1 = The Secure Network Time Protocol (NTPsec) Distribution
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7 {millshome}pictures.html['P.T. Bridgeport Bear'; from 'Pogo', Walt Kelly]
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15 * A list of all links is on the link:sitemap.html[Site Map] page.
21 * link:#intro[Introduction]
22 * link:#platforms[Supported Platforms]
23 * link:#build[Building and Installing NTP]
24 * link:#man[Manual Pages]
25 * link:#hand[The Handbook]
26 * link:#prob[Resolving Problems]
27 * link:#info[Further Information]
32 The Network Time Protocol software contained in this
33 distribution is available without charge under the conditions set
34 forth in the link:copyright.html[Copyright Notice].
36 This distribution is an implementation of RFC 5905 "Network Time
37 Protocol Version 4: Protocol and Algorithms Specification". NTP is
38 widely used to synchronize a computer to Internet time servers or
39 other sources, such as a radio or satellite receiver or telephone
40 modem service. It can also be used as a server for dependent
41 clients. It provides accuracies typically less than a millisecond on
42 LANs and up to a few tens of milliseconds on WANs. Typical NTP
43 configurations utilize multiple redundant servers and diverse network
44 paths in order to achieve high accuracy and reliability.
46 For background on the problems NTP solves, see
47 https://gpsd.io/time-service-intro.html[Introduction to
48 Time Service]. This white paper discusses time source types, relative
49 accuracy, relative cost, and how those figures of merit have changed
52 The link:ntpspeak.html[Glossary of NTP-speak] might also be a helpful
53 guide for the perplexed.
55 Use caution when employing search engines to dig up NTP material.
56 There are many, many copies of the NTP documentation out there, often
57 referring to very old versions and carrying stale information. It's
58 best to use only the HTML and manpages that come with your
61 For differences between NTPsec and legacy versions, see
62 link:ntpsec.html[this summary]. For details on relevant
63 RFCs and standards, see link:standards.html[here].
66 == Supported platforms
68 NTPsec supports all operating systems conforming to POSIX.1-2001 and
69 ISO/IEC 9899:1999 (aka C99). The POSIX.1-2008 clock calls
70 clock_gettime(2) and clock_settime(2) must also be present. Primary
71 platforms include Linux and the *BSD family; any reasonably modern
72 proprietary Unix will also serve. The OS must have either a
73 Linux-like adjtimex(2) call or a BSD-like ntp_adjtime(2) call.
75 Legacy Windows support has been removed from the NTPsec
76 codebase. Future Windows support will be conditional on the quality
77 of POSIX/C99 emulation environments such as Cygwin and/or the support
78 for Linux binary execution in Windows 10 and later.
80 If you have a requirement for time service on an OS we don't support,
81 and its API is reasonably close to our POSIX/C99 conformance baseline,
82 we'll try to meet you halfway. We're open to development partnerships
83 with individuals and organizations who have special needs and can
84 contribute either engineering time or money to meet our costs of
85 development; our only hard condition is that all joint results must be
86 redistributable as open source.
91 A good deal of tutorial and directive information is available in the
92 handbook pages. These should be read in conjunction with the command and
93 option information available on the pages listed on the
94 link:sitemap.html[Site Map] page.
96 link:quick.html[Client Quick Start Guide]::
97 Basic configuration for 99% of client installations. Introduces
98 concepts used later in the Handbook.
99 link:NTS-QuickStart.html[NTS Quick Start Guide]::
100 A short guide for setting up for NTS.
101 link:assoc.html[Association Management]::
102 Describes how to configure servers and peers and manage the various
103 options. Includes automatic server discovery schemes.
104 link:discover.html[Automatic Server Discovery Schemes]::
105 Describes automatic server discovery using broadcast
106 and server pool schemes.
107 link:access.html[Access Control Support]::
108 Describes the access control mechanisms that can be used to limit
109 client access to various time and management functions.
110 link:authentic.html[Authentication Support]::
111 Describes the cryptographic authentication mechanisms.
112 link:rate.html[Rate Management]::
113 Describes the principles of rate management to minimize network load
114 and defend against DoS attacks.
115 link:refclock.html[Reference Clock Support]::
116 Describes the collection of clocks and devices used to synchronize primary
118 link:warp.html[How NTP Works]::
119 Gives an overview of the NTP daemon architecture and how it works.
120 link:outside-tools.html[Outside Tools]::
121 A variety of tools not directly maintained by the NTPsec project
122 that can be useful for administering and monitoring NTP. This page
123 collects some references and links.
126 == Building and Installing NTP
128 The link:build.html[Building and Installing the Distribution] page
129 gives an overview of the procedures for building and installing NTPsec
130 on a typical system. For more details, see the INSTALL file in the
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137 == Resolving Problems
139 Like other things in modern Internet life, NTP problems can be
140 devilishly intricate. This distribution includes a number of utilities
141 designed to identify and resolve problems using an integrated management
142 protocol supported by the link:ntpq.html[+ntpq+] utility program.
144 The link:debug.html[NTP Debugging Techniques] page contains useful
145 information for identifying problems and devising solutions. Additional
146 information on reference clock driver construction and debugging is
147 in the link:rdebug.html[Debugging Hints for Reference Clock Drivers] page.
149 Users are invited to report bugs and offer suggestions via the
150 link:bugs.html[NTP Bug Reporting Procedures] page.
153 == Further Information
155 The link:sitemap.html[Site Map] page contains a list of document
156 collections arranged by topic. The Program Manual Pages collection may
157 be the best place to start. The link:comdex.html[Command Index]
158 collection contains a list of all configuration file commands together
159 with a short function description. There is a
160 link:ntpspeak.html[glossary of NTP-speak]. A great wealth of
161 additional information is available via the External Links collection,
162 including a book and numerous background papers and briefing
165 Background information on computer network time synchronization is on
166 the {millshome}exec.html[Executive Summary -
167 Computer Network Time Synchronization] page. Background information,
168 bibliography and briefing slides suitable for presentations are on the
169 {millshome}ntp.html[Network Time
170 Synchronization Research Project] page. Additional information is at
171 the NTPsec web site {project-weblink}.
173 You can also read a brief link:history.html[history of NTP].
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