NTP：修订间差异

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== /etc/ntp.conf 文件  ==
== /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 you place the IP addresses of the stratum 1 and stratum 2 servers you want to use. Here are the steps to create a configuration file using a pair of sample Internet-based NTP servers:
/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) 首先我们详细描述有兴趣的服务器:  
1) 首先指定有兴趣的服务器:  
<pre>server otherntp.server.org # A stratum 1 server at server.org
<pre>server otherntp.server.org     # A stratum 1 server at server.org
server ntp.research.gov # A stratum 2 server at research.gov  
server ntp.research.gov       # A stratum 2 server at research.gov  
</pre>  
</pre>  
<br>2) Restrict the type of access you allow these servers. In this example the servers are not allowed to modify the run-time configuration or query your Linux NTP server.
<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
<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  
restrict ntp.research.gov mask 255.255.255.255 nomodify notrap noquery  
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<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.  
<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) If this server is also going to provide time for other computers, such as PCs, other Linux servers and networking devices, then you'll have to define the networks from which this server will accept NTP synchronization requests. You do so with a modified restrict statement removing the noquery keyword to allow the network to query your NTP server. The syntax is:
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>restrict 192.168.1.0 mask 255.255.255.0 nomodify notrap  
</pre>  
</pre>  
<br>In this case the mask statement has been expanded to include all 255 possible IP addresses on the local network.  
<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) We also want to make sure that localhost (the universal IP address used to refer to a Linux server itself) has full access without any restricting keywords:  
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>restrict 127.0.0.1  
</pre>  
</pre>  
<br>5) Save the file and restart NTP for these settings to take effect. You can now configure other Linux hosts on your network to synchronize with this new master NTP server in a similar fashion.<br>
<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>


= How To Get NTP Started  =
= How To Get NTP Started  =

2008年6月22日 (日) 21:25的版本

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{{#ifeq:Quick_HOWTO_:_Ch24_:_The_NTP_Server|:NTP|请不要直接编辑翻译本页，本页将定期与来源同步。}}

{{#ifexist: :NTP/zh | | {{#ifexist: NTP/zh | | {{#ifeq: {{#titleparts:NTP|1|-1|}} | zh | | }} }} }} {{#ifeq: {{#titleparts:NTP|1|-1|}} | zh | | }}





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：


*第1类： NTP站点使用的原子钟计时.
*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/


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: 

server  otherntp.server.org     # A stratum 1 server at server.org
server  ntp.research.gov        # A stratum 2 server at research.gov


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:

restrict otherntp.server.org mask 255.255.255.255 nomodify notrap noquery
restrict ntp.research.gov mask 255.255.255.255 nomodify notrap noquery


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： 

restrict 192.168.1.0 mask 255.255.255.0 nomodify notrap


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:  

restrict 127.0.0.1


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.

How To Get NTP Started

You have to restart the NTP process every time you make a change to the configuration file for the changes to take effect on the running process.

To get NTP configured to start at boot, use the line: 

[root@bigboy tmp]# chkconfig ntpd on

To start, stop and restart NTP after booting, follow these examples: 

[root@bigboy tmp]# service ntpd start
[root@bigboy tmp]# service ntpd stop
[root@bigboy tmp]# service ntpd restart

Testing And Troubleshooting NTP

After configuring and starting NTP, you should test it to make sure it is working. Here are some guidelines you can follow to get NTP working correctly.

检查NTP运行

To test whether the NTP process is running use the command 

[root@bigboy tmp]# pgrep ntpd


You should get a response of plain old process ID numbers.


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.
[root@smallfry tmp]# date
Thu Aug 12 00:00:00 PDT 2004
[root@smallfry tmp]#
  • 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.
[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 : 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 : 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 : 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]#
  • The date is now corrected.
[root@smallfry tmp]# date
Thu Aug 12 08:03:45 PDT 2004
[root@smallfry tmp]#


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: 

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


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. 

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

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.
    * 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.
    * 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: 




  1. -- CLIENT NETWORK -------
  1. restrict 172.16.1.0 mask 255.255.255.0 notrust nomodify notrap

restrict 172.16.1.0 mask 255.255.255.0





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

You can use NTP to synchronize time on a variety of devices including networking equipment. I have included the necessary NTP commands for a variety of Cisco Systems products because it is one of the most popular manufacturers of networking equipment and would feature in the overall architectures of many home office/small office (SOHO) environments and corporate departments.


Cisco IOS

To make your router synchronize with NTP servers with IP addresses 192.168.1.100 and 192.168.1.201, use the commands: 

ciscorouter> 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

The ntp server command forms a server association with another system, and ntp update-calendar configures the system to update its hardware clock from the software clock at periodic intervals.


CATOS

To make your router synchronize with NTP servers with IP addresses 192.168.1.100 and 192.168.1.201, use the commands: 

ciscoswitch> enable
password: *********
ciscoswitch# set ntp client enable
ciscoswitch# ntp server 192.168.1.100
ciscoswitch# ntp server 192.168.1.201
ciscoswitch# exit

The ntp server command forms a server association with another system, and set ntp client enable activates the NTP client.


NTP安全

You should always be aware of how NTP can be affected by your network's security policy. Here are some common areas of concern.

防火墙和NTP

NTP servers communicate with one another using UDP with a destination port of 123. Unlike most UDP protocols, the source port isn't a high port (above 1023), but 123 also. You'll have to allow UDP traffic on source/destination port 123 between your server and the Stratum 1/2 server with which you are synchronizing.

A sample Linux iptables firewall script snippet is in Appendix II, "Codes, Scripts, and Configurations".

NTP认证

There may be cases where you want to not only restrict NTP synchronization to specific networks but also to require a synchronization password. This is beyond the scope of this book, but is covered in detail at the NTP website www.ntp.org.

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.
2. Click on the "Internet Time" tab of the dialog box
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.
4. Click on the "Update Now" button

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

结尾

It is important that all the systems under your control have the same accurate time. It can help to give a very clear indication of a chain of events that involve multiple devices and it can also help in the synchronization of time sensitive-transactions.

Having an NTP server on your local network can make this easier to do. Sometimes it isn't desirable for all your NTP clients to have access to the Internet to synchronize with stratum 1 and 2 servers, even when they all have access there is the risk of them losing synchronization if the central connection to the Internet is lost. The maintenance of firewall rules for multiple NTP connections to the Internet can also be daunting especially if the management of the firewall is handled by another group.

A local NTP server can ensure that the clients all have the same time relative to the server even when Internet connectivity is temporarily lost thereby reducing the problems of them being out of synchronization with each other. The firewall rules can also be greatly simplified. A local NTP server is frequently a good thing to have for these reasons.
取自"http://wiki.ubuntu.org.cn/index.php?title=Quick_HOWTO_:_Ch24_:_The_NTP_Server&variant=zh-cn"


取自“https://wiki.ubuntu.org.cn/index.php?title=NTP&oldid=88413”