在CentOS7中，可用新的工具Chrony来为主机作时间同步。Chrony可同时扮演NTP Client和NTP Server的角色，而且它非常简单。
安装Chrony
sudo yum install -y chrony
配置Chrony
编辑：/etc/chrony.conf
注释原有的server，加入本地区公共时间同步服务器。 访问：http://www.pool.ntp.org/zone/cn，获取中国区公用时间同步服务器。如：
- server 3.cn.pool.ntp.org
- server 3.asia.pool.ntp.org
- server 2.asia.pool.ntp.org
cat /etc/chrony.conf
......
# 注释原有的server
#server 0.centos.pool.ntp.org iburst
#server 1.centos.pool.ntp.org iburst
#server 2.centos.pool.ntp.org iburst
#server 3.centos.pool.ntp.org iburst
# 加入本地区公共时间同步服务器
server 3.cn.pool.ntp.org iburst
server 3.asia.pool.ntp.org iburst
server 2.asia.pool.ntp.org iburst
......
启用Chrony
sudo systemctl enable chronyd.service
sudo systemctl start chronyd.service
检查NTP来源状态
$ chronyc sourcestats
210 Number of sources = 3
Name/IP Address NP NR Span Frequency Freq Skew Offset Std Dev
==============================================================================
202.118.1.130 10 4 461 23.358 166.175 +2734us 16ms
dns1.synet.edu.cn 12 7 525 -13.554 114.141 -2144us 15ms
ns2.sol.az 8 5 397 -47.513 8.539 -40ms 629us
查看NTP详细同步状态
$ chronyc sources -v
210 Number of sources = 3
.-- 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
|| / xxxx = adjusted offset,
|| Log2(Polling interval) -. | yyyy = measured offset,
|| \ | zzzz = estimated error.
|| | |
MS Name/IP address Stratum Poll Reach LastRx Last sample
===============================================================================
^+ 202.118.1.130 2 6 337 95 -7332us[-4357us] +/- 75ms
^* dns1.synet.edu.cn 2 6 377 30 +2326us[+3677us] +/- 81ms
^- ns2.sol.az 2 6 377 158 -32ms[ -31ms] +/- 224ms
（完）