X11vnc - ArchWiki

# X11vnc

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x11vnc is a VNC server, it allows one to view remotely and interact with real X displays (i.e. a display corresponding to a physical monitor, keyboard, and mouse) with any VNC viewer. While it is not developed any longer by its original author Karl Runge, LibVNC and the GitHub community have taken over the development.

x11vnc does not create an extra display (or X desktop) for remote control. Instead, it shows in real time the existing X11 display, unlike Xvnc, part of TigerVNC, which is an alternatives VNC server available in the official repositories.

Also note that x11vnc is not shipped with a client viewer. Any VNC viewer should do the job and be compatible with the x11vnc server while not necessarily using all its functionalities. TigerVNC's vncviewer is a recommended client.

## Setting up x11vnc

### Installation

Install x11vnc from the official repositories.

### Starting

First, start X either by startx or through a display manager. You may need to set up X to run headless too.

Then, run the following command, all available options are explained in x11vnc(1).

    $ x11vnc -display :0

Another option is to place the x11vnc command line in a script which is called at login, for example:

    x11vnc -wait 50 -noxdamage -passwd PASSWORD -display :0 -forever -o /var/log/x11vnc.log -bg

Note: The password "PASSWORD" above is not secured; anyone who can run `ps` on the machine will see it. Also note that `/var/log/x11vnc.log` needs to be created manually and its ownership needs to match that of the user who will run it.

#### Setting X authority

You may set an X authority file for the VNC server. This is accomplished by using the `-auth` argument followed by the appropriate file, which will depend on how your X server was started. Generally, assigning an X authority file requires running x11vnc as root.

##### Start X

    $ x11vnc -display :0 -auth ~/.Xauthority

If that fails, you may have to run instead (as root):

    # x11vnc -display :0 -auth /home/user/.Xauthority

Where user is the username of the user who is running the X server.

##### Running from xinetd

X11vnc can be run using a xinetd service, which only starts X11vnc once a user connects.

Create an xinetd service entry for x11vnc, for example:

    /etc/xinetd/x11vnc

    service x11vncservice
    {
           port            = 5900
           type            = UNLISTED
           socket_type     = stream
           protocol        = tcp
           wait            = no
           user            = root
           server          = /usr/bin/x11vnc
           server_args     = -inetd -o /var/log/x11vnc.log -noxdamage -display :0 -auth guess
           disable         = no
    }

After reloading `xinetd.service`, X11vnc will start once a client connects to port 5900.

##### GDM

Note: Newer GDM packages ship with Xwayland as the default display server backend. The following instructions, however, only apply when using Xorg (else `.Xauthority` is not created, and x11vnc fails to start). You are therefore advised to uncomment `#WaylandEnable=false` setting in `/etc/gdm/custom.conf` in order to proceed.

    # x11vnc -display :0 -auth /var/lib/gdm/:0.Xauth

Newer versions of GDM uses /run/user. Example for user 120 (gdm), used for login screen.

    # x11vnc -display :0 -auth /run/user/120/gdm/Xauthority

or see Troubleshooting section below

##### Lightdm

    # x11vnc -display :0 -auth /var/run/lightdm/root/\:0

##### LXDM

    # x11vnc -display :0 -auth /var/run/lxdm/lxdm-\:0.auth

##### SDDM

SDDM uses an unpredictable UUID for the auth file [1] therefore one needs to:

    # x11vnc -display :0 -auth $(find /var/run/sddm/ -type f)

Embedding this into a systemd .service file will require a trick to evaluate the find command as shown here [2].

##### SLIM

    # x11vnc -display :0 -auth /var/run/slim.auth

Warning: This will set up VNC with NO PASSWORD. This means that ANYBODY who has access to the network the computer is on CAN SEE YOUR XSERVER. It is a fairly simple matter to tunnel your VNC connection through SSH to avoid this. Or, simply set a password, as described below.
Note: The password will only encrypt the login process itself. The transmission is still unencrypted[3].

### Setting a password

Running:

    $ x11vnc -usepw

uses the password found in `~/.vnc/passwd`, where the password is obscured with a fixed key in a VNC compatible format, or alternatively in `~/.vnc/passwdfile`, where the first line of the file contains the password. If none of these files can be located, it prompts the user for a password which is saved in `~/.vnc/passwd` and is used right away.

The VNC viewer should then prompt for a password when connecting.

### Running constantly

By default, x11vnc will accept the first VNC session and shutdown when the session disconnects. In order to avoid that, start x11vnc with either the `-many` or the `-forever` argument, like this:

    $ x11vnc -many -display :0

It is also possible to use the following command :

    $ x11vnc --loop

this will restart the server once the session is finished

### Accessing

Get a VNC client on another computer, and type in the IP address of the computer running x11vnc. Hit connect, and you should be set.

If you are attempting to access a VNC server / computer (running x11vnc) from outside of its network then you will need to ensure that it has port 5900 forwarded.

## SSH Tunnel

You need to have SSH installed and configured.

Use the `-localhost` flag with x11vnc for it to bind to the local interface. Once that is done, you can use SSH to tunnel the port; then, connect to VNC through SSH.

Simple example (from http://www.karlrunge.com/x11vnc/index.html#tunnelling ):

    $ ssh -t -L 5900:localhost:5900 remote_host 'x11vnc -localhost -display :0'

(You will likely have to provide passwords/passphrases to login from your current location into your remote_host Unix account; we assume you have a login account on remote_host and it is running the SSH server)

And then in another terminal window on your current machine run the command:

    $ vncviewer -PreferredEncoding=ZRLE localhost:0

## Troubleshooting

1. You can check your ip address and make sure port 5900 is forwarded by visiting this[dead link 2020-04-03 ⓘ] website.

The factual accuracy of this article or section is disputed.

Reason: please use the first argument of the template to provide a brief explanation. (Discuss in Talk:X11vnc#)

2. Tested only on GNOME + GDM

If you cannot start the tunnel, and get error like XOpenDisplay(":0") failed, Check if you have a `~/.Xauthority` directory. If that does not exist, You can create one easily (Actually a symlink to actual one) by running command given below as normal user NOT ROOT OR USING Sudo as below:

    $ ln -sv $(dirname $(xauth info | awk '/Authority file/{print $3}')) ~/.Xauthority

then try above tunneling example and it should work fine. Further if you want this to be automatically done each time Xorg is restarted, create the xprofile file & make is executable as below

    $ ln -sf $(dirname $(xauth info | awk '/Authority file/{print $3}')) ~/.Xauthority

3. GNOME 3 and x11vnc

If you are using GNOME 3 and x11vnc and you get the following errors

    *** XOpenDisplay failed (:0)

    *** x11vnc was unable to open the X DISPLAY: ":0", it cannot continue.

Try running x11vnc like

    $ x11vnc -noxdamage -many -display :0 -auth /var/run/gdm/$(sudo ls /var/run/gdm | grep $(whoami))/database -forever -bg

Please update if this works / not works for any other display manager or desktop environment.

### Screensaver problem

If screensaver starts every 1-2 second, start x11vnc with `-nodpms` key.

### IPv6 port different from IPv4 port

The default behavior for the command:

    $ x11vnc -display :0 -rfbport 5908

is for the server to listen to TCP port 5908 and TCP6 port 5900. For the server to listen to the same TCP6 port, also use the `-rfbportv6` option to force the IPv6 listening port. For example:

    $ x11vnc -display :0 -rfbport 5908 -rfbportv6 5908

## See also

- original author site
- https://github.com/LibVNC/x11vnc
- Wikipedia:x11vnc

Categories:

- Security
- Remote desktop

Hidden categories:

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