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diff --git a/html/ntpd.html b/html/ntpd.html index 3b70694a6efd..9a160007c142 100644 --- a/html/ntpd.html +++ b/html/ntpd.html @@ -10,123 +10,164 @@ </head> <body> - <h3><tt>ntpd</tt> - Network Time Protocol (NTP) daemon</h3> - <img src="pic/alice47.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> - <p>The mushroom knows all the command line options.</p> - <p>Last update: <csobj format="ShortTime" h="25" locale="00000409" region="0" t="DateTime" w="61">18:44</csobj> UTC <csobj format="LongDate" h="25" locale="00000409" region="0" t="DateTime" w="246">Thursday, July 28, 2005</csobj></p> - <br clear="left"> + <h3><tt>ntpd</tt> - Network Time Protocol (NTP) Daemon</h3> + <img src="pic/wingdorothy.gif" alt="gif" align="left"><a href="http://www.eecis.udel.edu/~mills/pictures.html">from <i>The Wizard of Oz</i>, L. Frank Baum</a> + <p>You need help from the monkeys.</p> + <p>Last update: <!-- #BeginDate format:En1m -->14-oct-09 22:23<!-- #EndDate --></p> +<br clear="left"> <h4>Related Links</h4> - <script type="text/javascript" language="javascript" src="scripts/links7.txt"></script> + <script type="text/javascript" language="javascript" src="scripts/command.txt"></script> <h4>Table of Contents</h4> <ul> - <li class="inline"><a href="#synop">Synopsis</a><br> - <li class="inline"><a href="#descr">Description</a><br> - <li class="inline"><a href="#op">How NTP Operates</a><br> - <li class="inline"><a href="#freq">Frequency Discipline</a><br> - <li class="inline"><a href="#modes">Operating Modes</a><br> - <li class="inline"><a href="#poll">Poll Interval Control</a><br> - <li class="inline"><a href="#poll">Poll Interval Control</a><br> - <li class="inline"><a href="#notes">Notes</a><br> - <li class="inline"><a href="#cmd">Command Line Options</a><br> - <li class="inline"><a href="#cfg">The Configuration File</a><br> - <li class="inline"><a href="#opt">Configuration Options</a><br> - <li class="inline"><a href="#files">Files</a> + <li class="inline"><a href="#synop">Synopsis</a></li> + <li class="inline"><a href="#descr">Description</a></li> + <li class="inline"><a href="#time">Setting the Time and Frequency</a></li> + <li class="inline"><a href="#modes">Operating Modes</a></li> + <li class="inline"><a href="#poll">Poll Interval Control</a></li> + <li class="inline"><a href="#leap">Leap Second Processing</a></li> + <li class="inline"><a href="#notes">Additional Features</a></li> + <li class="inline"><a href="#cmd">Command Line Options</a></li> + <li class="inline"><a href="#cfg">The Configuration File</a></li> + <li class="inline"><a href="#files">Files</a></li> </ul> <hr> <h4 id="synop">Synopsis</h4> - <tt>ntpd [ -46aAbdDgLmnNqx ] [ -c <i>conffile</i> ] [ -f <i>driftfile</i> ] [ -i <i>jaildir</i> ] [ -k <i>keyfile</i> ] [ -l <i>logfile</i> ] [ -p <i>pidfile</i> ] [ -P <i>priority</i> ] [ -r <i>broadcastdelay</i> ] [ -s <i>statsdir</i> ] [ -t <i>key</i> ] [ -u <i>user</i>[:<i>group</i>] ] [ -U <i>interface_update_interval</i> ] [ -v <i>variable</i> ] [ -V <i>variable</i> ]</tt> + <tt>ntpd [ -46aAbdDgLnNqx ] [ -c <i>conffile</i> ] [ -f <i>driftfile</i> ] [ -i <i>jaildir</i> ] [ -I <i>iface</i> ] [ -k <i>keyfile</i> ] [ -l <i>logfile</i> ] [ -p <i>pidfile</i> ] [ -P <i>priority</i> ] [ -r <i>broadcastdelay</i> ] [ -s <i>statsdir</i> ] [ -t <i>key</i> ] [ -u <i>user</i>[:<i>group</i>] ] [ -U <i>interface_update_interval</i> ] [ -v <i>variable</i> ] [ -V <i>variable</i> ]</tt> <h4 id="descr">Description</h4> - <p>The <tt>ntpd</tt> program is an operating system daemon which sets and maintains the system time of day in synchronism with Internet standard time servers. It is a complete implementation of the Network Time Protocol (NTP) version 4, but also retains compatibility with version 3, as defined by RFC-1305, and version 1 and 2, as defined by RFC-1059 and RFC-1119, respectively. <tt>ntpd</tt> does most computations in 64-bit floating point arithmetic and does relatively clumsy 64-bit fixed point operations only when necessary to preserve the ultimate precision, about 232 picoseconds. While the ultimate precision is not achievable with ordinary workstations and networks of today, it may be required with future gigahertz CPU clocks and gigabit LANs.</p> - <h4 id="op">How NTP Operates</h4> - <p>The <tt>ntpd</tt> program operates by exchanging messages with one or more configured servers at designated poll intervals. When started, whether for the first or subsequent times, the program requires several exchanges from the majority of these servers so the signal processing and mitigation algorithms can accumulate and groom the data and set the clock. In order to protect the network from bursts, the initial poll interval for each server is delayed an interval randomized over a few seconds. At the default initial poll interval of 64s, several minutes can elapse before the clock is set. The initial delay to set the clock can be reduced using the <tt>iburst</tt> keyword with the <tt>server</tt> configuration command, as described on the <a href="confopt.html">Configuration Options</a> page.</p> - <p>Most operating systems and hardware of today incorporate a time-of-year (TOY) chip to maintain the time during periods when the power is off. When the machine is booted, the chip is used to initialize the operating system time. After the machine has synchronized to a NTP server, the operating system corrects the chip from time to time. In case there is no TOY chip or for some reason its time is more than 1000s from the server time, <tt>ntpd</tt> assumes something must be terribly wrong and the only reliable action is for the operator to intervene and set the clock by hand. This causes <tt>ntpd</tt> to exit with a panic message to the system log. The <tt>-g</tt> option overrides this check and the clock will be set to the server time regardless of the chip time. However, and to protect against broken hardware, such as when the CMOS battery fails or the clock counter becomes defective, once the clock has been set, an error greater than 1000s will cause <tt>ntpd</tt> to exit anyway.</p> - <p>Under ordinary conditions, <tt>ntpd</tt> adjusts the clock in small steps so that the timescale is effectively continuous and without discontinuities. Under conditions of extreme network congestion, the roundtrip delay jitter can exceed three seconds and the synchronization distance, which is equal to one-half the roundtrip delay plus error budget terms, can become very large. The <tt>ntpd</tt> algorithms discard sample offsets exceeding 128 ms, unless the interval during which no sample offset is less than 128 ms exceeds 900s. The first sample after that, no matter what the offset, steps the clock to the indicated time. In practice this reduces the false alarm rate where the clock is stepped in error to a vanishingly low incidence.</p> - <p>As the result of this behavior, once the clock has been set, it very rarely strays more than 128 ms, even under extreme cases of network path congestion and jitter. Sometimes, in particular when <tt>ntpd</tt> is first started, the error might exceed 128 ms. This may on occasion cause the clock to be set backwards if the local clock time is more than 128 s in the future relative to the server. In some applications, this behavior may be unacceptable. If the <tt>-x</tt> option is included on the command line, the clock will never be stepped and only slew corrections will be used.</p> - <p>The issues should be carefully explored before deciding to use the <tt>-x</tt> option. The maximum slew rate possible is limited to 500 parts-per-million (PPM) as a consequence of the correctness principles on which the NTP protocol and algorithm design are based. As a result, the local clock can take a long time to converge to an acceptable offset, about 2,000 s for each second the clock is outside the acceptable range. During this interval the local clock will not be consistent with any other network clock and the system cannot be used for distributed applications that require correctly synchronized network time.</p> - <p>In spite of the above precautions, sometimes when large frequency errors are present the resulting time offsets stray outside the 128-ms range and an eventual step or slew time correction is required. If following such a correction the frequency error is so large that the first sample is outside the acceptable range, <tt>ntpd</tt> enters the same state as when the <tt>ntp.drift</tt> file is not present. The intent of this behavior is to quickly correct the frequency and restore operation to the normal tracking mode. In the most extreme cases (<tt>time.ien.it</tt> comes to mind), there may be occasional step/slew corrections and subsequent frequency corrections. It helps in these cases to use the <tt>burst</tt> keyword when configuring the server.</p> - <h4 id="freq">Frequency Discipline</h4> - <p>The <tt>ntpd</tt> behavior at startup depends on whether the frequency file, usually <tt>ntp.drift</tt>, exists. This file contains the latest estimate of clock frequency error. When the <tt>ntpd</tt> is started and the file does not exist, the <tt>ntpd</tt> enters a special mode designed to quickly adapt to the particular system clock oscillator time and frequency error. This takes approximately 15 minutes, after which the time and frequency are set to nominal values and the <tt>ntpd</tt> enters normal mode, where the time and frequency are continuously tracked relative to the server. After one hour the frequency file is created and the current frequency offset written to it. When the <tt>ntpd</tt> is started and the file does exist, the <tt>ntpd</tt> frequency is initialized from the file and enters normal mode immediately. After that the current frequency offset is written to the file at hourly intervals.</p> + <p>The <tt>ntpd</tt> program is an operating system daemon that synchronises the system clock with remote NTP time servers or local reference clocks. It is a complete implementation of the Network Time Protocol (NTP) version 4, but also retains compatibility with version 3, as defined by RFC-1305, and version 1 and 2, as defined by RFC-1059 and RFC-1119, respectively. The program can operate in any of several modes, as described on the <a href="assoc.html">Association Management</a> page, and with both symmetric key and public key cryptography, as described on the <a href="manyopt.html">Authentication Options</a> page.</p> + <p>The <tt>ntpd</tt> program ordinarily requires a configuration file as desccribe on the Configuration Commands and Options collection above. However a client can discover remote servers and configure them automatically. This makes it possible to deploy a fleet of workstations without specifying configuration details specific to the local environment. Further details are on the <a href="manyopt.html">Automatic Server Discovery</a> page.</p> + <p>Once the NTP software distribution has been compiled and installed and the configuration file constructed, the next step is to verify correct operation and fix any bugs that may result. Usually, the command line that starts the daemon is included in the system startup file, so it is executed only at system boot time; however, the daemon can be stopped and restarted from root at any time. Once started, the daemon will begin sending and receiving messages, as specified in the configuration file.</p> + <h4 id="time">Setting the Time and Frequency</h4> + <p>The <tt>ntpd</tt> program operates by exchanging messages with one or more servers at designated intervals ranging from about one minute to about 17 minutes. When started, the program requires several exchanges while the algorithms accumulate and groom the data before setting the clock. The initial delay to set the clock can be reduced using options on the <a href="confopt.html">Server Options</a> page.</p> + <p>Most compters today incorporate a time-of-year (TOY) chip to maintain the time during periods when the power is off. When the machine is booted, the chip is used to initialize the operating system time. In case there is no TOY chip or the TOY time is more than 1000 s from the server time, <tt>ntpd</tt> assumes something must be terribly wrong and exits with a panic message to the system operator. With the <tt>-g</tt> option the clock will be initially set to the server time regardless of the chip time. However, once the clock has been set, an error greater than 1000 s will cause <tt>ntpd</tt> to exit anyway.</p> + <p>Under ordinary conditions, <tt>ntpd</tt> slews the clock so that the time is effectively continuous and never runs backwards. If due to extreme network congestion an error spike exceeds the <i>step threshold</i>, by default 128 ms, the spike is discarded. However, if the error persists for more than the <i>stepout threshold</i>, by default 900 s, the system clock is stepped to the correct value. In practice the need for a step has is extremely rare and almost always the result of a hardware failure. With the <tt>-x</tt> option the step threshold is increased to 600 s. Other options are available using the <tt>tinker</tt> command on the <a href="miscopt.html">Miscellaneous Options</a> page.</p> + <p>The issues should be carefully considered before using these options. The maximum slew rate possible is limited to 500 parts-per-million (PPM) by the Unix kernel. As a result, the clock can take 2000 s for each second the clock is outside the acceptable range. During this interval the clock will not be consistent with any other network clock and the system cannot be used for distributed applications that require correctly synchronized network time.</p> + <p>The frequency file, usually called <tt>ntp.drift</tt>, contains the latest estimate of clock frequency. If this file does not exist when <tt>ntpd</tt> is started, it enters a special mode designed to measure the particular frequency directly. The measurement takes 15 minutes, after which the frequency is set and <tt>ntpd</tt> resumes normal mode where the time and frequency are continuously adjusted. The frequency file is updated at intervals of an hour or more depending on the measured clock stability.</p> <h4 id="modes">Operating Modes</h4> - <p><tt>ntpd</tt> can operate in any of several modes, including symmetric active/passive, client/server broadcast/multicast and manycast, as described in the <a href="assoc.html">Association Management</a> page. It normally operates continuously while monitoring for small changes in frequency and trimming the clock for the ultimate precision. However, it can operate in a one-time mode where the time is set from an external server and frequency is set from a previously recorded frequency file. A broadcast/multicast or manycast client can discover remote servers, compute server-client propagation delay correction factors and configure itself automatically. This makes it possible to deploy a fleet of workstations without specifying configuration details specific to the local environment.</p> - <p>By default, <tt>ntpd</tt> runs in continuous mode where each of possibly several external servers is polled at intervals determined by an intricate state machine. The state machine measures the incidental roundtrip delay jitter and oscillator frequency wander and determines the best poll interval using a heuristic algorithm. Ordinarily, and in most operating environments, the state machine will start with 64s intervals and eventually increase in steps to 1024s. A small amount of random variation is introduced in order to avoid bunching at the servers. In addition, should a server become unreachable for some time, the poll interval is increased in steps to 1024s in order to reduce network overhead.</p> - <p>In some cases it may not be practical for <tt>ntpd</tt> to run continuously. A common workaround has been to run the <tt>ntpdate</tt> program from a <tt>cron</tt> job at designated times. However, this program does not have the crafted signal processing, error checking and mitigation algorithms of <tt>ntpd</tt>. The <tt>-q</tt> option is intended for this purpose. Setting this option will cause <tt>ntpd</tt> to exit just after setting the clock for the first time. The procedure for initially setting the clock is the same as in continuous mode; most applications will probably want to specify the <tt>iburst</tt> keyword with the <tt>server</tt> configuration command. With this keyword a volley of messages are exchanged to groom the data and the clock is set in about 10 s. If nothing is heard after a couple of minutes, the daemon times out and exits. After a suitable period of mourning, the <tt>ntpdate</tt> program may be retired.</p> - <p>When kernel support is available to discipline the clock frequency, which is the case for stock Solaris, Tru64, Linux and FreeBSD, a useful feature is available to discipline the clock frequency. First, <tt>ntpd</tt> is run in continuous mode with selected servers in order to measure and record the intrinsic clock frequency offset in the frequency file. It may take some hours for the frequency and offset to settle down. Then the <tt>ntpd</tt> is stopped and run in one-time mode as required. At each startup, the frequency is read from the file and initializes the kernel frequency.</p> + <p>The <tt>ntpd</tt> program normally operates continuously while adjusting the time and frequency, but in some cases it may not be practical to run it continuously. With the <tt>-q</tt> option <tt>ntpd</tt> operates as in continous mode, but exits just after setting the clock for the first time with the configured servers. Most applications will probably want to specify the <tt>iburst</tt> option with the <tt>server</tt> command. With this option a volley of messages is exchanged to groom the data and set the clock in about 10 s. If nothing is heard after a few minutes, the daemon times out and exits.</p> <h4 id="poll">Poll Interval Control</h4> - <p>This version of NTP includes an intricate state machine to reduce the network load while maintaining a quality of synchronization consistent with the observed jitter and wander. There are a number of ways to tailor the operation in order enhance accuracy by reducing the interval or to reduce network overhead by increasing it. However, the user is advised to carefully consider the consequences of changing the poll adjustment range from the default minimum of 64 s to the default maximum of 1,024 s. The default minimum can be changed with the <tt>tinker minpoll</tt> command to a value not less than 16 s. This value is used for all configured associations, unless overridden by the <tt>minpoll</tt> option on the configuration command. Note that most device drivers will not operate properly if the poll interval is less than 64 s and that the broadcast server and manycast client associations will also use the default, unless overridden.</p> - <p>In some cases involving dial up or toll services, it may be useful to increase the minimum interval to a few tens of minutes and maximum interval to a day or so. Under normal operation conditions, once the clock discipline loop has stabilized the interval will be increased in steps from the minimum to the maximum. However, this assumes the intrinsic clock frequency error is small enough for the discipline loop correct it. The capture range of the loop is 500 PPM at an interval of 64s decreasing by a factor of two for each doubling of interval. At a minimum of 1,024 s, for example, the capture range is only 31 PPM. If the intrinsic error is greater than this, the drift file <tt>ntp.drift</tt> will have to be specially tailored to reduce the residual error below this limit. Once this is done, the drift file is automatically updated once per hour and is available to initialize the frequency on subsequent daemon restarts.</p> + <p>NTP uses an intricate heuristic algorithm to automatically control the poll interval for maximum accuracy consistent with minimum network overhead. The algorithm measures the incidental offset and jitter to determine the best poll interval. When <tt>ntpd</tt> starts, the interval is the default minimum 64 s. Under normal conditions when the clock discipline has stabilized, the interval increases in steps to the default maximum 1024 s. In addition, should a server become unreachable after some time, the interval increases in steps to the maximum in order to reduce network overhead.</p> + <p>The default poll interval range is suitable for most conditions, but can be changed using options on the <a href="confopt.html">Server Options</a> and <a href="miscopt.html">Miscellaneous Options</a> pages. However, when using maximum intervals much larger than the default, the residual clock frequency error must be small enough for the discipline loop to capture and correct. The capture range is 500 PPM with a 64-s interval decreasing by a factor of two for each interval doubling. At a 36-hr interval, for example, the capture range is only 0.24 PPM.</p> <h4 id="huff">The huff-n'-puff Filter</h4> - <p>In scenarios where a considerable amount of data are to be downloaded or uploaded over telephone modems, timekeeping quality can be seriously degraded. This occurs because the differential delays on the two directions of transmission can be quite large. In many cases the apparent time errors are so large as to exceed the step threshold and a step correction can occur during and after the data transfer is in progress.</p> - <p>The huff-n'-puff filter is designed to correct the apparent time offset in these cases. It depends on knowledge of the propagation delay when no other traffic is present. In common scenarios this occurs during other than work hours. The filter maintains a shift register that remembers the minimum delay over the most recent interval measured usually in hours. Under conditions of severe delay, the filter corrects the apparent offset using the sign of the offset and the difference between the apparent delay and minimum delay. The name of the filter reflects the negative (huff) and positive (puff) correction, which depends on the sign of the offset.</p> - <p>The filter is activated by the <tt>tinker</tt> command and <tt>huffpuff</tt> keyword, as described in the <a href="miscopt.html">Miscellaneous Options</a> page.</p> - <h4 id="notes">Notes</h4> - <p>If NetInfo support is built into <tt>ntpd</tt>, then <tt>ntpd</tt> will attempt to read its configuration from the NetInfo if the default ntp.conf file cannot be read and no file is specified by the <tt>-c</tt> option.</p> + <p>In scenarios where a considerable amount of data are to be downloaded or uploaded over telephone modems, timekeeping quality can be seriously degraded. This occurs because the differential delays on the two directions of transmission can be quite large. In many cases the apparent time errors are so large as to exceed the step threshold and a step correction can occur during and after the data transfer.</p> + <p>The huff-n'-puff filter is designed to correct the apparent time offset in these cases. It depends on knowledge of the propagation delay when no other traffic is present, such as during other than work hours. The filter remembers the minimum delay over the most recent interval measured usually in hours. Under conditions of severe delay, the filter corrects the apparent offset using the sign of the offset and the difference between the apparent delay and minimum delay. The name of the filter reflects the negative (huff) and positive (puff) correction, which depends on the sign of the offset. The filter is activated by the <tt>tinker huffpuff</tt> command, as described in the <a href="miscopt.html">Miscellaneous Options</a> page.</p> + <h4 id="leap">Leap Second Processing</h4> + <p>As provided by international agreement, an extra second is sometimes inserted + in Coordinated Universal Time (UTC) at the end of a selected month, + usually June or December. The National Institutes of Standards and + Technology (NIST) provides an historic leapseconds file at <tt>time.nist.gov</tt> for + retrieval via FTP. When this file, usually called <tt>ntp-leapseconds.list</tt>, + is copied and installed in a directory. + The <tt>leapfile</tt> configuration command specifies the path to + this file. At startup, <tt>ntpd</tt> reads + it and initializes three leapsecond values: the NTP seconds + at the next leap event, the offset of UTC relative to International + Atomic Time (TAI) after the leap and the NTP seconds when the leapseconds + file expires and should be retrieved again.</p> + <p>If a host does not have the leapsecond values, they can be obtained over the net using the Autokey security protocol. Ordinarily, the leapseconds file is installed on the primary servers and the values flow from them via secondary servers to the clients. When multiple servers are involved, the values with the latest expiration time are used.</p> + <p>If the latest leap is in the past, nothing further is done other than to install the TAI offset. If the leap is in the future less than 28 days, the leap warning bits are set. If in the future less than 23 hours, the kernel is armed to insert one second at the end of the current day. If the kernel is enabled, the leap is done automatically at that time; otherwise, the clock is effectively stopped for one second at the leap. Additional details are in the <a href='http://www.eecis.udel.edu/~mills/leap.html'>The NTP Timescale and Leap Seconds</a> white paper</p> + <p>If none of the above provisions are available, dsependent servers and clients + tally the leap warning bits of surviving servers and reference clocks. + When a majority of the survivors show warning, a leap is programmed + at the end of the current month. During the month and day of insertion, + they operate as above. In this way the leap is is propagated at all + dependent servers and clients.</p> + <h4 id="notes">Additional Features</h4> + <p>A new experimental feature called interleaved modes can be used in NTP + symmetric or broadcast modes. It is designed to improve accuracy + by avoiding kernel latency and queueing delay, as described on the <a href="xleave.html">NTP + Interleaved Modes</a> page. It is activated by the <tt>xleave</tt> option + with the <tt>peer</tt> or <tt>broadcast</tt> configuration commands. The NTP + protocol automatically reconfigures in normal or interleaved mode + as required. Ordinary broadcast clients can use the same servers + as interleaved clients at the same time. Further details are in the + white paper <a href="http://www.eecis.udel.edu/~mills/onwire.html">NTP + Interleaved On-Wire Protocol</a> and the briefing <a href="http://www.eecis.udel.edu/~mills/database/brief/onwire/onwire.ppt">Interleaved + Synchronization Protocols for LANs and Space Data Links</a>.</p> + <p>If <tt>ntpd</tt>, is configured with NetInfo support, it will attempt to read its configuration from the NetInfo service if the default <tt>ntp.conf</tt> file cannot be read and no file is specified by the <tt>-c</tt> option.</p> <p>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> <p>Various internal <tt>ntpd</tt> variables can be displayed and configuration options altered while the <tt>ntpd</tt> is running using the <tt><a href="ntpq.html">ntpq</a></tt> and <tt><a href="ntpdc.html">ntpdc</a></tt> utility programs.</p> <p>When <tt>ntpd</tt> starts it looks at the value of <tt>umask</tt>, and if zero <tt>ntpd</tt> will set the <tt>umask</tt> to <tt>022</tt>.</p> + <p>Unless the <tt>-n</tt>, <tt>-d</tt> or <tt>-D</tt> option is used, <tt>ntpd</tt> changes the current working directory to the root directory, so any options or commands specifying paths need to use an absolute path or a path relative to the root.</p> <h4 id="cmd">Command Line Options</h4> <dl> - <dt><tt>-a</tt> - <dd>Require cryptographic authentication for broadcast client, multicast client and symmetric passive associations. This is the default. - <dt><tt>-A</tt> - <dd>Do not require cryptographic authentication for broadcast client, multicast client and symmetric passive associations. This is almost never a good idea. - <dt><tt>-b</tt> - <dd>Enable the client to synchronize to broadcast servers. - <dt><tt>-c <i>conffile</i></tt> - <dd>Specify the name and path of the configuration file, default <tt>/etc/ntp.conf</tt>. - <dt><tt>-d</tt> - <dd>Specify debugging mode. This option may occur more than once, with each occurrence indicating greater detail of display. - <dt><tt>-D <i>level</i></tt> - <dd>Specify debugging level directly. - <dt><tt>-f <i>driftfile</i></tt> - <dd>Specify the name and path of the frequency file, default <tt>/etc/ntp.drift</tt>. This is the same operation as the <tt>driftfile <i>driftfile</i></tt> configuration command. - <dt><tt>-g</tt> - <dd>Normally, <tt>ntpd</tt> exits with a message to the system log if the offset exceeds the panic threshold, which is 1000 s by default. This option allows the time to be set to any value without restriction; however, this can happen only once. If the threshold is exceeded after that, <tt>ntpd</tt> will exit with a message to the system log. This option can be used with the <tt>-q</tt> and <tt>-x</tt> options. See the <tt>tinker</tt> command for other options. - <dt><tt>-i <i>jaildir</i></tt> - <dd>Chroot the server to the directory <i>jaildir</i>. This option also implies that the server attempts to drop root privileges at startup (otherwise, chroot gives very little additional security), and it is only available if the OS supports to run the server without full root privileges. You may need to also specify a <tt>-u</tt> option. - <dt><tt>-k <i>keyfile</i></tt> - <dd>Specify the name and path of the symmetric key file, default <tt>/etc/ntp.keys</tt>. This is the same operation as the <tt>keys <i>keyfile</i></tt> configuration command. - <dt><tt>-l <i>logfile</i></tt> - <dd>Specify the name and path of the log file. The default is the system log file. This is the same operation as the <tt>logfile <i>logfile</i></tt> configuration command. - <dt><tt>-L</tt> - <dd>Do not listen to virtual IPs. The default is to listen. - <dt><tt>-n</tt> - <dd>Don't fork. - <dt><tt>-N</tt> - <dd>To the extent permitted by the operating system, run the <tt>ntpd</tt> at the highest priority. - <dt><tt>-p <i>pidfile</i></tt> - <dd>Specify the name and path of the file used to record the <tt>ntpd</tt> process ID. This is the same operation as the <tt>pidfile <i>pidfile</i></tt> configuration command. - <dt><tt>-P <i>priority</i></tt> - <dd>To the extent permitted by the operating system, run the <tt>ntpd</tt> at the specified priority. - <dt><tt>-q</tt> - <dd>Exit the <tt>ntpd</tt> just after the first time the clock is set. This behavior mimics that of the <tt>ntpdate</tt> program, which is to be retired. The <tt>-g</tt> and <tt>-x</tt> options can be used with this option. Note: The kernel time discipline is disabled with this option. - <dt><tt>-r <i>broadcastdelay</i></tt> - <dd>Specify the default propagation delay from the broadcast/multicast server to this client. This is necessary only if the delay cannot be computed automatically by the protocol. - <dt><tt>-s <i>statsdir</i></tt> - <dd>Specify the directory path for files created by the statistics facility. This is the same operation as the <tt>statsdir <i>statsdir</i></tt> configuration command. - <dt><tt>-t <i>key</i></tt> - <dd>Add a key number to the trusted key list. This option can occur more than once. - <dt><tt>-u <i>user[:group]</i> </tt> - <dd>Specify a user, and optionally a group, to switch to. This option is only available if the OS supports to run the server without full root privileges. Currently, this option is supported under NetBSD (configure with --enable-clockctl) and Linux (configure with --enable-linuxcaps). - <dt><tt>-U <i>interface update interval</i></tt> + <dt><tt>-4</tt> + <dd>Force DNS resolution of host names to the IPv4 namespace. + <dt><tt>-6</tt> + <dd>Force DNS resolution of host names to the IPv6 namespace. + <dt><tt>-a</tt></dt> + <dd>Require cryptographic authentication for broadcast client, multicast client and symmetric passive associations. This is the same operation as the <tt>enable auth</tt> command and is the default.</dd> + <dt><tt>-A</tt></dt> + <dd>Do not require cryptographic authentication for broadcast client, multicast client and symmetric passive associations. This is the same operation as the <tt>disable auth</tt> command and almost never a good idea.</dd> + <dt><tt>-b</tt></dt> + <dd>Enable the client to synchronize to broadcast servers.</dd> + <dt><tt>-c <i>conffile</i></tt></dt> + <dd>Specify the name and path of the configuration file, default <tt>/etc/ntp.conf</tt>.</dd> + <dt><tt>-d</tt></dt> + <dd>Specify debugging mode. This option may occur more than once, with each occurrence indicating greater detail of display.</dd> + <dt><tt>-D <i>level</i></tt></dt> + <dd>Specify debugging level directly.</dd> + <dt><tt>-f <i>driftfile</i></tt></dt> + <dd>Specify the name and path of the frequency file. This is the same operation as the <tt>driftfile <i>driftfile</i></tt> command.</dd> + <dt><tt>-g</tt></dt> + <dd>Normally, <tt>ntpd</tt> exits with a message to the system log if the offset exceeds the panic threshold, which is 1000 s by default. This option allows the time to be set to any value without restriction; however, this can happen only once. If the threshold is exceeded after that, <tt>ntpd</tt> will exit with a message to the system log. This option can be used with the <tt>-q</tt> and <tt>-x</tt> options. See the <tt>tinker</tt> command for other options.</dd> + <dt><tt>-i <i>jaildir</i></tt></dt> + <dd>Chroot the server to the directory <i><tt>jaildir</tt></i>. This option also implies that the server attempts to drop root privileges at startup (otherwise, chroot gives very little additional security), and it is only available if the OS supports to run the server without full root privileges. You may need to also specify a <tt>-u</tt> option.</dd> + <dt id="--interface"><tt>-I [<i>address</i> | <i>interface name</i>]</tt></dt> + <dd>Open the network address given, or all the addresses associated with the given interface name. This option may appear multiple times. This option also implies not opening other addresses, except wildcard and localhost. This option is deprecated. Please consider using the configuration file <a href="miscopt.html#interface">interface</a> command, which is more versatile.</dd> + <dt><tt>-k <i>keyfile</i></tt></dt> + <dd>Specify the name and path of the symmetric key file. This is the same operation as the <tt>keys <i>keyfile</i></tt> command.</dd> + <dt><tt>-l <i>logfile</i></tt></dt> + <dd>Specify the name and path of the log file. The default is the system log file. This is the same operation as the <tt>logfile <i>logfile</i></tt> command.</dd> + <dt id="--novirtualips"><tt>-L</tt></dt> + <dd>Do not listen to virtual interfaces, defined as those with names containing a colon. This option is deprecated. Please consider using the configuration file <a href="miscopt.html#interface">interface</a> command, which is more versatile.</dd> + <dt><tt>-M</tt></dt> + <dd>Raise scheduler precision to its maximum (1 msec) using timeBeginPeriod. (Windows only)</dd> + <dt><tt>-n</tt></dt> + <dd>Don't fork.</dd> + <dt><tt>-N</tt></dt> + <dd>To the extent permitted by the operating system, run the <tt>ntpd</tt> at the highest priority.</dd> + <dt><tt>-p <i>pidfile</i></tt></dt> + <dd>Specify the name and path of the file used to record the <tt>ntpd</tt> process ID. This is the same operation as the <tt>pidfile <i>pidfile</i></tt> command.</dd> + <dt><tt>-P <i>priority</i></tt></dt> + <dd>To the extent permitted by the operating system, run the <tt>ntpd</tt> at the specified priority.</dd> + <dt><tt>-q</tt></dt> + <dd>Exit the <tt>ntpd</tt> just after the first time the clock is set. This behavior mimics that of the <tt>ntpdate</tt> program, which is to be retired. The <tt>-g</tt> and <tt>-x</tt> options can be used with this option. Note: The kernel time discipline is disabled with this option.</dd> + <dt><tt>-r <i>broadcastdelay</i></tt></dt> + <dd>Specify the default propagation delay from the broadcast/multicast server to this client. This is necessary only if the delay cannot be computed automatically by the protocol.</dd> + <dt><tt>-s <i>statsdir</i></tt></dt> + <dd>Specify the directory path for files created by the statistics facility. This is the same operation as the <tt>statsdir <i>statsdir</i></tt> command.</dd> + <dt><tt>-t <i>key</i></tt></dt> + <dd>Add a key number to the trusted key list. This option can occur more than once. This is the same operation as the <tt>trustedkey <i>key</i></tt> command.</dd> + <dt><tt>-u <i>user[:group]</i> </tt></dt> + <dd>Specify a user, and optionally a group, to switch to. This option is only available if the OS supports running the server without full root privileges. Currently, this option is supported under NetBSD (configure with <tt>--enable-clockctl</tt>) and Linux (configure with --<tt>enable-linuxcaps</tt>).</dd> + <dt><tt>-U <i>interface update interval</i></tt></dt> <dd>Number of seconds to wait between interface list scans to pick up new and delete network interface. Set to 0 to disable dynamic interface list updating. The default is to scan every 5 minutes.</dd> - <dt><tt>-v <i>variable</i></tt> - <dt><tt>-V <i>variable</i></tt> - <dd>Add a system variable listed by default. - <dt><tt>-x</tt> - <dd>Normally, the time is slewed if the offset is less than the step threshold, which is 128 ms by default, and stepped if above the threshold. This option sets the threshold to 600 s, which is well within the accuracy window to set the clock manually. Note: Since the slew rate of typical Unix kernels is limited to 0.5 ms/s, each second of adjustment requires an amortization interval of 2000 s. Thus, an adjustment as much as 600 s will take almost 14 days to complete. This option can be used with the <tt>-g</tt> and <tt>-q</tt> options. See the <tt>tinker</tt> command for other options. Note: The kernel time discipline is disabled with this option. - </dl> + <dt><tt>-v <i>variable</i></tt></dt> + <dt><tt>-V <i>variable</i></tt></dt> + <dd>Add a system variable listed by default.</dd> + <dt><tt>-x</tt></dt> + <dd>Normally, the time is slewed if the offset is less than the step threshold, which is 128 ms by default, and stepped if above the threshold. This option sets the threshold to 600 s, which is well within the accuracy window to set the clock manually. Note: Since the slew rate of typical Unix kernels is limited to 0.5 ms/s, each second of adjustment requires an amortization interval of 2000 s. Thus, an adjustment as much as 600 s will take almost 14 days to complete. This option can be used with the <tt>-g</tt> and <tt>-q</tt> options. See the <tt>tinker</tt> command for other options. Note: The kernel time discipline is disabled with this option.</dd> + <dt><tt>--pccfreq <i>frequency</i></tt></dt> + <dd>Substitute processor cycle counter for QueryPerformanceCounter unconditionally + using the given frequency (in Hz). <tt>--pccfreq</tt> can be used on systems + which do not use the PCC to implement QueryPerformanceCounter + and have a fixed PCC frequency. The frequency specified must + be accurate within 0.5 percent. <tt>--usepcc</tt> is equivalent on many systems and should + be tried first, as it does not require determining the frequency + of the processor cycle counter. For x86-compatible processors, the PCC is + also referred to as <tt>RDTSC</tt>, which is the assembly-language instruction to retrieve + the current value. (Windows only)</dd> + <dt><tt>--usepcc</tt></dt> + <dd>Substitute processor cycle counter for QueryPerformanceCounter if they + appear equivalent. This option should be used only if the PCC + frequency is fixed. Power-saving functionality on many laptops varies the + PCC frequency. (Windows only)</dd> + </dl> <h4 id="cfg">The Configuration File</h4> - <p>Ordinarily, <tt>ntpd</tt> reads the <tt>ntp.conf</tt> configuration file at startup time in order to determine the synchronization sources and operating modes. It is also possible to specify a working, although limited, configuration entirely on the command line, obviating the need for a configuration file. This may be particularly useful when the local host is to be configured as a broadcast/multicast client, with all peers being determined by listening to broadcasts at run time.</p> - <p>Usually, the configuration file is installed in the <tt>/etc</tt> directory, but could be installed elsewhere (see the <tt>-c <i>conffile</i></tt> command line option). The file format is similar to other Unix configuration files - comments begin with a <tt>#</tt> character and extend to the end of the line; blank lines are ignored.</p> - <p>Configuration commands consist of an initial keyword followed by a list of arguments, some of which may be optional, separated by whitespace. Commands may not be continued over multiple lines. Arguments may be host names, host addresses written in numeric, dotted-quad form, integers, floating point numbers (when specifying times in seconds) and text strings. Optional arguments are delimited by <tt>[ ]</tt> in the following descriptions, while alternatives are separated by <tt>|</tt>. The notation <tt>[ ... ]</tt> means an optional, indefinite repetition of the last item before the <tt>[ ... ]</tt>.</p> - <h4 id="opt">Configuration Options</h4> - <p><a href="confopt.html">Server Options</a><br> - <a href="authopt.html">Authentication Options</a><br> - <a href="monopt.html">Monitoring Options</a><br> - <a href="accopt.html">Access Control Options</a><br> - <a href="manyopt.html">Automatic NTP Configuration Options</a><br> - <a href="clockopt.html">Reference Clock Options</a><br> - <a href="miscopt.html">Miscellaneous Options</a></p> + <p>Ordinarily, <tt>ntpd</tt> reads the <tt>ntp.conf</tt> configuration file at startup in order to determine the synchronization sources and operating modes. It is also possible to specify a working, although limited, configuration entirely on the command line, obviating the need for a configuration file. This may be particularly useful when the local host is to be configured as a broadcast client, with servers determined by listening to broadcasts at run time.</p> + <p>Usually, the configuration file is installed as<tt>/etc/ntp.conf</tt>, but could be installed elsewhere (see the <tt>-c <i>conffile</i></tt> command line option). The file format is similar to other Unix configuration files - comments begin with a <tt>#</tt> character and extend to the end of the line; blank lines are ignored.</p> + <p>Configuration commands consist of an initial command keyword followed by a list of option keywords separated by whitespace. Commands may not be continued over multiple lines. Options may be host names, host addresses written in numeric, dotted-quad form, integers, floating point numbers (when specifying times in seconds) and text strings. Optional arguments are delimited by <tt>[ ]</tt> in the options pages, while alternatives are separated by <tt>|</tt>. The notation <tt>[ ... ]</tt> means an optional, indefinite repetition of the last item before the <tt>[ ... ]</tt>.</p> <h4 id="files">Files</h4> <table width="100%" border="1"> <tr> @@ -143,11 +184,17 @@ </tr> <tr> <td width="30%">frequency file</td> - <td width="30%"><tt>/etc/ntp.drift</tt></td> + <td width="30%">none</td> <td width="20%"><tt>-f</tt></td> <td width="20%"><tt>driftfile</tt></td> </tr> <tr> + <td width="30%">leapseconds file</td> + <td width="30%">none</td> + <td width="20%"></td> + <td width="20%"><tt>leapfile</tt></td> + </tr> + <tr> <td width="30%">process ID file</td> <td width="30%">none</td> <td width="20%"><tt>-p</tt></td> @@ -178,6 +225,9 @@ <td width="20%"><tt>keysdir</tt></td> </tr> </table> + <h4 id="codes">Exit Codes</h4> + <p>A non-zero exit code indicates an error. Any error messages are logged to the system log by default.</p> + <p>The exit code is 0 only when <tt>ntpd</tt> is terminated by a signal, or when the <tt>-q</tt> option is used and <tt>ntpd</tt> successfully sets the system clock.</p> <hr> <script type="text/javascript" language="javascript" src="scripts/footer.txt"></script> </body> |