X11vnc

Related articles

• TigerVNC

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.

Systemd

To run x11vnc when system boots, create the override with systemctl edit x11vnc.service. The content should be like the following

/etc/systemd/system/x11vnc.service.d/override.conf

[Service]
ExecStart=
ExecStart=/usr/bin/x11vnc -many -display :0 -no6 -rfbport 5901 -auth /var/run/lightdm/root/:0

[Install]
WantedBy=graphical.target

Replace the second ExecStart with the command you run interactively. Run systemctl enable x11vnc.service if you need.

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

Running from the bash:

# 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.

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

Copying and Pasting

If copying and pasting does not work as expected, particularly if pasting to the remote side is not working or clipboard behaviour is not as expected, try adding -xkb:

$ x11vnc -xkb -display :0

Although the documentation does not indicate -xkb specifically for clipboard problems, it resolved an issue where vim complained that there was nothing in the * register.

Session closes unexpectedly

x11vnc enables the X Damage extension by default, which significantly reduces the load when the screen is not changing much and detects changed areas more quickly. This extension is known to cause issues[4][5][6][7], and it may cause the session to close unexpectedly with caught XIO error messages appearing at the log. This issue can be circumvented by using the -noxdamage option.

Tips and tricks

Run x11vnc "system-wide" in (GDM and GNOME Shell)

Note: These instructions will only work if you are using GDM and GNOME shell in Xorg.

Perform the following steps to run x11vnc in GDM to log in and then run x11vnc in a GNOME shell user session for a "system-wide" x11vnc:

First we need to create a systemd service to launch an x11vnc server in GDM:

/etc/systemd/system/x11vnc-gdm.service

[Unit]
Description=x11vnc server for GDM
After=display-manager.service

[Service]
ExecStart=
ExecStart=/usr/bin/x11vnc -many -shared -display :0 -auth /run/user/120/gdm/Xauthority -noxdamage -rfbauth user_home/.vnc/passwd
Restart=on-failure
RestartSec=3

[Install]
WantedBy=graphical.target

This will start an x11vnc server protected by the password stored at user_home/.vnc/passwd that shows GDM to any connected VNC client, however as you may notice, if you click on any of the users, as soon as you log in, all the VNC clients will show a black screen. To fix this, we need to create another systemd service that will start another x11vnc server in the GNOME Shell session as soon as you log in:

/etc/systemd/system/x11vnc-gnome-shell-YOUR_USER.service

[Unit]
Description=x11vnc server for Gnome shell session of your_user

[Service]
User=YOUR_USER
Type=simple
ExecStartPre=/bin/sh -c 'while ! pgrep -U "your_user" Xorg; do sleep 2; done'
ExecStart=/bin/sh -c 'sudo systemctl stop x11vnc-gdm.service && /usr/bin/x11vnc -many -shared -display :1 -auth user_home/.Xauthority -rfbauth user_home/.vnc/passwd'
Restart=on-failure
RestartSec=3

[Install]
WantedBy=graphical.target

Now, you need to keep the following in mind:

1. As you may notice in the ExecStart part of the systemd service, the command that executes can be separated in two tasks: first it stops x11vnc-gdm.service (killing the GDM x11vnc server) and then it starts the x11vnc server for the user in the GNOME shell session. This is done because if you keep running the GDM x11vnc server in the background, the new x11vnc server for the user will use the next available port, and you would need to change your client connection settings to connect either to the GDM x11vnc server or for your user-specific x11vnc server. A setup like this is useful because the GDM x11vnc server stops as soon as you log in into your account.
2. You need to create a service like this for each user that you want to have this functionality. (Do not forget to replace your_user and user_home with your actual username.)
3. You may need to change the -display :X part of the command to match your system settings. You can view your current display by running echo $DISPLAY. Use the resulting output to match the systemd service.

Now, as you might notice, x11vnc-gnome-shell.service is executed as your (probably) unprivileged user. This presents a problem if we want to stop the x11vnc-gdm.service, so we need to allow the user to stop the GDM service. This can be accomplished using sudo, but we need to allow the execution of only that specific command without a password. This can be done as follows:

Execute visudo(8) as root:

$ visudo

At the end of the file, add the following line and save your changes:

YOUR_USER ALL=(root) NOPASSWD: /usr/bin/systemctl stop x11vnc-gdm.service

Now you simply need to enable x11vnc-gdm.service and x11vnc-gnome-shell-your_user.service. When you restart your computer, both of them will start running and you can connect to your GDM and GNOME Shell using VNC.

Run x11vnc "system-wide" in (SDDM and Plasma)

To run x11vnc when the system boots into SDDM (if the aforementioned methods do not work for you), just edit x11vnc.service as follows:

/etc/systemd/system/x11vnc.service.d/override.conf

[Service]
ExecStart=
ExecStart=/bin/bash -c "/usr/bin/x11vnc -auth /var/run/sddm/* -display :0 -forever -loop -noxdamage -repeat -rfbauth /home/your_user/.vnc/passwd -shared"

[Install]
WantedBy=graphical.target

Remember to change your_user in the path, or use the preferred auth method. Disable the old x11vnc.service and reload the systemd manager configuration. Reenable the x11vnc.service unit afterwards.

Change x11vnc password in each boot

A setup like this could be useful if you need to share your desktop with several people that you do not trust and if you do not want to manually change the password every time. Such a setup would generate boot-unique passwords, so if you share your password with someone, you only need to reboot your computer (or re-run the systemd service) to change the password.

The new generated password will be stored as plain text in ~/.vnc/autovncpass, so it can be accessed with

$ cat /home/$USER/.vnc/autovncpass

Warning: Storing the password as plain text can pose a security threat, so use this at your own risk.

To accomplish this, perform the following steps:

First install the expect package.

Then, create the following script anywhere in your home directory:

~/Automatic-x11vnc-Password-Changer.exp

#!/usr/bin/expect -f

set timeout -1

log_user 0

#Change your username here
set USER "your_user"

#First we need to generate the password, if you want to 
#change the password generation, change the "openssl rand -hex 4" line

set NewVNCPassword [exec openssl rand -hex 4]

#Now we invoke x11vnc to change the password

spawn x11vnc --storepasswd

match_max 100000

expect -exact "Enter VNC password: "

send -- "$NewVNCPassword\r"

expect -exact "\r
Verify password:    "

send -- "$NewVNCPassword\r"

expect -exact "\r
Write password to /home/$USER/.vnc/passwd?  \[y\]/n "

send -- "y\r"

expect eof

#Save the Password to the /home/$USER/.vnc/ directory as plaintext, 

exec echo "$NewVNCPassword" > /home/$USER/.vnc/autovncpass

Now we need to create a systemd unit file that will execute the script at boot time:

/etc/systemd/system/vnc-automatic-password-changer.service

[Unit]
Description=x11vnc automatic password changer
Before=display-manager.service

[Service]
User=YOUR_USER
Type=oneshot
ExecStart=/path/to/script/Automatic-x11vnc-Password-Changer.exp                 

[Install]
WantedBy=graphical.target

Finally, start/enable the service to change the password. You can access the current password with

$ cat /home/$USER/.vnc/autovncpass

See also

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