Comment 8 for bug 1307546

Actually - nvidia-prime seems less likely now that I read gpu-manager code. It's a "new" tool for upgrades, and consequently would run it's enable_nvidia routine the first boot.

It checks how many cards are in the system, and if it only finds 1, removes the old xorg.conf without making a new one.

    /* See if enabling the driver failed */
    if (status) {
        /* If xorg.conf exists, make sure it contains
         * the right BusId and NO NOUVEAU or FGLRX. If it doesn't, create a
         * xorg.conf from scratch */
        if (!check_vendor_bus_id_xorg_conf(devices, cards_n,
                                           vendor_id, "nvidia")) {
            fprintf(log_handle, "Check failed\n");

            /* Remove xorg.conf */
            remove_xorg_conf();

            /* Only useful if more than one card is available */
            if (cards_n > 1) {
                /* Write xorg.conf */
                write_to_xorg_conf(devices, cards_n, vendor_id);
            }
        }
        else {
            fprintf(log_handle, "No need to modify xorg.conf. Path: %s\n", xorg_conf_file);
        }
    }