Specify a criterion that specifies when B<Dumpcap> is to stop writing
to a capture file. The criterion is of the form I<test>B<:>I<value>,
where I<test> is one of:
B<duration>:I<value> Stop writing to a capture file after I<value> seconds have elapsed.
B<filesize>:I<value> Stop writing to a capture file after it reaches a size of I<value>
kilobytes (where a kilobyte is 1024 bytes). If this option
is used together with the -b option, dumpcap will stop writing to the
current capture file and switch to the next one if filesize is reached.
B<files>:I<value> Stop writing to capture files after I<value> number of files were written.
=item -b E<lt>capture ring buffer optionE<gt>
Cause B<Dumpcap> to run in "multiple files" mode. In "multiple files" mode,
B<Dumpcap> will write to several capture files. When the first capture file
fills up, B<Dumpcap> will switch writing to the next file and so on.
The created filenames are based on the filename given with the B<-w> option, the number of
the file and on the creation date and time,
e.g. outfile_00001_20050604120117.pcap, outfile_00001_20050604120523.pcap, ...
With the I<files> option it's also possible to form a "ring buffer".
This will fill up new files until the number of files specified,
at which point B<Dumpcap> will discard the data in the first file and start
writing to that file and so on. If the I<files> option is not set,
new files filled up until one of the capture stop conditions match (or
until the disk if full).
The criterion is of the form I<key>B<:>I<value>,
where I<key> is one of:
B<duration>:I<value> switch to the next file after I<value> seconds have
elapsed, even if the current file is not completely filled up.
B<filesize>:I<value> switch to the next file after it reaches a size of
I<value> kilobytes (where a kilobyte is 1024 bytes).
B<files>:I<value> begin again with the first file after I<value> number of
files were written (form a ring buffer).
=item -B E<lt>capture buffer size (Win32 only)E<gt>
Win32 only: set capture buffer size (in MB, default is 1MB). This is used by the
the capture driver to buffer packet data until that data can be written to
disk. If you encounter packet drops while capturing, try to increase this size.
=item -c E<lt>capture packet countE<gt>
Set the maximum number of packets to read when capturing live
Print a list of the interfaces on which B<Dumpcap> can capture, and
exit. For each network interface, a number and an
interface name, possibly followed by a text description of the
interface, is printed. The interface name or the number can be supplied
to the B<-i> option to specify an interface on which to capture.
This can be useful on systems that don't have a command to list them
(e.g., Windows systems, or UNIX systems lacking B<ifconfig -a>);
the number can be useful on Windows 2000 and later systems, where the
interface name is a somewhat complex string.
Note that "can capture" means that B<Dumpcap> was able to open
that device to do a live capture. Depending on your system you may need to
run dumpcap from an account with special privileges (for example, as root)
to be able to capture network traffic.
If "B<dumpcap -D>" is not run from such an account, it will not list
=item -f E<lt>capture filterE<gt>
Set the capture filter expression.
The entire filter expression must be specified as a single argument (which means
that if it contains spaces, it must be quoted).
Print the version and options and exits.
=item -i E<lt>capture interfaceE<gt>|-
Set the name of the network interface or pipe to use for live packet
Network interface names should match one of the names listed in
"B<dumpcap -D>" (described above); a number, as reported by
"B<dumpcap -D>", can also be used. If you're using UNIX, "B<netstat
-i>" or "B<ifconfig -a>" might also work to list interface names,
although not all versions of UNIX support the B<-a> option to B<ifconfig>.
If no interface is specified, B<Dumpcap> searches the list of
interfaces, choosing the first non-loopback interface if there are any
non-loopback interfaces, and choosing the first loopback interface if
there are no non-loopback interfaces. If there are no interfaces at all,
B<Dumpcap> reports an error and doesn't start the capture.
Pipe names should be either the name of a FIFO (named pipe) or ``-'' to
read data from the standard input. Data read from pipes must be in
standard libpcap format.
Note: the Win32 version of B<Dumpcap> doesn't support capturing from
pipes or stdin!
List the data link types supported by the interface and exit. The reported
link types can be used for the B<-y> option.
I<Don't> put the interface into promiscuous mode. Note that the
interface might be in promiscuous mode for some other reason; hence,
B<-p> cannot be used to ensure that the only traffic that is captured is
traffic sent to or from the machine on which B<Dumpcap> is running,
broadcast traffic, and multicast traffic to addresses received by that
=item -s E<lt>capture snaplenE<gt>
Set the default snapshot length to use when capturing live data.
No more than I<snaplen> bytes of each network packet will be read into
memory, or saved to disk.
Print the version and exit.
=item -w E<lt>outfileE<gt>
Write raw packet data to I<outfile>.
NOTE: The usage of "-" for stdout is not allowed here!
=item -y E<lt>capture link typeE<gt>
Set the data link type to use while capturing packets. The values
reported by B<-L> are the values that can be used.
=head1 CAPTURE FILTER SYNTAX
See the manual page of I<tcpdump(8)>.
=head1 SEE ALSO
I<ethereal(1)>, I<tethereal(1)>, I<editcap(1)>, I<tcpdump(8)>, I<pcap(3)>
B<Dumpcap> is part of the B<Ethereal> distribution. The latest version
of B<Ethereal> can be found at B<http://www.ethereal.com>.
HTML versions of the Wireshark project man pages are available at:
B<Dumpcap> is derived from the B<Ethereal> capturing engine code;
see the list of
authors in the B<Ethereal> man page for a list of authors of that code.