apt-get install x11vnc

x11vnc -storepasswd

Enter VNC password: *********
Verify password: *********  
Write password to /root/.vnc/passwd?  [y]/n y
Password written to: /root/.vnc/passwd

x11vnc -auth guess -forever -loop -noxdamage -repeat -rfbauth /root/.vnc/passwd -rfbport 5900 -shared

nano /etc/systemd/system/x11vnc.service

[Unit]
Description=x11vnc remote desktop server
After=multi-user.target

[Service]
Type=simple
ExecStart=/usr/bin/x11vnc -auth guess -forever -loop -noxdamage -repeat -rfbauth /root/.vnc/passwd -rfbport 5900 -shared

Restart=on-failure

[Install]
WantedBy=multi-user.target

systemctl daemon-reload
systemctl start x11vnc
systemctl status x11vnc
-------------
if active (running)
systemctl enable x11vnc.service