ntp server 的搭建和配置见 https://www.cnblogs.com/30go/p/11231110.html
客户端同步时间的操作见：https://cloud.tencent.com/developer/article/1832436
https://www.farland.vip/2021/01/26/ubuntu-change-timezone-ntp-server/
使用 timedatectl 的操作如下：
timedatectl --help
timedatectl [OPTIONS...] COMMAND ...
Query or change system time and date settings.
Commands:
status Show current time settings
show Show properties of systemd-timedated
set-time TIME Set system time
set-timezone ZONE Set system time zone
list-timezones Show known time zones
set-local-rtc BOOL Control whether RTC is in local time
set-ntp BOOL Enable or disable network time synchronization
systemd-timesyncd Commands:
timesync-status Show status of systemd-timesyncd
show-timesync Show properties of systemd-timesyncd
Options:
-h --help Show this help message
--version Show package version
--no-pager Do not pipe output into a pager
--no-ask-password Do not prompt for password
-H --host=[USER@]HOST Operate on remote host
-M --machine=ConTAINER Operate on local container
--adjust-system-clock Adjust system clock when changing local RTC mode
--monitor Monitor status of systemd-timesyncd
-p --property=NAME Show only properties by this name
-a --all Show all properties, including empty ones
--value When showing properties, only print the value
See the timedatectl(1) man page for details.
关闭时间同步服务的操作： timedatectl set-ntp false，打开时间同步服务的操作：timedatectl set-ntp true，具体的执行结果可以通过 timedatectl status 查看
配置文件 /etc/systemd/timesyncd.conf 中的下列两个配置表示轮询的最低时间和轮询的最大时间，单位 秒，测试证明两者设置为同一个值也可以工作
# 表时 ntp 服务的 ip #NTP=192.168.1.2 #轮询的最小时间间隔 #PollIntervalMinSec=32 #轮询的最大时间间隔 #PollIntervalMaxSec=2048
