ntpd.1ntpdmdoc revision 1.1.1.2.4.3
1 1.1.1.2.4.3 snj .Dd October 21 2015 2 1.1.1.2.4.2 snj .Dt NTPD 1ntpdmdoc User Commands 3 1.1.1.2.4.2 snj .Os 4 1.1.1.2.4.2 snj .\" EDIT THIS FILE WITH CAUTION (ntpd-opts.mdoc) 5 1.1.1.2.4.2 snj .\" 6 1.1.1.2.4.3 snj .\" It has been AutoGen-ed October 21, 2015 at 12:38:30 PM by AutoGen 5.18.5 7 1.1.1.2.4.2 snj .\" From the definitions ntpd-opts.def 8 1.1.1.2.4.2 snj .\" and the template file agmdoc-cmd.tpl 9 1.1.1.2.4.2 snj .Sh NAME 10 1.1.1.2.4.2 snj .Nm ntpd 11 1.1.1.2.4.2 snj .Nd NTP daemon program 12 1.1.1.2.4.2 snj .Sh SYNOPSIS 13 1.1.1.2.4.2 snj .Nm 14 1.1.1.2.4.2 snj .\" Mixture of short (flag) options and long options 15 1.1.1.2.4.2 snj .Op Fl flags 16 1.1.1.2.4.2 snj .Op Fl flag Op Ar value 17 1.1.1.2.4.2 snj .Op Fl \-option\-name Ns Oo Oo Ns "=| " Oc Ns Ar value Oc 18 1.1.1.2.4.2 snj [ <server1> ... <serverN> ] 19 1.1.1.2.4.2 snj .Pp 20 1.1.1.2.4.2 snj .Sh DESCRIPTION 21 1.1.1.2.4.2 snj The 22 1.1.1.2.4.2 snj .Nm 23 1.1.1.2.4.2 snj utility is an operating system daemon which sets 24 1.1.1.2.4.2 snj and maintains the system time of day in synchronism with Internet 25 1.1.1.2.4.2 snj standard time servers. 26 1.1.1.2.4.2 snj It is a complete implementation of the 27 1.1.1.2.4.2 snj Network Time Protocol (NTP) version 4, as defined by RFC\-5905, 28 1.1.1.2.4.2 snj but also retains compatibility with 29 1.1.1.2.4.2 snj version 3, as defined by RFC\-1305, and versions 1 30 1.1.1.2.4.2 snj and 2, as defined by RFC\-1059 and RFC\-1119, respectively. 31 1.1.1.2.4.2 snj .Pp 32 1.1.1.2.4.2 snj The 33 1.1.1.2.4.2 snj .Nm 34 1.1.1.2.4.2 snj utility does most computations in 64\-bit floating point 35 1.1.1.2.4.2 snj arithmetic and does relatively clumsy 64\-bit fixed point operations 36 1.1.1.2.4.2 snj only when necessary to preserve the ultimate precision, about 232 37 1.1.1.2.4.2 snj picoseconds. 38 1.1.1.2.4.2 snj While the ultimate precision is not achievable with 39 1.1.1.2.4.2 snj ordinary workstations and networks of today, it may be required 40 1.1.1.2.4.2 snj with future gigahertz CPU clocks and gigabit LANs. 41 1.1.1.2.4.2 snj .Pp 42 1.1.1.2.4.2 snj Ordinarily, 43 1.1.1.2.4.2 snj .Nm 44 1.1.1.2.4.2 snj reads the 45 1.1.1.2.4.2 snj .Xr ntp.conf 5 46 1.1.1.2.4.2 snj configuration file at startup time in order to determine the 47 1.1.1.2.4.2 snj synchronization sources and operating modes. 48 1.1.1.2.4.2 snj It is also possible to 49 1.1.1.2.4.2 snj specify a working, although limited, configuration entirely on the 50 1.1.1.2.4.2 snj command line, obviating the need for a configuration file. 51 1.1.1.2.4.2 snj This may 52 1.1.1.2.4.2 snj be particularly useful when the local host is to be configured as a 53 1.1.1.2.4.2 snj broadcast/multicast client, with all peers being determined by 54 1.1.1.2.4.2 snj listening to broadcasts at run time. 55 1.1.1.2.4.2 snj .Pp 56 1.1.1.2.4.2 snj If NetInfo support is built into 57 1.1.1.2.4.2 snj .Nm , 58 1.1.1.2.4.2 snj then 59 1.1.1.2.4.2 snj .Nm 60 1.1.1.2.4.2 snj will attempt to read its configuration from the 61 1.1.1.2.4.2 snj NetInfo if the default 62 1.1.1.2.4.2 snj .Xr ntp.conf 5 63 1.1.1.2.4.2 snj file cannot be read and no file is 64 1.1.1.2.4.2 snj specified by the 65 1.1.1.2.4.2 snj .Fl c 66 1.1.1.2.4.2 snj option. 67 1.1.1.2.4.2 snj .Pp 68 1.1.1.2.4.2 snj Various internal 69 1.1.1.2.4.2 snj .Nm 70 1.1.1.2.4.2 snj variables can be displayed and 71 1.1.1.2.4.2 snj configuration options altered while the 72 1.1.1.2.4.2 snj .Nm 73 1.1.1.2.4.2 snj is running 74 1.1.1.2.4.2 snj using the 75 1.1.1.2.4.2 snj .Xr ntpq 1ntpqmdoc 76 1.1.1.2.4.2 snj and 77 1.1.1.2.4.2 snj .Xr ntpdc 1ntpdcmdoc 78 1.1.1.2.4.2 snj utility programs. 79 1.1.1.2.4.2 snj .Pp 80 1.1.1.2.4.2 snj When 81 1.1.1.2.4.2 snj .Nm 82 1.1.1.2.4.2 snj starts it looks at the value of 83 1.1.1.2.4.2 snj .Xr umask 2 , 84 1.1.1.2.4.2 snj and if zero 85 1.1.1.2.4.2 snj .Nm 86 1.1.1.2.4.2 snj will set the 87 1.1.1.2.4.2 snj .Xr umask 2 88 1.1.1.2.4.2 snj to 022. 89 1.1.1.2.4.2 snj .Sh "OPTIONS" 90 1.1.1.2.4.2 snj .Bl -tag 91 1.1.1.2.4.2 snj .It Fl 4 , Fl \-ipv4 92 1.1.1.2.4.2 snj Force IPv4 DNS name resolution. 93 1.1.1.2.4.2 snj This option must not appear in combination with any of the following options: 94 1.1.1.2.4.2 snj ipv6. 95 1.1.1.2.4.2 snj .sp 96 1.1.1.2.4.2 snj Force DNS resolution of following host names on the command line 97 1.1.1.2.4.2 snj to the IPv4 namespace. 98 1.1.1.2.4.2 snj .It Fl 6 , Fl \-ipv6 99 1.1.1.2.4.2 snj Force IPv6 DNS name resolution. 100 1.1.1.2.4.2 snj This option must not appear in combination with any of the following options: 101 1.1.1.2.4.2 snj ipv4. 102 1.1.1.2.4.2 snj .sp 103 1.1.1.2.4.2 snj Force DNS resolution of following host names on the command line 104 1.1.1.2.4.2 snj to the IPv6 namespace. 105 1.1.1.2.4.2 snj .It Fl a , Fl \-authreq 106 1.1.1.2.4.2 snj Require crypto authentication. 107 1.1.1.2.4.2 snj This option must not appear in combination with any of the following options: 108 1.1.1.2.4.2 snj authnoreq. 109 1.1.1.2.4.2 snj .sp 110 1.1.1.2.4.2 snj Require cryptographic authentication for broadcast client, 111 1.1.1.2.4.2 snj multicast client and symmetric passive associations. 112 1.1.1.2.4.2 snj This is the default. 113 1.1.1.2.4.2 snj .It Fl A , Fl \-authnoreq 114 1.1.1.2.4.2 snj Do not require crypto authentication. 115 1.1.1.2.4.2 snj This option must not appear in combination with any of the following options: 116 1.1.1.2.4.2 snj authreq. 117 1.1.1.2.4.2 snj .sp 118 1.1.1.2.4.2 snj Do not require cryptographic authentication for broadcast client, 119 1.1.1.2.4.2 snj multicast client and symmetric passive associations. 120 1.1.1.2.4.2 snj This is almost never a good idea. 121 1.1.1.2.4.2 snj .It Fl b , Fl \-bcastsync 122 1.1.1.2.4.2 snj Allow us to sync to broadcast servers. 123 1.1.1.2.4.2 snj .sp 124 1.1.1.2.4.2 snj .It Fl c Ar string , Fl \-configfile Ns = Ns Ar string 125 1.1.1.2.4.2 snj configuration file name. 126 1.1.1.2.4.2 snj .sp 127 1.1.1.2.4.2 snj The name and path of the configuration file, 128 1.1.1.2.4.2 snj \fI/etc/ntp.conf\fP 129 1.1.1.2.4.2 snj by default. 130 1.1.1.2.4.2 snj .It Fl d , Fl \-debug\-level 131 1.1.1.2.4.2 snj Increase debug verbosity level. 132 1.1.1.2.4.2 snj This option may appear an unlimited number of times. 133 1.1.1.2.4.2 snj .sp 134 1.1.1.2.4.2 snj .It Fl D Ar number , Fl \-set\-debug\-level Ns = Ns Ar number 135 1.1.1.2.4.2 snj Set the debug verbosity level. 136 1.1.1.2.4.2 snj This option may appear an unlimited number of times. 137 1.1.1.2.4.2 snj This option takes an integer number as its argument. 138 1.1.1.2.4.2 snj .sp 139 1.1.1.2.4.2 snj .It Fl f Ar string , Fl \-driftfile Ns = Ns Ar string 140 1.1.1.2.4.2 snj frequency drift file name. 141 1.1.1.2.4.2 snj .sp 142 1.1.1.2.4.2 snj The name and path of the frequency file, 143 1.1.1.2.4.2 snj \fI/etc/ntp.drift\fP 144 1.1.1.2.4.2 snj by default. 145 1.1.1.2.4.2 snj This is the same operation as the 146 1.1.1.2.4.2 snj \fBdriftfile\fP \fIdriftfile\fP 147 1.1.1.2.4.3 snj configuration specification in the 148 1.1.1.2.4.2 snj \fI/etc/ntp.conf\fP 149 1.1.1.2.4.2 snj file. 150 1.1.1.2.4.2 snj .It Fl g , Fl \-panicgate 151 1.1.1.2.4.2 snj Allow the first adjustment to be Big. 152 1.1.1.2.4.2 snj This option may appear an unlimited number of times. 153 1.1.1.2.4.2 snj .sp 154 1.1.1.2.4.2 snj Normally, 155 1.1.1.2.4.2 snj \fBntpd\fP 156 1.1.1.2.4.2 snj 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, 157 1.1.1.2.4.2 snj \fBntpd\fP 158 1.1.1.2.4.2 snj will exit with a message to the system log. This option can be used with the 159 1.1.1.2.4.2 snj \fB\-q\fP 160 1.1.1.2.4.2 snj and 161 1.1.1.2.4.2 snj \fB\-x\fP 162 1.1.1.2.4.2 snj options. 163 1.1.1.2.4.2 snj See the 164 1.1.1.2.4.2 snj \fBtinker\fP 165 1.1.1.2.4.2 snj configuration file directive for other options. 166 1.1.1.2.4.3 snj .It Fl G , Fl \-force\-step\-once 167 1.1.1.2.4.3 snj Step any initial offset correction.. 168 1.1.1.2.4.3 snj .sp 169 1.1.1.2.4.3 snj Normally, 170 1.1.1.2.4.3 snj \fBntpd\fP 171 1.1.1.2.4.3 snj steps the time if the time offset exceeds the step threshold, 172 1.1.1.2.4.3 snj which is 128 ms by default, and otherwise slews the time. 173 1.1.1.2.4.3 snj This option forces the initial offset correction to be stepped, 174 1.1.1.2.4.3 snj so the highest time accuracy can be achieved quickly. 175 1.1.1.2.4.3 snj However, this may also cause the time to be stepped back 176 1.1.1.2.4.3 snj so this option must not be used if 177 1.1.1.2.4.3 snj applications requiring monotonic time are running. 178 1.1.1.2.4.3 snj See the \fBtinker\fP configuration file directive for other options. 179 1.1.1.2.4.2 snj .It Fl i Ar string , Fl \-jaildir Ns = Ns Ar string 180 1.1.1.2.4.2 snj Jail directory. 181 1.1.1.2.4.2 snj .sp 182 1.1.1.2.4.2 snj Chroot the server to the directory 183 1.1.1.2.4.2 snj \fIjaildir\fP 184 1.1.1.2.4.2 snj . 185 1.1.1.2.4.2 snj This option also implies that the server attempts to drop root privileges at startup. 186 1.1.1.2.4.2 snj You may need to also specify a 187 1.1.1.2.4.2 snj \fB\-u\fP 188 1.1.1.2.4.2 snj option. 189 1.1.1.2.4.2 snj This option is only available if the OS supports adjusting the clock 190 1.1.1.2.4.2 snj without full root privileges. 191 1.1.1.2.4.2 snj This option is supported under NetBSD (configure with 192 1.1.1.2.4.2 snj \fB\-\-enable\-clockctl\fP) or Linux (configure with 193 1.1.1.2.4.2 snj \fB\-\-enable\-linuxcaps\fP) or Solaris (configure with \fB\-\-enable\-solarisprivs\fP). 194 1.1.1.2.4.2 snj .It Fl I Ar iface , Fl \-interface Ns = Ns Ar iface 195 1.1.1.2.4.2 snj Listen on an interface name or address. 196 1.1.1.2.4.2 snj This option may appear an unlimited number of times. 197 1.1.1.2.4.2 snj .sp 198 1.1.1.2.4.2 snj Open the network address given, or all the addresses associated with the 199 1.1.1.2.4.2 snj given interface name. This option may appear multiple times. This option 200 1.1.1.2.4.2 snj also implies not opening other addresses, except wildcard and localhost. 201 1.1.1.2.4.2 snj This option is deprecated. Please consider using the configuration file 202 1.1.1.2.4.3 snj \fBinterface\fP command, which is more versatile. 203 1.1.1.2.4.2 snj .It Fl k Ar string , Fl \-keyfile Ns = Ns Ar string 204 1.1.1.2.4.2 snj path to symmetric keys. 205 1.1.1.2.4.2 snj .sp 206 1.1.1.2.4.2 snj Specify the name and path of the symmetric key file. 207 1.1.1.2.4.2 snj \fI/etc/ntp.keys\fP 208 1.1.1.2.4.2 snj is the default. 209 1.1.1.2.4.2 snj This is the same operation as the 210 1.1.1.2.4.2 snj \fBkeys\fP \fIkeyfile\fP 211 1.1.1.2.4.2 snj configuration file directive. 212 1.1.1.2.4.2 snj .It Fl l Ar string , Fl \-logfile Ns = Ns Ar string 213 1.1.1.2.4.2 snj path to the log file. 214 1.1.1.2.4.2 snj .sp 215 1.1.1.2.4.2 snj Specify the name and path of the log file. 216 1.1.1.2.4.2 snj The default is the system log file. 217 1.1.1.2.4.2 snj This is the same operation as the 218 1.1.1.2.4.2 snj \fBlogfile\fP \fIlogfile\fP 219 1.1.1.2.4.2 snj configuration file directive. 220 1.1.1.2.4.2 snj .It Fl L , Fl \-novirtualips 221 1.1.1.2.4.2 snj Do not listen to virtual interfaces. 222 1.1.1.2.4.2 snj .sp 223 1.1.1.2.4.2 snj Do not listen to virtual interfaces, defined as those with 224 1.1.1.2.4.2 snj names containing a colon. This option is deprecated. Please 225 1.1.1.2.4.2 snj consider using the configuration file \fBinterface\fP command, which 226 1.1.1.2.4.2 snj is more versatile. 227 1.1.1.2.4.2 snj .It Fl M , Fl \-modifymmtimer 228 1.1.1.2.4.2 snj Modify Multimedia Timer (Windows only). 229 1.1.1.2.4.2 snj .sp 230 1.1.1.2.4.2 snj Set the Windows Multimedia Timer to highest resolution. This 231 1.1.1.2.4.2 snj ensures the resolution does not change while ntpd is running, 232 1.1.1.2.4.2 snj avoiding timekeeping glitches associated with changes. 233 1.1.1.2.4.2 snj .It Fl n , Fl \-nofork 234 1.1.1.2.4.2 snj Do not fork. 235 1.1.1.2.4.2 snj This option must not appear in combination with any of the following options: 236 1.1.1.2.4.2 snj wait\-sync. 237 1.1.1.2.4.2 snj .sp 238 1.1.1.2.4.2 snj .It Fl N , Fl \-nice 239 1.1.1.2.4.2 snj Run at high priority. 240 1.1.1.2.4.2 snj .sp 241 1.1.1.2.4.2 snj To the extent permitted by the operating system, run 242 1.1.1.2.4.2 snj \fBntpd\fP 243 1.1.1.2.4.2 snj at the highest priority. 244 1.1.1.2.4.2 snj .It Fl p Ar string , Fl \-pidfile Ns = Ns Ar string 245 1.1.1.2.4.2 snj path to the PID file. 246 1.1.1.2.4.2 snj .sp 247 1.1.1.2.4.2 snj Specify the name and path of the file used to record 248 1.1.1.2.4.2 snj \fBntpd\fP's 249 1.1.1.2.4.2 snj process ID. 250 1.1.1.2.4.2 snj This is the same operation as the 251 1.1.1.2.4.2 snj \fBpidfile\fP \fIpidfile\fP 252 1.1.1.2.4.2 snj configuration file directive. 253 1.1.1.2.4.2 snj .It Fl P Ar number , Fl \-priority Ns = Ns Ar number 254 1.1.1.2.4.2 snj Process priority. 255 1.1.1.2.4.2 snj This option takes an integer number as its argument. 256 1.1.1.2.4.2 snj .sp 257 1.1.1.2.4.2 snj To the extent permitted by the operating system, run 258 1.1.1.2.4.2 snj \fBntpd\fP 259 1.1.1.2.4.2 snj at the specified 260 1.1.1.2.4.2 snj \fBsched_setscheduler(SCHED_FIFO)\fP 261 1.1.1.2.4.2 snj priority. 262 1.1.1.2.4.2 snj .It Fl q , Fl \-quit 263 1.1.1.2.4.2 snj Set the time and quit. 264 1.1.1.2.4.2 snj This option must not appear in combination with any of the following options: 265 1.1.1.2.4.2 snj saveconfigquit, wait\-sync. 266 1.1.1.2.4.2 snj .sp 267 1.1.1.2.4.2 snj \fBntpd\fP 268 1.1.1.2.4.2 snj will not daemonize and will exit after the clock is first 269 1.1.1.2.4.2 snj synchronized. This behavior mimics that of the 270 1.1.1.2.4.2 snj \fBntpdate\fP 271 1.1.1.2.4.2 snj program, which will soon be replaced with a shell script. 272 1.1.1.2.4.2 snj The 273 1.1.1.2.4.2 snj \fB\-g\fP 274 1.1.1.2.4.2 snj and 275 1.1.1.2.4.2 snj \fB\-x\fP 276 1.1.1.2.4.2 snj options can be used with this option. 277 1.1.1.2.4.2 snj Note: The kernel time discipline is disabled with this option. 278 1.1.1.2.4.2 snj .It Fl r Ar string , Fl \-propagationdelay Ns = Ns Ar string 279 1.1.1.2.4.2 snj Broadcast/propagation delay. 280 1.1.1.2.4.2 snj .sp 281 1.1.1.2.4.2 snj 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. 282 1.1.1.2.4.2 snj .It Fl \-saveconfigquit Ns = Ns Ar string 283 1.1.1.2.4.2 snj Save parsed configuration and quit. 284 1.1.1.2.4.2 snj This option must not appear in combination with any of the following options: 285 1.1.1.2.4.2 snj quit, wait\-sync. 286 1.1.1.2.4.2 snj .sp 287 1.1.1.2.4.2 snj Cause \fBntpd\fP to parse its startup configuration file and save an 288 1.1.1.2.4.2 snj equivalent to the given filename and exit. This option was 289 1.1.1.2.4.2 snj designed for automated testing. 290 1.1.1.2.4.2 snj .It Fl s Ar string , Fl \-statsdir Ns = Ns Ar string 291 1.1.1.2.4.2 snj Statistics file location. 292 1.1.1.2.4.2 snj .sp 293 1.1.1.2.4.2 snj Specify the directory path for files created by the statistics facility. 294 1.1.1.2.4.2 snj This is the same operation as the 295 1.1.1.2.4.2 snj \fBstatsdir\fP \fIstatsdir\fP 296 1.1.1.2.4.2 snj configuration file directive. 297 1.1.1.2.4.2 snj .It Fl t Ar tkey , Fl \-trustedkey Ns = Ns Ar tkey 298 1.1.1.2.4.2 snj Trusted key number. 299 1.1.1.2.4.2 snj This option may appear an unlimited number of times. 300 1.1.1.2.4.2 snj .sp 301 1.1.1.2.4.2 snj Add the specified key number to the trusted key list. 302 1.1.1.2.4.2 snj .It Fl u Ar string , Fl \-user Ns = Ns Ar string 303 1.1.1.2.4.2 snj Run as userid (or userid:groupid). 304 1.1.1.2.4.2 snj .sp 305 1.1.1.2.4.2 snj Specify a user, and optionally a group, to switch to. 306 1.1.1.2.4.2 snj This option is only available if the OS supports adjusting the clock 307 1.1.1.2.4.2 snj without full root privileges. 308 1.1.1.2.4.2 snj This option is supported under NetBSD (configure with 309 1.1.1.2.4.2 snj \fB\-\-enable\-clockctl\fP) or Linux (configure with 310 1.1.1.2.4.2 snj \fB\-\-enable\-linuxcaps\fP) or Solaris (configure with \fB\-\-enable\-solarisprivs\fP). 311 1.1.1.2.4.2 snj .It Fl U Ar number , Fl \-updateinterval Ns = Ns Ar number 312 1.1.1.2.4.2 snj interval in seconds between scans for new or dropped interfaces. 313 1.1.1.2.4.2 snj This option takes an integer number as its argument. 314 1.1.1.2.4.2 snj .sp 315 1.1.1.2.4.2 snj Give the time in seconds between two scans for new or dropped interfaces. 316 1.1.1.2.4.2 snj For systems with routing socket support the scans will be performed shortly after the interface change 317 1.1.1.2.4.2 snj has been detected by the system. 318 1.1.1.2.4.2 snj Use 0 to disable scanning. 60 seconds is the minimum time between scans. 319 1.1.1.2.4.2 snj .It Fl \-var Ns = Ns Ar nvar 320 1.1.1.2.4.2 snj make ARG an ntp variable (RW). 321 1.1.1.2.4.2 snj This option may appear an unlimited number of times. 322 1.1.1.2.4.2 snj .sp 323 1.1.1.2.4.2 snj .It Fl \-dvar Ns = Ns Ar ndvar 324 1.1.1.2.4.2 snj make ARG an ntp variable (RW|DEF). 325 1.1.1.2.4.2 snj This option may appear an unlimited number of times. 326 1.1.1.2.4.2 snj .sp 327 1.1.1.2.4.2 snj .It Fl w Ar number , Fl \-wait\-sync Ns = Ns Ar number 328 1.1.1.2.4.2 snj Seconds to wait for first clock sync. 329 1.1.1.2.4.2 snj This option must not appear in combination with any of the following options: 330 1.1.1.2.4.2 snj nofork, quit, saveconfigquit. 331 1.1.1.2.4.2 snj This option takes an integer number as its argument. 332 1.1.1.2.4.2 snj .sp 333 1.1.1.2.4.2 snj If greater than zero, alters \fBntpd\fP's behavior when forking to 334 1.1.1.2.4.2 snj daemonize. Instead of exiting with status 0 immediately after 335 1.1.1.2.4.2 snj the fork, the parent waits up to the specified number of 336 1.1.1.2.4.2 snj seconds for the child to first synchronize the clock. The exit 337 1.1.1.2.4.2 snj status is zero (success) if the clock was synchronized, 338 1.1.1.2.4.2 snj otherwise it is \fBETIMEDOUT\fP. 339 1.1.1.2.4.2 snj This provides the option for a script starting \fBntpd\fP to easily 340 1.1.1.2.4.2 snj wait for the first set of the clock before proceeding. 341 1.1.1.2.4.2 snj .It Fl x , Fl \-slew 342 1.1.1.2.4.2 snj Slew up to 600 seconds. 343 1.1.1.2.4.2 snj .sp 344 1.1.1.2.4.2 snj 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. 345 1.1.1.2.4.2 snj This option sets the threshold to 600 s, which is well within the accuracy window to set the clock manually. 346 1.1.1.2.4.2 snj 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. 347 1.1.1.2.4.2 snj Thus, an adjustment as much as 600 s will take almost 14 days to complete. 348 1.1.1.2.4.2 snj This option can be used with the 349 1.1.1.2.4.2 snj \fB\-g\fP 350 1.1.1.2.4.2 snj and 351 1.1.1.2.4.2 snj \fB\-q\fP 352 1.1.1.2.4.2 snj options. 353 1.1.1.2.4.2 snj See the 354 1.1.1.2.4.2 snj \fBtinker\fP 355 1.1.1.2.4.2 snj configuration file directive for other options. 356 1.1.1.2.4.2 snj Note: The kernel time discipline is disabled with this option. 357 1.1.1.2.4.2 snj .It Fl \-usepcc 358 1.1.1.2.4.2 snj Use CPU cycle counter (Windows only). 359 1.1.1.2.4.2 snj .sp 360 1.1.1.2.4.2 snj Attempt to substitute the CPU counter for \fBQueryPerformanceCounter\fP. 361 1.1.1.2.4.2 snj The CPU counter and \fBQueryPerformanceCounter\fP are compared, and if 362 1.1.1.2.4.2 snj they have the same frequency, the CPU counter (RDTSC on x86) is 363 1.1.1.2.4.2 snj used directly, saving the overhead of a system call. 364 1.1.1.2.4.2 snj .It Fl \-pccfreq Ns = Ns Ar string 365 1.1.1.2.4.2 snj Force CPU cycle counter use (Windows only). 366 1.1.1.2.4.2 snj .sp 367 1.1.1.2.4.2 snj Force substitution the CPU counter for \fBQueryPerformanceCounter\fP. 368 1.1.1.2.4.2 snj The CPU counter (RDTSC on x86) is used unconditionally with the 369 1.1.1.2.4.2 snj given frequency (in Hz). 370 1.1.1.2.4.2 snj .It Fl m , Fl \-mdns 371 1.1.1.2.4.2 snj Register with mDNS as a NTP server. 372 1.1.1.2.4.2 snj .sp 373 1.1.1.2.4.2 snj Registers as an NTP server with the local mDNS server which allows 374 1.1.1.2.4.2 snj the server to be discovered via mDNS client lookup. 375 1.1.1.2.4.2 snj .It Fl \&? , Fl \-help 376 1.1.1.2.4.2 snj Display usage information and exit. 377 1.1.1.2.4.2 snj .It Fl \&! , Fl \-more\-help 378 1.1.1.2.4.2 snj Pass the extended usage information through a pager. 379 1.1.1.2.4.2 snj .It Fl \-version Op Brq Ar v|c|n 380 1.1.1.2.4.2 snj Output version of program and exit. The default mode is `v', a simple 381 1.1.1.2.4.2 snj version. The `c' mode will print copyright information and `n' will 382 1.1.1.2.4.2 snj print the full copyright notice. 383 1.1.1.2.4.2 snj .El 384 1.1.1.2.4.2 snj .Sh "OPTION PRESETS" 385 1.1.1.2.4.2 snj Any option that is not marked as \fInot presettable\fP may be preset 386 1.1.1.2.4.2 snj by loading values from environment variables named: 387 1.1.1.2.4.2 snj .nf 388 1.1.1.2.4.2 snj \fBNTPD_<option\-name>\fP or \fBNTPD\fP 389 1.1.1.2.4.2 snj .fi 390 1.1.1.2.4.2 snj .ad 391 1.1.1.2.4.2 snj .Sh USAGE 392 1.1.1.2.4.2 snj .Ss "How NTP Operates" 393 1.1.1.2.4.2 snj The 394 1.1.1.2.4.2 snj .Nm 395 1.1.1.2.4.2 snj utility operates by exchanging messages with 396 1.1.1.2.4.2 snj one or more configured servers over a range of designated poll intervals. 397 1.1.1.2.4.2 snj When 398 1.1.1.2.4.2 snj started, whether for the first or subsequent times, the program 399 1.1.1.2.4.2 snj requires several exchanges from the majority of these servers so 400 1.1.1.2.4.2 snj the signal processing and mitigation algorithms can accumulate and 401 1.1.1.2.4.2 snj groom the data and set the clock. 402 1.1.1.2.4.2 snj In order to protect the network 403 1.1.1.2.4.2 snj from bursts, the initial poll interval for each server is delayed 404 1.1.1.2.4.2 snj an interval randomized over a few seconds. 405 1.1.1.2.4.2 snj At the default initial poll 406 1.1.1.2.4.2 snj interval of 64s, several minutes can elapse before the clock is 407 1.1.1.2.4.2 snj set. 408 1.1.1.2.4.2 snj This initial delay to set the clock 409 1.1.1.2.4.2 snj can be safely and dramatically reduced using the 410 1.1.1.2.4.2 snj .Cm iburst 411 1.1.1.2.4.2 snj keyword with the 412 1.1.1.2.4.2 snj .Ic server 413 1.1.1.2.4.2 snj configuration 414 1.1.1.2.4.2 snj command, as described in 415 1.1.1.2.4.2 snj .Xr ntp.conf 5 . 416 1.1.1.2.4.2 snj .Pp 417 1.1.1.2.4.2 snj Most operating systems and hardware of today incorporate a 418 1.1.1.2.4.2 snj time\-of\-year (TOY) chip to maintain the time during periods when 419 1.1.1.2.4.2 snj the power is off. 420 1.1.1.2.4.2 snj When the machine is booted, the chip is used to 421 1.1.1.2.4.2 snj initialize the operating system time. 422 1.1.1.2.4.2 snj After the machine has 423 1.1.1.2.4.2 snj synchronized to a NTP server, the operating system corrects the 424 1.1.1.2.4.2 snj chip from time to time. 425 1.1.1.2.4.2 snj In the default case, if 426 1.1.1.2.4.2 snj .Nm 427 1.1.1.2.4.2 snj detects that the time on the host 428 1.1.1.2.4.2 snj is more than 1000s from the server time, 429 1.1.1.2.4.2 snj .Nm 430 1.1.1.2.4.2 snj assumes something must be terribly wrong and the only 431 1.1.1.2.4.2 snj reliable action is for the operator to intervene and set the clock 432 1.1.1.2.4.2 snj by hand. 433 1.1.1.2.4.2 snj (Reasons for this include there is no TOY chip, 434 1.1.1.2.4.2 snj or its battery is dead, or that the TOY chip is just of poor quality.) 435 1.1.1.2.4.2 snj This causes 436 1.1.1.2.4.2 snj .Nm 437 1.1.1.2.4.2 snj to exit with a panic message to 438 1.1.1.2.4.2 snj the system log. 439 1.1.1.2.4.2 snj The 440 1.1.1.2.4.2 snj .Fl g 441 1.1.1.2.4.2 snj option overrides this check and the 442 1.1.1.2.4.2 snj clock will be set to the server time regardless of the chip time 443 1.1.1.2.4.2 snj (up to 68 years in the past or future \(em 444 1.1.1.2.4.2 snj this is a limitation of the NTPv4 protocol). 445 1.1.1.2.4.2 snj However, and to protect against broken hardware, such as when the 446 1.1.1.2.4.2 snj CMOS battery fails or the clock counter becomes defective, once the 447 1.1.1.2.4.2 snj clock has been set an error greater than 1000s will cause 448 1.1.1.2.4.2 snj .Nm 449 1.1.1.2.4.2 snj to exit anyway. 450 1.1.1.2.4.2 snj .Pp 451 1.1.1.2.4.2 snj Under ordinary conditions, 452 1.1.1.2.4.2 snj .Nm 453 1.1.1.2.4.2 snj adjusts the clock in 454 1.1.1.2.4.2 snj small steps so that the timescale is effectively continuous and 455 1.1.1.2.4.2 snj without discontinuities. 456 1.1.1.2.4.2 snj Under conditions of extreme network 457 1.1.1.2.4.2 snj congestion, the roundtrip delay jitter can exceed three seconds and 458 1.1.1.2.4.2 snj the synchronization distance, which is equal to one\-half the 459 1.1.1.2.4.2 snj roundtrip delay plus error budget terms, can become very large. 460 1.1.1.2.4.2 snj The 461 1.1.1.2.4.2 snj .Nm 462 1.1.1.2.4.2 snj algorithms discard sample offsets exceeding 128 ms, 463 1.1.1.2.4.2 snj unless the interval during which no sample offset is less than 128 464 1.1.1.2.4.2 snj ms exceeds 900s. 465 1.1.1.2.4.2 snj The first sample after that, no matter what the 466 1.1.1.2.4.2 snj offset, steps the clock to the indicated time. 467 1.1.1.2.4.2 snj In practice this 468 1.1.1.2.4.2 snj reduces the false alarm rate where the clock is stepped in error to 469 1.1.1.2.4.2 snj a vanishingly low incidence. 470 1.1.1.2.4.2 snj .Pp 471 1.1.1.2.4.2 snj As the result of this behavior, once the clock has been set it 472 1.1.1.2.4.2 snj very rarely strays more than 128 ms even under extreme cases of 473 1.1.1.2.4.2 snj network path congestion and jitter. 474 1.1.1.2.4.2 snj Sometimes, in particular when 475 1.1.1.2.4.2 snj .Nm 476 1.1.1.2.4.2 snj is first started without a valid drift file 477 1.1.1.2.4.2 snj on a system with a large intrinsic drift 478 1.1.1.2.4.2 snj the error might grow to exceed 128 ms, 479 1.1.1.2.4.2 snj which would cause the clock to be set backwards 480 1.1.1.2.4.2 snj if the local clock time is more than 128 s 481 1.1.1.2.4.2 snj in the future relative to the server. 482 1.1.1.2.4.2 snj In some applications, this behavior may be unacceptable. 483 1.1.1.2.4.2 snj There are several solutions, however. 484 1.1.1.2.4.2 snj If the 485 1.1.1.2.4.2 snj .Fl x 486 1.1.1.2.4.2 snj option is included on the command line, the clock will 487 1.1.1.2.4.2 snj never be stepped and only slew corrections will be used. 488 1.1.1.2.4.2 snj But this choice comes with a cost that 489 1.1.1.2.4.2 snj should be carefully explored before deciding to use 490 1.1.1.2.4.2 snj the 491 1.1.1.2.4.2 snj .Fl x 492 1.1.1.2.4.2 snj option. 493 1.1.1.2.4.2 snj The maximum slew rate possible is limited 494 1.1.1.2.4.2 snj to 500 parts\-per\-million (PPM) as a consequence of the correctness 495 1.1.1.2.4.2 snj principles on which the NTP protocol and algorithm design are 496 1.1.1.2.4.2 snj based. 497 1.1.1.2.4.2 snj As a result, the local clock can take a long time to 498 1.1.1.2.4.2 snj converge to an acceptable offset, about 2,000 s for each second the 499 1.1.1.2.4.2 snj clock is outside the acceptable range. 500 1.1.1.2.4.2 snj During this interval the 501 1.1.1.2.4.2 snj local clock will not be consistent with any other network clock and 502 1.1.1.2.4.2 snj the system cannot be used for distributed applications that require 503 1.1.1.2.4.2 snj correctly synchronized network time. 504 1.1.1.2.4.2 snj .Pp 505 1.1.1.2.4.2 snj In spite of the above precautions, sometimes when large 506 1.1.1.2.4.2 snj frequency errors are present the resulting time offsets stray 507 1.1.1.2.4.2 snj outside the 128\-ms range and an eventual step or slew time 508 1.1.1.2.4.2 snj correction is required. 509 1.1.1.2.4.2 snj If following such a correction the 510 1.1.1.2.4.2 snj frequency error is so large that the first sample is outside the 511 1.1.1.2.4.2 snj acceptable range, 512 1.1.1.2.4.2 snj .Nm 513 1.1.1.2.4.2 snj enters the same state as when the 514 1.1.1.2.4.2 snj .Pa ntp.drift 515 1.1.1.2.4.2 snj file is not present. 516 1.1.1.2.4.2 snj The intent of this behavior 517 1.1.1.2.4.2 snj is to quickly correct the frequency and restore operation to the 518 1.1.1.2.4.2 snj normal tracking mode. 519 1.1.1.2.4.2 snj In the most extreme cases 520 1.1.1.2.4.2 snj (the host 521 1.1.1.2.4.2 snj .Cm time.ien.it 522 1.1.1.2.4.2 snj comes to mind), there may be occasional 523 1.1.1.2.4.2 snj step/slew corrections and subsequent frequency corrections. 524 1.1.1.2.4.2 snj It 525 1.1.1.2.4.2 snj helps in these cases to use the 526 1.1.1.2.4.2 snj .Cm burst 527 1.1.1.2.4.2 snj keyword when 528 1.1.1.2.4.2 snj configuring the server, but 529 1.1.1.2.4.2 snj ONLY 530 1.1.1.2.4.2 snj when you have permission to do so from the owner of the target host. 531 1.1.1.2.4.2 snj .Pp 532 1.1.1.2.4.2 snj Finally, 533 1.1.1.2.4.2 snj in the past many startup scripts would run 534 1.1.1.2.4.2 snj .Xr ntpdate 1ntpdatemdoc 535 1.1.1.2.4.3 snj or 536 1.1.1.2.4.3 snj .Xr sntp 1sntpmdoc 537 1.1.1.2.4.2 snj to get the system clock close to correct before starting 538 1.1.1.2.4.2 snj .Xr ntpd 1ntpdmdoc , 539 1.1.1.2.4.2 snj but this was never more than a mediocre hack and is no longer needed. 540 1.1.1.2.4.2 snj If you are following the instructions in 541 1.1.1.2.4.2 snj .Sx "Starting NTP (Best Current Practice)" 542 1.1.1.2.4.2 snj and you still need to set the system time before starting 543 1.1.1.2.4.2 snj .Nm , 544 1.1.1.2.4.2 snj please open a bug report and document what is going on, 545 1.1.1.2.4.2 snj and then look at using 546 1.1.1.2.4.3 snj .Xr sntp 1sntpmdoc 547 1.1.1.2.4.3 snj if you really need to set the clock before starting 548 1.1.1.2.4.3 snj .Nm . 549 1.1.1.2.4.2 snj .Pp 550 1.1.1.2.4.2 snj There is a way to start 551 1.1.1.2.4.2 snj .Xr ntpd 1ntpdmdoc 552 1.1.1.2.4.2 snj that often addresses all of the problems mentioned above. 553 1.1.1.2.4.2 snj .Ss "Starting NTP (Best Current Practice)" 554 1.1.1.2.4.2 snj First, use the 555 1.1.1.2.4.2 snj .Cm iburst 556 1.1.1.2.4.2 snj option on your 557 1.1.1.2.4.2 snj .Cm server 558 1.1.1.2.4.2 snj entries. 559 1.1.1.2.4.2 snj .Pp 560 1.1.1.2.4.2 snj If you can also keep a good 561 1.1.1.2.4.2 snj .Pa ntp.drift 562 1.1.1.2.4.2 snj file then 563 1.1.1.2.4.2 snj .Xr ntpd 1ntpdmdoc 564 1.1.1.2.4.2 snj will effectively "warm\-start" and your system's clock will 565 1.1.1.2.4.2 snj be stable in under 11 seconds' time. 566 1.1.1.2.4.2 snj .Pp 567 1.1.1.2.4.2 snj As soon as possible in the startup sequence, start 568 1.1.1.2.4.2 snj .Xr ntpd 1ntpdmdoc 569 1.1.1.2.4.2 snj with at least the 570 1.1.1.2.4.2 snj .Fl g 571 1.1.1.2.4.2 snj and perhaps the 572 1.1.1.2.4.2 snj .Fl N 573 1.1.1.2.4.2 snj options. 574 1.1.1.2.4.2 snj Then, 575 1.1.1.2.4.2 snj start the rest of your "normal" processes. 576 1.1.1.2.4.2 snj This will give 577 1.1.1.2.4.2 snj .Xr ntpd 1ntpdmdoc 578 1.1.1.2.4.2 snj as much time as possible to get the system's clock synchronized and stable. 579 1.1.1.2.4.2 snj .Pp 580 1.1.1.2.4.2 snj Finally, 581 1.1.1.2.4.2 snj if you have processes like 582 1.1.1.2.4.2 snj .Cm dovecot 583 1.1.1.2.4.2 snj or database servers 584 1.1.1.2.4.2 snj that require 585 1.1.1.2.4.2 snj monotonically\-increasing time, 586 1.1.1.2.4.2 snj run 587 1.1.1.2.4.2 snj .Xr ntp\-wait 1ntp\-waitmdoc 588 1.1.1.2.4.2 snj as late as possible in the boot sequence 589 1.1.1.2.4.2 snj (perhaps with the 590 1.1.1.2.4.2 snj .Fl v 591 1.1.1.2.4.2 snj flag) 592 1.1.1.2.4.2 snj and after 593 1.1.1.2.4.2 snj .Xr ntp\-wait 1ntp\-waitmdoc 594 1.1.1.2.4.2 snj exits successfully 595 1.1.1.2.4.2 snj it is as safe as it will ever be to start any process that require 596 1.1.1.2.4.2 snj stable time. 597 1.1.1.2.4.2 snj .Ss "Frequency Discipline" 598 1.1.1.2.4.2 snj The 599 1.1.1.2.4.2 snj .Nm 600 1.1.1.2.4.2 snj behavior at startup depends on whether the 601 1.1.1.2.4.2 snj frequency file, usually 602 1.1.1.2.4.2 snj .Pa ntp.drift , 603 1.1.1.2.4.2 snj exists. 604 1.1.1.2.4.2 snj This file 605 1.1.1.2.4.2 snj contains the latest estimate of clock frequency error. 606 1.1.1.2.4.2 snj When the 607 1.1.1.2.4.2 snj .Nm 608 1.1.1.2.4.2 snj is started and the file does not exist, the 609 1.1.1.2.4.2 snj .Nm 610 1.1.1.2.4.2 snj enters a special mode designed to quickly adapt to 611 1.1.1.2.4.2 snj the particular system clock oscillator time and frequency error. 612 1.1.1.2.4.2 snj This takes approximately 15 minutes, after which the time and 613 1.1.1.2.4.2 snj frequency are set to nominal values and the 614 1.1.1.2.4.2 snj .Nm 615 1.1.1.2.4.2 snj enters 616 1.1.1.2.4.2 snj normal mode, where the time and frequency are continuously tracked 617 1.1.1.2.4.2 snj relative to the server. 618 1.1.1.2.4.2 snj After one hour the frequency file is 619 1.1.1.2.4.2 snj created and the current frequency offset written to it. 620 1.1.1.2.4.2 snj When the 621 1.1.1.2.4.2 snj .Nm 622 1.1.1.2.4.2 snj is started and the file does exist, the 623 1.1.1.2.4.2 snj .Nm 624 1.1.1.2.4.2 snj frequency is initialized from the file and enters normal mode 625 1.1.1.2.4.2 snj immediately. 626 1.1.1.2.4.2 snj After that the current frequency offset is written to 627 1.1.1.2.4.2 snj the file at hourly intervals. 628 1.1.1.2.4.2 snj .Ss "Operating Modes" 629 1.1.1.2.4.2 snj The 630 1.1.1.2.4.2 snj .Nm 631 1.1.1.2.4.2 snj utility can operate in any of several modes, including 632 1.1.1.2.4.2 snj symmetric active/passive, client/server broadcast/multicast and 633 1.1.1.2.4.2 snj manycast, as described in the 634 1.1.1.2.4.2 snj .Qq Association Management 635 1.1.1.2.4.2 snj page 636 1.1.1.2.4.2 snj (available as part of the HTML documentation 637 1.1.1.2.4.2 snj provided in 638 1.1.1.2.4.2 snj .Pa /usr/share/doc/ntp ) . 639 1.1.1.2.4.2 snj It normally operates continuously while 640 1.1.1.2.4.2 snj monitoring for small changes in frequency and trimming the clock 641 1.1.1.2.4.2 snj for the ultimate precision. 642 1.1.1.2.4.2 snj However, it can operate in a one\-time 643 1.1.1.2.4.2 snj mode where the time is set from an external server and frequency is 644 1.1.1.2.4.2 snj set from a previously recorded frequency file. 645 1.1.1.2.4.2 snj A 646 1.1.1.2.4.2 snj broadcast/multicast or manycast client can discover remote servers, 647 1.1.1.2.4.2 snj compute server\-client propagation delay correction factors and 648 1.1.1.2.4.2 snj configure itself automatically. 649 1.1.1.2.4.2 snj This makes it possible to deploy a 650 1.1.1.2.4.2 snj fleet of workstations without specifying configuration details 651 1.1.1.2.4.2 snj specific to the local environment. 652 1.1.1.2.4.2 snj .Pp 653 1.1.1.2.4.2 snj By default, 654 1.1.1.2.4.2 snj .Nm 655 1.1.1.2.4.2 snj runs in continuous mode where each of 656 1.1.1.2.4.2 snj possibly several external servers is polled at intervals determined 657 1.1.1.2.4.2 snj by an intricate state machine. 658 1.1.1.2.4.2 snj The state machine measures the 659 1.1.1.2.4.2 snj incidental roundtrip delay jitter and oscillator frequency wander 660 1.1.1.2.4.2 snj and determines the best poll interval using a heuristic algorithm. 661 1.1.1.2.4.2 snj Ordinarily, and in most operating environments, the state machine 662 1.1.1.2.4.2 snj will start with 64s intervals and eventually increase in steps to 663 1.1.1.2.4.2 snj 1024s. 664 1.1.1.2.4.2 snj A small amount of random variation is introduced in order to 665 1.1.1.2.4.2 snj avoid bunching at the servers. 666 1.1.1.2.4.2 snj In addition, should a server become 667 1.1.1.2.4.2 snj unreachable for some time, the poll interval is increased in steps 668 1.1.1.2.4.2 snj to 1024s in order to reduce network overhead. 669 1.1.1.2.4.2 snj .Pp 670 1.1.1.2.4.2 snj In some cases it may not be practical for 671 1.1.1.2.4.2 snj .Nm 672 1.1.1.2.4.2 snj to run continuously. 673 1.1.1.2.4.2 snj A common workaround has been to run the 674 1.1.1.2.4.2 snj .Xr ntpdate 1ntpdatemdoc 675 1.1.1.2.4.2 snj or 676 1.1.1.2.4.2 snj .Xr sntp 1sntpmdoc 677 1.1.1.2.4.2 snj programs from a 678 1.1.1.2.4.2 snj .Xr cron 8 679 1.1.1.2.4.2 snj job at designated 680 1.1.1.2.4.2 snj times. 681 1.1.1.2.4.2 snj However, these programs do not have the crafted signal 682 1.1.1.2.4.2 snj processing, error checking or mitigation algorithms of 683 1.1.1.2.4.2 snj .Nm . 684 1.1.1.2.4.2 snj The 685 1.1.1.2.4.2 snj .Fl q 686 1.1.1.2.4.2 snj option is intended for this purpose. 687 1.1.1.2.4.2 snj Setting this option will cause 688 1.1.1.2.4.2 snj .Nm 689 1.1.1.2.4.2 snj to exit just after 690 1.1.1.2.4.2 snj setting the clock for the first time. 691 1.1.1.2.4.2 snj The procedure for initially 692 1.1.1.2.4.2 snj setting the clock is the same as in continuous mode; most 693 1.1.1.2.4.2 snj applications will probably want to specify the 694 1.1.1.2.4.2 snj .Cm iburst 695 1.1.1.2.4.2 snj keyword with the 696 1.1.1.2.4.2 snj .Ic server 697 1.1.1.2.4.2 snj configuration command. 698 1.1.1.2.4.2 snj With this 699 1.1.1.2.4.2 snj keyword a volley of messages are exchanged to groom the data and 700 1.1.1.2.4.2 snj the clock is set in about 10 s. 701 1.1.1.2.4.2 snj If nothing is heard after a 702 1.1.1.2.4.2 snj couple of minutes, the daemon times out and exits. 703 1.1.1.2.4.2 snj After a suitable 704 1.1.1.2.4.2 snj period of mourning, the 705 1.1.1.2.4.2 snj .Xr ntpdate 1ntpdatemdoc 706 1.1.1.2.4.2 snj program will be 707 1.1.1.2.4.2 snj retired. 708 1.1.1.2.4.2 snj .Pp 709 1.1.1.2.4.2 snj When kernel support is available to discipline the clock 710 1.1.1.2.4.2 snj frequency, which is the case for stock Solaris, Tru64, Linux and 711 1.1.1.2.4.2 snj .Fx , 712 1.1.1.2.4.2 snj a useful feature is available to discipline the clock 713 1.1.1.2.4.2 snj frequency. 714 1.1.1.2.4.2 snj First, 715 1.1.1.2.4.2 snj .Nm 716 1.1.1.2.4.2 snj is run in continuous mode with 717 1.1.1.2.4.2 snj selected servers in order to measure and record the intrinsic clock 718 1.1.1.2.4.2 snj frequency offset in the frequency file. 719 1.1.1.2.4.2 snj It may take some hours for 720 1.1.1.2.4.2 snj the frequency and offset to settle down. 721 1.1.1.2.4.2 snj Then the 722 1.1.1.2.4.2 snj .Nm 723 1.1.1.2.4.2 snj is 724 1.1.1.2.4.2 snj stopped and run in one\-time mode as required. 725 1.1.1.2.4.2 snj At each startup, the 726 1.1.1.2.4.2 snj frequency is read from the file and initializes the kernel 727 1.1.1.2.4.2 snj frequency. 728 1.1.1.2.4.2 snj .Ss "Poll Interval Control" 729 1.1.1.2.4.2 snj This version of NTP includes an intricate state machine to 730 1.1.1.2.4.2 snj reduce the network load while maintaining a quality of 731 1.1.1.2.4.2 snj synchronization consistent with the observed jitter and wander. 732 1.1.1.2.4.2 snj There are a number of ways to tailor the operation in order enhance 733 1.1.1.2.4.2 snj accuracy by reducing the interval or to reduce network overhead by 734 1.1.1.2.4.2 snj increasing it. 735 1.1.1.2.4.2 snj However, the user is advised to carefully consider 736 1.1.1.2.4.2 snj the consequences of changing the poll adjustment range from the 737 1.1.1.2.4.2 snj default minimum of 64 s to the default maximum of 1,024 s. 738 1.1.1.2.4.2 snj The 739 1.1.1.2.4.2 snj default minimum can be changed with the 740 1.1.1.2.4.2 snj .Ic tinker 741 1.1.1.2.4.2 snj .Cm minpoll 742 1.1.1.2.4.2 snj command to a value not less than 16 s. 743 1.1.1.2.4.2 snj This value is used for all 744 1.1.1.2.4.2 snj configured associations, unless overridden by the 745 1.1.1.2.4.2 snj .Cm minpoll 746 1.1.1.2.4.2 snj option on the configuration command. 747 1.1.1.2.4.2 snj Note that most device drivers 748 1.1.1.2.4.2 snj will not operate properly if the poll interval is less than 64 s 749 1.1.1.2.4.2 snj and that the broadcast server and manycast client associations will 750 1.1.1.2.4.2 snj also use the default, unless overridden. 751 1.1.1.2.4.2 snj .Pp 752 1.1.1.2.4.2 snj In some cases involving dial up or toll services, it may be 753 1.1.1.2.4.2 snj useful to increase the minimum interval to a few tens of minutes 754 1.1.1.2.4.2 snj and maximum interval to a day or so. 755 1.1.1.2.4.2 snj Under normal operation 756 1.1.1.2.4.2 snj conditions, once the clock discipline loop has stabilized the 757 1.1.1.2.4.2 snj interval will be increased in steps from the minimum to the 758 1.1.1.2.4.2 snj maximum. 759 1.1.1.2.4.2 snj However, this assumes the intrinsic clock frequency error 760 1.1.1.2.4.2 snj is small enough for the discipline loop correct it. 761 1.1.1.2.4.2 snj The capture 762 1.1.1.2.4.2 snj range of the loop is 500 PPM at an interval of 64s decreasing by a 763 1.1.1.2.4.2 snj factor of two for each doubling of interval. 764 1.1.1.2.4.2 snj At a minimum of 1,024 765 1.1.1.2.4.2 snj s, for example, the capture range is only 31 PPM. 766 1.1.1.2.4.2 snj If the intrinsic 767 1.1.1.2.4.2 snj error is greater than this, the drift file 768 1.1.1.2.4.2 snj .Pa ntp.drift 769 1.1.1.2.4.2 snj will 770 1.1.1.2.4.2 snj have to be specially tailored to reduce the residual error below 771 1.1.1.2.4.2 snj this limit. 772 1.1.1.2.4.2 snj Once this is done, the drift file is automatically 773 1.1.1.2.4.2 snj updated once per hour and is available to initialize the frequency 774 1.1.1.2.4.2 snj on subsequent daemon restarts. 775 1.1.1.2.4.2 snj .Ss "The huff\-n'\-puff Filter" 776 1.1.1.2.4.2 snj In scenarios where a considerable amount of data are to be 777 1.1.1.2.4.2 snj downloaded or uploaded over telephone modems, timekeeping quality 778 1.1.1.2.4.2 snj can be seriously degraded. 779 1.1.1.2.4.2 snj This occurs because the differential 780 1.1.1.2.4.2 snj delays on the two directions of transmission can be quite large. 781 1.1.1.2.4.2 snj In 782 1.1.1.2.4.2 snj many cases the apparent time errors are so large as to exceed the 783 1.1.1.2.4.2 snj step threshold and a step correction can occur during and after the 784 1.1.1.2.4.2 snj data transfer is in progress. 785 1.1.1.2.4.2 snj .Pp 786 1.1.1.2.4.2 snj The huff\-n'\-puff filter is designed to correct the apparent time 787 1.1.1.2.4.2 snj offset in these cases. 788 1.1.1.2.4.2 snj It depends on knowledge of the propagation 789 1.1.1.2.4.2 snj delay when no other traffic is present. 790 1.1.1.2.4.2 snj In common scenarios this 791 1.1.1.2.4.2 snj occurs during other than work hours. 792 1.1.1.2.4.2 snj The filter maintains a shift 793 1.1.1.2.4.2 snj register that remembers the minimum delay over the most recent 794 1.1.1.2.4.2 snj interval measured usually in hours. 795 1.1.1.2.4.2 snj Under conditions of severe 796 1.1.1.2.4.2 snj delay, the filter corrects the apparent offset using the sign of 797 1.1.1.2.4.2 snj the offset and the difference between the apparent delay and 798 1.1.1.2.4.2 snj minimum delay. 799 1.1.1.2.4.2 snj The name of the filter reflects the negative (huff) 800 1.1.1.2.4.2 snj and positive (puff) correction, which depends on the sign of the 801 1.1.1.2.4.2 snj offset. 802 1.1.1.2.4.2 snj .Pp 803 1.1.1.2.4.2 snj The filter is activated by the 804 1.1.1.2.4.2 snj .Ic tinker 805 1.1.1.2.4.2 snj command and 806 1.1.1.2.4.2 snj .Cm huffpuff 807 1.1.1.2.4.2 snj keyword, as described in 808 1.1.1.2.4.2 snj .Xr ntp.conf 5 . 809 1.1.1.2.4.2 snj .Sh "ENVIRONMENT" 810 1.1.1.2.4.2 snj See \fBOPTION PRESETS\fP for configuration environment variables. 811 1.1.1.2.4.2 snj .Sh FILES 812 1.1.1.2.4.2 snj .Bl -tag -width /etc/ntp.drift -compact 813 1.1.1.2.4.2 snj .It Pa /etc/ntp.conf 814 1.1.1.2.4.2 snj the default name of the configuration file 815 1.1.1.2.4.2 snj .It Pa /etc/ntp.drift 816 1.1.1.2.4.2 snj the default name of the drift file 817 1.1.1.2.4.2 snj .It Pa /etc/ntp.keys 818 1.1.1.2.4.2 snj the default name of the key file 819 1.1.1.2.4.2 snj .El 820 1.1.1.2.4.2 snj .Sh "EXIT STATUS" 821 1.1.1.2.4.2 snj One of the following exit values will be returned: 822 1.1.1.2.4.2 snj .Bl -tag 823 1.1.1.2.4.2 snj .It 0 " (EXIT_SUCCESS)" 824 1.1.1.2.4.2 snj Successful program execution. 825 1.1.1.2.4.2 snj .It 1 " (EXIT_FAILURE)" 826 1.1.1.2.4.2 snj The operation failed or the command syntax was not valid. 827 1.1.1.2.4.2 snj .It 70 " (EX_SOFTWARE)" 828 1.1.1.2.4.2 snj libopts had an internal operational error. Please report 829 1.1.1.2.4.2 snj it to autogen\-users (a] lists.sourceforge.net. Thank you. 830 1.1.1.2.4.2 snj .El 831 1.1.1.2.4.2 snj .Sh "SEE ALSO" 832 1.1.1.2.4.2 snj .Xr ntp.conf 5 , 833 1.1.1.2.4.2 snj .Xr ntpdate 1ntpdatemdoc , 834 1.1.1.2.4.2 snj .Xr ntpdc 1ntpdcmdoc , 835 1.1.1.2.4.2 snj .Xr ntpq 1ntpqmdoc , 836 1.1.1.2.4.2 snj .Xr sntp 1sntpmdoc 837 1.1.1.2.4.2 snj .Pp 838 1.1.1.2.4.2 snj In addition to the manual pages provided, 839 1.1.1.2.4.2 snj comprehensive documentation is available on the world wide web 840 1.1.1.2.4.2 snj at 841 1.1.1.2.4.2 snj .Li http://www.ntp.org/ . 842 1.1.1.2.4.2 snj A snapshot of this documentation is available in HTML format in 843 1.1.1.2.4.2 snj .Pa /usr/share/doc/ntp . 844 1.1.1.2.4.2 snj .Rs 845 1.1.1.2.4.2 snj .%A David L. Mills 846 1.1.1.2.4.2 snj .%T Network Time Protocol (Version 1) 847 1.1.1.2.4.2 snj .%O RFC1059 848 1.1.1.2.4.2 snj .Re 849 1.1.1.2.4.2 snj .Rs 850 1.1.1.2.4.2 snj .%A David L. Mills 851 1.1.1.2.4.2 snj .%T Network Time Protocol (Version 2) 852 1.1.1.2.4.2 snj .%O RFC1119 853 1.1.1.2.4.2 snj .Re 854 1.1.1.2.4.2 snj .Rs 855 1.1.1.2.4.2 snj .%A David L. Mills 856 1.1.1.2.4.2 snj .%T Network Time Protocol (Version 3) 857 1.1.1.2.4.2 snj .%O RFC1305 858 1.1.1.2.4.2 snj .Re 859 1.1.1.2.4.2 snj .Rs 860 1.1.1.2.4.2 snj .%A David L. Mills 861 1.1.1.2.4.2 snj .%A J. Martin, Ed. 862 1.1.1.2.4.2 snj .%A J. Burbank 863 1.1.1.2.4.2 snj .%A W. Kasch 864 1.1.1.2.4.2 snj .%T Network Time Protocol Version 4: Protocol and Algorithms Specification 865 1.1.1.2.4.2 snj .%O RFC5905 866 1.1.1.2.4.2 snj .Re 867 1.1.1.2.4.2 snj .Rs 868 1.1.1.2.4.2 snj .%A David L. Mills 869 1.1.1.2.4.2 snj .%A B. Haberman, Ed. 870 1.1.1.2.4.2 snj .%T Network Time Protocol Version 4: Autokey Specification 871 1.1.1.2.4.2 snj .%O RFC5906 872 1.1.1.2.4.2 snj .Re 873 1.1.1.2.4.2 snj .Rs 874 1.1.1.2.4.2 snj .%A H. Gerstung 875 1.1.1.2.4.2 snj .%A C. Elliott 876 1.1.1.2.4.2 snj .%A B. Haberman, Ed. 877 1.1.1.2.4.2 snj .%T Definitions of Managed Objects for Network Time Protocol Version 4: (NTPv4) 878 1.1.1.2.4.2 snj .%O RFC5907 879 1.1.1.2.4.2 snj .Re 880 1.1.1.2.4.2 snj .Rs 881 1.1.1.2.4.2 snj .%A R. Gayraud 882 1.1.1.2.4.2 snj .%A B. Lourdelet 883 1.1.1.2.4.2 snj .%T Network Time Protocol (NTP) Server Option for DHCPv6 884 1.1.1.2.4.2 snj .%O RFC5908 885 1.1.1.2.4.2 snj .Re 886 1.1.1.2.4.2 snj .Sh "AUTHORS" 887 1.1.1.2.4.3 snj The University of Delaware and Network Time Foundation 888 1.1.1.2.4.2 snj .Sh "COPYRIGHT" 889 1.1.1.2.4.3 snj Copyright (C) 1992\-2015 The University of Delaware and Network Time Foundation all rights reserved. 890 1.1.1.2.4.2 snj This program is released under the terms of the NTP license, <http://ntp.org/license>. 891 1.1.1.2.4.2 snj .Sh BUGS 892 1.1.1.2.4.2 snj The 893 1.1.1.2.4.2 snj .Nm 894 1.1.1.2.4.2 snj utility has gotten rather fat. 895 1.1.1.2.4.2 snj While not huge, it has gotten 896 1.1.1.2.4.2 snj larger than might be desirable for an elevated\-priority 897 1.1.1.2.4.2 snj .Nm 898 1.1.1.2.4.2 snj running on a workstation, particularly since many of 899 1.1.1.2.4.2 snj the fancy features which consume the space were designed more with 900 1.1.1.2.4.2 snj a busy primary server, rather than a high stratum workstation in 901 1.1.1.2.4.2 snj mind. 902 1.1.1.2.4.2 snj .Pp 903 1.1.1.2.4.2 snj Please send bug reports to: http://bugs.ntp.org, bugs (a] ntp.org 904 1.1.1.2.4.2 snj .Sh NOTES 905 1.1.1.2.4.2 snj Portions of this document came from FreeBSD. 906 1.1.1.2.4.2 snj .Pp 907 1.1.1.2.4.2 snj This manual page was \fIAutoGen\fP\-erated from the \fBntpd\fP 908 1.1.1.2.4.2 snj option definitions. 909
Indexes created Mon Aug 24 00:24:59 UTC 2026