sudo apt-get install x11vnc
    sudo x11vnc -storepasswd /etc/x11vnc.pass

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

[Unit]
    Description=Start x11vnc at startup.
    After=multi-user.target
    [Service]
    Type=simple
    ExecStart=/usr/bin/x11vnc -auth guess -forever -loop -noxdamage -repeat -rfbauth /etc/x11vnc.pass -rfbport 5900 -shared
    [Install]
    WantedBy=multi-user.target

sudo systemctl enable x11vnc.service
    sudo systemctl daemon-reload

...
     [xrdp1]
     name=Remote Session
     lib=libvnc.so
     username=ask
     password=ask
     ip=127.0.0.1
     port=ask-1

     [xrdp2]
     name=Local Session
     lib=libvnc.so
     username=
     password=ask
     ip=127.0.0.1
     port=5900
     ...

sudo shutdown -r now