1330567Sgordon.Dd February 27 2018 2285612Sdelphij.Dt NTPD 8 User Commands 3285612Sdelphij.Os 4285612Sdelphij.\" EDIT THIS FILE WITH CAUTION (ntpd-opts.mdoc) 555857Ssheldonh.\" 655857Ssheldonh.\" $FreeBSD: releng/10.3/usr.sbin/ntp/doc/ntpd.8 330567 2018-03-07 05:58:24Z gordon $ 755857Ssheldonh.\" 8330567Sgordon.\" It has been AutoGen-ed February 27, 2018 at 05:14:47 PM by AutoGen 5.18.5 9285612Sdelphij.\" From the definitions ntpd-opts.def 10285612Sdelphij.\" and the template file agmdoc-cmd.tpl 1155857Ssheldonh.Sh NAME 1255857Ssheldonh.Nm ntpd 13285612Sdelphij.Nd NTP daemon program 1455857Ssheldonh.Sh SYNOPSIS 1568965Sru.Nm 16285612Sdelphij.\" Mixture of short (flag) options and long options 17285612Sdelphij.Op Fl flags 18285612Sdelphij.Op Fl flag Op Ar value 19285612Sdelphij.Op Fl \-option\-name Ns Oo Oo Ns "=| " Oc Ns Ar value Oc 20285612Sdelphij[ <server1> ... <serverN> ] 21285612Sdelphij.Pp 2255857Ssheldonh.Sh DESCRIPTION 2382501SsheldonhThe 2455857Ssheldonh.Nm 2599968Scharnierutility is an operating system daemon which sets 2682501Ssheldonhand maintains the system time of day in synchronism with Internet 2782501Ssheldonhstandard time servers. 2882501SsheldonhIt is a complete implementation of the 29285612SdelphijNetwork Time Protocol (NTP) version 4, as defined by RFC\-5905, 30285612Sdelphijbut also retains compatibility with 31285612Sdelphijversion 3, as defined by RFC\-1305, and versions 1 32285612Sdelphijand 2, as defined by RFC\-1059 and RFC\-1119, respectively. 3382501Ssheldonh.Pp 3499968ScharnierThe 3555857Ssheldonh.Nm 36285612Sdelphijutility does most computations in 64\-bit floating point 37285612Sdelphijarithmetic and does relatively clumsy 64\-bit fixed point operations 3882501Ssheldonhonly when necessary to preserve the ultimate precision, about 232 3982501Ssheldonhpicoseconds. 40168248SchinsanWhile the ultimate precision is not achievable with 4182501Ssheldonhordinary workstations and networks of today, it may be required 4282501Ssheldonhwith future gigahertz CPU clocks and gigabit LANs. 4355857Ssheldonh.Pp 4455857SsheldonhOrdinarily, 4555857Ssheldonh.Nm 4655857Ssheldonhreads the 4755895Ssheldonh.Xr ntp.conf 5 4882501Ssheldonhconfiguration file at startup time in order to determine the 4982501Ssheldonhsynchronization sources and operating modes. 5082501SsheldonhIt is also possible to 5182501Ssheldonhspecify a working, although limited, configuration entirely on the 5282501Ssheldonhcommand line, obviating the need for a configuration file. 5382501SsheldonhThis may 5482501Ssheldonhbe particularly useful when the local host is to be configured as a 5582501Ssheldonhbroadcast/multicast client, with all peers being determined by 5682501Ssheldonhlistening to broadcasts at run time. 5755857Ssheldonh.Pp 5855857SsheldonhIf NetInfo support is built into 5968965Sru.Nm , 6055857Ssheldonhthen 6155857Ssheldonh.Nm 6282501Ssheldonhwill attempt to read its configuration from the 6382501SsheldonhNetInfo if the default 6482501Ssheldonh.Xr ntp.conf 5 6582501Ssheldonhfile cannot be read and no file is 6682501Ssheldonhspecified by the 6755857Ssheldonh.Fl c 6855857Ssheldonhoption. 6955857Ssheldonh.Pp 7082501SsheldonhVarious internal 7155857Ssheldonh.Nm 7282501Ssheldonhvariables can be displayed and 7382501Ssheldonhconfiguration options altered while the 7482501Ssheldonh.Nm 7582501Ssheldonhis running 7682501Ssheldonhusing the 7755857Ssheldonh.Xr ntpq 8 7855857Ssheldonhand 7955857Ssheldonh.Xr ntpdc 8 8082501Ssheldonhutility programs. 8155857Ssheldonh.Pp 8255857SsheldonhWhen 8355857Ssheldonh.Nm 8455857Ssheldonhstarts it looks at the value of 85285612Sdelphij.Xr umask 2 , 8682501Ssheldonhand if zero 8782501Ssheldonh.Nm 8882501Ssheldonhwill set the 89285612Sdelphij.Xr umask 2 9082501Ssheldonhto 022. 91285612Sdelphij.Sh "OPTIONS" 92285612Sdelphij.Bl -tag 93285612Sdelphij.It Fl 4 , Fl \-ipv4 94285612SdelphijForce IPv4 DNS name resolution. 95285612SdelphijThis option must not appear in combination with any of the following options: 96285612Sdelphijipv6. 97285612Sdelphij.sp 98285612SdelphijForce DNS resolution of following host names on the command line 99285612Sdelphijto the IPv4 namespace. 100285612Sdelphij.It Fl 6 , Fl \-ipv6 101285612SdelphijForce IPv6 DNS name resolution. 102285612SdelphijThis option must not appear in combination with any of the following options: 103285612Sdelphijipv4. 104285612Sdelphij.sp 105285612SdelphijForce DNS resolution of following host names on the command line 106285612Sdelphijto the IPv6 namespace. 107285612Sdelphij.It Fl a , Fl \-authreq 108285612SdelphijRequire crypto authentication. 109285612SdelphijThis option must not appear in combination with any of the following options: 110285612Sdelphijauthnoreq. 111285612Sdelphij.sp 112158688SpavRequire cryptographic authentication for broadcast client, 113158688Spavmulticast client and symmetric passive associations. 114158688SpavThis is the default. 115285612Sdelphij.It Fl A , Fl \-authnoreq 116285612SdelphijDo not require crypto authentication. 117285612SdelphijThis option must not appear in combination with any of the following options: 118285612Sdelphijauthreq. 119285612Sdelphij.sp 120158688SpavDo not require cryptographic authentication for broadcast client, 121158688Spavmulticast client and symmetric passive associations. 122158688SpavThis is almost never a good idea. 123285612Sdelphij.It Fl b , Fl \-bcastsync 124285612SdelphijAllow us to sync to broadcast servers. 125285612Sdelphij.sp 126285612Sdelphij.It Fl c Ar string , Fl \-configfile Ns = Ns Ar string 127285612Sdelphijconfiguration file name. 128285612Sdelphij.sp 129285612SdelphijThe name and path of the configuration file, 130285612Sdelphij\fI/etc/ntp.conf\fP 131285612Sdelphijby default. 132285612Sdelphij.It Fl d , Fl \-debug\-level 133285612SdelphijIncrease debug verbosity level. 134285612SdelphijThis option may appear an unlimited number of times. 135285612Sdelphij.sp 136285612Sdelphij.It Fl D Ar number , Fl \-set\-debug\-level Ns = Ns Ar number 137285612SdelphijSet the debug verbosity level. 138285612SdelphijThis option may appear an unlimited number of times. 139285612SdelphijThis option takes an integer number as its argument. 140285612Sdelphij.sp 141285612Sdelphij.It Fl f Ar string , Fl \-driftfile Ns = Ns Ar string 142285612Sdelphijfrequency drift file name. 143285612Sdelphij.sp 144285612SdelphijThe name and path of the frequency file, 145285612Sdelphij\fI/etc/ntp.drift\fP 146285612Sdelphijby default. 147158688SpavThis is the same operation as the 148285612Sdelphij\fBdriftfile\fP \fIdriftfile\fP 149289997Sglebiusconfiguration specification in the 150285612Sdelphij\fI/etc/ntp.conf\fP 151285612Sdelphijfile. 152285612Sdelphij.It Fl g , Fl \-panicgate 153285612SdelphijAllow the first adjustment to be Big. 154285612SdelphijThis option may appear an unlimited number of times. 155285612Sdelphij.sp 15682501SsheldonhNormally, 157285612Sdelphij\fBntpd\fP 158285612Sdelphijexits 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, 159285612Sdelphij\fBntpd\fP 160285612Sdelphijwill exit with a message to the system log. This option can be used with the 161285612Sdelphij\fB\-q\fP 162158688Spavand 163285612Sdelphij\fB\-x\fP 164162806Sruoptions. 165162806SruSee the 166285612Sdelphij\fBtinker\fP 167285612Sdelphijconfiguration file directive for other options. 168289997Sglebius.It Fl G , Fl \-force\-step\-once 169289997SglebiusStep any initial offset correction.. 170289997Sglebius.sp 171289997SglebiusNormally, 172289997Sglebius\fBntpd\fP 173289997Sglebiussteps the time if the time offset exceeds the step threshold, 174289997Sglebiuswhich is 128 ms by default, and otherwise slews the time. 175289997SglebiusThis option forces the initial offset correction to be stepped, 176289997Sglebiusso the highest time accuracy can be achieved quickly. 177289997SglebiusHowever, this may also cause the time to be stepped back 178289997Sglebiusso this option must not be used if 179289997Sglebiusapplications requiring monotonic time are running. 180289997SglebiusSee the \fBtinker\fP configuration file directive for other options. 181285612Sdelphij.It Fl i Ar string , Fl \-jaildir Ns = Ns Ar string 182285612SdelphijJail directory. 183285612Sdelphij.sp 184285612SdelphijChroot the server to the directory 185285612Sdelphij\fIjaildir\fP 186285612Sdelphij. 187285612SdelphijThis option also implies that the server attempts to drop root privileges at startup. 188285612SdelphijYou may need to also specify a 189285612Sdelphij\fB\-u\fP 190285612Sdelphijoption. 191285612SdelphijThis option is only available if the OS supports adjusting the clock 192285612Sdelphijwithout full root privileges. 193285612SdelphijThis option is supported under NetBSD (configure with 194285612Sdelphij\fB\-\-enable\-clockctl\fP) or Linux (configure with 195285612Sdelphij\fB\-\-enable\-linuxcaps\fP) or Solaris (configure with \fB\-\-enable\-solarisprivs\fP). 196285612Sdelphij.It Fl I Ar iface , Fl \-interface Ns = Ns Ar iface 197285612SdelphijListen on an interface name or address. 198285612SdelphijThis option may appear an unlimited number of times. 199285612Sdelphij.sp 200285612SdelphijOpen the network address given, or all the addresses associated with the 201285612Sdelphijgiven interface name. This option may appear multiple times. This option 202285612Sdelphijalso implies not opening other addresses, except wildcard and localhost. 203285612SdelphijThis option is deprecated. Please consider using the configuration file 204289997Sglebius\fBinterface\fP command, which is more versatile. 205285612Sdelphij.It Fl k Ar string , Fl \-keyfile Ns = Ns Ar string 206285612Sdelphijpath to symmetric keys. 207285612Sdelphij.sp 208285612SdelphijSpecify the name and path of the symmetric key file. 209285612Sdelphij\fI/etc/ntp.keys\fP 210285612Sdelphijis the default. 211158688SpavThis is the same operation as the 212285612Sdelphij\fBkeys\fP \fIkeyfile\fP 213285612Sdelphijconfiguration file directive. 214285612Sdelphij.It Fl l Ar string , Fl \-logfile Ns = Ns Ar string 215285612Sdelphijpath to the log file. 216285612Sdelphij.sp 21755857SsheldonhSpecify the name and path of the log file. 218158688SpavThe default is the system log file. 219158688SpavThis is the same operation as the 220285612Sdelphij\fBlogfile\fP \fIlogfile\fP 221285612Sdelphijconfiguration file directive. 222285612Sdelphij.It Fl L , Fl \-novirtualips 223285612SdelphijDo not listen to virtual interfaces. 224285612Sdelphij.sp 225285612SdelphijDo not listen to virtual interfaces, defined as those with 226285612Sdelphijnames containing a colon. This option is deprecated. Please 227285612Sdelphijconsider using the configuration file \fBinterface\fP command, which 228285612Sdelphijis more versatile. 229285612Sdelphij.It Fl M , Fl \-modifymmtimer 230285612SdelphijModify Multimedia Timer (Windows only). 231285612Sdelphij.sp 232285612SdelphijSet the Windows Multimedia Timer to highest resolution. This 233285612Sdelphijensures the resolution does not change while ntpd is running, 234285612Sdelphijavoiding timekeeping glitches associated with changes. 235285612Sdelphij.It Fl n , Fl \-nofork 236141846SruDo not fork. 237285612SdelphijThis option must not appear in combination with any of the following options: 238285612Sdelphijwait\-sync. 239285612Sdelphij.sp 240285612Sdelphij.It Fl N , Fl \-nice 241285612SdelphijRun at high priority. 242285612Sdelphij.sp 243285612SdelphijTo the extent permitted by the operating system, run 244285612Sdelphij\fBntpd\fP 245158688Spavat the highest priority. 246285612Sdelphij.It Fl p Ar string , Fl \-pidfile Ns = Ns Ar string 247285612Sdelphijpath to the PID file. 248285612Sdelphij.sp 249285612SdelphijSpecify the name and path of the file used to record 250285612Sdelphij\fBntpd\fP's 251158688Spavprocess ID. 252158688SpavThis is the same operation as the 253285612Sdelphij\fBpidfile\fP \fIpidfile\fP 254285612Sdelphijconfiguration file directive. 255285612Sdelphij.It Fl P Ar number , Fl \-priority Ns = Ns Ar number 256285612SdelphijProcess priority. 257285612SdelphijThis option takes an integer number as its argument. 258285612Sdelphij.sp 259285612SdelphijTo the extent permitted by the operating system, run 260285612Sdelphij\fBntpd\fP 261285612Sdelphijat the specified 262285612Sdelphij\fBsched_setscheduler(SCHED_FIFO)\fP 263285612Sdelphijpriority. 264285612Sdelphij.It Fl q , Fl \-quit 265285612SdelphijSet the time and quit. 266285612SdelphijThis option must not appear in combination with any of the following options: 267285612Sdelphijsaveconfigquit, wait\-sync. 268285612Sdelphij.sp 269285612Sdelphij\fBntpd\fP 270285612Sdelphijwill not daemonize and will exit after the clock is first 271285612Sdelphijsynchronized. This behavior mimics that of the 272285612Sdelphij\fBntpdate\fP 273285612Sdelphijprogram, which will soon be replaced with a shell script. 27482501SsheldonhThe 275285612Sdelphij\fB\-g\fP 27682501Ssheldonhand 277285612Sdelphij\fB\-x\fP 278285612Sdelphijoptions can be used with this option. 279158688SpavNote: The kernel time discipline is disabled with this option. 280285612Sdelphij.It Fl r Ar string , Fl \-propagationdelay Ns = Ns Ar string 281285612SdelphijBroadcast/propagation delay. 282285612Sdelphij.sp 283285612SdelphijSpecify 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. 284285612Sdelphij.It Fl \-saveconfigquit Ns = Ns Ar string 285285612SdelphijSave parsed configuration and quit. 286285612SdelphijThis option must not appear in combination with any of the following options: 287285612Sdelphijquit, wait\-sync. 288285612Sdelphij.sp 289285612SdelphijCause \fBntpd\fP to parse its startup configuration file and save an 290285612Sdelphijequivalent to the given filename and exit. This option was 291285612Sdelphijdesigned for automated testing. 292285612Sdelphij.It Fl s Ar string , Fl \-statsdir Ns = Ns Ar string 293285612SdelphijStatistics file location. 294285612Sdelphij.sp 295285612SdelphijSpecify the directory path for files created by the statistics facility. 296158688SpavThis is the same operation as the 297285612Sdelphij\fBstatsdir\fP \fIstatsdir\fP 298285612Sdelphijconfiguration file directive. 299285612Sdelphij.It Fl t Ar tkey , Fl \-trustedkey Ns = Ns Ar tkey 300285612SdelphijTrusted key number. 301285612SdelphijThis option may appear an unlimited number of times. 302285612Sdelphij.sp 303285612SdelphijAdd the specified key number to the trusted key list. 304285612Sdelphij.It Fl u Ar string , Fl \-user Ns = Ns Ar string 305285612SdelphijRun as userid (or userid:groupid). 306285612Sdelphij.sp 307285612SdelphijSpecify a user, and optionally a group, to switch to. 308285612SdelphijThis option is only available if the OS supports adjusting the clock 309285612Sdelphijwithout full root privileges. 310285612SdelphijThis option is supported under NetBSD (configure with 311285612Sdelphij\fB\-\-enable\-clockctl\fP) or Linux (configure with 312285612Sdelphij\fB\-\-enable\-linuxcaps\fP) or Solaris (configure with \fB\-\-enable\-solarisprivs\fP). 313285612Sdelphij.It Fl U Ar number , Fl \-updateinterval Ns = Ns Ar number 314285612Sdelphijinterval in seconds between scans for new or dropped interfaces. 315285612SdelphijThis option takes an integer number as its argument. 316285612Sdelphij.sp 317285612SdelphijGive the time in seconds between two scans for new or dropped interfaces. 318285612SdelphijFor systems with routing socket support the scans will be performed shortly after the interface change 319285612Sdelphijhas been detected by the system. 320285612SdelphijUse 0 to disable scanning. 60 seconds is the minimum time between scans. 321285612Sdelphij.It Fl \-var Ns = Ns Ar nvar 322285612Sdelphijmake ARG an ntp variable (RW). 323285612SdelphijThis option may appear an unlimited number of times. 324285612Sdelphij.sp 325285612Sdelphij.It Fl \-dvar Ns = Ns Ar ndvar 326285612Sdelphijmake ARG an ntp variable (RW|DEF). 327285612SdelphijThis option may appear an unlimited number of times. 328285612Sdelphij.sp 329285612Sdelphij.It Fl w Ar number , Fl \-wait\-sync Ns = Ns Ar number 330285612SdelphijSeconds to wait for first clock sync. 331285612SdelphijThis option must not appear in combination with any of the following options: 332285612Sdelphijnofork, quit, saveconfigquit. 333285612SdelphijThis option takes an integer number as its argument. 334285612Sdelphij.sp 335285612SdelphijIf greater than zero, alters \fBntpd\fP's behavior when forking to 336285612Sdelphijdaemonize. Instead of exiting with status 0 immediately after 337285612Sdelphijthe fork, the parent waits up to the specified number of 338285612Sdelphijseconds for the child to first synchronize the clock. The exit 339285612Sdelphijstatus is zero (success) if the clock was synchronized, 340285612Sdelphijotherwise it is \fBETIMEDOUT\fP. 341285612SdelphijThis provides the option for a script starting \fBntpd\fP to easily 342285612Sdelphijwait for the first set of the clock before proceeding. 343285612Sdelphij.It Fl x , Fl \-slew 344285612SdelphijSlew up to 600 seconds. 345285612Sdelphij.sp 346285612SdelphijNormally, 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. 347285612SdelphijThis option sets the threshold to 600 s, which is well within the accuracy window to set the clock manually. 348285612SdelphijNote: 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. 349158688SpavThus, an adjustment as much as 600 s will take almost 14 days to complete. 35082501SsheldonhThis option can be used with the 351285612Sdelphij\fB\-g\fP 352158688Spavand 353285612Sdelphij\fB\-q\fP 354158688Spavoptions. 355158688SpavSee the 356285612Sdelphij\fBtinker\fP 357285612Sdelphijconfiguration file directive for other options. 358158688SpavNote: The kernel time discipline is disabled with this option. 359285612Sdelphij.It Fl \-usepcc 360285612SdelphijUse CPU cycle counter (Windows only). 361285612Sdelphij.sp 362285612SdelphijAttempt to substitute the CPU counter for \fBQueryPerformanceCounter\fP. 363285612SdelphijThe CPU counter and \fBQueryPerformanceCounter\fP are compared, and if 364285612Sdelphijthey have the same frequency, the CPU counter (RDTSC on x86) is 365285612Sdelphijused directly, saving the overhead of a system call. 366285612Sdelphij.It Fl \-pccfreq Ns = Ns Ar string 367285612SdelphijForce CPU cycle counter use (Windows only). 368285612Sdelphij.sp 369285612SdelphijForce substitution the CPU counter for \fBQueryPerformanceCounter\fP. 370285612SdelphijThe CPU counter (RDTSC on x86) is used unconditionally with the 371285612Sdelphijgiven frequency (in Hz). 372285612Sdelphij.It Fl m , Fl \-mdns 373285612SdelphijRegister with mDNS as a NTP server. 374285612Sdelphij.sp 375285612SdelphijRegisters as an NTP server with the local mDNS server which allows 376285612Sdelphijthe server to be discovered via mDNS client lookup. 377285612Sdelphij.It Fl \&? , Fl \-help 378285612SdelphijDisplay usage information and exit. 379285612Sdelphij.It Fl \&! , Fl \-more\-help 380285612SdelphijPass the extended usage information through a pager. 381285612Sdelphij.It Fl \-version Op Brq Ar v|c|n 382285612SdelphijOutput version of program and exit. The default mode is `v', a simple 383285612Sdelphijversion. The `c' mode will print copyright information and `n' will 384285612Sdelphijprint the full copyright notice. 38555857Ssheldonh.El 386285612Sdelphij.Sh "OPTION PRESETS" 387285612SdelphijAny option that is not marked as \fInot presettable\fP may be preset 388285612Sdelphijby loading values from environment variables named: 389285612Sdelphij.nf 390285612Sdelphij \fBNTPD_<option\-name>\fP or \fBNTPD\fP 391285612Sdelphij.fi 392285612Sdelphij.ad 393285612Sdelphij.Sh USAGE 39482501Ssheldonh.Ss "How NTP Operates" 39582501SsheldonhThe 39682501Ssheldonh.Nm 39799968Scharnierutility operates by exchanging messages with 398285612Sdelphijone or more configured servers over a range of designated poll intervals. 39982501SsheldonhWhen 40082501Ssheldonhstarted, whether for the first or subsequent times, the program 40197735Sschweikhrequires several exchanges from the majority of these servers so 40282501Ssheldonhthe signal processing and mitigation algorithms can accumulate and 40382501Ssheldonhgroom the data and set the clock. 40482501SsheldonhIn order to protect the network 40582501Ssheldonhfrom bursts, the initial poll interval for each server is delayed 406158688Spavan interval randomized over a few seconds. 40782501SsheldonhAt the default initial poll 40882501Ssheldonhinterval of 64s, several minutes can elapse before the clock is 40982501Ssheldonhset. 410285612SdelphijThis initial delay to set the clock 411285612Sdelphijcan be safely and dramatically reduced using the 41282501Ssheldonh.Cm iburst 41382501Ssheldonhkeyword with the 41482501Ssheldonh.Ic server 41582501Ssheldonhconfiguration 41682501Ssheldonhcommand, as described in 41782501Ssheldonh.Xr ntp.conf 5 . 41855895Ssheldonh.Pp 41982501SsheldonhMost operating systems and hardware of today incorporate a 420285612Sdelphijtime\-of\-year (TOY) chip to maintain the time during periods when 42182501Ssheldonhthe power is off. 42282501SsheldonhWhen the machine is booted, the chip is used to 42382501Ssheldonhinitialize the operating system time. 42482501SsheldonhAfter the machine has 42582501Ssheldonhsynchronized to a NTP server, the operating system corrects the 42682501Ssheldonhchip from time to time. 427285612SdelphijIn the default case, if 42882501Ssheldonh.Nm 429285612Sdelphijdetects that the time on the host 430285612Sdelphijis more than 1000s from the server time, 431285612Sdelphij.Nm 43282501Ssheldonhassumes something must be terribly wrong and the only 43382501Ssheldonhreliable action is for the operator to intervene and set the clock 43482501Ssheldonhby hand. 435285612Sdelphij(Reasons for this include there is no TOY chip, 436285612Sdelphijor its battery is dead, or that the TOY chip is just of poor quality.) 43782501SsheldonhThis causes 43882501Ssheldonh.Nm 43982501Ssheldonhto exit with a panic message to 44082501Ssheldonhthe system log. 44182501SsheldonhThe 44282501Ssheldonh.Fl g 44382501Ssheldonhoption overrides this check and the 444285612Sdelphijclock will be set to the server time regardless of the chip time 445285612Sdelphij(up to 68 years in the past or future \(em 446285612Sdelphijthis is a limitation of the NTPv4 protocol). 44782501SsheldonhHowever, and to protect against broken hardware, such as when the 44882501SsheldonhCMOS battery fails or the clock counter becomes defective, once the 449285612Sdelphijclock has been set an error greater than 1000s will cause 45082501Ssheldonh.Nm 45182501Ssheldonhto exit anyway. 45282501Ssheldonh.Pp 45397735SschweikhUnder ordinary conditions, 45482501Ssheldonh.Nm 45582501Ssheldonhadjusts the clock in 45682501Ssheldonhsmall steps so that the timescale is effectively continuous and 45782501Ssheldonhwithout discontinuities. 45882501SsheldonhUnder conditions of extreme network 45982501Ssheldonhcongestion, the roundtrip delay jitter can exceed three seconds and 460285612Sdelphijthe synchronization distance, which is equal to one\-half the 46182501Ssheldonhroundtrip delay plus error budget terms, can become very large. 46282501SsheldonhThe 46382501Ssheldonh.Nm 46482501Ssheldonhalgorithms discard sample offsets exceeding 128 ms, 46582501Ssheldonhunless the interval during which no sample offset is less than 128 46682501Ssheldonhms exceeds 900s. 46782501SsheldonhThe first sample after that, no matter what the 46882501Ssheldonhoffset, steps the clock to the indicated time. 46982501SsheldonhIn practice this 47082501Ssheldonhreduces the false alarm rate where the clock is stepped in error to 47182501Ssheldonha vanishingly low incidence. 47282501Ssheldonh.Pp 473285612SdelphijAs the result of this behavior, once the clock has been set it 474285612Sdelphijvery rarely strays more than 128 ms even under extreme cases of 47582501Ssheldonhnetwork path congestion and jitter. 47682501SsheldonhSometimes, in particular when 47782501Ssheldonh.Nm 478285612Sdelphijis first started without a valid drift file 479285612Sdelphijon a system with a large intrinsic drift 480285612Sdelphijthe error might grow to exceed 128 ms, 481285612Sdelphijwhich would cause the clock to be set backwards 482285612Sdelphijif the local clock time is more than 128 s 483285612Sdelphijin the future relative to the server. 48482501SsheldonhIn some applications, this behavior may be unacceptable. 485285612SdelphijThere are several solutions, however. 48682501SsheldonhIf the 48782501Ssheldonh.Fl x 48882501Ssheldonhoption is included on the command line, the clock will 48982501Ssheldonhnever be stepped and only slew corrections will be used. 490285612SdelphijBut this choice comes with a cost that 491285612Sdelphijshould be carefully explored before deciding to use 49282501Ssheldonhthe 49382501Ssheldonh.Fl x 49482501Ssheldonhoption. 49582501SsheldonhThe maximum slew rate possible is limited 496285612Sdelphijto 500 parts\-per\-million (PPM) as a consequence of the correctness 49782501Ssheldonhprinciples on which the NTP protocol and algorithm design are 49882501Ssheldonhbased. 49982501SsheldonhAs a result, the local clock can take a long time to 50082501Ssheldonhconverge to an acceptable offset, about 2,000 s for each second the 50182501Ssheldonhclock is outside the acceptable range. 50282501SsheldonhDuring this interval the 50382501Ssheldonhlocal clock will not be consistent with any other network clock and 50482501Ssheldonhthe system cannot be used for distributed applications that require 50582501Ssheldonhcorrectly synchronized network time. 50682501Ssheldonh.Pp 50782501SsheldonhIn spite of the above precautions, sometimes when large 50882501Ssheldonhfrequency errors are present the resulting time offsets stray 509285612Sdelphijoutside the 128\-ms range and an eventual step or slew time 51082501Ssheldonhcorrection is required. 51182501SsheldonhIf following such a correction the 51282501Ssheldonhfrequency error is so large that the first sample is outside the 51382501Ssheldonhacceptable range, 51482501Ssheldonh.Nm 51582501Ssheldonhenters the same state as when the 51682501Ssheldonh.Pa ntp.drift 51782501Ssheldonhfile is not present. 51882501SsheldonhThe intent of this behavior 51982501Ssheldonhis to quickly correct the frequency and restore operation to the 52082501Ssheldonhnormal tracking mode. 52182501SsheldonhIn the most extreme cases 522285612Sdelphij(the host 523158688Spav.Cm time.ien.it 524158688Spavcomes to mind), there may be occasional 52582501Ssheldonhstep/slew corrections and subsequent frequency corrections. 52682501SsheldonhIt 52782501Ssheldonhhelps in these cases to use the 52882501Ssheldonh.Cm burst 52982501Ssheldonhkeyword when 530285612Sdelphijconfiguring the server, but 531285612SdelphijONLY 532285612Sdelphijwhen you have permission to do so from the owner of the target host. 533285612Sdelphij.Pp 534285612SdelphijFinally, 535285612Sdelphijin the past many startup scripts would run 536285612Sdelphij.Xr ntpdate 8 537289997Sglebiusor 538289997Sglebius.Xr sntp 8 539285612Sdelphijto get the system clock close to correct before starting 540285612Sdelphij.Xr ntpd 8 , 541285612Sdelphijbut this was never more than a mediocre hack and is no longer needed. 542285612SdelphijIf you are following the instructions in 543285612Sdelphij.Sx "Starting NTP (Best Current Practice)" 544285612Sdelphijand you still need to set the system time before starting 545285612Sdelphij.Nm , 546285612Sdelphijplease open a bug report and document what is going on, 547285612Sdelphijand then look at using 548289997Sglebius.Xr sntp 8 549289997Sglebiusif you really need to set the clock before starting 550289997Sglebius.Nm . 551285612Sdelphij.Pp 552285612SdelphijThere is a way to start 553285612Sdelphij.Xr ntpd 8 554285612Sdelphijthat often addresses all of the problems mentioned above. 555285612Sdelphij.Ss "Starting NTP (Best Current Practice)" 556285612SdelphijFirst, use the 557285612Sdelphij.Cm iburst 558285612Sdelphijoption on your 559285612Sdelphij.Cm server 560285612Sdelphijentries. 561285612Sdelphij.Pp 562285612SdelphijIf you can also keep a good 563285612Sdelphij.Pa ntp.drift 564285612Sdelphijfile then 565285612Sdelphij.Xr ntpd 8 566285612Sdelphijwill effectively "warm\-start" and your system's clock will 567285612Sdelphijbe stable in under 11 seconds' time. 568285612Sdelphij.Pp 569285612SdelphijAs soon as possible in the startup sequence, start 570285612Sdelphij.Xr ntpd 8 571285612Sdelphijwith at least the 572285612Sdelphij.Fl g 573285612Sdelphijand perhaps the 574285612Sdelphij.Fl N 575285612Sdelphijoptions. 576285612SdelphijThen, 577285612Sdelphijstart the rest of your "normal" processes. 578285612SdelphijThis will give 579285612Sdelphij.Xr ntpd 8 580285612Sdelphijas much time as possible to get the system's clock synchronized and stable. 581285612Sdelphij.Pp 582285612SdelphijFinally, 583285612Sdelphijif you have processes like 584285612Sdelphij.Cm dovecot 585285612Sdelphijor database servers 586285612Sdelphijthat require 587285612Sdelphijmonotonically\-increasing time, 588285612Sdelphijrun 589285612Sdelphij.Xr ntp\-wait 1ntp\-waitmdoc 590285612Sdelphijas late as possible in the boot sequence 591285612Sdelphij(perhaps with the 592285612Sdelphij.Fl v 593285612Sdelphijflag) 594285612Sdelphijand after 595285612Sdelphij.Xr ntp\-wait 1ntp\-waitmdoc 596285612Sdelphijexits successfully 597285612Sdelphijit is as safe as it will ever be to start any process that require 598285612Sdelphijstable time. 59982501Ssheldonh.Ss "Frequency Discipline" 60082501SsheldonhThe 60182501Ssheldonh.Nm 60282501Ssheldonhbehavior at startup depends on whether the 60382501Ssheldonhfrequency file, usually 60482501Ssheldonh.Pa ntp.drift , 60582501Ssheldonhexists. 60682501SsheldonhThis file 60782501Ssheldonhcontains the latest estimate of clock frequency error. 60882501SsheldonhWhen the 60982501Ssheldonh.Nm 61082501Ssheldonhis started and the file does not exist, the 61182501Ssheldonh.Nm 61282501Ssheldonhenters a special mode designed to quickly adapt to 61382501Ssheldonhthe particular system clock oscillator time and frequency error. 61482501SsheldonhThis takes approximately 15 minutes, after which the time and 61582501Ssheldonhfrequency are set to nominal values and the 61682501Ssheldonh.Nm 61782501Ssheldonhenters 61882501Ssheldonhnormal mode, where the time and frequency are continuously tracked 61982501Ssheldonhrelative to the server. 62082501SsheldonhAfter one hour the frequency file is 62182501Ssheldonhcreated and the current frequency offset written to it. 62282501SsheldonhWhen the 62382501Ssheldonh.Nm 62482501Ssheldonhis started and the file does exist, the 62582501Ssheldonh.Nm 62682501Ssheldonhfrequency is initialized from the file and enters normal mode 62782501Ssheldonhimmediately. 62882501SsheldonhAfter that the current frequency offset is written to 62982501Ssheldonhthe file at hourly intervals. 63082501Ssheldonh.Ss "Operating Modes" 63199968ScharnierThe 63282501Ssheldonh.Nm 63399968Scharnierutility can operate in any of several modes, including 63482501Ssheldonhsymmetric active/passive, client/server broadcast/multicast and 63582501Ssheldonhmanycast, as described in the 63682501Ssheldonh.Qq Association Management 63782501Ssheldonhpage 63882501Ssheldonh(available as part of the HTML documentation 63982501Ssheldonhprovided in 64082501Ssheldonh.Pa /usr/share/doc/ntp ) . 64182501SsheldonhIt normally operates continuously while 64282501Ssheldonhmonitoring for small changes in frequency and trimming the clock 64382501Ssheldonhfor the ultimate precision. 644285612SdelphijHowever, it can operate in a one\-time 64582501Ssheldonhmode where the time is set from an external server and frequency is 64682501Ssheldonhset from a previously recorded frequency file. 64782501SsheldonhA 64882501Ssheldonhbroadcast/multicast or manycast client can discover remote servers, 649285612Sdelphijcompute server\-client propagation delay correction factors and 65082501Ssheldonhconfigure itself automatically. 65182501SsheldonhThis makes it possible to deploy a 65282501Ssheldonhfleet of workstations without specifying configuration details 65382501Ssheldonhspecific to the local environment. 65482501Ssheldonh.Pp 65582501SsheldonhBy default, 65682501Ssheldonh.Nm 65782501Ssheldonhruns in continuous mode where each of 65882501Ssheldonhpossibly several external servers is polled at intervals determined 65982501Ssheldonhby an intricate state machine. 66082501SsheldonhThe state machine measures the 66182501Ssheldonhincidental roundtrip delay jitter and oscillator frequency wander 66282501Ssheldonhand determines the best poll interval using a heuristic algorithm. 66382501SsheldonhOrdinarily, and in most operating environments, the state machine 66482501Ssheldonhwill start with 64s intervals and eventually increase in steps to 66582501Ssheldonh1024s. 66682501SsheldonhA small amount of random variation is introduced in order to 66782501Ssheldonhavoid bunching at the servers. 66882501SsheldonhIn addition, should a server become 66982501Ssheldonhunreachable for some time, the poll interval is increased in steps 67082501Ssheldonhto 1024s in order to reduce network overhead. 67182501Ssheldonh.Pp 67282501SsheldonhIn some cases it may not be practical for 67382501Ssheldonh.Nm 674285612Sdelphijto run continuously. 67582501SsheldonhA common workaround has been to run the 67682501Ssheldonh.Xr ntpdate 8 677285612Sdelphijor 678285612Sdelphij.Xr sntp 8 679285612Sdelphijprograms from a 68082501Ssheldonh.Xr cron 8 68182501Ssheldonhjob at designated 68282501Ssheldonhtimes. 683285612SdelphijHowever, these programs do not have the crafted signal 684285612Sdelphijprocessing, error checking or mitigation algorithms of 68582501Ssheldonh.Nm . 68682501SsheldonhThe 68782501Ssheldonh.Fl q 68882501Ssheldonhoption is intended for this purpose. 68982501SsheldonhSetting this option will cause 69082501Ssheldonh.Nm 69182501Ssheldonhto exit just after 69282501Ssheldonhsetting the clock for the first time. 69382501SsheldonhThe procedure for initially 69482501Ssheldonhsetting the clock is the same as in continuous mode; most 69582501Ssheldonhapplications will probably want to specify the 69682501Ssheldonh.Cm iburst 69782501Ssheldonhkeyword with the 69882501Ssheldonh.Ic server 69982501Ssheldonhconfiguration command. 70082501SsheldonhWith this 70182501Ssheldonhkeyword a volley of messages are exchanged to groom the data and 702158688Spavthe clock is set in about 10 s. 70382501SsheldonhIf nothing is heard after a 70482501Ssheldonhcouple of minutes, the daemon times out and exits. 70582501SsheldonhAfter a suitable 70682501Ssheldonhperiod of mourning, the 70782501Ssheldonh.Xr ntpdate 8 708285612Sdelphijprogram will be 70982501Ssheldonhretired. 71082501Ssheldonh.Pp 71182501SsheldonhWhen kernel support is available to discipline the clock 71282501Ssheldonhfrequency, which is the case for stock Solaris, Tru64, Linux and 71382501Ssheldonh.Fx , 71482501Ssheldonha useful feature is available to discipline the clock 71582501Ssheldonhfrequency. 71682501SsheldonhFirst, 71782501Ssheldonh.Nm 71882501Ssheldonhis run in continuous mode with 71982501Ssheldonhselected servers in order to measure and record the intrinsic clock 72082501Ssheldonhfrequency offset in the frequency file. 72182501SsheldonhIt may take some hours for 72282501Ssheldonhthe frequency and offset to settle down. 72382501SsheldonhThen the 72482501Ssheldonh.Nm 72582501Ssheldonhis 726285612Sdelphijstopped and run in one\-time mode as required. 72782501SsheldonhAt each startup, the 72882501Ssheldonhfrequency is read from the file and initializes the kernel 72982501Ssheldonhfrequency. 73082501Ssheldonh.Ss "Poll Interval Control" 73182501SsheldonhThis version of NTP includes an intricate state machine to 73282501Ssheldonhreduce the network load while maintaining a quality of 73382501Ssheldonhsynchronization consistent with the observed jitter and wander. 73482501SsheldonhThere are a number of ways to tailor the operation in order enhance 73582501Ssheldonhaccuracy by reducing the interval or to reduce network overhead by 73682501Ssheldonhincreasing it. 73782501SsheldonhHowever, the user is advised to carefully consider 73897735Sschweikhthe consequences of changing the poll adjustment range from the 73982501Ssheldonhdefault minimum of 64 s to the default maximum of 1,024 s. 74082501SsheldonhThe 74182501Ssheldonhdefault minimum can be changed with the 74282501Ssheldonh.Ic tinker 74382501Ssheldonh.Cm minpoll 74482501Ssheldonhcommand to a value not less than 16 s. 74582501SsheldonhThis value is used for all 74697735Sschweikhconfigured associations, unless overridden by the 74782501Ssheldonh.Cm minpoll 74882501Ssheldonhoption on the configuration command. 74982501SsheldonhNote that most device drivers 75082501Ssheldonhwill not operate properly if the poll interval is less than 64 s 75182501Ssheldonhand that the broadcast server and manycast client associations will 75297735Sschweikhalso use the default, unless overridden. 75382501Ssheldonh.Pp 75482501SsheldonhIn some cases involving dial up or toll services, it may be 75582501Ssheldonhuseful to increase the minimum interval to a few tens of minutes 75682501Ssheldonhand maximum interval to a day or so. 75782501SsheldonhUnder normal operation 75882501Ssheldonhconditions, once the clock discipline loop has stabilized the 75997735Sschweikhinterval will be increased in steps from the minimum to the 76082501Ssheldonhmaximum. 76182501SsheldonhHowever, this assumes the intrinsic clock frequency error 76282501Ssheldonhis small enough for the discipline loop correct it. 76382501SsheldonhThe capture 76482501Ssheldonhrange of the loop is 500 PPM at an interval of 64s decreasing by a 76582501Ssheldonhfactor of two for each doubling of interval. 76682501SsheldonhAt a minimum of 1,024 76782501Ssheldonhs, for example, the capture range is only 31 PPM. 76882501SsheldonhIf the intrinsic 76982501Ssheldonherror is greater than this, the drift file 77082501Ssheldonh.Pa ntp.drift 77182501Ssheldonhwill 77282501Ssheldonhhave to be specially tailored to reduce the residual error below 77382501Ssheldonhthis limit. 77482501SsheldonhOnce this is done, the drift file is automatically 77582501Ssheldonhupdated once per hour and is available to initialize the frequency 77682501Ssheldonhon subsequent daemon restarts. 777285612Sdelphij.Ss "The huff\-n'\-puff Filter" 77882501SsheldonhIn scenarios where a considerable amount of data are to be 77982501Ssheldonhdownloaded or uploaded over telephone modems, timekeeping quality 78082501Ssheldonhcan be seriously degraded. 78182501SsheldonhThis occurs because the differential 78282501Ssheldonhdelays on the two directions of transmission can be quite large. 78382501SsheldonhIn 78482501Ssheldonhmany cases the apparent time errors are so large as to exceed the 78582501Ssheldonhstep threshold and a step correction can occur during and after the 78682501Ssheldonhdata transfer is in progress. 78782501Ssheldonh.Pp 788285612SdelphijThe huff\-n'\-puff filter is designed to correct the apparent time 78982501Ssheldonhoffset in these cases. 79082501SsheldonhIt depends on knowledge of the propagation 79182501Ssheldonhdelay when no other traffic is present. 79282501SsheldonhIn common scenarios this 79382501Ssheldonhoccurs during other than work hours. 79482501SsheldonhThe filter maintains a shift 79582501Ssheldonhregister that remembers the minimum delay over the most recent 79682501Ssheldonhinterval measured usually in hours. 79782501SsheldonhUnder conditions of severe 79882501Ssheldonhdelay, the filter corrects the apparent offset using the sign of 79982501Ssheldonhthe offset and the difference between the apparent delay and 80082501Ssheldonhminimum delay. 80182501SsheldonhThe name of the filter reflects the negative (huff) 80282501Ssheldonhand positive (puff) correction, which depends on the sign of the 80382501Ssheldonhoffset. 80482501Ssheldonh.Pp 80582501SsheldonhThe filter is activated by the 806158688Spav.Ic tinker 807158688Spavcommand and 80882501Ssheldonh.Cm huffpuff 80982501Ssheldonhkeyword, as described in 81082501Ssheldonh.Xr ntp.conf 5 . 811285612Sdelphij.Sh "ENVIRONMENT" 812285612SdelphijSee \fBOPTION PRESETS\fP for configuration environment variables. 81355896Ssheldonh.Sh FILES 81455896Ssheldonh.Bl -tag -width /etc/ntp.drift -compact 81555896Ssheldonh.It Pa /etc/ntp.conf 81655896Ssheldonhthe default name of the configuration file 81755896Ssheldonh.It Pa /etc/ntp.drift 81855896Ssheldonhthe default name of the drift file 81955896Ssheldonh.It Pa /etc/ntp.keys 82055896Ssheldonhthe default name of the key file 82155896Ssheldonh.El 822285612Sdelphij.Sh "EXIT STATUS" 823285612SdelphijOne of the following exit values will be returned: 824285612Sdelphij.Bl -tag 825285612Sdelphij.It 0 " (EXIT_SUCCESS)" 826285612SdelphijSuccessful program execution. 827285612Sdelphij.It 1 " (EXIT_FAILURE)" 828285612SdelphijThe operation failed or the command syntax was not valid. 829285612Sdelphij.It 70 " (EX_SOFTWARE)" 830285612Sdelphijlibopts had an internal operational error. Please report 831285612Sdelphijit to autogen\-users@lists.sourceforge.net. Thank you. 832285612Sdelphij.El 833285612Sdelphij.Sh "SEE ALSO" 83455895Ssheldonh.Xr ntp.conf 5 , 83555857Ssheldonh.Xr ntpdate 8 , 83655857Ssheldonh.Xr ntpdc 8 , 837285612Sdelphij.Xr ntpq 8 , 838285612Sdelphij.Xr sntp 8 83955857Ssheldonh.Pp 84055857SsheldonhIn addition to the manual pages provided, 84155857Ssheldonhcomprehensive documentation is available on the world wide web 84255857Ssheldonhat 84355857Ssheldonh.Li http://www.ntp.org/ . 84455857SsheldonhA snapshot of this documentation is available in HTML format in 84555857Ssheldonh.Pa /usr/share/doc/ntp . 84655857Ssheldonh.Rs 84755857Ssheldonh.%A David L. Mills 84855857Ssheldonh.%T Network Time Protocol (Version 1) 84955857Ssheldonh.%O RFC1059 85055857Ssheldonh.Re 85155857Ssheldonh.Rs 85255857Ssheldonh.%A David L. Mills 85355857Ssheldonh.%T Network Time Protocol (Version 2) 85455857Ssheldonh.%O RFC1119 85555857Ssheldonh.Re 85655857Ssheldonh.Rs 85755857Ssheldonh.%A David L. Mills 85855857Ssheldonh.%T Network Time Protocol (Version 3) 85955857Ssheldonh.%O RFC1305 86055857Ssheldonh.Re 861285612Sdelphij.Rs 862285612Sdelphij.%A David L. Mills 863285612Sdelphij.%A J. Martin, Ed. 864285612Sdelphij.%A J. Burbank 865285612Sdelphij.%A W. Kasch 866285612Sdelphij.%T Network Time Protocol Version 4: Protocol and Algorithms Specification 867285612Sdelphij.%O RFC5905 868285612Sdelphij.Re 869285612Sdelphij.Rs 870285612Sdelphij.%A David L. Mills 871285612Sdelphij.%A B. Haberman, Ed. 872285612Sdelphij.%T Network Time Protocol Version 4: Autokey Specification 873285612Sdelphij.%O RFC5906 874285612Sdelphij.Re 875285612Sdelphij.Rs 876285612Sdelphij.%A H. Gerstung 877285612Sdelphij.%A C. Elliott 878285612Sdelphij.%A B. Haberman, Ed. 879285612Sdelphij.%T Definitions of Managed Objects for Network Time Protocol Version 4: (NTPv4) 880285612Sdelphij.%O RFC5907 881285612Sdelphij.Re 882285612Sdelphij.Rs 883285612Sdelphij.%A R. Gayraud 884285612Sdelphij.%A B. Lourdelet 885285612Sdelphij.%T Network Time Protocol (NTP) Server Option for DHCPv6 886285612Sdelphij.%O RFC5908 887285612Sdelphij.Re 888285612Sdelphij.Sh "AUTHORS" 889285612SdelphijThe University of Delaware and Network Time Foundation 890285612Sdelphij.Sh "COPYRIGHT" 891316722SdelphijCopyright (C) 1992\-2017 The University of Delaware and Network Time Foundation all rights reserved. 892285612SdelphijThis program is released under the terms of the NTP license, <http://ntp.org/license>. 89355857Ssheldonh.Sh BUGS 89499968ScharnierThe 89555857Ssheldonh.Nm 89699968Scharnierutility has gotten rather fat. 89782501SsheldonhWhile not huge, it has gotten 898285612Sdelphijlarger than might be desirable for an elevated\-priority 89982501Ssheldonh.Nm 90082501Ssheldonhrunning on a workstation, particularly since many of 90182501Ssheldonhthe fancy features which consume the space were designed more with 90282501Ssheldonha busy primary server, rather than a high stratum workstation in 90382501Ssheldonhmind. 904285612Sdelphij.Pp 905285612SdelphijPlease send bug reports to: http://bugs.ntp.org, bugs@ntp.org 906285612Sdelphij.Sh NOTES 907285612SdelphijPortions of this document came from FreeBSD. 908285612Sdelphij.Pp 909285612SdelphijThis manual page was \fIAutoGen\fP\-erated from the \fBntpd\fP 910285612Sdelphijoption definitions. 911