# Use public servers from the pool.ntp.org project.
# Please consider joining the pool (http://www.pool.ntp.org/join.html).
pool ntp5.aliyun.com iburst
# Record the rate at which the system clock gains/losses time.
driftfile /var/lib/chrony/drift
# Allow the system clock to be stepped in the first three updates
# if its offset is larger than 1 second.
makestep 1.0 3
# Enable kernel synchronization of the real-time clock (RTC).
rtcsync
# Enable hardware timestamping on all interfaces that support it.
#hwtimestamp *
# Increase the minimum number of selectable sources required to adjust
# the system clock.
#minsources 2
# Allow NTP client access from local network.
#allow 192.168.0.0/16
# Serve time even if not synchronized to a time source.
#local stratum 10
# Specify file containing keys for NTP authentication.
keyfile /etc/chrony.keys
# Get TAI-UTC offset and leap seconds from the system tz database.
leapsectz right/UTC
# Specify directory for log files.
logdir /var/log/chrony
# Select which information is logged.
#log measurements statistics tracking

chronyd -q 'pool ntp1.aliyun.com iburst'
# output
2021-01-20T13:43:30Z chronyd version 3.5 starting (+CMDMON +NTP +REFCLOCK +RTC +PRIVDROP +SCFILTER +SIGND +ASYNCDNS +SECHASH +IPV6 +DEBUG)
2021-01-20T13:43:34Z System clock wrong by -0.001392 seconds (step)
2021-01-20T13:43:34Z chronyd exiting

systemctl enable chronyd
systemctl start chronyd

[root@linux ~] chronyc tracking
Reference ID    : 00000000 ()
Stratum         : 0
Ref time (UTC)  : Thu Jan 01 00:00:00 1970
System time     : 0.000000000 seconds fast of NTP time
Last offset     : +0.000000000 seconds
RMS offset      : 0.000000000 seconds
Frequency       : 20.852 ppm fast
Residual freq   : +0.000 ppm
Skew            : 0.000 ppm
Root delay      : 1.000000000 seconds
Root dispersion : 1.000000000 seconds
Update interval : 0.0 seconds
Leap status     : Not synchronised
Reference ID    : 00000000 ()
Stratum         : 0
Ref time (UTC)  : Thu Jan 01 00:00:00 1970
System time     : 0.000000000 seconds fast of NTP time
Last offset     : +0.000000000 seconds
RMS offset      : 0.000000000 seconds
Frequency       : 20.852 ppm fast
Residual freq   : +0.000 ppm
Skew            : 0.000 ppm
Root delay      : 1.000000000 seconds
Root dispersion : 1.000000000 seconds
Update interval : 0.0 seconds
Leap status     : Not synchronised
[root@imac ~]# chronyc sources
210 Number of sources = 4
MS Name/IP address         Stratum Poll Reach LastRx Last sample
===============================================================================
^* 119.28.183.184                2   6    73    11  -2557ns[ -876us] +/-   57ms
^? ntp.wdc1.us.leaseweb.net      2   7     2    72   -487us[-1360us] +/-  248ms
^- time.cloudflare.com           3   6   123    70   +376us[ -497us] +/-   86ms
^- undefined.hostname.local>     2   6    37    10  -3071us[-3071us] +/-  118ms
~]$ timedatectl	# 显示本地时间和通用时间、当前使用的时区、NTP (Network time Protocol)配置状态以及与夏令时相关的附加信息。
               Local time: Wed 2021-01-20 22:00:22 CST
           Universal time: Wed 2021-01-20 14:00:22 UTC
                 RTC time: Wed 2021-01-20 22:00:22
                Time zone: Asia/Shanghai (CST, +0800)
System clock synchronized: yes
              NTP service: active
          RTC in local TZ: yes
缺省情况下，系统配置为UTC。要配置您的系统以本地时间维护时钟，以root用户身份运行带有set-local-rtc选项的timedatectl命令，如果要配置您的系统维护本地时间的时钟，将布尔值替换为yes(或者，或者，y, true, t，或1)。如果要配置系统使用UTC，将布尔值替换为no(或者，或者，n, false, f，或0)。
~] timedatectl set-local-rtc false
~] timedatectl list-timezones              # 列出所有可用的时区
~] timedatectl set-timezone time_zone      # 将time_zone替换为timedatectl列表-timezones中列出的任何值
~] timedatectl list-timezones | grep Asia  # 列出与当前位置最近的时区，使用timedatectl命令和list-timezones命令行选项。例如，要列出亚洲所有可用的时区
~] timedatectl set-timezone Asia/Shanghai  # 将时区改为：亚洲/Shanghai
与远程服务器同步系统时钟
要使系统与远程NTP服务器同步系统时钟，将boolean替换为yes(默认选项)。要禁用此特性，请将布尔值替换为no。
timedatectl set-ntp yes
设置硬件时钟为本地时区
~] timedatectl set-local-rtc 1  # 设置硬件时钟为本地时区
~] timedatectl set-local-rtc 0  # 设置硬件时钟为协调世界时(UTC)
~] timedatectl set-ntp true     # 启用与远程NTP服务器的自动时间同步
~] timedatectl set-ntp false    # 禁用与远程NTP服务器的自动时间同步
同步日期和时间
同步硬件时钟和系统时间时，还可以通过添加–utc或–localtime选项来指定将硬件时钟保持在本地时间还是UTC 。与使用相似–set，UTC或LOCAL记录在/etc/adjtime文件中。
该hwclock –systohc –utc 命令在功能上与相似，timedatectl set-local-rtc false 并且 hwclock –systohc –local 是的替代方法 timedatectl set-local-rtc true
有两个方向可以同步硬件时钟和当前系统时间
hwclock --systohc  #  设置硬件时钟为当前系统时间
hwclock --hctosys  #  设置硬件时钟为系统时间
将硬件时钟与系统时间同步
要将硬件时钟设置为当前系统时间并将硬件时钟保持在本地时间
~] hwclock --systohc --localtime
为避免时区和DST切换问题，建议将硬件时钟保持为UTC。所示的示例3.11“将硬件时钟与系统时间同步”很有用，例如，在Windows系统的多重启动的情况下，假定默认情况下硬件时钟在本地时间运行，并且所有其他系统都需要适应也可以使用当地时间 虚拟机可能也需要它；如果主机提供的虚拟硬件时钟以本地时间运行，则也需要将来宾系统配置为使用本地时间。
CONFIGURING THE DATE AND TIME
&nbsp&nbspCreated：&nbsp2021-01-20 21:23:40&nbsp&nbsp&nbsp3101&nbsp&nbsp