CentOS7搭建NTP服务器及客户端同步时间

在配置时钟同步服务器时第一次同步时间时，使用ntpdate命令；后续通过ntpd服务与服务器同步时间。

一、搭建NTP服务器

1、查看服务器、客户端操作系统版本

[root@web ~]# cat /etc/redhat-release
CentOS Linux release 7.5.1804 (Core)

2、查看服务器是否安装ntp，系统默认安装ntpdate；

[root@web ~]# rpm -qa | grep ntp
fontpackages-filesystem-1.44-8.el7.noarch
ntpdate-4.2.6p5-28.el7.centos.x86_64
python-ntplib-0.3.2-1.el7.noarch

3、安装ntp ntpdate，其中ntpdate默认安装，可以只安装ntp；

yum install ntp ntpdate -y

4、查看是否已安装完成，与第2步对比

[root@web ~]# rpm -qa | grep ntp
fontpackages-filesystem-1.44-8.el7.noarch
ntpdate-4.2.6p5-28.el7.centos.x86_64
ntp-4.2.6p5-28.el7.centos.x86_64
python-ntplib-0.3.2-1.el7.noarch

5、查看ntp服务器状态，两条命令效果一样

[root@web ~]# systemctl status ntpd
● ntpd.service - Network Time Service
   Loaded: loaded (/usr/lib/systemd/system/ntpd.service; disabled; vendor preset: disabled)
   Active: inactive (dead)

或

[root@web ~]# service ntpd status
Redirecting to /bin/systemctl status ntpd.service
● ntpd.service - Network Time Service
   Loaded: loaded (/usr/lib/systemd/system/ntpd.service; disabled; vendor preset: disabled)
   Active: inactive (dead)

6、修改配置文件，使该NTP服务器在不联网的情况下，使用本服务器的时间作为同步时间

vim /etc/ntp.conf

把如下四行代码注释掉

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

在下面再添加一行

server 127.127.1.0 iburst

7、启动ntp服务

systemctl start ntpd

或

service ntpd start

8、再次查看服务器状态

[root@web ~]# systemctl status ntpd
● ntpd.service - Network Time Service
   Loaded: loaded (/usr/lib/systemd/system/ntpd.service; enabled; vendor preset: disabled)
   Active: active (running) since Tue 2018-08-21 14:29:12 CST; 8s ago
  Process: 6588 ExecStart=/usr/sbin/ntpd -u ntp:ntp $OPTIONS (code=exited, status=0/SUCCESS)
 Main PID: 6589 (ntpd)
    Tasks: 1
   CGroup: /system.slice/ntpd.service
           └─6589 /usr/sbin/ntpd -u ntp:ntp -g

Aug 21 14:29:12 web ntpd[6589]: Listen normally on 2 lo 127.0.0.1 UDP 123
Aug 21 14:29:12 web ntpd[6589]: Listen normally on 3 eno1 192.168.0.163 UDP 123
Aug 21 14:29:12 web ntpd[6589]: Listen normally on 4 virbr0 192.168.122.1 UDP 123
Aug 21 14:29:12 web ntpd[6589]: Listen normally on 5 lo ::1 UDP 123
Aug 21 14:29:12 web ntpd[6589]: Listen normally on 6 eno1 fe80::6e92:bfff:fe6f:daea UDP 123
Aug 21 14:29:12 web ntpd[6589]: Listening on routing socket on fd #23 for interface updates
Aug 21 14:29:12 web ntpd[6589]: 0.0.0.0 c016 06 restart
Aug 21 14:29:12 web ntpd[6589]: 0.0.0.0 c012 02 freq_set kernel 0.000 PPM
Aug 21 14:29:12 web ntpd[6589]: 0.0.0.0 c011 01 freq_not_set
Aug 21 14:29:13 web ntpd[6589]: 0.0.0.0 c514 04 freq_mode

或 

[root@web ~]# service ntpd status
Redirecting to /bin/systemctl status ntpd.service
● ntpd.service - Network Time Service
   Loaded: loaded (/usr/lib/systemd/system/ntpd.service; enabled; vendor preset: disabled)
   Active: active (running) since Tue 2018-08-21 14:29:12 CST; 56s ago
  Process: 6588 ExecStart=/usr/sbin/ntpd -u ntp:ntp $OPTIONS (code=exited, status=0/SUCCESS)
 Main PID: 6589 (ntpd)
    Tasks: 1
   CGroup: /system.slice/ntpd.service
           └─6589 /usr/sbin/ntpd -u ntp:ntp -g

Aug 21 14:29:12 web ntpd[6589]: Listen normally on 2 lo 127.0.0.1 UDP 123
Aug 21 14:29:12 web ntpd[6589]: Listen normally on 3 eno1 192.168.0.163 UDP 123
Aug 21 14:29:12 web ntpd[6589]: Listen normally on 4 virbr0 192.168.122.1 UDP 123
Aug 21 14:29:12 web ntpd[6589]: Listen normally on 5 lo ::1 UDP 123
Aug 21 14:29:12 web ntpd[6589]: Listen normally on 6 eno1 fe80::6e92:bfff:fe6f:daea UDP 123
Aug 21 14:29:12 web ntpd[6589]: Listening on routing socket on fd #23 for interface updates
Aug 21 14:29:12 web ntpd[6589]: 0.0.0.0 c016 06 restart
Aug 21 14:29:12 web ntpd[6589]: 0.0.0.0 c012 02 freq_set kernel 0.000 PPM
Aug 21 14:29:12 web ntpd[6589]: 0.0.0.0 c011 01 freq_not_set
Aug 21 14:29:13 web ntpd[6589]: 0.0.0.0 c514 04 freq_mode

9、查看是否同步

[root@web ~]# ntpq -p
     remote           refid      st t when poll reach   delay   offset  jitter
==============================================================================
*LOCAL(0)        .LOCL.           5 l   20   64    7    0.000    0.000   0.000

10、设置开机启动

[root@web ~]# systemctl enable ntpd
Created symlink from /etc/systemd/system/multi-user.target.wants/ntpd.service to /usr/lib/systemd/system/ntpd
service.

11、设置防火墙，打开udp123端口

[root@web ~]# firewall-cmd --permanent --add-port=123/udp
success
[root@web ~]# firewall-cmd --reload
success

12、查看防火墙已打开端口

iptables -L -n

二、客户端配置

前5步与服务器一致

6、修改配置文件，将刚刚搭建好的NTP服务器作为客户端上游时间服务器

vim /etc/ntp.conf

#注释掉其他上游时间服务器
#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
#配置上游时间服务器为本地的ntpd Server服务器
server 192.168.0.163
#配置允许上游时间服务器主动修改本机的时间
restrict 192.168.0.163 nomodify notrap noquery

7、与本地ntpd Server同步一下

ntpdate -u 192.168.0.163

8、启动ntp服务

systemctl start ntpd

或

service ntpd start

9、设置开机启动

[root@db3 ~]# systemctl enable ntpd
Created symlink from /etc/systemd/system/multi-user.target.wants/ntpd.service to /usr/lib/systemd/system/ntpd.service.

10、查看状态

[root@db3 ~]# ntpq -p
     remote           refid      st t when poll reach   delay   offset  jitter
==============================================================================
*192.168.0.163   LOCAL(0)        11 u   21   64  377    0.068   -0.824   0.367