snf-vncauthproxy’s documentation

snf-vncauthproxy is a daemon, which acts as a VNC authentication proxy between a VNC client and server.

snf-vncauthproxy daemon listens on a TCP socket for control messages and sets up one-time port forwardings upon request.

Main features include:
  • Lightweight, coroutine-based main loop with gevent
  • Support for the RFB protocol version 3.8
  • IPv4 and IPv6 support
  • Configurable timeout for client connections
  • Support for HTML5 WebSocket clients

Its main use is to enable VNC clients to connect to firewalled VNC servers.

It is used by Synnefo to provide users with (VNC) console access to their VMs.


snf-vncauthproxy is currently packaged only for Debian (stable).

You can find and install the latest version snf-vncauthproxy at Synnefo’s apt repository: {release}

To import the GPG key of the repo, use:

curl | apt-key add -

In case you’re upgrading from an older snf-vncauthproxy version or it’s the first time you’re installing snf-vncauthproxy, you should create a vncauthproxy user, in order to have a functional vncauthproxy installation (see below for more information on user management).


snf-vncauthproxy listens on a TCP socket for control (JSON) messages from clients. The format of the control messages is:

Control request, in JSON:
        <source port or 0 for automatic allocation>,
        <destination address of backend server>,
        <destination port>
        <the password to use to authenticate clients>
        <user for control connection authentication>,
        <password for control connection authentication>,
        <interface to use (vnc, vnc-ws, vnc-wss)>,

The <password> is used for MITM authentication of clients
connecting to <proxy_address:source_port>, who will subsequently be
forwarded to a VNC server listening at

Control reply, in JSON:
    "source_port": <the allocated source port>
    "status": <one of "OK" or "FAILED">
    "proxy_address": <listening address / host  for client

snf-vncauthproxy will then spawn a greenlet to handle the incoming control message, establish the connection with the server (RFB handshake) and set up a listening socket for the client to connect (with a configurable timeout).

When the client connects, the greenlet will proxy the traffic between the client and server (reading and writing to the client and server socket when needed).

The handling of control connections, client connections and the actual proxying is implemented using gevent and greenlets.

Since release 1.6, snf-vncauthproxy supports configurable client socket ‘types’. The client can request a specific type, via the json control request. The vnc type will behave the same way as pre-1.6 releases (i.e. plain RFB over TCP), while vnc-ws and vnc-wss will set up an (HTTP(s)) WebSocket server for HTML5 clients (eg noVNC). In the case of vnc-wss, you will need to provide snf-vncauthproxy with a public and private SSL certificate (in PEM format – see below).

The WebSocket support uses WS4PY and the gevent.pywsgi WSGI server.


The snf-vncauthproxy daemon can be either run manually or managed via its init script.

If you’re using the init script, snf-vncauthproxy reads its options from its default file (DAEMON_OPTS parameter in /etc/default/vncauthproxy). Refer to the vncauthproxy help output for a detailed listing and information on all available options:

# vncauthproxy --help

By default snf-vncauthproxy will listen to TCP, for incoming control connections and uses the 25000-30000 range for the listening / data sockets.

Version 1.5 replaced Unix domain control sockets with TCP control sockets. This change made it necessary to introduce an authentication file to replace the POSIX file permissions, which protected the domain sockets.

The default path for the auth file is /var/lib/vncauthproxy/users (configurable by the --auth-file option). Each line in the file represents one user which is allowed to use the control socket and should be in the following format:


The password part of the line (after the colon) is the output of crypt(), using a random 16-char salt with SHA-512.

To manage the authentication file, you can use the vncauthproxy-passwd tool, to easily add, update and delete users:

To add a user:

# vncauthproxy-passwd /var/lib/vncauthproxy/users user

You will be prompted for a password.

To delete a user:

# vncauthproxy-passwd -D /var/lib/vncauthproxy/users user

See the help output of the tool for more options:

# vncauthproxy-passwd -h


The vncauthproxy daemon requires a restart for the changes in the authentication file to take effect.


After installing snf-vncauthproxy for the fist time, make sure that you create a valid authentication file and define any users needed. The vncauthproxy daemon will start but will not be usable if no users are defined or if no authentication file is present.

Version 1.5 introduced also support for SSL for the control socket. If you enable SSL support (--enable-ssl parameter, disabled by default) you will have to provide a certificate and key file (--cert-file and --key-file parameters). The default values for certificate and key files are /var/lib/vncauthrpoxy/{cert,key}.pem respectively.

With version 1.6, the private and public certificates are necessary for the secure WebSocket (vnc-wss) console type. Otherwise, any vnc-wss request will fail.

For detailed help on its configuration parameters, either consult its man page or run:

snf-vncauthproxy --help

on the command line.

snf-vncauthproxy also provides a client which can be used to test from the command line that snf-vncauhtproxy has been deployed correctly. It also provides a method (request_forwarding) which can be used from any Python program to request forwarding from the snf-vncauthproxy daemon.

See the client’s usage / help output and the method’s signature for more information on how to use the them

Regarding the WebSocket functionality, snf-authproxy will try to use wsaccell (WebSockets accelerator), if installed (currently not in the Debian repos), to patch ws4py.

Usage with Synnefo

Synnefo (snf-cyclades-app) uses snf-vncauthproxy to provide users (VNC) console access to their VMs. In release 0.16, the Java (applet) VNC client was replaced with an HTML5 WebSocket client (noVNC).

Synnefo uses Ganeti and KVM for the cluster and VM management. In the common case the Ganeti nodes, running the KVM instances are firewalled, and only the Cyclades (Compute) app server (snf-cyclades-app) is publicly accessible. In order for users to be able to access the VNC console /server (spawned by the KVM instances on the Ganeti nodes), snf-cyclades-app uses snf-vncauthproxy to allow users to connect to the VNC servers and access the VNC consoles of their VMs.

If you’re running snf-vncauthproxy on the same host as snf-cyclades-app, you will only need to configure one Synnefo setting. Specifically, the CYCLADES_VNCAUTHPROXY_OPTS dict in /etc/synnefo/20-snf-cyclades-app-api.conf should be edited to match snf-vncauthproxy configuration (user, password, SSL support, certificate file).

In case you want to deploy snf-vncauthproxy on a different host other than snf-cyclades-app, you should make sure that you change the default listening address (and / or port) and the proxy address (--proxy-listen-address) for snf-vncauthproxy and make sure that snf-cyclades-app can connect to the snf-vncauthproxy on the listening address / port and that clients can connect to the proxy address. It’s also recommended to enable SSL on the control socket in that case. You can refer to the Synnefo admin guide for more information.

Starting with v0.16, Synnefo supports WebSockets for the VNC console (the Synnefo Compute API supports all the ‘console types’ supported by snf-vncauthproxy, ie vnc, vnc-ws and vnc-wss).

The Synnefo UI was also updated to include a WebSockets / HTML5 VNC client (noVNC)` and by default requests a vnc-wss console. This means that in order to avoid browser issues / warning about insecure certificates and have a functional / working Synnefo out-of-band VM access / console, you should either provide snf-vncauthrpoxy with SSL certificates signed by a trusted CA or pre-accept a self-signed certificate. Note that there is currently a known issue with Firefox requiring the user to accept self-signed / untrusted certificates for each different destination port. This means that using Firefox to access the Synnefo console, while running snf-vncauthproxy with self-signed certificates, won’t work.

Please refer to the Synnefo documentation for detailed instructions on setting up your own CA and importing the CA certificate into your browser.



For questions or bug reports you can contact the Synnefo team at the following mailing lists:


snf-vncauthproxy is licensed under GNU Generic Public License version 2 (GPLv2), please see LICENSE for the full text.

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