sudo apt-get install x11vnc
Set password
x11vnc -storepasswd password /path/to/passfile
or
x11vnc -storepasswd
to use ~/.vnc/passwd
x11vnc -display :0 -auth .Xauthority -rfbauth /path/to/passfile
or
x11vnc -usepw
to automatically use your ~/.vnc/passwd