Krdytkyu

Install x11vnc:

sudo apt-get install x11vnc

Create a password for your user:

x11vnc -storepasswd

If you have ssh setup you can use it to start x11vnc assuming you are logged in already, but remember to tell it to use your password file:

x11vnc -usepw

If you are not logged in you will get an error with the explanation:

If NO ONE is logged into an X session yet, but there is a greeter login

program like "gdm", "kdm", "xdm", or "dtlogin" running, you will need

to find and use the raw display manager MIT-MAGIC-COOKIE file.

Some examples for various display managers:



 gdm:     -auth /var/gdm/:0.Xauth

          -auth /var/lib/gdm/:0.Xauth

 kdm:     -auth /var/lib/kdm/A:0-crWk72

          -auth /var/run/xauth/A:0-crWk72

 xdm:     -auth /var/lib/xdm/authdir/authfiles/A:0-XQvaJk

 dtlogin: -auth /var/dt/A:0-UgaaXa

Assuming you are using lightdm for the login you can fix this problem you can start x11vnc with the command:

sudo x11vnc -xkb -noxrecord -noxfixes -noxdamage -display :0 -auth /var/run/lightdm/root/:0 -usepw

I am not sure this is the best idea to run x11vnc as root. Maybe someone could edit with a way to access the login without using sudo.

Once this is running you should be able to connect using a vnc client such as krdc (for KDE). You might want to use GNU Screen to keep x11vnc running without needing the ssh session open

I was able to figure this out using http://ubuntuforums.org/showthread.php?t=2039022.

Here is a sample upstart job you can use to make it run at startup. It needs to be put in /etc/init/x11vnc.conf. (Note that newer versions of Ubuntu use systemd so see the other answer that has a sample systemd config):

# description "start and stop x11vnc"



description "x11vnc"



start on runlevel [2345]

stop on runlevel [^2345]



console log

#chdir /home/

#setuid 1000

#setgid 1000



respawn

respawn limit 20 5



exec x11vnc -xkb -noxrecord -noxfixes -noxdamage -display :0 -auth /var/run/lightdm/root/:0 -usepw

Once you have made this file you can start it by running:
sudo start x11vnc
You can check the log at: /var/log/upstart/x11vnc.log

The above answers solve the problem, though a couple of amendments for versions of Ubuntu with systemd (15.04+), as follows:

• Take advantage of new -auth guess functionality in x11vnc - which helps!


• Update for systemd (not upstart)

Run the following to install:

sudo apt-get install x11vnc

sudo x11vnc -storepasswd yourVNCpasswordHERE /etc/x11vnc.pass

# for Ubuntu 15.04+

sudo nano /lib/systemd/system/x11vnc.service

# for Ubuntu 16.10+

sudo nano /etc/systemd/system/x11vnc.service

Insert this into the file:

[Unit]

Description="x11vnc"

Requires=display-manager.service

After=display-manager.service



[Service]

ExecStart=/usr/bin/x11vnc -xkb -noxrecord -noxfixes -noxdamage -display :0 -auth guess -rfbauth /etc/x11vnc.pass

ExecStop=/usr/bin/killall x11vnc

Restart=on-failure

Restart-sec=2



[Install]

WantedBy=multi-user.target

Then, start with:

sudo systemctl daemon-reload

sudo systemctl start x11vnc

And ensure the service starts on boot:

sudo systemctl enable x11vnc

Here's how:

1. 
   

   Install the X11VNC server (or through Ubuntu
   Software Center -> X11VNC Server)

   
   
   

   sudo apt-get install x11vnc
   
   

   
   


2. 
   

   Create a VNC password file.

   
   
   

   sudo x11vnc -storepasswd yourVNCpasswordHERE /etc/x11vnc.pass
   
   

   
   


3. 
   

   Create a job file in the editor nano (or gedit, leafpad etc.).

   
   
   

   sudo nano /etc/init/x11vnc.conf
   
   

   
   


4. 
   

   Paste this into the file:

   
   
   

   start on login-session-start
   
   
   
   script
   
   
   
   /usr/bin/x11vnc -xkb -forever -auth /var/run/lightdm/root/:0 -display :0 -rfbauth /etc/x11vnc.pass -rfbport 5900 -bg -o /var/log/x11vnc.log
   
   
   
   end script
   
   

   
   



5. Save the file. You created a job for the Upstart event login-session-start.



6. Restart Ubuntu.

That's it! You should now be able to connect with any VNC client even before login.

babelmonks answer as a bash script, copy and save as x11vnc.sh & run with sudo bash /path/to/file/x11vnc.sh (sorry dont have enough rep to post a comment)

#!/bin/bash

#install x11vnc & set password

apt-get install x11vnc -y

x11vnc -storepasswd 123456 /etc/x11vnc.pass

#create config file for  system service

cat > /lib/systemd/system/x11vnc.service <<-EOF

[Unit]

Description="x11vnc"

Requires=display-manager.service

After=display-manager.service



[Service]

 ExecStart=/usr/bin/x11vnc -xkb -noxrecord -noxfixes -noxdamage -display :0 -auth guess -rfbauth /etc/x11vnc.pass

ExecStop=/usr/bin/killall x11vnc



[Install]

WantedBy=multi-user.target

EOF

#restart new services &  enable on boot

systemctl daemon-reload

systemctl start x11vnc

systemctl enable x11vnc

Use my script for easy set up: installvncubuntu1604.sh

Usage:

chmod +x ./installvncubuntu1604.sh; sudo ./installvncubuntu1604.sh

Here is a config works for sddm (for KDE 5). Currently, -auth guess does not work for sddm, the auth file is different every time, so we need something like -auth /var/run/sddm/*.
The service looks like,

[Unit]

Description="x11vnc"

After=multi-user.target



[Service]

ExecStart=/bin/sh -c "/usr/bin/x11vnc -xkb -noxrecord -display :0 -auth /var/run/sddm/* -rfbauth /etc/x11vnc.pass"

ExecStop=/usr/bin/killall x11vnc



[Install]

WantedBy=multi-user.target

I have to put it after multi-user.target, if after display-manager.service, x11vnc cannot find auth file, maybe sddm generates auth file later. This is tested on Manjaro 18.

I use my own shell: https://github.com/dvdvideo1234/UbuntuBatches/tree/master/x11VNC

start on login-session-start



script



sudo /usr/bin/x11vnc -xkb -auth /var/run/lightdm/root/:0 -noxrecord -noxfixes -noxdamage -rfbauth /var/srv/x11vnc/x11vnc.pass -forever -bg -rfbport <your_port> -o /var/srv/x11vnc/x11vnc.log



end script

into the file:

/etc/init/x11vnc.conf

It makes it auto-start on boot, even on the logon screen it asks for a password.

Install x11vnc package

#sudo apt-get install x11vnc

Then set the password

#x11vnc -usepw

Then create startup script for x11vnc

#sudo nano /etc/x11vnc.sh

In File:

/usr/bin/x11vnc -bg -forever -shared -reopen -usepw

Then save

#sudo chmod 777 /etc/x11vnc.sh

Then add the script file to Control Center=>Startup Application
Then Click Add

> Name-----------x11vnc

> Command-----<map the script file

> Comment------service

This is must be required to add for all user

This will run after user login only