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c53ea2f8 | 1 | .TH ntpdate 8 |
2 | .SH NAME | |
3 | ntpdate \- set the date and time via NTP | |
4 | .SH SYNOPSIS | |
5 | .B ntpdate | |
6 | .RB [\| \-bBdoqsuv \|] | |
7 | .RB [\| \-a | |
8 | .IR key \|] | |
9 | .RB [\| \-e | |
10 | .IR authdelay \|] | |
11 | .RB [\| \-k | |
12 | .IR keyfile \|] | |
13 | .RB [\| \-o | |
14 | .IR version \|] | |
15 | .RB [\| \-p | |
16 | .IR samples \|] | |
17 | .RB [\| \-t | |
18 | .IR timeout \|] | |
19 | .IR server | |
20 | .RB [\| ... \|] | |
21 | .SH DESCRIPTION | |
22 | .B ntpdate | |
23 | sets the local date and time by polling the Network Time | |
24 | Protocol (NTP) server(s) given as the | |
25 | .I server | |
26 | arguments to determine | |
27 | the correct time. It must be run as root on the local host. A number | |
28 | of samples are obtained from each of the servers specified and a | |
29 | subset of the NTP clock filter and selection algorithms are applied to | |
30 | select the best of these. Note that the accuracy and reliability of | |
31 | ntpdate depends on the number of servers, the number of polls each | |
32 | time it is run and the interval between runs. | |
33 | ||
34 | ntpdate can be run manually as necessary to set the host clock, or it | |
35 | can be run from the host startup script to set the clock at boot time. | |
36 | This is useful in some cases to set the clock initially before | |
37 | starting the NTP daemon ntpd. It is also possible to run ntpdate from | |
38 | a cron script. However, it is important to note that ntpdate with | |
39 | contrived cron scripts is no substitute for the NTP daemon, which uses | |
40 | sophisticated algorithms to maximize accuracy and reliability while | |
41 | minimizing resource use. Finally, since ntpdate does not discipline | |
42 | the host clock frequency as does ntpd, the accuracy using ntpdate is | |
43 | limited. | |
44 | ||
45 | Time adjustments are made by ntpdate in one of two ways. If ntpdate | |
46 | determines the clock is in error more than 0.5 second it will simply | |
47 | step the time by calling the system settimeofday() routine. If the | |
48 | error is less than 0.5 seconds, it will slew the time by calling the | |
49 | system adjtime() routine. The latter technique is less disruptive and | |
50 | more accurate when the error is small, and works quite well when | |
51 | ntpdate is run by cron every hour or two. | |
52 | ||
53 | ntpdate will decline to set the date if an NTP server daemon (e.g., | |
54 | ntpd) is running on the same host. When running ntpdate on a regular | |
55 | basis from cron as an alternative to running a daemon, doing so once | |
56 | every hour or two will result in precise enough timekeeping to avoid | |
57 | stepping the clock. | |
58 | .SH OPTIONS | |
59 | .TP | |
60 | .BI \-a \ key | |
61 | Enable the authentication function and specify the key | |
62 | identifier to be used for authentication as the argument | |
63 | keyntpdate. The keys and key identifiers must match in both the | |
64 | client and server key files. The default is to disable the | |
65 | authentication function. | |
66 | .TP | |
67 | .B \-B | |
68 | Force the time to always be slewed using the adjtime() system | |
69 | call, even if the measured offset is greater than +-128 ms. The | |
70 | default is to step the time using settimeofday() if the offset | |
71 | is greater than +-128 ms. Note that, if the offset is much | |
72 | greater than +-128 ms in this case, that it can take a long | |
73 | time (hours) to slew the clock to the correct value. During | |
74 | this time. the host should not be used to synchronize clients. | |
75 | .TP | |
76 | .B \-b | |
77 | Force the time to be stepped using the settimeofday() system | |
78 | call, rather than slewed (default) using the adjtime() system | |
79 | call. This option should be used when called from a startup | |
80 | file at boot time. | |
81 | .TP | |
82 | .B \-d | |
83 | Enable the debugging mode, in which ntpdate will go through all | |
84 | the steps, but not adjust the local clock. Information useful | |
85 | for general debugging will also be printed. | |
86 | .TP | |
87 | .BI \-e \ authdelay | |
88 | Specify the processing delay to perform an authentication | |
89 | function as the value authdelay, in seconds and fraction (see | |
90 | ntpd for details). This number is usually small enough to be | |
91 | negligible for most purposes, though specifying a value may | |
92 | improve timekeeping on very slow CPU's. | |
93 | .TP | |
94 | .BI \-k \ keyfile | |
95 | Specify the path for the authentication key file as the string | |
96 | keyfile. The default is /etc/ntp.keys. This file should be in | |
97 | the format described in ntpd. | |
98 | .TP | |
99 | .BI \-o \ version | |
100 | Specify the NTP version for outgoint packets as the integer | |
101 | version, which can be 1 or 2. The default is 3. This allows | |
102 | ntpdate to be used with older NTP versions. | |
103 | .TP | |
104 | .BI \-p \ samples | |
105 | Specify the number of samples to be acquired from each server | |
106 | as the integer samples, with values from 1 to 8 inclusive. The | |
107 | default is 4. | |
108 | .TP | |
109 | .B \-q | |
110 | Query only - don't set the clock. | |
111 | .TP | |
112 | .B \-s | |
113 | Divert logging output from the standard output (default) to the | |
114 | system syslog facility. This is designed primarily for | |
115 | convenience of cron scripts. | |
116 | .TP | |
117 | .BI \-t \ timeout | |
118 | Specify the maximum time waiting for a server response as the | |
119 | value timeout, in seconds and fraction. The value is is rounded | |
120 | to a multiple of 0.2 seconds. The default is 1 second, a value | |
121 | suitable for polling across a LAN. | |
122 | .TP | |
123 | .B \-u | |
124 | Direct ntpdate to use an unprivileged port or outgoing packets. | |
125 | This is most useful when behind a firewall that blocks incoming | |
126 | traffic to privileged ports, and you want to synchronise with | |
127 | hosts beyond the firewall. Note that the -d option always uses | |
128 | unprivileged ports. | |
129 | .TP | |
130 | .B \-v | |
131 | Be verbose. This option will cause ntpdate's version | |
132 | identification string to be logged. | |
133 | .SH FILES | |
134 | .TP | |
135 | .I /etc/ntp.keys | |
136 | \- encryption keys used by ntpdate. | |
137 | .SH BUGS | |
138 | The slew adjustment is actually 50% larger than the measured offset, | |
139 | since this (it is argued) will tend to keep a badly drifting clock | |
140 | more accurate. This is probably not a good idea and may cause a | |
141 | troubling hunt for some values of the kernel variables tick and | |
142 | tickadj. | |
143 | .SH AUTHOR | |
144 | David L. Mills (mills@udel.edu) | |
145 | .br | |
146 | This manpage converted from html to roff by | |
147 | Fabrizio Polacco <fpolacco@debian.org> | |
148 |