apt-get install x11vnc
x11vnc -storepasswd VNCpasswordHERE /etc/x11vnc.pass
vi /lib/systemd/system/x11vnc.service
[Unit]
Description="x11vnc"
Requires=display-manager.service
After=display-manager.service

[Service]
ExecStart=/usr/bin/x11vnc -xkb -noxrecord -noxfixes -noxdamage -display :0 -auth guess -ncache 10 -rfbauth /etc/x11vnc.pass -rfbport 55528 -forever -shared
ExecStop=/usr/bin/killall x11vnc
Restart=on-failure
Restart-sec=2

[Install]
WantedBy=multi-user.target
chmod 775 /lib/systemd/system/x11vnc.servicesystemctl daemon-reload
systemctl start x11vnc
systemctl enable x11vnc