先简单介绍一下chrony
chrony是linux7开始使用的时间同步服务，系统内置。比ntp更加快捷，简单
实际配置中总是出现各种问题，排除时，首先关闭selinux，关闭防火墙。
尝试过多次，最近一次成功的案例是，服务端的配置文件修改了三项
自己是自己的服务器
# Please consider joining the pool (http://www.pool.ntp.org/join.html).
server 192.168.102.11 iburst
开启同步许可
# Allow NTP client access from local network.
allow 192.168.102.0/24
开启同步层
# Serve time even if not synchronized to a time source.
local stratum 10
保存后，本地重启chronyd服务，客户端也重启chronyd服务。可以自动同步
含有服务端和客户端：服务名为 chronyd，客户端工具chronyc
配置文件 /etc/chron.conf
# Use public servers from the pool.ntp.org project.
# Please consider joining the pool (http://www.pool.ntp.org/join.html).
server 192.168.102.131 iburst
此项为时间源地址
修改后需要重启服务，然后用chronyc sources -v 查看同步情况
[root@student ~]# 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
===============================================================================
^? 192.168.102.131 0 8 0 - +0ns[ +0ns] +/- 0ns
这是服务器不可达，时间未同步的反馈
[root@student ~]# 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
===============================================================================
^* 192.168.102.131 3 6 17 13 +5813ns[ +120us] +/- 41ms
这是正常同步的信息反馈
理论上，只要服务安装了，配置文件没错，重启过服务，关闭了selinux和firewalld，网络通，就会很对进行同步，此次却无法进行同步。
结果发现是客户端的chrony版本比服务端的chrony版本高导致，全部更新到最新版本后马上就同步了