linux下使用ntpdate同步网络时间

为什么需要网络同步时间：

Linux服务器运行久时，系统时间就会存在一定的误差，一般情况下可以使用date命令进行时间设置，但在做数据库集群分片等操作时对多台机器的时间差是有要求的，此时就需要使用ntpdate进行时间同步

安装ntpdate

[fanmaolin@Centeros ~]$ sudo yum install ntpdate
Loaded plugins: fastestmirror, refresh-packagekit, security
Setting up Install Process
Loading mirror speeds from cached hostfile
 * base: mirrors.163.com
 * extras: mirrors.163.com
 * updates: mirrors.163.com
Resolving Dependencies
--> Running transaction check
---> Package ntpdate.x86_64 0:4.2.6p5-5.el6.centos will be updated
--> Processing Dependency: ntpdate = 4.2.6p5-5.el6.centos for package: ntp-4.2.6p5-5.el6.centos.x86_64
---> Package ntpdate.x86_64 0:4.2.6p5-10.el6.centos.2 will be an update
--> Running transaction check
---> Package ntp.x86_64 0:4.2.6p5-5.el6.centos will be updated
---> Package ntp.x86_64 0:4.2.6p5-10.el6.centos.2 will be an update
--> Finished Dependency Resolution

Dependencies Resolved

====================================================================================================================================
 Package                     Arch                       Version                                      Repository                Size
====================================================================================================================================
Updating:
 ntpdate                     x86_64                     4.2.6p5-10.el6.centos.2                      base                      78 k
Updating for dependencies:
 ntp                         x86_64                     4.2.6p5-10.el6.centos.2                      base                     599 k

Transaction Summary
====================================================================================================================================
Upgrade       2 Package(s)

Total download size: 678 k
Is this ok [y/N]: y
Downloading Packages:
(1/2): ntp-4.2.6p5-10.el6.centos.2.x86_64.rpm                                                                | 599 kB     00:00     
(2/2): ntpdate-4.2.6p5-10.el6.centos.2.x86_64.rpm                                                            |  78 kB     00:00     
------------------------------------------------------------------------------------------------------------------------------------
Total                                                                                               1.3 MB/s | 678 kB     00:00     
Running rpm_check_debug
Running Transaction Test
Transaction Test Succeeded
Running Transaction
  Updating   : ntpdate-4.2.6p5-10.el6.centos.2.x86_64                                                                           1/4 
  Updating   : ntp-4.2.6p5-10.el6.centos.2.x86_64                                                                               2/4 
  Cleanup    : ntp-4.2.6p5-5.el6.centos.x86_64                                                                                  3/4 
  Cleanup    : ntpdate-4.2.6p5-5.el6.centos.x86_64                                                                              4/4 
  Verifying  : ntpdate-4.2.6p5-10.el6.centos.2.x86_64                                                                           1/4 
  Verifying  : ntp-4.2.6p5-10.el6.centos.2.x86_64                                                                               2/4 
  Verifying  : ntp-4.2.6p5-5.el6.centos.x86_64                                                                                  3/4 
  Verifying  : ntpdate-4.2.6p5-5.el6.centos.x86_64                                                                              4/4 

Updated:
  ntpdate.x86_64 0:4.2.6p5-10.el6.centos.2                                                                                          

Dependency Updated:
  ntp.x86_64 0:4.2.6p5-10.el6.centos.2                                                                                              

Complete!

同步过程

[fanmaolin@Centeros ~]$ date  //date可以查看当前系统时间
Sun Aug  6 12:30:39 CST 2017

[fanmaolin@Centeros ~]$ sudo ntpdate -u 133.100.11.8  //同步到日本的服务器时间
 4 Sep 10:24:56 ntpdate[125261]: step time server 133.100.11.8 offset 2497915.211260 sec
[fanmaolin@Centeros ~]$ date    //查看同步后的时间
Mon Sep  4 10:25:19 CST 2017

[fanmaolin@Centeros ~]$ sudo ntpdate -u 210.72.145.44
 4 Sep 10:26:30 ntpdate[125277]: no server suitable for synchronization found    //这个IP有问题，有可能是服务器不能用了

[fanmaolin@Centeros ~]$ date
Mon Sep  4 10:43:51 CST 2017
[fanmaolin@Centeros ~]$ sudo ntpdate -u ntp.api.bz //直接用域名同步中国上海时间
 4 Sep 10:44:42 ntpdate[3228]: adjust time server 17.253.68.253 offset 0.043394 sec
[fanmaolin@Centeros ~]$ date
Mon Sep  4 10:44:46 CST 2017
[fanmaolin@Centeros ~]$ sudo ntpdate -u 17.253.68.253 //中国上海时间同步服务器IP
 4 Sep 10:45:28 ntpdate[3240]: adjust time server 17.253.68.253 offset 0.011387 sec
[fanmaolin@Centeros ~]$ date
Mon Sep  4 10:45:31 CST 2017

完成.

以下是一些可能可以用的NTP服务器地址（仅供参考，网上找的）