NTP时间服务器 搭建

1.1 NTP简介

NTP（Network Time Protocol，网络时间协议）是用来使网络中的各个计算机时间同步的一种协议。它的用途是把计算机的时钟同步到世界协调时UTC，其精度在局域网内可达0.1ms，在互联网上绝大多数的地方其精度可以达到1-50ms。

NTP服务器就是利用NTP协议提供时间同步服务的。

系统版本

[root@test ~]# cat /etc/redhat-release 
CentOS release 6.9 (Final)

1.2 NTP服务器安装

[root@test ~]# rpm -qa ntp
ntp-4.2.6p5-10.el6.centos.2.x86_64

   如果没有安装就yum install ntp -y进行安装

1.3 配置NTP服务

备份配置文件

[root@test ~]# cp /etc/ntp.conf{,.bak}
[root@test ~]# ll /etc/ntp.conf*
-rw-r--r--. 1 root root 1778 Jan 11  2017 /etc/ntp.conf
-rw-r--r--  1 root root 1778 Oct 23 23:10 /etc/ntp.conf.bak

精简化配置文件

[root@test ~]# egrep -v "^$|#" /etc/ntp.conf.bak  >/etc/ntp.conf

修改配置文件

# For more information about this file, see the man pages
# ntp.conf(5), ntp_acc(5), ntp_auth(5), ntp_clock(5), ntp_misc(5), ntp_mon(5).

driftfile /var/lib/ntp/drift

# Permit time synchronization with our time source, but do not
# permit the source to query or modify the service on this system.
restrict default kod nomodify notrap nopeer noquery
restrict -6 default kod nomodify notrap nopeer noquery

# Permit all access over the loopback interface.  This could
# be tightened as well, but to do so would effect some of
# the administrative functions.
restrict 127.0.0.1 
restrict -6 ::1

# Hosts on local network are less restricted.
#restrict 192.168.1.0 mask 255.255.255.0 nomodify notrap
# 允许内网其他机器同步时间
restrict 172.16.1.0 mask 255.255.255.0 nomodify notrap

# Use public servers from the pool.ntp.org project.
# Please consider joining the pool (http://www.pool.ntp.org/join.html).
#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

# 定义使用的上游 ntp服务器，将原来的注释
server time1.aliyun.com
server ntp1.aliyun.com
    
#broadcast 192.168.1.255 autokey    # broadcast server
#broadcastclient            # broadcast client
#broadcast 224.0.1.1 autokey        # multicast server
#multicastclient 224.0.1.1        # multicast client
#manycastserver 239.255.254.254        # manycast server
#manycastclient 239.255.254.254 autokey # manycast client

# 允许上层时间服务器主动修改本机时间
restrict time1.aliyun.com  nomodify notrap noquery
restrict ntp1.aliyun.com  nomodify notrap noquery

# 外部时间服务器不可用时，以本地时间作为时间服务
server  127.127.1.0    
fudge   127.127.1.0 stratum 10

# Enable public key cryptography.
#crypto

includefile /etc/ntp/crypto/pw

# Key file containing the keys and key identifiers used when operating
# with symmetric key cryptography. 
keys /etc/ntp/keys

# Specify the key identifiers which are trusted.
#trustedkey 4 8 42

# Specify the key identifier to use with the ntpdc utility.
#requestkey 8

# Specify the key identifier to use with the ntpq utility.
#controlkey 8

# Enable writing of statistics records.
#statistics clockstats cryptostats loopstats peerstats

1.4 启动NTP服务器

注意：如果有同步时间的定时任务要将其注销，否则会冲突

[root@test ~]# /etc/init.d/ntpd start
Starting ntpd:                                             [  OK  ]

显示节点列表

[root@test ~]# ntpq -p
     remote           refid      st t when poll reach   delay   offset  jitter
==============================================================================
 time5.aliyun.co 10.137.38.86     2 u   28   64    3    5.092  6241215 185.623

 132.163.96.4    .INIT.          16 u    -   64    0    0.000    0.000   0.000

1.5 客户机时间同步

客户机要等几分钟再与新启动的ntp服务器进行时间同步，否则会提示

no server suitable for synchronization found错误

[root@client ~]# ntpdate 10.0.0.250
24 Oct 16:46:58 ntpdate[26694]: adjust time server 10.0.0.250 offset 0.320652 sec