|
HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
|
|
NAME | DESCRIPTION | GRAMMAR ELEMENTS | EXAMPLES | TABLE FIELD | SECURITY CONSIDERATIONS | SEE ALSO | NOTES |
|
|
|
EXTCAP(4) EXTCAP(4)
extcap - The external capture interface
The extcap (external capture) interface is a versatile plugin
interface that allows external binaries to act as capture
interfaces directly in Wireshark. It is used in scenarios, where
the source of the capture is not a traditional capture model (live
capture from an interface, from a pipe, from a file, etc). The
typical example is connecting esoteric hardware of some kind to
the main Wireshark application.
Without extcap, a capture can always be achieved by directly
writing to a capture file:
the-esoteric-binary --the-strange-flag --interface=stream1 --file dumpfile.pcap &
wireshark dumpfile.pcap
but the extcap interface allows for such a connection to be easily
established and configured using the Wireshark GUI.
The extcap subsystem is made of multiple extcap binaries that are
automatically called by the GUI in a row. In the following
chapters we will refer to them as "the extcaps".
Extcaps may be any binary or script within the extcap/wireshark or
extcap/stratoshark directories. Please note that scripts need to
be executable without prefacing a script interpreter before the
call.
WINDOWS USERS: Because of restrictions directly calling the script
may not always work. In such a case, a batch file may be provided,
which then in turn executes the script. Please refer to
doc/extcap_example.py for more information.
When Wireshark launches an extcap, it automatically adds its
installation path (normally C:\Program Files\Wireshark\) to the
DLL search path so that the extcap library dependencies can be
found (it is not designed to be launched by hand). This is done on
purpose. There should only be extcap programs (executables, Python
scripts, ...) in the extcap folder to reduce the startup time and
not have Wireshark trying to execute other file types.
Grammar elements:
arg (options)
argument for CLI calling
number
Reference # of argument for other values, display order
call
Literal argument to call (--call=...)
display
Displayed name
default
Default value, in proper form for type
range
Range of valid values for UI checking (min,max) in proper form
type
Argument type for UI filtering for raw, or UI type for
selector:
integer
unsigned
long (may include scientific / special notation)
double
string (display a textbox)
selector (display selector table, all values as strings)
editselector (selector table which can be overridden, all values as strings)
boolean (display checkbox)
booleanflag (display checkbox)
radio (display group of radio buttons with provided values, all values as strings)
fileselect (display a dialog to select a file from the filesystem, value as string)
multicheck (display a textbox for selecting multiple options, values as strings)
table (display a table that is populated by the user, selections can be configured, values as commandlines arguments)
password (display a textbox with masked text)
timestamp (display a calendar)
value (options)
Values for argument selection
arg Argument # this value applies to
Example 1:
arg {number=0}{call=--channel}{display=Wi-Fi Channel}{type=integer}{required=true}
arg {number=1}{call=--chanflags}{display=Channel Flags}{type=radio}
arg {number=2}{call=--interface}{display=Interface}{type=selector}
value {arg=0}{range=1,11}
value {arg=1}{value=ht40p}{display=HT40+}
value {arg=1}{value=ht40m}{display=HT40-}
value {arg=1}{value=ht20}{display=HT20}
value {arg=2}{value=wlan0}{display=wlan0}
Example 2:
arg {number=0}{call=--usbdevice}{USB Device}{type=selector}
value {arg=0}{call=/dev/sysfs/usb/foo/123}{display=Ubertooth One sn 1234}
value {arg=0}{call=/dev/sysfs/usb/foo/456}{display=Ubertooth One sn 8901}
Example 3:
arg {number=0}{call=--usbdevice}{USB Device}{type=selector}
arg {number=1}{call=--server}{display=IP address for log server}{type=string}{validation=(?:\d{1,3}\.){3}\d{1,3}}
flag {failure=Permission denied opening Ubertooth device}
Example 4:
arg {number=0}{call=--username}{display=Username}{type=string}
arg {number=1}{call=--password}{display=Password}{type=password}
Example 5: timestamp
arg {number=0}{call=--start}{display=Start Time}{type=timestamp}
arg {number=1}{call=--end}{display=End Time}{type=timestamp}
Example 6: multicheck
arg {number=0}{call=--device}{display=Device}{type=multicheck}
value {arg=0}{value=USBDEV}{display=USB devices}{enabled=false}
value {arg=0}{value=/dev/sysfs/usb/foo/123}{display=Ubertooth One sn 1234}{parent=USBDEV}
value {arg=0}{value=/dev/sysfs/usb/foo/456}{display=Ubertooth One sn 8901}{parent=USBDEV}
value {arg=0}{value=PCIDEV}{display=PCI devices}{enabled=false}
value {arg=0}{value=/sys/devices/pci123}{display=Device 1}{parent=PCIDEV}
value {arg=0}{value=/sys/devices/pci456}{display=Device 2}{parent=PCIDEV}
The "table" field is a bit different, in that its values can have
additional configuration options. The values can either be entered
manually by the user, or a list of available values can be
provided using the same API as "multicheck". Unlike most APIs, the
value is provided using a commandline-like API, separated by
spaces instead of comas. For instance, a configured "myparam"
attribute where the user selected three values (1, 2 and 3) would
receive:
--myparam "1 2 3"
If a "prefix" is configured to be "--p", it would receive the
following:
--myparam "--p 1 --p 2 --p 3"
The values selected in a table field may have specific
configuration options, if "configurable=true" for the "multicheck"
field. In this case, the extcap will be called again when the user
presses the configuration wheel that matches a value in the table,
with the additional "--extcap-config-option-name <option_name>
--extcap-config-option-value <option_value>" with no prefix. An
extcap program should respond with an additional set of arguments,
which will be opened in a popup. Once those are configured, the
extcap might get the following, assuming for instance that an
additional "param1" is requested when value is 1, and "param2"
when value is 2.
--myparam "--p 1 --param1 1 --p 2 --param2 true --p 3"
• If you’re running Wireshark as root, we can’t save you.
• Dumpcap retains suid/setgid and group execute permissions for
users in the “wireshark” group only.
• Third-party capture programs run with whatever privileges
they’re installed with.
• If an attacker can write to a system binary directory, it’s
game over.
• You can find your local extcap directory in About › Folders.
wireshark(1), tshark(1), dumpcap(1), androiddump(1), sshdig(1),
sshdump(1), randpktdump(1)
Extcap is feature of Wireshark. The latest version of Wireshark
can be found at https://www.wireshark.org.
HTML versions of the Wireshark project man pages are available at
https://www.wireshark.org/docs/man-pages. This page is part of the
wireshark (Interactively dump and analyze network traffic)
project. Information about the project can be found at
⟨https://www.wireshark.org/⟩. If you have a bug report for this
manual page, see
⟨https://gitlab.com/wireshark/wireshark/-/issues⟩. This page was
obtained from the project's upstream Git repository
⟨https://gitlab.com/wireshark/wireshark.git⟩ on 2025-08-11. (At
that time, the date of the most recent commit that was found in
the repository was 2025-08-11.) If you discover any rendering
problems in this HTML version of the page, or you believe there is
a better or more up-to-date source for the page, or you have
corrections or improvements to the information in this COLOPHON
(which is not part of the original manual page), send a mail to
[email protected]
2025-08-09 EXTCAP(4)
Pages that refer to this page: androiddump(1), ciscodump(1), dpauxmon(1), etwdump(1), falcodump(1), randpktdump(1), sdjournal(1), sshdig(1), sshdump(1), udpdump(1), wifidump(1)
|
HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
|