systemd-timesyncd 的預設 NTP 伺服器是什麼？

在我的 yocto 發行版中啟用了該服務systemd-timesyncd.service。其配置文件（timesyncd.conf）如下：

#  This file is part of systemd.
#
#  systemd is free software; you can redistribute it and/or modify it
#  under the terms of the GNU Lesser General Public License as published by
#  the Free Software Foundation; either version 2.1 of the License, or
#  (at your option) any later version.
#
# Entries in this file show the compile time defaults.
# You can change settings by editing this file.
# Defaults can be restored by simply deleting this file.
#
# See timesyncd.conf(5) for details.

[Time]
#NTP=
#FallbackNTP=time1.google.com time2.google.com time3.google.com time4.google.com
#RootDistanceMaxSec=5
#PollIntervalMinSec=32
#PollIntervalMaxSec=2048

如您所見，NTP未設置配置文件的選項。儘管如此，服務設置了系統日期，並且通過一些登錄journalctl，我看到 NTP 伺服器可能是time1.google.com.

我的問題是：NTP 伺服器在哪裡設置systemd-timesyncd？

謝謝

來自 timesyncd.conf 手冊頁。

CONFIGURATION DIRECTORIES AND PRECEDENCE
  The default configuration is defined during compilation, so a configuration file
  is only needed when it is necessary to deviate from those defaults. By default,
  the configuration file in /etc/systemd/ contains commented out entries showing the
  defaults as a guide to the administrator. This file can be edited to create local
  overrides.

引用自：https://serverfault.com/questions/1111885