gsettings: no change after configuring settings

I have a system running Ubuntu 14.04.1. I would like to set the proxy settings globally via gsettings, but unfortunately I can't seem to change anything. I run the following command as root:

gsettings set org.gnome.system.proxy mode manual

When I try to retrieve the configuration, the mode is still set to 'none':

# gsettings get org.gnome.system.proxy mode
'none'

Any hints or ideas?

Running gsettings only changes the settings for the user who owns the X session that $DISPLAY points to. If you use sudo that's your current user. You can see that by the file $HOME/.config/dconf/user being modified.

To change the default settings for all users create the file /usr/share/glib-2.0/schemas/org.gnome.system.proxy.gschema.override with the content

[org.gnome.system.proxy]
mode="manual"

Then run

sudo glib-compile-schemas /usr/share/glib-2.0/schemas/