RealVNC xstartup script for Ubuntu 13.04. To use, save this file to `/etc/vnc/xstartup.custom` and make it executable. Then ensure that you have installed the `gnome-session-fallback` package.

xstartup.custom

#!/bin/sh

# VNC Server (Virtual-Mode) start-up script.

unset XDG_RUNTIME_DIR

[ -r $HOME/.Xresources ] && xrdb $HOME/.Xresources
xsetroot -solid grey

if [ -f /usr/bin/gnome-session ]; then
  # Some gnome session types won't work with Xvnc, try to pick a sensible 
  # default.
  for SESSION in "gnome-fallback" "ubuntu-2d" "2d-gnome"; do
    if [ -f /usr/share/gnome-session/sessions/$SESSION.session ]; then
      DESKTOP_SESSION=$SESSION; export DESKTOP_SESSION
      GDMSESSION=$SESSION; export GDMSESSION
      STARTUP="/usr/bin/gnome-session --session=$SESSION"; export STARTUP
    fi
  done
fi

if   [ -x /etc/X11/Xsession ]; then /etc/X11/Xsession
elif [ -x /etc/X11/xdm/Xsession ]; then /etc/X11/xdm/Xsession
elif [ -x /etc/X11/xinit/Xsession ]; then /etc/X11/xinit/Xsession
elif [ -x /etc/gdm/Xsession ]; then /etc/gdm/Xsession gnome-session
elif [ -x /etc/kde/kdm/Xsession ]; then /etc/kde/kdm/Xsession
elif [ -x /usr/dt/bin/Xsession ]; then
  XSTATION=1 DTXSERVERLOCATION=local /usr/dt/bin/Xsession
elif [ -x /usr/dt/bin/dtsession ]; then /usr/dt/bin/dtsession
else
  if which twm > /dev/null 2>&1; then
    xterm -geometry 80x24+10+10 -ls -title "$VNCDESKTOP Desktop" &
    twm
  else
    xterm -geometry 80x24+10+10 -ls -title "$VNCDESKTOP Desktop"
  fi
fi

vncserver-virtual -kill $DISPLAY