Bloqueando o background no gnome 3

 Usuários de computdor tem mania de mexer no papel de parede, e sabe, sai cada besteira, às vezes algo impróprio para um laboratório de escola. No laboratório em que trabalho tenho duas versões do ubuntu 11.10 e 10.10, pra falar a verdade nem lembro se o gconftool-2 funciona no 10.10, mas fiz um script que permite que você administrador impeça a alteração do background independente de sistema, gsettings ou gconftool-2. Uma dica é que você pode copiar um arquivo chamado default.jpg para /usr/share/backgrounds ou deixar que ele faça o download sugerido na linha com wget, veja o script

	#!/bin/bash
	# set mandatory wallpaper gnome3
	# script to change kd3 3.5 wallpaper https://gist.github.com/1621547
	# http://www.marcusmoeller.ch/misc/using-dconf-magic-to-change-background-image.html
	# http://askubuntu.com/questions/52120/how-to-change-wallpapers-of-all-clients
	# http://blog.sriunplugged.com/shell-scripting/automatic-desktop-wallpaper-changer/
	# download
	# wget -c https://raw.github.com/gist/1372927/ -O ~/mandatory-wallpaper.sh && chmod +x $_
	# In Ubuntu 11.10 (or any GNOME 3 system), you should be able to do this with:
	#
	# Create a file /etc/dconf/profile/user with the contents:
	#
	# user
	# site
	#
	# Make a default setting by creating a file /etc/dconf/db/site.d/background with
	# the contents:
	#
	# [org/gnome/desktop/background]
	# picture-uri='file:///usr/share/backgrounds/default.jpg'
	#
	# And finally make the default mandatory by creating
	# /etc/dconf/db/site.d/locks/background with the contents:
	#
	# /org/gnome/desktop/background/picture-uri
	#
	# dconf settings need to be compiled to work so run sudo dconf update The first
	# time you run this, you'll need to reboot to see the effect. Currently, there's
	# a bug where users will still see the normal Background chooser; it just won't
	# actually change the background.
	# pega somente a extensão do arquivo arq
	# echo ${arq##*.}
	#wget -c http://ns223506.ovh.net/rozne/1ea221a3af6573ed5b35806d5823d3e0/wallpaper-740152.jpg -O /usr/share/backgrounds/default.jpg
	# put this in your crontab -- crontab -e
	# */15 * * * * /root/mandatory-wallpaper.sh
	# get random file
	FILE=`find /usr/share/backgrounds/ -type f -iregex ".*\.png\|.*\.jpg" | shuf -n1`
	ON_USER=aluno #your username here
	export DBUS_SESSION=$(grep -v "^#" /home/$ON_USER/.dbus/session-bus/`cat /var/lib/dbus/machine-id`-0)
	# Change lines containing filename default.jpg
	if [ `lsb_release -sc` == "oneiric" ] ; then
	which dconf-editor &>/dev/null || apt-get install -y dconf-tools
	[ -d /etc/dconf/profile ] || mkdir -p /etc/dconf/profile/
	echo "user" > /etc/dconf/profile/user
	echo "site" >> /etc/dconf/profile/user
	[ -d /etc/dconf/db/site.d ] || mkdir -p /etc/dconf/db/site.d
	echo "[org/gnome/desktop/background]" > /etc/dconf/db/site.d/background
	echo "picture-uri='file://$FILE'" >> /etc/dconf/db/site.d/background
	[ -d /etc/dconf/db/site.d/locks ] || mkdir -p /etc/dconf/db/site.d/locks/
	echo "/org/gnome/desktop/background/picture-uri" > /etc/dconf/db/site.d/locks/background
	dconf update
	else
	#gconftool-2 --direct --config-source xml:readwrite:/etc/gconf/gconf.xml.mandatory --set /desktop/gnome/background/picture_filename --type string "$file"
	# Setting wallpaper default to all users
	gconftool-2 --direct \
	--config-source xml:readwrite:/etc/gconf/gconf.xml.defaults \
	-t str -s /desktop/gnome/background/picture_filename "$FILE"
	# setting wallpaper to current user
	sudo -u $ON_USER $DBUS_SESSION /usr/bin/gconftool-2 -t string -s /desktop/gnome/background/picture_filename "$FILE"
	sudo -u $ON_USER $DBUS_SESSION /usr/bin/gconftool-2 -t string -s /desktop/gnome/background/picture_options stretched
	fi

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