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Except for discussion of iptables/ipchains firewalling, this discussion applies to Unix systems in general as well as Linux in particular. I have worked with ntpd, also known as xntpd, versions 4.1 and 4.2, using Red Hat 7.3, 9.0 and SuSE 9.1. 31574
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The documentation for NTP is voluminous and much of it is devoted to complex issues that may concern an expert setting up groups of time servers for other systems to access. Practical information for the average system administrator can be hard to extract from all of this, so a short focused article aimed at practical setup issues seemed like it would be valuable. The material here reflects some of the author's personal experiences in setting up ntpd on various Linux systems and can hopefully serve as a practical "NTP HOWTO".
This article is probably most useful for someone with system administration experience. The setup steps are relatively simple, but it may be hard to resolve a problem without some background. It is aimed at managers of one or a few Linux systems who want to keep their system clocks close enough to correct time for most practical purposes. This does not attempt to help you set up a time server that other systems can synchronize to; only with setting up NTP clients. Feedback or new information are welcomed by the author.
Configuration 论文网
Even on modern Linux systems, a little NTP client setup is needed. In my experience this little setup does not always go right, so I try to help you do a little bit of debugging. The minimum system configuration is a couple of lines in your ntp configuration file, typically /etc/ntp.conf. You will need a line or two or three like this:
server some.timeserver.com
server othertime.server.org
Synchronizing with more than one NTP server gives you redundancy in case of server or network problems, and it may improve the accuracy of your time synchronization. IP addresses are also accepted, but I prefer hostnames, since the IP address of a server may change from time to time.
Note: The version of ntpd released with Red Hat 7.3 (4.1.1) could not handle hostnames in the configuration, only IP addresses. The server would send requests and the remote servers would respond, but the local server would ignore the responses. For older versions of ntpd you may need to use IP addresses instead of names.
First you will need to select an NTP server or two. The implementors of NTP itself provide a very useful list of public NTP servers. You might also wish to try pool.ntp.org, which provides access to a number of different time servers all answering to the same hostname.
Before you synchronize with a time server you will want to check how close your system clock is to the correct time and whether it is ahead or behind the correct time. If your clock is within a minute or two of the correct time you may be happy with the standard simple procedure. If your clock is behind the correct time you are probably still OK, but be aware that your clock may jump forward some time within the first hour after you start your local time server. If your clock is ahead, starting the time server may make your system time jump backward while the system is running. This can have effects like making copies of files look older than the original, and can confuse your system in a number of ways. This tends to affect services that deal with data modification times: database servers, network file systems, distributed file synchronization, some cryptographic protocols, etc.. See Carefully Adjusting Your Clock for a procedure to set your clock back carefully.
B.原文的翻译
使用Linux中的网络时间协议
说明除了对iptables/ ipchains防火墙的论述，本篇文章适用于一般的Unix系统以及Linux发行版。我曾参与NTPD的工作，它也被称为xntpd，使用Red Hat 7.3，9.0和SuSE 9.1