~]# timedatectl  status

      Local time: Sun -- :: CST        ==> 本地系统实际时间，设置时间timedatectl set-time ::

                                                                           设置日期timedatectl set-time

                                                                           设置时间日期timedatectl set-time '16:10:40 2015-11-20'

      Universal time: Sun -- :: UTC    ==> 世界统一时间

      RTC time: Sun -- ::              ==> 硬件时钟的时间

      Time zone: Asia/Shanghai (CST, +)          ==> 当前时区，查看可用时区timedatectl list-timezones

                                                                   设置当前时区timedatectl set-timezone "Asia/Shanghai"

                                                                   设置世界统一时区timedatectl set-timezone UTC

      NTP enabled: yes                               ==> 开启自动同步时间服务器功能，timedatectl set-ntp true 或 timedatectl set-ntp false

      NTP synchronized: yes                          ==> 与时间服务器的同步状态，如果显示yes，则同步成功

      RTC in local TZ: no                            ==> 将时区设置为本地时区，timedatectl set-local-rtc

                                                         硬件时钟设置为协调世界时（UTC）timedatectl set-local-rtc

      DST active: n/a

[root@network ~]# chronyc sources -v

 Number of sources = 

  .-- 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                                  +123us[ +123us] +/-   25ms           ==>如果前面是有个？表明时间服务器不可达 

如果一直显示为？ 表示网络没有设置正确，需要设置配置文件中的网络
server : 10.50.10.10
client : 10.50.10.20
编辑 /etc/chrony.conf

【client】

# Allow NTP client access from local network.
#allow 192.168.0.0/16
allow 10.50.10.0/16

【server】

# Allow NTP client access from local network.
#allow 192.168.0.0/16
allow 10.50.10.20/24

再重新检查是否可以同步

[root@network ~]# chronyc sources -v

 Number of sources = 

  .-- 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                                  +19us[  -65us] +/-   36ms         ==>如果前面是有个*表明时间服务器可同步

常用的命令：

启动chronyd进程

systemctl start chronyd.service

强制单次进行时间同步

chronyd -q 'server <时间服务器域名> iburst'

或者

ntpdate <ntp_server_name>

## 查看 ntp服务器是否可以正常同步

ntpdate -d <ntp_server_name>

## 查看 ntp_servers 状态

chronyc sources -v

## 查看 ntp_sync 状态

chronyc sourcestats -v

## 查看 ntp_servers 是否在线

chronyc activity -v

## 查看 ntp 详细信息

chronyc tracking -v

当执行ntpdate -d <ntp_server_name>出现 NTP. Server dropped: strata too high

可能原因是时间服务器stratum 值过高  调低就可以了  比如server为    client为9  则正常

当执行ntpdate -d <ntp_server_name>出现Server dropped: no data

可能原因可以使用journalctl -xe 来查看，可能是selinux没有关闭 可以在/etc/selinux/conf中disable