I believe that the changes to mandatory settings won't affect any users that are currently logged in and running GNOME. So log out any users running GNOME, set the relevant settings, then log in as someone and run GNOME.
On machines I manage (SUSE Linux Enterprise Desktop, GNOME 2.24) I have a script which sets gconf stuff during boot to ensure my desired config it already in place. Here's what I use:
Code:
gconftool-2 --direct --config-source xml:readwrite:/etc/gconf/gconf.xml.mandatory --type int --set /apps/gnome-screensaver/idle_delay 4
gconftool-2 --direct --config-source xml:readwrite:/etc/gconf/gconf.xml.mandatory --type boolean --set /apps/gnome-screensaver/lock_enabled true
gconftool-2 --direct --config-source xml:readwrite:/etc/gconf/gconf.xml.mandatory --type boolean --set /apps/gnome-screensaver/idle_activation_enabled true
gconftool-2 --direct --config-source xml:readwrite:/etc/gconf/gconf.xml.defaults --set --type list --list-type=string /apps/gnome-screensaver/themes [blank-only]
Which means
- The screensaver activates after four minutes. Users cannot change this.
- The screensaver will lock the screen. Users cannot change this.
- Users cannot disable the screensaver.
- The default screensaver is to just blank the screen, but users can change this if they desire.
Change 4 to 20 in the first command and defaults to mandatory in the last command and I think you have what you want.