Comment # 7 on bug 934901 from Dominique Leuenberger

It's an Xorg message we see in the log, not x-gdm-session (that's just the
logging daemon, which happens to start X for us)

The log is produced in the file ./hw/xfree86/os-support/linux/systemd-logind.c

    if (dbus_message_is_signal(message,
                               "org.freedesktop.DBus", "NameOwnerChanged")) {
        char *name, *old_owner, *new_owner;

        dbus_message_get_args(message, &error,
                              DBUS_TYPE_STRING, &name,
                              DBUS_TYPE_STRING, &old_owner,
                              DBUS_TYPE_STRING, &new_owner, DBUS_TYPE_INVALID);
        if (dbus_error_is_set(&error)) {
            LogMessage(X_ERROR, "systemd-logind: NameOwnerChanged: %s\n",
                       error.message);
            dbus_error_free(&error);
            return DBUS_HANDLER_RESULT_NOT_YET_HANDLED;
        }

        if (name && strcmp(name, "org.freedesktop.login1") == 0)
            FatalError("systemd-logind disappeared (stopped/restarted?)\n");

        return DBUS_HANDLER_RESULT_NOT_YET_HANDLED;