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1 perry 1 ntpdate
2 !!!ntpdate
3 NAME
4 SYNOPSIS
5 DESCRIPTION
6 OPTIONS
7 FILES
8 BUGS
9 AUTHOR
10 ----
11 !!NAME
12
13
14 ntpdate - set the date and time via NTP
15 !!SYNOPSIS
16
17
18 __ntpdate__ [[__-bBdoqsuv__] [[__-a__ ''key'']
19 [[__-e__ ''authdelay''] [[__-k__ ''keyfile'']
20 [[__-o__ ''version''] [[__-p__ ''samples'']
21 [[__-t__ ''timeout''] ''server''
22 [[__...__]
23 !!DESCRIPTION
24
25
26 __ntpdate__ sets the local date and time by polling the
27 Network Time Protocol (NTP) server(s) given as the
28 ''server'' arguments to determine the correct time. It
29 must be run as root on the local host. A number of samples
30 are obtained from each of the servers specified and a subset
31 of the NTP clock filter and selection algorithms are applied
32 to select the best of these. Note that the accuracy and
33 reliability of ntpdate depends on the number of servers, the
34 number of polls each time it is run and the interval between
35 runs.
36
37
38 ntpdate can be run manually as necessary to set the host
39 clock, or it can be run from the host startup script to set
40 the clock at boot time. This is useful in some cases to set
41 the clock initially before starting the NTP daemon ntpd. It
42 is also possible to run ntpdate from a cron script. However,
43 it is important to note that ntpdate with contrived cron
44 scripts is no substitute for the NTP daemon, which uses
45 sophisticated algorithms to maximize accuracy and
46 reliability while minimizing resource use. Finally, since
47 ntpdate does not discipline the host clock frequency as does
48 ntpd, the accuracy using ntpdate is limited.
49
50
51 Time adjustments are made by ntpdate in one of two ways. If
52 ntpdate determines the clock is in error more than 0.5
53 second it will simply step the time by calling the system
54 settimeofday() routine. If the error is less than 0.5
55 seconds, it will slew the time by calling the system
56 adjtime() routine. The latter technique is less disruptive
57 and more accurate when the error is small, and works quite
58 well when ntpdate is run by cron every hour or
59 two.
60
61
62 ntpdate will decline to set the date if an NTP server daemon
63 (e.g., ntpd) is running on the same host. When running
64 ntpdate on a regular basis from cron as an alternative to
65 running a daemon, doing so once every hour or two will
66 result in precise enough timekeeping to avoid stepping the
67 clock.
68 !!OPTIONS
69
70
71 __-a__ ''key''
72
73
74 Enable the authentication function and specify the key
75 identifier to be used for authentication as the argument
76 keyntpdate. The keys and key identifiers must match in both
77 the client and server key files. The default is to disable
78 the authentication function.
79
80
81 __-B__
82
83
84 Force the time to always be slewed using the adjtime()
85 system call, even if the measured offset is greater than
86 +-128 ms. The default is to step the time using
87 settimeofday() if the offset is greater than +-128 ms. Note
88 that, if the offset is much greater than +-128 ms in this
89 case, that it can take a long time (hours) to slew the clock
90 to the correct value. During this time. the host should not
91 be used to synchronize clients.
92
93
94 __-b__
95
96
97 Force the time to be stepped using the settimeofday() system
98 call, rather than slewed (default) using the adjtime()
99 system call. This option should be used when called from a
100 startup file at boot time.
101
102
103 __-d__
104
105
106 Enable the debugging mode, in which ntpdate will go through
107 all the steps, but not adjust the local clock. Information
108 useful for general debugging will also be
109 printed.
110
111
112 __-e__ ''authdelay''
113
114
115 Specify the processing delay to perform an authentication
116 function as the value authdelay, in seconds and fraction
117 (see ntpd for details). This number is usually small enough
118 to be negligible for most purposes, though specifying a
119 value may improve timekeeping on very slow
120 CPU's.
121
122
123 __-k__ ''keyfile''
124
125
126 Specify the path for the authentication key file as the
127 string keyfile. The default is /etc/ntp.keys. This file
128 should be in the format described in ntpd.
129
130
131 __-o__ ''version''
132
133
134 Specify the NTP version for outgoint packets as the integer
135 version, which can be 1 or 2. The default is 3. This allows
136 ntpdate to be used with older NTP versions.
137
138
139 __-p__ ''samples''
140
141
142 Specify the number of samples to be acquired from each
143 server as the integer samples, with values from 1 to 8
144 inclusive. The default is 4.
145
146
147 __-q__
148
149
150 Query only - don't set the clock.
151
152
153 __-s__
154
155
156 Divert logging output from the standard output (default) to
157 the system syslog facility. This is designed primarily for
158 convenience of cron scripts.
159
160
161 __-t__ ''timeout''
162
163
164 Specify the maximum time waiting for a server response as
165 the value timeout, in seconds and fraction. The value is is
166 rounded to a multiple of 0.2 seconds. The default is 1
167 second, a value suitable for polling across a
168 LAN.
169
170
171 __-u__
172
173
174 Direct ntpdate to use an unprivileged port or outgoing
175 packets. This is most useful when behind a firewall that
176 blocks incoming traffic to privileged ports, and you want to
177 synchronise with hosts beyond the firewall. Note that the -d
178 option always uses unprivileged ports.
179
180
181 __-v__
182
183
184 Be verbose. This option will cause ntpdate's version
185 identification string to be logged.
186 !!FILES
187
188
189 ''/etc/ntp.keys''
190
191
192 - encryption keys used by ntpdate.
193 !!BUGS
194
195
196 The slew adjustment is actually 50% larger than the measured
197 offset, since this (it is argued) will tend to keep a badly
198 drifting clock more accurate. This is probably not a good
199 idea and may cause a troubling hunt for some values of the
200 kernel variables tick and tickadj.
201 !!AUTHOR
202
203
204 David L. Mills (mills@udel.edu)
205 This manpage converted from html to roff by Fabrizio Polacco
206 ----
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