File X11-displaymanager-gdm of Package gdm

gdm_vars() {
    case "${DISPLAYMANAGER##*/}" in
        gdm|GDM|Gnome|GNOME)
            RELOADSIGNAL="-USR1"
            DISPLAYMANAGER=/usr/sbin/gdm
            PIDFILE=/run/gdm/gdm.pid

            # let gdm run the Xserver as root if access to /dev/fb*
            # is required (bsc#1075805)
            # The GDM_DISABLE_USER_DISPLAY_SERVER variable is added by patch
            # gdm-add-runtime-option-to-disable-starting-X-server-as-u.patch
            if [ ! -c /dev/dri/card0 -a \
                 ! -c /dev/nvidiactl ]; then
                export GDM_DISABLE_USER_DISPLAY_SERVER=1
            fi

            return 0 ;;
       *) return 1 ;;
    esac

    return 1
}