前言
在CentOS7以前，都是用ntpd来同步时间的，如何配置详见之前的文章：https://blog.terrynow.com/2021/10/17/centos7-sync-time-automatically-with-ntp/
安装
装了CentOS8后，发现yun仓库里已经找不到ntp了，原来CentOS8已经把时间同步软件换成了chrony了，一般来说默认安装的CentOS8已经包含chrony了，如果没有安装，可以手动安装下
#检查chrony是否安装 [root@localhost ~]#rpm -q chrony package chrony is not installed #没有安装的话，就用yum安装chrony [root@localhost ~]#yum install chrony
配置
chrony和ntpd一样，都是既做服务端，又可以当做客户端的。配置文件在/etc/chrony.conf
- 作为服务器端的配置
修改配置文件/etc/chrony.conf
server后面的就是上游ntp服务器的地址，这里是ntp.aliyun.com的公益ntp服务器地址，allow 192.168/16 如果取消注释，就是允许192.168.0.0/16网段的客户机作为客户端来同步时间
#启动chronyd服务 systemctl start chronyd #开机启动 systemctl enable chronyd
- 作为客户端的配置
修改配置文件/etc/chrony.conf
同样是这个配置文件，只需要把server后面ntp.aliyun.com修改成实际的地址即可，后者填入内网的ntp服务器的ip地址
- 防火墙端口放行
防火墙端口和ntp一样，也是使用的123/udp端口，可以根据自己的防火墙（firewalld或者iptables）添加放行端口
#firewalld
firewall-cmd --permanent --add-service=ntp
firewall-cmd --reload
#iptables iptables -A INPUT -p udp --dport 123 -j ACCEPT
- chrony其他命令介绍
chronyc sources: 查看当前的同步源
chronyc sourcestats -v: 查看当前的同步状态
chronyc -a makestep: 手动同步时间
chronyc tracking: 显示系统时间信息
chronyc: 进入交互式界面进行相关的操作，具体可以输入help查看对应的帮助.
[root@ecs-587c ~]# 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 =============================================================================== ^* 100.125.0.251 3 6 377 43 +13us[ +13us] +/- 146ms [root@ecs-587c ~]# chronyc sources 210 Number of sources = 1 MS Name/IP address Stratum Poll Reach LastRx Last sample =============================================================================== [root@ecs-587c ~]# chronyc sourcestats -v 210 Number of sources = 1 .- Number of sample points in measurement set. / .- Number of residual runs with same sign. | / .- Length of measurement set (time). | | / .- Est. clock freq error (ppm). | | | / .- Est. error in freq. | | | | / .- Est. offset. | | | | | | On the -. | | | | | | samples. \ | | | | | | | Name/IP Address NP NR Span Frequency Freq Skew Offset Std Dev ============================================================================== 100.125.0.251 30 18 929 +0.000 0.025 +10ns 8817ns
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