su -
su - gdm -s /bin/bash
gdm@opteron ~ $ dbus-launch
No protocol specified
DBUS_SESSION_BUS_ADDRESS=unix:abstract=/tmp/dbus-tDdIT0TeFd,guid=842b21d1eef42fd311455f2d00001199
DBUS_SESSION_BUS_PID=7002
gdm@opteron ~ $ export DBUS_SESSION_BUS_ADDRESS=unix:abstract=/tmp/dbus-tDdIT0TeFd,guid=842b21d1eef42fd311455f2d00001199
gdm@opteron ~ $ export DBUS_SESSION_BUS_PID=7002
gdm@opteron ~ $  ps aux | grep dconf
david     6716  0.0  0.0 128544  2908 ?        Sl   11:20   0:00 /usr/libexec/dconf-service
gdm       7005  0.0  0.0   7960   824 pts/0    S+   11:27   0:00 grep --colour=auto dconf
gdm@opteron ~ $ /usr/libexec/dconf-service &
[1] 7007
gdm@opteron ~ $ GSETTINGS_BACKEND=dconf gsettings set org.gnome.desktop.background picture-uri "file:////usr/share/backgrounds/gnome/stripes-gentoo.jpg"
gdm@opteron ~ $