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

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

2、NTP服务器安装

  1. [root@test ~]# rpm -qa ntp
  2. 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

3、配置NTP服务

备份配置文件

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

精简化配置文件

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

修改配置文件

  1. # For more information about this file, see the man pages
  2. # ntp.conf(5), ntp_acc(5), ntp_auth(5), ntp_clock(5), ntp_misc(5), ntp_mon(5).
  4. driftfile /var/lib/ntp/drift
  6. # Permit time synchronization with our time source, but do not
  7. # permit the source to query or modify the service on this system.
  8. restrict default kod nomodify notrap nopeer noquery
  9. restrict -6 default kod nomodify notrap nopeer noquery
  11. # Permit all access over the loopback interface.  This could
  12. # be tightened as well, but to do so would effect some of
  13. # the administrative functions.
  14. restrict 127.0.0.1 
  15. restrict -6 ::1
  17. # Hosts on local network are less restricted.
  18. #restrict 192.168.1.0 mask 255.255.255.0 nomodify notrap
  19. # 允许内网其他机器同步时间
  20. restrict 172.16.1.0 mask 255.255.255.0 nomodify notrap
  22. # Use public servers from the pool.ntp.org project.
  23. # Please consider joining the pool (http://www.pool.ntp.org/join.html).
  24. #server 0.centos.pool.ntp.org iburst
  25. #server 1.centos.pool.ntp.org iburst
  26. #server 2.centos.pool.ntp.org iburst
  27. #server 3.centos.pool.ntp.org iburst
  29. # 定义使用的上游 ntp服务器，将原来的注释
  30. server time1.aliyun.com
  31. server ntp1.aliyun.com
  33. #broadcast 192.168.1.255 autokey    # broadcast server
  34. #broadcastclient            # broadcast client
  35. #broadcast 224.0.1.1 autokey        # multicast server
  36. #multicastclient 224.0.1.1        # multicast client
  37. #manycastserver 239.255.254.254        # manycast server
  38. #manycastclient 239.255.254.254 autokey # manycast client
  40. # 允许上层时间服务器主动修改本机时间
  41. restrict time1.aliyun.com  nomodify notrap noquery
  42. restrict ntp1.aliyun.com  nomodify notrap noquery
  44. # 外部时间服务器不可用时，以本地时间作为时间服务
  45. server  127.127.1.0    
  46. fudge   127.127.1.0 stratum 10
  48. # Enable public key cryptography.
  49. #crypto
  51. includefile /etc/ntp/crypto/pw
  53. # Key file containing the keys and key identifiers used when operating
  54. # with symmetric key cryptography. 
  55. keys /etc/ntp/keys
  57. # Specify the key identifiers which are trusted.
  58. #trustedkey 4 8 42
  60. # Specify the key identifier to use with the ntpdc utility.
  61. #requestkey 8
  63. # Specify the key identifier to use with the ntpq utility.
  64. #controlkey 8
  66. # Enable writing of statistics records.
  67. #statistics clockstats cryptostats loopstats peerstats

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

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

显示节点列表

  1. [root@test ~]# ntpq -p
  2.      remote           refid      st t when poll reach   delay   offset  jitter
  3. ==============================================================================
  4.  time5.aliyun.co 10.137.38.86     2 u   28   64    3    5.092  6241215 185.623
  6.  132.163.96.4    .INIT.          16 u    -   64    0    0.000    0.000   0.000

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

  1. [root@client ~]# ntpdate 10.0.0.250
  2. 24 Oct 16:46:58 ntpdate[26694]: adjust time server 10.0.0.250 offset 0.320652 sec