[root@localhost ~]# timedatectl --help
timedatectl [OPTIONS...] COMMAND ...
Query or change system time and date settings.
  -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
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

hwclock [--adjust][--debug][--directisa][--hctosys][--show][--systohc][--test]
[--utc][--version][--set --date=<日期与时间>]

yum install ntp
# 报如下错，
Error: Unable to find a match
# 使用如下方法 安装ntp服务
# 添加源
rpm -ivh http://mirrors.wlnmp.com/centos/wlnmp-release-centos.noarch.rpm
# 安装ntp服务
dnf  install wntp
# 时间同步
ntpdate ntp1.aliyun.com

[root@localhost etc]# chronyc --help
Usage: chronyc [-h HOST] [-p PORT] [-n] [-c] [-d] [-4|-6] [-m] [COMMAND]
[root@localhost etc]# chronyc help
System clock:               
tracking                    Display system time information
makestep                    Correct clock by stepping immediately
makestep <threshold> <updates>
                            Configure automatic clock stepping
maxupdateskew <skew>        Modify maximum valid skew to update frequency
waitsync [<max-tries> [<max-correction> [<max-skew> [<interval>]]]]
                            Wait until synchronised in specified limits
Time sources:               
sources [-v]                Display information about current sources
sourcestats [-v]            Display statistics about collected measurements
reselect                    Force reselecting synchronisation source
reselectdist <dist>         Modify reselection distance
NTP sources:                
activity                    Check how many NTP sources are online/offline
ntpdata [<address>]         Display information about last valid measurement
add server <address> [options]
                            Add new NTP server
add peer <address> [options]
                            Add new NTP peer
delete <address>            Remove server or peer
burst <n-good>/<n-max> [<mask>/<address>]
                            Start rapid set of measurements
maxdelay <address> <delay>  Modify maximum valid sample delay
maxdelayratio <address> <ratio>
                            Modify maximum valid delay/minimum ratio
maxdelaydevratio <address> <ratio>
                            Modify maximum valid delay/deviation ratio
minpoll <address> <poll>    Modify minimum polling interval
maxpoll <address> <poll>    Modify maximum polling interval
minstratum <address> <stratum>
                            Modify minimum stratum
offline [<mask>/<address>]  Set sources in subnet to offline status
online [<mask>/<address>]   Set sources in subnet to online status
onoffline                   Set all sources to online or offline status
                            according to network configuration
polltarget <address> <target>
                            Modify poll target
refresh                     Refresh IP addresses
Manual time input:          
manual off|on|reset         Disable/enable/reset settime command
manual list                 Show previous settime entries
manual delete <index>       Delete previous settime entry
settime <time>              Set daemon time
                            (e.g. Sep 25, 2015 16:30:05 or 16:30:05)
NTP access:                 
accheck <address>           Check whether address is allowed
clients                     Report on clients that have accessed the server
serverstats                 Display statistics of the server
allow [<subnet>]            Allow access to subnet as a default
allow all [<subnet>]        Allow access to subnet and all children
deny [<subnet>]             Deny access to subnet as a default
deny all [<subnet>]         Deny access to subnet and all children
local [options]             Serve time even when not synchronised
local off                   Don't serve time when not synchronised
smoothtime reset|activate   Reset/activate time smoothing
smoothing                   Display current time smoothing state
Monitoring access:          
cmdaccheck <address>        Check whether address is allowed
cmdallow [<subnet>]         Allow access to subnet as a default
cmdallow all [<subnet>]     Allow access to subnet and all children
cmddeny [<subnet>]          Deny access to subnet as a default
cmddeny all [<subnet>]      Deny access to subnet and all children
Real-time clock:            
rtcdata                     Print current RTC performance parameters
trimrtc                     Correct RTC relative to system clock
writertc                    Save RTC performance parameters to file
Other daemon commands:      
cyclelogs                   Close and re-open log files
dump                        Dump all measurements to save files
rekey                       Re-read keys from key file
shutdown                    Stop daemon
Client commands:            
dns -n|+n                   Disable/enable resolving IP addresses to hostnames
dns -4|-6|-46               Resolve hostnames only to IPv4/IPv6/both addresses
timeout <milliseconds>      Set initial response timeout
retries <retries>           Set maximum number of retries
keygen [<id> [<type> [<bits>]]]
                            Generate key for key file
exit|quit                   Leave the program
help                        Generate this help

[root@localhost etc]# chronyc 
chrony version 3.5
Copyright (C) 1997-2003, 2007, 2009-2019 Richard P. Curnow and others
chrony comes with ABSOLUTELY NO WARRANTY.  This is free software, and
you are welcome to redistribute it under certain conditions.  See the
GNU General Public License version 2 for details.
chronyc> sources -v
210 Number of sources = 2
  .-- Source mode  '^' = server, '=' = peer, '#' = local clock.
 / .- Source state '*' = current synced, '+' = combined , '-' = not combined,
| /   '?' = unreachable, 'x' = time may be in error, '~' = time too variable.
||                                                 .- xxxx [ yyyy ] +/- zzzz
||      Reachability register (octal) -.           |  xxxx = adjusted offset,
||      Log2(Polling interval) --.      |          |  yyyy = measured offset,
||                                \     |          |  zzzz = estimated error.
||                                 |    |           \
MS Name/IP address         Stratum Poll Reach LastRx Last sample               
===============================================================================
^* 120.25.115.20                 2   6   377    25  -1078us[-1292us] +/-   19ms
^- 203.107.6.88                  2   6   377    25  -5231us[-5445us] +/-   23ms
chronyc> exit
exit

* 表示chronyd当前同步到的源。
+ 表示可接受的信号源，与选定的信号源组合在一起。
- 表示被合并算法排除的可接受源。
？ 指示已失去连接性或其数据包未通过所有测试的源。它也显示在启动时，直到从中至少收集了3个样本为止。
x 表示chronyd认为是虚假行情的时钟（即，其时间与大多数其他来源不一致）。
〜 表示时间似乎具有太多可变性的来源。