查看“NTP”的源代码

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{{From|http://www.linuxhomenetworking.com/wiki/index.php/Quick_HOWTO_:_Ch24_:_The_NTP_Server}} 

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{{Languages|Quick_HOWTO_:_Ch24_:_The_NTP_Server}} 

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= 简介  =

网络时间协议(NTP)是用来帮助Linux系统时钟与准确的时间源同步的协议.允许让网上所有站点同步时间.分为两类：

<br>*第1类： NTP站点使用的原子钟计时.<br>*第2类： NTP站点和较小的准确时间源.( NTP sites with slightly less accurate time sources)

这个做法好处是至少有一个服务器在您的网络上成为本地时间服务器，为其他设备服务。(This makes the correlation of system events on different systems much easie)这使得在不同的系统上的系统事件相关性对比变得容易。它也降低了由于NTP的通讯需要的互联网带宽使用量，并减少为每个NTP的客户端配置防火墙规则.而且并非所有服务器将有因特网接入.在这种情况下，您需要一个中央服务器处理所有访问.

查询可用的第1类和第2类服务器清单,清请访问http://www.ntp.org/

= <br>下载和安装NTP包  =

最版RedHat和Fedora Linux软件产品都可以用RPM的格式.从RPMS中下载并安装并不难.如果您需要复修,参考第6章"安装Linux软件"("Installing Linux Software")有所有的细节。

当寻找该文件，记住NTP RPMs的文件名通常用NTP加版本号,如:NTP - 4.1.2 - 5.i386.rpm

== /etc/ntp.conf 文件  ==

/etc/ntp.conf 文件是Linux NTP的主要配置文件,你可以设置NTP服务器的ip地址.下面是建立互联网基础的NTP服务器的步骤

1) 首先指定有兴趣的服务器: 
<pre>server  otherntp.server.org     # A stratum 1 server at server.org
server  ntp.research.gov        # A stratum 2 server at research.gov 
</pre> 
<br>2)限制你允许的这些服务器的访问类型,在这个例子中的服务器是不容许修改运行时配置或查询您的Linux NTP服务器:<br>
<pre>restrict otherntp.server.org mask 255.255.255.255 nomodify notrap noquery
restrict ntp.research.gov mask 255.255.255.255 nomodify notrap noquery 
</pre> 
<br>The mask 255.255.255.255 statement is really a subnet mask limiting access to the single IP address of the remote NTP servers. 

3)如果此服务器也是要提供时间给其他计算机,如PC,其他Linux服务器和网络设备,那么您必须界定网络从这个服务器接受NTP同步的请求。你要修改restric语句，去掉noquery关键字，让网络查询您的NTP服务器。语法是：
<pre>restrict 192.168.1.0 mask 255.255.255.0 nomodify notrap 
</pre> 
<br>在这种情况下，mask包括所有255个在本地网络内可能的IP地址.

4) 还要确保localhost（这个常用的IP地址用来指Linux服务器本身）有足够权限.使用没有任何限制关键词的语法:&nbsp; 
<pre>restrict 127.0.0.1 
</pre> 
<br>5) 保存文件并重新启动NTP,这些设置才会生效.现在，您可以用相似的方式设定您的网络上其他的Linux主机与这个新的主NTP服务器同步.<br>

= 怎样开始NTP  =

当你修改了配置信息，你必须重新启动NTP进程以取得及时的效果. 

开始配置NTP,用下面的命令: 
<pre>[root@bigboy tmp]# chkconfig ntpd on 
</pre> 
启动,停止,重启NTP,用下面的命令: 
<pre>[root@bigboy tmp]# service ntpd start
[root@bigboy tmp]# service ntpd stop
[root@bigboy tmp]# service ntpd restart 
</pre> 
测试和解决NTP问题 

在配置和启动NTP后,你应该测试以确定NTP是否在工作,参考下面的指引去检测NTP的工作. 

== 检查NTP运行  ==

使用下面的命令检查NTP服务是否运行 
<pre>[root@bigboy tmp]# pgrep ntpd 
</pre> 
<br>这时你应该能得到一个进程ID. 

== <br>同步初始化  ==

If the time on the local server is very different from that of its primary time server your NTP daemon will eventually terminate itself leaving an error message in the /var/log/messages file. You should run the ntpdate -u command to force your server to become instantly synchronized with its NTP servers before starting the NTP daemon for the first time. The ntpdate command doesn't run continuously in the background, you will still have to run the ntpd daemon to get continuous NTP updates. 

Take a look at some sample output of the ntpdate command in which a server whose initial time was set to midnight, was correctly set to 8:03 am. 

*The date was originally set to midnight which was verified by using the date command.
<pre>[root@smallfry tmp]# date
Thu Aug 12 00:00:00 PDT 2004
[root@smallfry tmp]# 
</pre> 
*The ntpdate command is run three times to synchronize smallfry's clock to server 192.168.1.100, but it must be run while the ntpd process is stopped. So you'll have to stop ntpd, run ntpdate and then start ntpd again.
<pre>[root@smallfry tmp]# service ntpd stop
[root@smallfry tmp]# ntpdate -u 192.168.1.100
Looking for host 192.168.1.100 and service ntp
host found&nbsp;: bigboy.my-site.com
12 Aug 08:03:38 ntpdate[2472]: step time server 192.168.1.100 offset 28993.084943 sec
[root@smallfry tmp]# ntpdate -u 192.168.1.100
Looking for host 192.168.1.100 and service ntp
host found&nbsp;: bigboy.my-site.com
12 Aug 08:03:40 ntpdate[2472]: step time server 192.168.1.100 offset 2.467652 sec
[root@smallfry tmp]# ntpdate -u 192.168.1.100
Looking for host 192.168.1.100 and service ntp
host found&nbsp;: bigboy.my-site.com
12 Aug 08:03:42 ntpdate[2472]: step time server 192.168.1.100 offset 0.084943 sec
[root@smallfry tmp]# service ntpd start
[root@smallfry tmp]# 
</pre> 
*The date is now corrected.
<pre>[root@smallfry tmp]# date
Thu Aug 12 08:03:45 PDT 2004
[root@smallfry tmp]# 
</pre> 
== <br>检定NTP 同步  ==

Use the ntpq command to see the servers with which you are synchronized. It provided you with a list of configured time servers and the delay, offset and jitter that your server is experiencing with them. For correct synchronization, the delay and offset values should be non-zero and the jitter value should be under 100. 

[root@bigboy tmp]# ntpq -p 

Here is some sample output of the command: 
<pre>remote refid st t when poll reach delay offset jitter
==============================================================================
-jj.cs.umb.edu gandalf.sigmaso 3 u 95 1024 377 31.681 -18.549 1.572 
milo.mcs.anl.go ntp0.mcs.anl.go 2 u 818 1024 125 41.993 -15.264 1.392
-mailer1.psc.edu ntp1.usno.navy. 2 u 972 1024 377 38.206 19.589 28.028
-dr-zaius.cs.wis ben.cs.wisc.edu 2 u 502 1024 357 55.098 3.979 0.333
+taylor.cs.wisc. ben.cs.wisc.edu 2 u 454 1024 347 54.127 3.379 0.047
-ntp0.cis.strath harris.cc.strat 3 u 507 1024 377 115.274 -5.025 1.642
*clock.via.net .GPS. 1 u 426 1024 377 107.424 -3.018 2.534
ntp1.conectiv.c 0.0.0.0 16 u - 1024 0 0.000 0.000 4000.00 
</pre> 
== <br>Linux NTP 客户端无法同步  ==

A telltale sign that you haven't got proper synchronization is when all the remote servers have jitters of 4000 with delay and reach values of 0. 
<pre>remote refid st t when poll reach delay offset jitter
 =============================================================================
LOCAL(0) LOCAL(0) 10 l - 64 7 0.000 0.000 0.008
ntp-cup.externa 0.0.0.0 16 u - 64 0 0.000 0.000 4000.00
snvl-smtp1.trim 0.0.0.0 16 u - 64 0 0.000 0.000 4000.00
nist1.aol-ca.tr 0.0.0.0 16 u - 64 0 0.000 0.000 4000.00 
</pre> 
This could be caused by the following: 

*Older versions of the NTP package that don't work correctly if you use the DNS name for the NTP servers. In these cases you will want to use the actual IP addresses instead.<br> * A firewall blocking access to your Stratum 1 and 2 NTP servers. This could be located on one of the networks between the NTP server and its time source, or firewall software such as iptables could be running on the server itself.<br> * The notrust nomodify notrap keywords are present in the restrict statement for the NTP client. In some versions of the Fedora Core 2's implementation of NTP, clients will not be able to synchronize with a Fedora Core 2 time server unless the notrust nomodify notrap keywords are removed from the NTP client's restrict statement.

In this example the restrict statement has only the client network defined without any keywords and the configuration line that works with other NTP versions has been commented out: 
<pre>#-- CLIENT NETWORK -------
#restrict 172.16.1.0 mask 255.255.255.0 notrust nomodify notrap
restrict 172.16.1.0 mask 255.255.255.0
</pre> 
== <br> <br>Fedora Core 2 File Permissions  ==

All the Fedora/RedHat NTP daemons write temporary files to the /etc/ntp directory. Unfortunately, in Fedora Core 2, the permissions on this directory don't allow writing of temporary files. Instead you have to set the group and owner of the directory to be ntp. 

[root@bigboy tmp]# chown ntp:ntp /etc/ntp 

If you don't, you'll get errors like this in the /var/log/messages file. 

Aug 12 00:29:45 smallfry ntpd[2097]: can't open /etc/ntp/drift.TEMP: Permission denied

= 配置Cisco 设备去使用NTP服务器  =

您可以使用的NTP对各种设备同步时间，包括网络设备。我已概括必要的用于多种思科系统公司产品的NTP命令，因为这是一个最热门的网络设备制造商，整体架构将可能用于的许多家庭办公/小型办公室（ SOHO ）环境和企业部门<br>

== Cisco IOS  ==

使您的路由器与IP地址 192.168.1.100和192.168.1.201 的NTP服务器同步,使用命令： 

<br> 
<pre>ciscorouter&gt; enable
password: *********
ciscorouter# config t
ciscorouter(config)# ntp update-calendar
ciscorouter(config)# ntp server 192.168.1.100
ciscorouter(config)# ntp server 192.168.1.201
ciscorouter(config)# exit
ciscorouter# wr mem 
</pre> 
NTP server 命令结合其他系统，形成了一个服务关联，而且NTP的更新日历能配置系统定时从软件时钟更新其硬件时钟.<br>

== CATOS  ==

使您的路由器与IP地址 192.168.1.100和192.168.1.201 的NTP服务器同步,使用命令： 
<pre>ciscoswitch&gt; enable
password: *********
ciscoswitch# set ntp client enable
ciscoswitch# ntp server 192.168.1.100
ciscoswitch# ntp server 192.168.1.201
ciscoswitch# exit 
</pre> 
NTP server命令与其他系统，形成了服务关联，set nip client enable 设置激活NTP客户端

= <br>NTP安全  =

你应该知道NTP如何受到您的网络安全政策影响。这里有一些共同关注的领域.<br> 

== 防火墙和NTP  ==

NTP服务器使用UDP的123目的端口通讯.不同于大多数UDP协议，源端口不是一个高端口(1023以上).您必须允许UDP源/目的端口123在您的服务器和straum1/2类服务器之间通讯.<br>

Linux iptables 防火墙脚本片段样本在附录 II, "Codes, Scripts, and Configurations".<br> 

== NTP认证  ==

有可的情况下，你不仅想限制的NTP同步到指定的网络，还需要一个同步密码。但这是本书范围以外的，所涵盖的详细信息可以去NTP网站www.ntp.org<br>

= 配置windows NTP 客户端 =

Windows clients that are part of an Active Directory domain automatically get their time synchronized from the domain server. If your client is not part of a domain you can add your new NTP server to your Windows client. Here's how: 

1. Click on the time at the bottom right hand side of your screen.<br> 2. Click on the "Internet Time" tab of the dialog box<br> 3. Click the check box labeled "Automatically synchronize with an Internet time server" and enter the name or IP address in the box underneath it.<br> 4. Click on the "Update Now" button 

You will get a message saying "Your time has been successfully synchronized" when the operation is complete.<br>

= 结尾  =

在您的控制下的所有系统具有相同的准确时间,这是很重要的.它可以帮助你在多种设备下很清楚的了解一连串的事件,它也可以协助对时间敏感的交易的同步.

在您的本地网络有一个NTP服务器，可以很容易做这些事.有时,您的所有NTP的客户都有机会在互联网上获得与1类2类服务器同步,这不是合意的办法，如果中央到Internet的连接丢失,就有风险，失去同步.并且为多个NTP服务连接到互联网维护防火墙规则，也是艰巨的，特别是如果管理防火墙的是其他部门。

本地的NTP服务器，甚至当网际网路连线暂时丢失,也可确保客户端均拥有相同的时间，从而减少的问题.防火墙规则也可以大大简化。设置本地的NTP服务器也是经常基于这些原因。