root@muletto-debian:~# pico x11vnc.log
  GNU nano 2.2.4             File: x11vnc.log

03/04/2011 17:50:23 passing arg to libvncserver: -rfbport
03/04/2011 17:50:23 passing arg to libvncserver: 5900
03/04/2011 17:50:23 passing arg to libvncserver: -passwd
03/04/2011 17:50:23 x11vnc version: 0.9.10 lastmod: 2010-04-28  pid: 4710
03/04/2011 17:50:23 XOpenDisplay(":0") failed.
03/04/2011 17:50:23 Trying again with XAUTHLOCALHOSTNAME=localhost ...

03/04/2011 17:50:23 ***************************************
03/04/2011 17:50:23 *** XOpenDisplay failed (:0)

*** x11vnc was unable to open the X DISPLAY: ":0", it cannot continue.
*** There may be "Xlib:" error messages above with details about the failure.

Some tips and guidelines:

** An X server (the one you wish to view) must be running before x11vnc is
   started: x11vnc does not start the X server.  (however, see the -create
   option if that is what you really want).