Plug-in Interface Options

OpenVPN can be extended by loading external plug-in modules at runtime. These plug-ins must be prebuilt and adhere to the OpenVPN Plug-In API.

--plugin args Loads an OpenVPN plug-in module.

Valid syntax: ::

 plugin module-name
 plugin module-name "arguments"

The module-name needs to be the first argument, indicating the plug-in to load. The second argument is an optional init string which will be passed directly to the plug-in. If the init consists of multiple arguments it must be enclosed in double-quotes ("). Multiple plugin modules may be loaded into one OpenVPN process.

The module-name argument can be just a filename or a filename with a relative or absolute path. The format of the filename and path defines if the plug-in will be loaded from a default plug-in directory or outside this directory. ::

--plugin path         Effective directory used
===================== =============================
 myplug.so            DEFAULT_DIR/myplug.so
 subdir/myplug.so     DEFAULT_DIR/subdir/myplug.so
 ./subdir/myplug.so   CWD/subdir/myplug.so
 /usr/lib/my/plug.so  /usr/lib/my/plug.so

DEFAULT_DIR is replaced by the default plug-in directory, which is configured at the build time of OpenVPN. CWD is the current directory where OpenVPN was started or the directory OpenVPN have switched into via the --cd option before the --plugin option.

For more information and examples on how to build OpenVPN plug-in modules, see the README file in the plugin folder of the OpenVPN source distribution.

If you are using an RPM install of OpenVPN, see :code:/usr/share/openvpn/plugin. The documentation is in doc and the actual plugin modules are in lib.

Multiple plugin modules can be cascaded, and modules can be used in tandem with scripts. The modules will be called by OpenVPN in the order that they are declared in the config file. If both a plugin and script are configured for the same callback, the script will be called last. If the return code of the module/script controls an authentication function (such as tls-verify, auth-user-pass-verify, or client-connect), then every module and script must return success (:code:0) in order for the connection to be authenticated.

WARNING: Plug-ins may do deferred execution, meaning the plug-in will return the control back to the main OpenVPN process and provide the plug-in result later on via a different thread or process. OpenVPN does NOT support multiple authentication plug-ins where more than one plugin tries to do deferred authentication. If this behaviour is detected, OpenVPN will shut down upon first authentication.