19c2daa00SOllivier Robert<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> 29c2daa00SOllivier Robert<html> 39c2daa00SOllivier Robert<head> 4ea906c41SOllivier Robert<meta http-equiv="content-type" content="text/html;charset=iso-8859-1"> 59c2daa00SOllivier Robert<meta name="generator" content="HTML Tidy, see www.w3.org"> 69c2daa00SOllivier Robert<title>ntpdate - set the date and time via NTP</title> 79c2daa00SOllivier Robert<link href="scripts/style.css" type="text/css" rel="stylesheet"> 89c2daa00SOllivier Robert</head> 99c2daa00SOllivier Robert<body> 109c2daa00SOllivier Robert<h3><tt>ntpdate</tt> - set the date and time via NTP</h3> 119c2daa00SOllivier 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> 129c2daa00SOllivier Robert<p>I told you it was eyeball and wristwatch.</p> 132b15cb3dSCy Schubert<p>Last update: 14*4e1ef62aSXin LI <!-- #BeginDate format:En2m -->21-Jul-2018 04:09<!-- #EndDate --> 152b15cb3dSCy Schubert UTC</p> 169c2daa00SOllivier Robert<br clear="left"> 179c2daa00SOllivier Robert<hr> 182b15cb3dSCy Schubert<p>Disclaimer: This program has known bugs and deficiencies and nobody 192b15cb3dSCy Schuberthas volunteered to fix them in a long time. The good news is the 202b15cb3dSCy Schubertfunctionality originally intended for this program is available in the <tt>ntpd</tt> and 212b15cb3dSCy Schubert<tt>sntp</tt> programs. See the <a 222b15cb3dSCy Schuberthref="http://support.ntp.org/Dev/DeprecatingNtpdate">Deprecating 232b15cb3dSCy Schubert<tt>ntpdate</tt> topic</a> in the NTP Support wiki 242b15cb3dSCy Schubertfor a thorough discussion and analysis of the issues. 252b15cb3dSCy SchubertSee the <tt>-q</tt> command line option in the <a 262b15cb3dSCy Schuberthref="ntpd.html"><tt>ntpd</tt> - Network Time Protocol (NTP) daemon</a> 272b15cb3dSCy Schubertpage and/or the <a href="sntp.html"><tt>sntp</tt> - Simple Network Time 282b15cb3dSCy SchubertProtocol (SNTP) Client</a> page. After a suitable period of mourning, the <tt>ntpdate</tt> program will be retired from this distribution.</p> 299c2daa00SOllivier Robert<h4>Synopsis</h4> 302b15cb3dSCy Schubert<tt>ntpdate [ -46bBdqsuv ] [ -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> 319c2daa00SOllivier Robert<h4>Description</h4> 322b15cb3dSCy Schubert<p><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.</p> 339c2daa00SOllivier 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> 349c2daa00SOllivier 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> 352b15cb3dSCy Schubert<p><tt>ntpdate</tt> will, if the <tt>-u</tt> flag was not specified, 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> 369c2daa00SOllivier 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> 379c2daa00SOllivier 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> 389c2daa00SOllivier Robert<h4>Command Line Options</h4> 399c2daa00SOllivier Robert<dl> 402b15cb3dSCy Schubert <dt><tt>-4</tt></dt> 412b15cb3dSCy Schubert <dd>Force DNS resolution of following host names on the command line to the IPv4 namespace.</dd> 422b15cb3dSCy Schubert <dt><tt>-6</tt></dt> 432b15cb3dSCy Schubert <dd>Force DNS resolution of following host names on the command line to the IPv6 namespace.</dd> 442b15cb3dSCy Schubert <dt><tt>-a <i>key</i></tt></dt> 452b15cb3dSCy Schubert <dd>Enable the authentication function and specify the key identifier to be used for authentication as the argument <i>key</i>. The keys and key identifiers must match in both the client and server key files. The default is to disable the authentication function. 462b15cb3dSCy Schubert <dt><tt>-B</tt></dt> 472b15cb3dSCy Schubert <dd>Force the time to always be slewed using the adjtime() system call, even if the measured offset is greater than +-500 ms. The default is to step the time using settimeofday() if the offset is greater than +-500 ms. Note that, if the offset is much greater than +-500 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. 482b15cb3dSCy Schubert <dt><tt>-b</tt></dt> 492b15cb3dSCy Schubert <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.</dd> 502b15cb3dSCy Schubert <dt><tt>-d</tt></dt> 512b15cb3dSCy Schubert <dd>Enable the debugging mode, in which <tt>ntpdate</tt> will go through all the steps, but not adjust the local clock and using an unprivileged port. Information useful for general debugging will also be printed.</dd> 522b15cb3dSCy Schubert <dt><tt>-e <i>authdelay</i></tt></dt> 532b15cb3dSCy Schubert <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.</dd> 542b15cb3dSCy Schubert <dt><tt>-k <i>keyfile</i></tt></dt> 552b15cb3dSCy Schubert <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>.</dd> 562b15cb3dSCy Schubert <dt><tt>-o <i>version</i></tt></dt> 572b15cb3dSCy Schubert <dd>Specify the NTP version for outgoing packets as the integer 582b15cb3dSCy Schubert <i>version</i>, which can be 1, 2, 3 or 4. The default is 4. This allows <tt>ntpdate</tt> to be used with older NTP versions.</dd> 592b15cb3dSCy Schubert <dt><tt>-p <i>samples</i></tt></dt> 602b15cb3dSCy Schubert <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.</dd> 612b15cb3dSCy Schubert <dt><i><tt>-q</tt></i></dt> 622b15cb3dSCy Schubert <dd>Query only - don't set the clock.</dd> 632b15cb3dSCy Schubert <dt><tt>-s</tt></dt> 642b15cb3dSCy Schubert <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.</dd> 652b15cb3dSCy Schubert <dt><tt>-t <i>timeout</i></tt></dt> 66*4e1ef62aSXin LI <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 2 seconds, a value suitable for polling across a LAN.</dd> 672b15cb3dSCy Schubert <dt><tt>-u</tt></dt> 682b15cb3dSCy Schubert <dd>Direct <tt>ntpdate</tt> to use an unprivileged port for outgoing packets. This is most useful when behind a firewall that blocks incoming traffic to privileged ports, and you want to synchronize with hosts beyond the firewall. Note that the <tt>-d</tt> option always uses unprivileged ports. 692b15cb3dSCy Schubert <dt><tt>-<i>v</i></tt></dt> 702b15cb3dSCy Schubert <dd>Be verbose. This option will cause <tt>ntpdate</tt>'s version identification string to be logged.</dd> 719c2daa00SOllivier Robert</dl> 72ea906c41SOllivier Robert<h4>Diagnostics</h4> 73ea906c41SOllivier Robert<tt>ntpdate</tt>'s exit status is zero if it finds a server and updates the clock, and nonzero otherwise. 749c2daa00SOllivier Robert<h4>Files</h4> 759c2daa00SOllivier Robert<tt>/etc/ntp.keys</tt> - encryption keys used by <tt>ntpdate</tt>. 769c2daa00SOllivier Robert<h4>Bugs</h4> 779c2daa00SOllivier RobertThe 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>. 789c2daa00SOllivier Robert<hr> 799c2daa00SOllivier Robert<script type="text/javascript" language="javascript" src="scripts/footer.txt"></script> 809c2daa00SOllivier Robert</body> 819c2daa00SOllivier Robert</html> 82
