installer xvfb sous ubuntu

salut.
 en fait j'ai installé xvfb sous ubuntu/ et apés lancement , il me donne ce message:

root@benouda:/home/benouda# /etc/init.d/scriptxvfb_ubuntu.sh  start

Starting Virtual Frame Buffer X Server (Xvfb).

Fatal server error:
Server is already active for display 8101
    If this server is no longer running, remove /tmp/.X8101-lock
    and start again.
........................................................voici mon scripte......................
voici le lien: http://scenari-platform.org/trac/scenari/wiki/InstallServerLinux/serviceXvfb
......................................................................................................................

#!/bin/sh
# chkconfig: 345 90 10
# description: Start/stop/restart the virtual frame buffer based X Server (Xvfb)
#

#==============================================================================
# Configuration
xvfb_path=/usr/bin/Xvfb
xvfb_display=1
killall_path=/usr/bin/killall
#==============================================================================

xvfb_start() {
  if [ -x $xvfb_path ]; then
    echo "Starting Virtual Frame Buffer X Server (Xvfb)."
    $xvfb_path :$xvfb_display -screen 0 800x600x16 &
  else
    echo "Error: Could not find $xvfb_path. Cannot start Xvfb."
  fi
}

xvfb_stop() {
  if [ -x $killall_path ]; then
    echo "Stopping Virtual Frame Buffer X Server (Xvfb)."
    $killall_path Xvfb 2> /dev/null
  else
    echo "Error: Could not find $killall_path. Cannot stop Xvfb."
  fi
}

case "$1" in
  'start')
    xvfb_start
    ;;
  'stop')
    xvfb_stop
    ;;
  'restart')
    xvfb_stop
    sleep 1
    xvfb_start
    ;;
  *)
    if [ -x /usr/bin/basename ]; then
      echo "usage: `/usr/bin/basename $0` start|stop|restart"
    else
      echo "usage: $0 start|stop|restart"
    fi
esac

merci d'avance