~]# timedatectl  status
      Local time: Sun 2018-08-26 21:01:15 CST        ==> 本地系統實際時間，設置時間timedatectl set-time 15:58:30
                                                                           設置日期timedatectl set-time 20151120
                                                                           設置時間日期timedatectl set
 
-time ‘16:10:40 2015-11-20‘
      Universal time: Sun 2018-08-26 13:01:15 UTC    ==> 世界統一時間
      RTC time: Sun 2018-08-26 13:01:15              ==> 硬件時鐘的時間
      Time zone: Asia/Shanghai (CST, +0800)          ==> 當前時區，查看可用時區timedatectl list-timezones
                                                                   設置當前時區timedatectl set
 
-timezone "Asia/Shanghai"
                                                                   設置世界統一時區timedatectl set-timezone UTC
      NTP enabled: yes                               ==> 開啟自動同步時間服務器功能，timedatectl set-ntp true 或 timedatectl set-ntp false
      NTP synchronized: yes                          
 
==> 與時間服務器的同步狀態，如果顯示yes，則同步成功
      RTC in local TZ: no                            ==> 將時區設置為本地時區，timedatectl set-local-rtc 1
                                                         硬件時鐘設置為協調世界時（UTC）timedatectl set-local-rtc 0
      DST active: n/a



[root@network ~]# chronyc sources -v
210 Number of sources = 1

  .-- 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               
===============================================================================
^? controller                    9   6    37    47   +123us[ +123us] +/-   25ms           ==>如果前面是有個？表明時間服務器不可達


[root@network ~]# chronyc sources -v
210 Number of sources = 1

  .-- 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               
===============================================================================
^* controller                    9   6   177    46    +19us[  -65us] +/-   36ms         ==>如果前面是有個*表明時間服務器可同步








常用的命令：
啟動chronyd進程
systemctl start chronyd.service
強制單次進行時間同步  
chronyd -q ‘server <時間服務器域名> iburst‘
或者
ntpdate <ntp_server_name>
## 查看 ntp服務器是否可以正常同步
ntpdate -d <ntp_server_name>
## 查看 ntp_servers 狀態
chronyc sources -v
## 查看 ntp_sync 狀態
chronyc sourcestats -v
## 查看 ntp_servers 是否在線
chronyc activity -v
## 查看 ntp 詳細信息
chronyc tracking -v







當執行ntpdate -d <ntp_server_name>出現 NTP. Server dropped: strata too high  
可能原因是時間服務器stratum 值過高  調低就可以了  比如server為 8   client為9  則正常
當執行ntpdate -d <ntp_server_name>出現Server dropped: no data  
可能原因是沒有reach到時間服務器的時間服務，沒有獲取到數據，需要重新獲取一次或多次數據

[原]CentOS 7 chrony 筆記