13 .TH ntpd 1ntpdman "04 Feb 2015" "4.2.8p1" "User Commands"
15 .\" EDIT THIS FILE WITH CAUTION (/tmp/.ag-YYaqWo/ag-.YaiVo)
17 .\" It has been AutoGen-ed February 4, 2015 at 02:41:54 AM by AutoGen 5.18.5pre4
18 .\" From the definitions ntpd-opts.def
19 .\" and the template file agman-cmd.tpl
25 .\" Mixture of short (flag) options and long options
26 [\f\*[B-Font]\-flags\f[]]
27 [\f\*[B-Font]\-flag\f[] [\f\*[I-Font]value\f[]]]
28 [\f\*[B-Font]\-\-option-name\f[][[=| ]\f\*[I-Font]value\f[]]]
29 [ <server1> ... <serverN> ]
36 utility is an operating system daemon which sets
37 and maintains the system time of day in synchronism with Internet
38 standard time servers.
39 It is a complete implementation of the
40 Network Time Protocol (NTP) version 4, as defined by RFC-5905,
41 but also retains compatibility with
42 version 3, as defined by RFC-1305, and versions 1
43 and 2, as defined by RFC-1059 and RFC-1119, respectively.
49 utility does most computations in 64-bit floating point
50 arithmetic and does relatively clumsy 64-bit fixed point operations
51 only when necessary to preserve the ultimate precision, about 232
53 While the ultimate precision is not achievable with
54 ordinary workstations and networks of today, it may be required
55 with future gigahertz CPU clocks and gigabit LANs.
63 configuration file at startup time in order to determine the
64 synchronization sources and operating modes.
65 It is also possible to
66 specify a working, although limited, configuration entirely on the
67 command line, obviating the need for a configuration file.
69 be particularly useful when the local host is to be configured as a
70 broadcast/multicast client, with all peers being determined by
71 listening to broadcasts at run time.
75 If NetInfo support is built into
79 will attempt to read its configuration from the
80 NetInfo if the default
82 file cannot be read and no file is
91 variables can be displayed and
92 configuration options altered while the
96 \fCntpq\fR(1ntpqmdoc)\f[]
98 \fCntpdc\fR(1ntpdcmdoc)\f[]
105 starts it looks at the value of
114 .NOP \f\*[B-Font]\-4\f[], \f\*[B-Font]\-\-ipv4\f[]
115 Force IPv4 DNS name resolution.
116 This option must not appear in combination with any of the following options:
119 Force DNS resolution of following host names on the command line
120 to the IPv4 namespace.
122 .NOP \f\*[B-Font]\-6\f[], \f\*[B-Font]\-\-ipv6\f[]
123 Force IPv6 DNS name resolution.
124 This option must not appear in combination with any of the following options:
127 Force DNS resolution of following host names on the command line
128 to the IPv6 namespace.
130 .NOP \f\*[B-Font]\-a\f[], \f\*[B-Font]\-\-authreq\f[]
131 Require crypto authentication.
132 This option must not appear in combination with any of the following options:
135 Require cryptographic authentication for broadcast client,
136 multicast client and symmetric passive associations.
139 .NOP \f\*[B-Font]\-A\f[], \f\*[B-Font]\-\-authnoreq\f[]
140 Do not require crypto authentication.
141 This option must not appear in combination with any of the following options:
144 Do not require cryptographic authentication for broadcast client,
145 multicast client and symmetric passive associations.
146 This is almost never a good idea.
148 .NOP \f\*[B-Font]\-b\f[], \f\*[B-Font]\-\-bcastsync\f[]
149 Allow us to sync to broadcast servers.
152 .NOP \f\*[B-Font]\-c\f[] \f\*[I-Font]string\f[], \f\*[B-Font]\-\-configfile\f[]=\f\*[I-Font]string\f[]
153 configuration file name.
155 The name and path of the configuration file,
159 .NOP \f\*[B-Font]\-d\f[], \f\*[B-Font]\-\-debug\-level\f[]
160 Increase debug verbosity level.
161 This option may appear an unlimited number of times.
164 .NOP \f\*[B-Font]\-D\f[] \f\*[I-Font]number\f[], \f\*[B-Font]\-\-set\-debug\-level\f[]=\f\*[I-Font]number\f[]
165 Set the debug verbosity level.
166 This option may appear an unlimited number of times.
167 This option takes an integer number as its argument.
170 .NOP \f\*[B-Font]\-f\f[] \f\*[I-Font]string\f[], \f\*[B-Font]\-\-driftfile\f[]=\f\*[I-Font]string\f[]
171 frequency drift file name.
173 The name and path of the frequency file,
176 This is the same operation as the
177 \fBdriftfile\fP \fIdriftfile\fP
178 configuration specification in the
182 .NOP \f\*[B-Font]\-g\f[], \f\*[B-Font]\-\-panicgate\f[]
183 Allow the first adjustment to be Big.
184 This option may appear an unlimited number of times.
188 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,
190 will exit with a message to the system log. This option can be used with the
197 configuration file directive for other options.
199 .NOP \f\*[B-Font]\-i\f[] \f\*[I-Font]string\f[], \f\*[B-Font]\-\-jaildir\f[]=\f\*[I-Font]string\f[]
202 Chroot the server to the directory
205 This option also implies that the server attempts to drop root privileges at startup.
206 You may need to also specify a
209 This option is only available if the OS supports adjusting the clock
210 without full root privileges.
211 This option is supported under NetBSD (configure with
212 \fB--enable-clockctl\fP) or Linux (configure with
213 \fB--enable-linuxcaps\fP) or Solaris (configure with \fB--enable-solarisprivs\fP).
215 .NOP \f\*[B-Font]\-I\f[] \f\*[I-Font]iface\f[], \f\*[B-Font]\-\-interface\f[]=\f\*[I-Font]iface\f[]
216 Listen on an interface name or address.
217 This option may appear an unlimited number of times.
219 Open the network address given, or all the addresses associated with the
220 given interface name. This option may appear multiple times. This option
221 also implies not opening other addresses, except wildcard and localhost.
222 This option is deprecated. Please consider using the configuration file
223 \fBinterface\fP command, which is more versatile.
225 .NOP \f\*[B-Font]\-k\f[] \f\*[I-Font]string\f[], \f\*[B-Font]\-\-keyfile\f[]=\f\*[I-Font]string\f[]
226 path to symmetric keys.
228 Specify the name and path of the symmetric key file.
231 This is the same operation as the
232 \fBkeys\fP \fIkeyfile\fP
233 configuration file directive.
235 .NOP \f\*[B-Font]\-l\f[] \f\*[I-Font]string\f[], \f\*[B-Font]\-\-logfile\f[]=\f\*[I-Font]string\f[]
236 path to the log file.
238 Specify the name and path of the log file.
239 The default is the system log file.
240 This is the same operation as the
241 \fBlogfile\fP \fIlogfile\fP
242 configuration file directive.
244 .NOP \f\*[B-Font]\-L\f[], \f\*[B-Font]\-\-novirtualips\f[]
245 Do not listen to virtual interfaces.
247 Do not listen to virtual interfaces, defined as those with
248 names containing a colon. This option is deprecated. Please
249 consider using the configuration file \fBinterface\fP command, which
252 .NOP \f\*[B-Font]\-M\f[], \f\*[B-Font]\-\-modifymmtimer\f[]
253 Modify Multimedia Timer (Windows only).
255 Set the Windows Multimedia Timer to highest resolution. This
256 ensures the resolution does not change while ntpd is running,
257 avoiding timekeeping glitches associated with changes.
259 .NOP \f\*[B-Font]\-n\f[], \f\*[B-Font]\-\-nofork\f[]
261 This option must not appear in combination with any of the following options:
265 .NOP \f\*[B-Font]\-N\f[], \f\*[B-Font]\-\-nice\f[]
266 Run at high priority.
268 To the extent permitted by the operating system, run
270 at the highest priority.
272 .NOP \f\*[B-Font]\-p\f[] \f\*[I-Font]string\f[], \f\*[B-Font]\-\-pidfile\f[]=\f\*[I-Font]string\f[]
273 path to the PID file.
275 Specify the name and path of the file used to record
278 This is the same operation as the
279 \fBpidfile\fP \fIpidfile\fP
280 configuration file directive.
282 .NOP \f\*[B-Font]\-P\f[] \f\*[I-Font]number\f[], \f\*[B-Font]\-\-priority\f[]=\f\*[I-Font]number\f[]
284 This option takes an integer number as its argument.
286 To the extent permitted by the operating system, run
289 \fBsched_setscheduler(SCHED_FIFO)\fP
292 .NOP \f\*[B-Font]\-q\f[], \f\*[B-Font]\-\-quit\f[]
293 Set the time and quit.
294 This option must not appear in combination with any of the following options:
295 saveconfigquit, wait-sync.
298 will not daemonize and will exit after the clock is first
299 synchronized. This behavior mimics that of the
301 program, which will soon be replaced with a shell script.
306 options can be used with this option.
307 Note: The kernel time discipline is disabled with this option.
309 .NOP \f\*[B-Font]\-r\f[] \f\*[I-Font]string\f[], \f\*[B-Font]\-\-propagationdelay\f[]=\f\*[I-Font]string\f[]
310 Broadcast/propagation delay.
312 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.
314 .NOP \f\*[B-Font]\-\-saveconfigquit\f[]=\f\*[I-Font]string\f[]
315 Save parsed configuration and quit.
316 This option must not appear in combination with any of the following options:
319 Cause \fBntpd\fP to parse its startup configuration file and save an
320 equivalent to the given filename and exit. This option was
321 designed for automated testing.
323 .NOP \f\*[B-Font]\-s\f[] \f\*[I-Font]string\f[], \f\*[B-Font]\-\-statsdir\f[]=\f\*[I-Font]string\f[]
324 Statistics file location.
326 Specify the directory path for files created by the statistics facility.
327 This is the same operation as the
328 \fBstatsdir\fP \fIstatsdir\fP
329 configuration file directive.
331 .NOP \f\*[B-Font]\-t\f[] \f\*[I-Font]tkey\f[], \f\*[B-Font]\-\-trustedkey\f[]=\f\*[I-Font]tkey\f[]
333 This option may appear an unlimited number of times.
335 Add the specified key number to the trusted key list.
337 .NOP \f\*[B-Font]\-u\f[] \f\*[I-Font]string\f[], \f\*[B-Font]\-\-user\f[]=\f\*[I-Font]string\f[]
338 Run as userid (or userid:groupid).
340 Specify a user, and optionally a group, to switch to.
341 This option is only available if the OS supports adjusting the clock
342 without full root privileges.
343 This option is supported under NetBSD (configure with
344 \fB--enable-clockctl\fP) or Linux (configure with
345 \fB--enable-linuxcaps\fP) or Solaris (configure with \fB--enable-solarisprivs\fP).
347 .NOP \f\*[B-Font]\-U\f[] \f\*[I-Font]number\f[], \f\*[B-Font]\-\-updateinterval\f[]=\f\*[I-Font]number\f[]
348 interval in seconds between scans for new or dropped interfaces.
349 This option takes an integer number as its argument.
351 Give the time in seconds between two scans for new or dropped interfaces.
352 For systems with routing socket support the scans will be performed shortly after the interface change
353 has been detected by the system.
354 Use 0 to disable scanning. 60 seconds is the minimum time between scans.
356 .NOP \f\*[B-Font]\-\-var\f[]=\f\*[I-Font]nvar\f[]
357 make ARG an ntp variable (RW).
358 This option may appear an unlimited number of times.
361 .NOP \f\*[B-Font]\-\-dvar\f[]=\f\*[I-Font]ndvar\f[]
362 make ARG an ntp variable (RW|DEF).
363 This option may appear an unlimited number of times.
366 .NOP \f\*[B-Font]\-w\f[] \f\*[I-Font]number\f[], \f\*[B-Font]\-\-wait\-sync\f[]=\f\*[I-Font]number\f[]
367 Seconds to wait for first clock sync.
368 This option must not appear in combination with any of the following options:
369 nofork, quit, saveconfigquit.
370 This option takes an integer number as its argument.
372 If greater than zero, alters \fBntpd\fP's behavior when forking to
373 daemonize. Instead of exiting with status 0 immediately after
374 the fork, the parent waits up to the specified number of
375 seconds for the child to first synchronize the clock. The exit
376 status is zero (success) if the clock was synchronized,
377 otherwise it is \fBETIMEDOUT\fP.
378 This provides the option for a script starting \fBntpd\fP to easily
379 wait for the first set of the clock before proceeding.
381 .NOP \f\*[B-Font]\-x\f[], \f\*[B-Font]\-\-slew\f[]
382 Slew up to 600 seconds.
384 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.
385 This option sets the threshold to 600 s, which is well within the accuracy window to set the clock manually.
386 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.
387 Thus, an adjustment as much as 600 s will take almost 14 days to complete.
388 This option can be used with the
395 configuration file directive for other options.
396 Note: The kernel time discipline is disabled with this option.
398 .NOP \f\*[B-Font]\-\-usepcc\f[]
399 Use CPU cycle counter (Windows only).
401 Attempt to substitute the CPU counter for \fBQueryPerformanceCounter\fP.
402 The CPU counter and \fBQueryPerformanceCounter\fP are compared, and if
403 they have the same frequency, the CPU counter (RDTSC on x86) is
404 used directly, saving the overhead of a system call.
406 .NOP \f\*[B-Font]\-\-pccfreq\f[]=\f\*[I-Font]string\f[]
407 Force CPU cycle counter use (Windows only).
409 Force substitution the CPU counter for \fBQueryPerformanceCounter\fP.
410 The CPU counter (RDTSC on x86) is used unconditionally with the
411 given frequency (in Hz).
413 .NOP \f\*[B-Font]\-m\f[], \f\*[B-Font]\-\-mdns\f[]
414 Register with mDNS as a NTP server.
416 Registers as an NTP server with the local mDNS server which allows
417 the server to be discovered via mDNS client lookup.
419 .NOP \f\*[B-Font]\-\&?\f[], \f\*[B-Font]\-\-help\f[]
420 Display usage information and exit.
422 .NOP \f\*[B-Font]\-\&!\f[], \f\*[B-Font]\-\-more-help\f[]
423 Pass the extended usage information through a pager.
425 .NOP \f\*[B-Font]\-\-version\f[] [{\f\*[I-Font]v|c|n\f[]}]
426 Output version of program and exit. The default mode is `v', a simple
427 version. The `c' mode will print copyright information and `n' will
428 print the full copyright notice.
431 Any option that is not marked as \fInot presettable\fP may be preset
432 by loading values from environment variables named:
434 \fBNTPD_<option-name>\fP or \fBNTPD\fP
438 .SS "How NTP Operates"
441 utility operates by exchanging messages with
442 one or more configured servers over a range of designated poll intervals.
444 started, whether for the first or subsequent times, the program
445 requires several exchanges from the majority of these servers so
446 the signal processing and mitigation algorithms can accumulate and
447 groom the data and set the clock.
448 In order to protect the network
449 from bursts, the initial poll interval for each server is delayed
450 an interval randomized over a few seconds.
451 At the default initial poll
452 interval of 64s, several minutes can elapse before the clock is
454 This initial delay to set the clock
455 can be safely and dramatically reduced using the
456 \f\*[B-Font]iburst\f[]
458 \f\*[B-Font]server\f[]
460 command, as described in
461 \fCntp.conf\fR(5)\f[].
465 Most operating systems and hardware of today incorporate a
466 time-of-year (TOY) chip to maintain the time during periods when
468 When the machine is booted, the chip is used to
469 initialize the operating system time.
470 After the machine has
471 synchronized to a NTP server, the operating system corrects the
472 chip from time to time.
473 In the default case, if
475 detects that the time on the host
476 is more than 1000s from the server time,
478 assumes something must be terribly wrong and the only
479 reliable action is for the operator to intervene and set the clock
481 (Reasons for this include there is no TOY chip,
482 or its battery is dead, or that the TOY chip is just of poor quality.)
485 to exit with a panic message to
489 option overrides this check and the
490 clock will be set to the server time regardless of the chip time
491 (up to 68 years in the past or future \(em
492 this is a limitation of the NTPv4 protocol).
493 However, and to protect against broken hardware, such as when the
494 CMOS battery fails or the clock counter becomes defective, once the
495 clock has been set an error greater than 1000s will cause
501 Under ordinary conditions,
504 small steps so that the timescale is effectively continuous and
505 without discontinuities.
506 Under conditions of extreme network
507 congestion, the roundtrip delay jitter can exceed three seconds and
508 the synchronization distance, which is equal to one-half the
509 roundtrip delay plus error budget terms, can become very large.
512 algorithms discard sample offsets exceeding 128 ms,
513 unless the interval during which no sample offset is less than 128
515 The first sample after that, no matter what the
516 offset, steps the clock to the indicated time.
518 reduces the false alarm rate where the clock is stepped in error to
519 a vanishingly low incidence.
523 As the result of this behavior, once the clock has been set it
524 very rarely strays more than 128 ms even under extreme cases of
525 network path congestion and jitter.
526 Sometimes, in particular when
528 is first started without a valid drift file
529 on a system with a large intrinsic drift
530 the error might grow to exceed 128 ms,
531 which would cause the clock to be set backwards
532 if the local clock time is more than 128 s
533 in the future relative to the server.
534 In some applications, this behavior may be unacceptable.
535 There are several solutions, however.
538 option is included on the command line, the clock will
539 never be stepped and only slew corrections will be used.
540 But this choice comes with a cost that
541 should be carefully explored before deciding to use
545 The maximum slew rate possible is limited
546 to 500 parts-per-million (PPM) as a consequence of the correctness
547 principles on which the NTP protocol and algorithm design are
549 As a result, the local clock can take a long time to
550 converge to an acceptable offset, about 2,000 s for each second the
551 clock is outside the acceptable range.
552 During this interval the
553 local clock will not be consistent with any other network clock and
554 the system cannot be used for distributed applications that require
555 correctly synchronized network time.
559 In spite of the above precautions, sometimes when large
560 frequency errors are present the resulting time offsets stray
561 outside the 128-ms range and an eventual step or slew time
562 correction is required.
563 If following such a correction the
564 frequency error is so large that the first sample is outside the
567 enters the same state as when the
570 The intent of this behavior
571 is to quickly correct the frequency and restore operation to the
572 normal tracking mode.
573 In the most extreme cases
575 \f\*[B-Font]time.ien.it\f[]
576 comes to mind), there may be occasional
577 step/slew corrections and subsequent frequency corrections.
579 helps in these cases to use the
580 \f\*[B-Font]burst\f[]
582 configuring the server, but
584 when you have permission to do so from the owner of the target host.
589 in the past many startup scripts would run
590 \fCntpdate\fR(1ntpdatemdoc)\f[]
591 to get the system clock close to correct before starting
592 \fCntpd\fR(1ntpdmdoc)\f[],
593 but this was never more than a mediocre hack and is no longer needed.
594 If you are following the instructions in
595 \fIStarting NTP (Best Current Practice)\f[]
596 and you still need to set the system time before starting
598 please open a bug report and document what is going on,
599 and then look at using
600 \fCsntp\fR(1sntpmdoc)\f[].
604 There is a way to start
605 \fCntpd\fR(1ntpdmdoc)\f[]
606 that often addresses all of the problems mentioned above.
607 .SS "Starting NTP (Best Current Practice)"
609 \f\*[B-Font]iburst\f[]
611 \f\*[B-Font]server\f[]
616 If you can also keep a good
619 \fCntpd\fR(1ntpdmdoc)\f[]
620 will effectively "warm-start" and your system's clock will
621 be stable in under 11 seconds' time.
625 As soon as possible in the startup sequence, start
626 \fCntpd\fR(1ntpdmdoc)\f[]
633 start the rest of your "normal" processes.
635 \fCntpd\fR(1ntpdmdoc)\f[]
636 as much time as possible to get the system's clock synchronized and stable.
641 if you have processes like
642 \f\*[B-Font]dovecot\f[]
645 monotonically-increasing time,
647 \fCntp-wait\fR(1ntp-waitmdoc)\f[]
648 as late as possible in the boot sequence
653 \fCntp-wait\fR(1ntp-waitmdoc)\f[]
655 it is as safe as it will ever be to start any process that require
657 .SS "Frequency Discipline"
660 behavior at startup depends on whether the
661 frequency file, usually
665 contains the latest estimate of clock frequency error.
668 is started and the file does not exist, the
670 enters a special mode designed to quickly adapt to
671 the particular system clock oscillator time and frequency error.
672 This takes approximately 15 minutes, after which the time and
673 frequency are set to nominal values and the
676 normal mode, where the time and frequency are continuously tracked
677 relative to the server.
678 After one hour the frequency file is
679 created and the current frequency offset written to it.
682 is started and the file does exist, the
684 frequency is initialized from the file and enters normal mode
686 After that the current frequency offset is written to
687 the file at hourly intervals.
688 .SS "Operating Modes"
691 utility can operate in any of several modes, including
692 symmetric active/passive, client/server broadcast/multicast and
693 manycast, as described in the
694 "Association Management"
696 (available as part of the HTML documentation
698 \fI/usr/share/doc/ntp\f[]).
699 It normally operates continuously while
700 monitoring for small changes in frequency and trimming the clock
701 for the ultimate precision.
702 However, it can operate in a one-time
703 mode where the time is set from an external server and frequency is
704 set from a previously recorded frequency file.
706 broadcast/multicast or manycast client can discover remote servers,
707 compute server-client propagation delay correction factors and
708 configure itself automatically.
709 This makes it possible to deploy a
710 fleet of workstations without specifying configuration details
711 specific to the local environment.
717 runs in continuous mode where each of
718 possibly several external servers is polled at intervals determined
719 by an intricate state machine.
720 The state machine measures the
721 incidental roundtrip delay jitter and oscillator frequency wander
722 and determines the best poll interval using a heuristic algorithm.
723 Ordinarily, and in most operating environments, the state machine
724 will start with 64s intervals and eventually increase in steps to
726 A small amount of random variation is introduced in order to
727 avoid bunching at the servers.
728 In addition, should a server become
729 unreachable for some time, the poll interval is increased in steps
730 to 1024s in order to reduce network overhead.
734 In some cases it may not be practical for
737 A common workaround has been to run the
738 \fCntpdate\fR(1ntpdatemdoc)\f[]
740 \fCsntp\fR(1sntpmdoc)\f[]
745 However, these programs do not have the crafted signal
746 processing, error checking or mitigation algorithms of
750 option is intended for this purpose.
751 Setting this option will cause
754 setting the clock for the first time.
755 The procedure for initially
756 setting the clock is the same as in continuous mode; most
757 applications will probably want to specify the
758 \f\*[B-Font]iburst\f[]
760 \f\*[B-Font]server\f[]
761 configuration command.
763 keyword a volley of messages are exchanged to groom the data and
764 the clock is set in about 10 s.
765 If nothing is heard after a
766 couple of minutes, the daemon times out and exits.
768 period of mourning, the
769 \fCntpdate\fR(1ntpdatemdoc)\f[]
775 When kernel support is available to discipline the clock
776 frequency, which is the case for stock Solaris, Tru64, Linux and
778 a useful feature is available to discipline the clock
782 is run in continuous mode with
783 selected servers in order to measure and record the intrinsic clock
784 frequency offset in the frequency file.
785 It may take some hours for
786 the frequency and offset to settle down.
790 stopped and run in one-time mode as required.
792 frequency is read from the file and initializes the kernel
794 .SS "Poll Interval Control"
795 This version of NTP includes an intricate state machine to
796 reduce the network load while maintaining a quality of
797 synchronization consistent with the observed jitter and wander.
798 There are a number of ways to tailor the operation in order enhance
799 accuracy by reducing the interval or to reduce network overhead by
801 However, the user is advised to carefully consider
802 the consequences of changing the poll adjustment range from the
803 default minimum of 64 s to the default maximum of 1,024 s.
805 default minimum can be changed with the
806 \f\*[B-Font]tinker\f[]
807 \f\*[B-Font]minpoll\f[]
808 command to a value not less than 16 s.
809 This value is used for all
810 configured associations, unless overridden by the
811 \f\*[B-Font]minpoll\f[]
812 option on the configuration command.
813 Note that most device drivers
814 will not operate properly if the poll interval is less than 64 s
815 and that the broadcast server and manycast client associations will
816 also use the default, unless overridden.
820 In some cases involving dial up or toll services, it may be
821 useful to increase the minimum interval to a few tens of minutes
822 and maximum interval to a day or so.
823 Under normal operation
824 conditions, once the clock discipline loop has stabilized the
825 interval will be increased in steps from the minimum to the
827 However, this assumes the intrinsic clock frequency error
828 is small enough for the discipline loop correct it.
830 range of the loop is 500 PPM at an interval of 64s decreasing by a
831 factor of two for each doubling of interval.
832 At a minimum of 1,024
833 s, for example, the capture range is only 31 PPM.
835 error is greater than this, the drift file
838 have to be specially tailored to reduce the residual error below
840 Once this is done, the drift file is automatically
841 updated once per hour and is available to initialize the frequency
842 on subsequent daemon restarts.
843 .SS "The huff-n'-puff Filter"
844 In scenarios where a considerable amount of data are to be
845 downloaded or uploaded over telephone modems, timekeeping quality
846 can be seriously degraded.
847 This occurs because the differential
848 delays on the two directions of transmission can be quite large.
850 many cases the apparent time errors are so large as to exceed the
851 step threshold and a step correction can occur during and after the
852 data transfer is in progress.
856 The huff-n'-puff filter is designed to correct the apparent time
857 offset in these cases.
858 It depends on knowledge of the propagation
859 delay when no other traffic is present.
860 In common scenarios this
861 occurs during other than work hours.
862 The filter maintains a shift
863 register that remembers the minimum delay over the most recent
864 interval measured usually in hours.
865 Under conditions of severe
866 delay, the filter corrects the apparent offset using the sign of
867 the offset and the difference between the apparent delay and
869 The name of the filter reflects the negative (huff)
870 and positive (puff) correction, which depends on the sign of the
875 The filter is activated by the
876 \f\*[B-Font]tinker\f[]
878 \f\*[B-Font]huffpuff\f[]
879 keyword, as described in
880 \fCntp.conf\fR(5)\f[].
882 See \fBOPTION PRESETS\fP for configuration environment variables.
885 .NOP \fI/etc/ntp.conf\f[]
886 the default name of the configuration file
890 .NOP \fI/etc/ntp.drift\f[]
891 the default name of the drift file
895 .NOP \fI/etc/ntp.keys\f[]
896 the default name of the key file
899 One of the following exit values will be returned:
901 .NOP 0 " (EXIT_SUCCESS)"
902 Successful program execution.
904 .NOP 1 " (EXIT_FAILURE)"
905 The operation failed or the command syntax was not valid.
907 .NOP 70 " (EX_SOFTWARE)"
908 libopts had an internal operational error. Please report
909 it to autogen-users@lists.sourceforge.net. Thank you.
912 \fCntp.conf\fR(5)\f[],
913 \fCntpdate\fR(1ntpdatemdoc)\f[],
914 \fCntpdc\fR(1ntpdcmdoc)\f[],
915 \fCntpq\fR(1ntpqmdoc)\f[],
916 \fCsntp\fR(1sntpmdoc)\f[]
920 In addition to the manual pages provided,
921 comprehensive documentation is available on the world wide web
923 \f[C]http://www.ntp.org/\f[].
924 A snapshot of this documentation is available in HTML format in
925 \fI/usr/share/doc/ntp\f[].
927 \fINetwork Time Protocol (Version 1)\fR,
932 \fINetwork Time Protocol (Version 2)\fR,
937 \fINetwork Time Protocol (Version 3)\fR,
941 David L. Mills and J. Martin, Ed. and J. Burbank and W. Kasch,
942 \fINetwork Time Protocol Version 4: Protocol and Algorithms Specification\fR,
946 David L. Mills and B. Haberman, Ed.,
947 \fINetwork Time Protocol Version 4: Autokey Specification\fR,
951 H. Gerstung and C. Elliott and B. Haberman, Ed.,
952 \fIDefinitions of Managed Objects for Network Time Protocol Version 4: (NTPv4)\fR,
956 R. Gayraud and B. Lourdelet,
957 \fINetwork Time Protocol (NTP) Server Option for DHCPv6\fR,
962 The University of Delaware and Network Time Foundation
964 Copyright (C) 1992-2015 The University of Delaware and Network Time Foundation all rights reserved.
965 This program is released under the terms of the NTP license, <http://ntp.org/license>.
969 utility has gotten rather fat.
970 While not huge, it has gotten
971 larger than might be desirable for an elevated-priority
973 running on a workstation, particularly since many of
974 the fancy features which consume the space were designed more with
975 a busy primary server, rather than a high stratum workstation in
980 Please send bug reports to: http://bugs.ntp.org, bugs@ntp.org
982 Portions of this document came from FreeBSD.
986 This manual page was \fIAutoGen\fP-erated from the \fBntpd\fP