19c2daa00SOllivier Robert<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> 29c2daa00SOllivier Robert 39c2daa00SOllivier Robert<html> 49c2daa00SOllivier Robert 59c2daa00SOllivier Robert <head> 69c2daa00SOllivier Robert <meta name="generator" content="HTML Tidy, see www.w3.org"> 79c2daa00SOllivier Robert <title>ntpdate - set the date and time via NTP</title> 89c2daa00SOllivier Robert <link href="scripts/style.css" type="text/css" rel="stylesheet"> 99c2daa00SOllivier Robert </head> 109c2daa00SOllivier Robert 119c2daa00SOllivier Robert <body> 129c2daa00SOllivier Robert <h3><tt>ntpdate</tt> - set the date and time via NTP</h3> 139c2daa00SOllivier Robert <img src="pic/rabbit.gif" alt="gif" align="left"><a href="http://www.eecis.udel.edu/~mills/pictures.html">from <i>Alice's Adventures in Wonderland</i>, Lewis Carroll</a> 149c2daa00SOllivier Robert <p>I told you it was eyeball and wristwatch.</p> 159c2daa00SOllivier Robert <p>Last update: <csobj format="ShortTime" h="24" locale="00000409" region="0" t="DateTime" w="50">01:13</csobj> UTC <csobj format="LongDate" h="24" locale="00000409" region="0" t="DateTime" w="252">Sunday, December 22, 2002</csobj></p> 169c2daa00SOllivier Robert <br clear="left"> 179c2daa00SOllivier Robert <hr> 189c2daa00SOllivier Robert <p>Disclaimer: The functionality of this program is now available in the <tt>ntpd</tt> program. See the <tt>-q</tt> command line option in the <a href="ntpd.html"><tt>ntpd</tt> - Network Time Protocol (NTP) daemon</a> page. After a suitable period of mourning, the <tt>ntpdate</tt> program is to be retired from this distribution</p> 199c2daa00SOllivier Robert <h4>Synopsis</h4> 209c2daa00SOllivier Robert <tt>ntpdate [ -bBdoqsuv ] [ -a <i>key</i> ] [ -e <i>authdelay</i> ] [ -k <i>keyfile</i> ] [ -o <i>version</i> ] [ -p <i>samples</i> ] [ -t <i>timeout</i> ] <i>server</i> [ ... ]</tt> 219c2daa00SOllivier Robert <h4>Description</h4> 229c2daa00SOllivier Robert <tt>ntpdate</tt> sets the local date and time by polling the Network Time Protocol (NTP) server(s) given as the <i>server</i> arguments to determine the correct time. It must be run as root on the local host. A number of samples are obtained from each of the servers specified and a subset of the NTP clock filter and selection algorithms are applied to select the best of these. Note that the accuracy and reliability of <tt>ntpdate</tt> depends on the number of servers, the number of polls each time it is run and the interval between runs. 239c2daa00SOllivier Robert <p><tt>ntpdate</tt> can be run manually as necessary to set the host clock, or it can be run from the host startup script to set the clock at boot time. This is useful in some cases to set the clock initially before starting the NTP daemon <tt>ntpd</tt>. It is also possible to run <tt>ntpdate</tt> from a <tt>cron</tt> script. However, it is important to note that <tt>ntpdate</tt> with contrived <tt>cron</tt> scripts is no substitute for the NTP daemon, which uses sophisticated algorithms to maximize accuracy and reliability while minimizing resource use. Finally, since <tt>ntpdate</tt> does not discipline the host clock frequency as does <tt>ntpd</tt>, the accuracy using <tt>ntpdate</tt> is limited.</p> 249c2daa00SOllivier Robert <p>Time adjustments are made by <tt>ntpdate</tt> in one of two ways. If <tt>ntpdate</tt> determines the clock is in error more than 0.5 second it will simply step the time by calling the system <tt>settimeofday()</tt> routine. If the error is less than 0.5 seconds, it will slew the time by calling the system <tt>adjtime()</tt> routine. The latter technique is less disruptive and more accurate when the error is small, and works quite well when <tt>ntpdate</tt> is run by <tt>cron</tt> every hour or two.</p> 259c2daa00SOllivier Robert <p><tt>ntpdate</tt> will decline to set the date if an NTP server daemon (e.g., <tt>ntpd</tt>) is running on the same host. When running <tt>ntpdate</tt> on a regular basis from <tt>cron</tt> as an alternative to running a daemon, doing so once every hour or two will result in precise enough timekeeping to avoid stepping the clock.</p> 269c2daa00SOllivier Robert <p>Note that in contexts where a host name is expected, a <tt>-4</tt> qualifier preceding the host name forces DNS resolution to the IPv4 namespace, while a <tt>-6</tt> qualifier forces DNS resolution to the IPv6 namespace.</p> 279c2daa00SOllivier Robert <p>If NetInfo support is compiled into <tt>ntpdate</tt>, then the <tt>server</tt> argument is optional if <tt>ntpdate</tt> can find a time server in the NetInfo configuration for <tt>ntpd</tt>.</p> 289c2daa00SOllivier Robert <h4>Command Line Options</h4> 299c2daa00SOllivier Robert <dl> 309c2daa00SOllivier Robert <dt><tt>-4</tt> 319c2daa00SOllivier Robert <dd>Force DNS resolution of following host names on the command line to the IPv4 namespace. 329c2daa00SOllivier Robert <dt><tt>-6</tt> 339c2daa00SOllivier Robert <dd>Force DNS resolution of following host names on the command line to the IPv6 namespace. 349c2daa00SOllivier Robert <dt><tt>-a <i>key</i></tt> 359c2daa00SOllivier Robert <dd>Enable the authentication function and specify the key identifier to be used for authentication as the argument <i>key</i><tt>ntpdate</tt>. The keys and key identifiers must match in both the client and server key files. The default is to disable the authentication function. 369c2daa00SOllivier Robert <dt><tt>-B</tt> 379c2daa00SOllivier Robert <dd>Force the time to always be slewed using the adjtime() system call, even if the measured offset is greater than +-128 ms. The default is to step the time using settimeofday() if the offset is greater than +-128 ms. Note that, if the offset is much greater than +-128 ms in this case, that it can take a long time (hours) to slew the clock to the correct value. During this time. the host should not be used to synchronize clients. 389c2daa00SOllivier Robert <dt><tt>-b</tt> 399c2daa00SOllivier Robert <dd>Force the time to be stepped using the settimeofday() system call, rather than slewed (default) using the adjtime() system call. This option should be used when called from a startup file at boot time. 409c2daa00SOllivier Robert <dt><tt>-d</tt> 419c2daa00SOllivier Robert <dd>Enable the debugging mode, in which <tt>ntpdate</tt> will go through all the steps, but not adjust the local clock. Information useful for general debugging will also be printed. 429c2daa00SOllivier Robert <dt><tt>-e <i>authdelay</i></tt> 439c2daa00SOllivier Robert <dd>Specify the processing delay to perform an authentication function as the value <i>authdelay</i>, in seconds and fraction (see <tt>ntpd</tt> for details). This number is usually small enough to be negligible for most purposes, though specifying a value may improve timekeeping on very slow CPU's. 449c2daa00SOllivier Robert <dt><tt>-k <i>keyfile</i></tt> 459c2daa00SOllivier Robert <dd>Specify the path for the authentication key file as the string <i>keyfile</i>. The default is <tt>/etc/ntp.keys</tt>. This file should be in the format described in <tt>ntpd</tt>. 469c2daa00SOllivier Robert <dt><tt>-o <i>version</i></tt> 479c2daa00SOllivier Robert <dd>Specify the NTP version for outgoing packets as the integer <i>version</i>, which can be 1 or 2. The default is 3. This allows <tt>ntpdate</tt> to be used with older NTP versions. 489c2daa00SOllivier Robert <dt><tt>-p <i>samples</i></tt> 499c2daa00SOllivier Robert <dd>Specify the number of samples to be acquired from each server as the integer <i>samples</i>, with values from 1 to 8 inclusive. The default is 4. 509c2daa00SOllivier Robert <dt><i><tt>-q</tt></i> 519c2daa00SOllivier Robert <dd>Query only - don't set the clock. 529c2daa00SOllivier Robert <dt><tt>-s</tt> 539c2daa00SOllivier Robert <dd>Divert logging output from the standard output (default) to the system <tt>syslog</tt> facility. This is designed primarily for convenience of <tt>cron</tt> scripts. 549c2daa00SOllivier Robert <dt><tt>-t <i>timeout</i></tt> 559c2daa00SOllivier Robert <dd>Specify the maximum time waiting for a server response as the value <i>timeout</i>, in seconds and fraction. The value is is rounded to a multiple of 0.2 seconds. The default is 1 second, a value suitable for polling across a LAN. 569c2daa00SOllivier Robert <dt><tt>-u</tt> 579c2daa00SOllivier Robert <dd>Direct <tt>ntpdate</tt> to use an unprivileged port or outgoing packets. This is most useful when behind a firewall that blocks incoming traffic to privileged ports, and you want to synchronise with hosts beyond the firewall. Note that the <tt>-d</tt> option always uses unprivileged ports. 589c2daa00SOllivier Robert <dt><tt>-<i>v</i></tt> 599c2daa00SOllivier Robert <dd>Be verbose. This option will cause <tt>ntpdate</tt>'s version identification string to be logged. 609c2daa00SOllivier Robert </dl> 619c2daa00SOllivier Robert <h4>Files</h4> 629c2daa00SOllivier Robert <tt>/etc/ntp.keys</tt> - encryption keys used by <tt>ntpdate</tt>. 639c2daa00SOllivier Robert <h4>Bugs</h4> 649c2daa00SOllivier Robert The slew adjustment is actually 50% larger than the measured offset, since this (it is argued) will tend to keep a badly drifting clock more accurate. This is probably not a good idea and may cause a troubling hunt for some values of the kernel variables <tt>tick</tt> and <tt>tickadj</tt>. 659c2daa00SOllivier Robert <hr> 669c2daa00SOllivier Robert <script type="text/javascript" language="javascript" src="scripts/footer.txt"></script> 679c2daa00SOllivier Robert </body> 689c2daa00SOllivier Robert 699c2daa00SOllivier Robert</html>
