ntpd.1ntpdmdoc revision 1.1.1.2.2.2
1 1.1.1.2.2.2 snj .Dd December 19 2014 2 1.1.1.2.2.2 snj .Dt NTPD 1ntpdmdoc User Commands 3 1.1.1.2.2.2 snj .Os 4 1.1.1.2.2.2 snj .\" EDIT THIS FILE WITH CAUTION (ntpd-opts.mdoc) 5 1.1.1.2.2.2 snj .\" 6 1.1.1.2.2.2 snj .\" It has been AutoGen-ed December 19, 2014 at 07:49:14 AM by AutoGen 5.18.5pre4 7 1.1.1.2.2.2 snj .\" From the definitions ntpd-opts.def 8 1.1.1.2.2.2 snj .\" and the template file agmdoc-cmd.tpl 9 1.1.1.2.2.2 snj .Sh NAME 10 1.1.1.2.2.2 snj .Nm ntpd 11 1.1.1.2.2.2 snj .Nd NTP daemon program 12 1.1.1.2.2.2 snj .Sh SYNOPSIS 13 1.1.1.2.2.2 snj .Nm 14 1.1.1.2.2.2 snj .\" Mixture of short (flag) options and long options 15 1.1.1.2.2.2 snj .Op Fl flags 16 1.1.1.2.2.2 snj .Op Fl flag Op Ar value 17 1.1.1.2.2.2 snj .Op Fl \-option\-name Ns Oo Oo Ns "=| " Oc Ns Ar value Oc 18 1.1.1.2.2.2 snj [ <server1> ... <serverN> ] 19 1.1.1.2.2.2 snj .Pp 20 1.1.1.2.2.2 snj .Sh DESCRIPTION 21 1.1.1.2.2.2 snj The 22 1.1.1.2.2.2 snj .Nm 23 1.1.1.2.2.2 snj utility is an operating system daemon which sets 24 1.1.1.2.2.2 snj and maintains the system time of day in synchronism with Internet 25 1.1.1.2.2.2 snj standard time servers. 26 1.1.1.2.2.2 snj It is a complete implementation of the 27 1.1.1.2.2.2 snj Network Time Protocol (NTP) version 4, as defined by RFC\-5905, 28 1.1.1.2.2.2 snj but also retains compatibility with 29 1.1.1.2.2.2 snj version 3, as defined by RFC\-1305, and versions 1 30 1.1.1.2.2.2 snj and 2, as defined by RFC\-1059 and RFC\-1119, respectively. 31 1.1.1.2.2.2 snj .Pp 32 1.1.1.2.2.2 snj The 33 1.1.1.2.2.2 snj .Nm 34 1.1.1.2.2.2 snj utility does most computations in 64\-bit floating point 35 1.1.1.2.2.2 snj arithmetic and does relatively clumsy 64\-bit fixed point operations 36 1.1.1.2.2.2 snj only when necessary to preserve the ultimate precision, about 232 37 1.1.1.2.2.2 snj picoseconds. 38 1.1.1.2.2.2 snj While the ultimate precision is not achievable with 39 1.1.1.2.2.2 snj ordinary workstations and networks of today, it may be required 40 1.1.1.2.2.2 snj with future gigahertz CPU clocks and gigabit LANs. 41 1.1.1.2.2.2 snj .Pp 42 1.1.1.2.2.2 snj Ordinarily, 43 1.1.1.2.2.2 snj .Nm 44 1.1.1.2.2.2 snj reads the 45 1.1.1.2.2.2 snj .Xr ntp.conf 5 46 1.1.1.2.2.2 snj configuration file at startup time in order to determine the 47 1.1.1.2.2.2 snj synchronization sources and operating modes. 48 1.1.1.2.2.2 snj It is also possible to 49 1.1.1.2.2.2 snj specify a working, although limited, configuration entirely on the 50 1.1.1.2.2.2 snj command line, obviating the need for a configuration file. 51 1.1.1.2.2.2 snj This may 52 1.1.1.2.2.2 snj be particularly useful when the local host is to be configured as a 53 1.1.1.2.2.2 snj broadcast/multicast client, with all peers being determined by 54 1.1.1.2.2.2 snj listening to broadcasts at run time. 55 1.1.1.2.2.2 snj .Pp 56 1.1.1.2.2.2 snj If NetInfo support is built into 57 1.1.1.2.2.2 snj .Nm , 58 1.1.1.2.2.2 snj then 59 1.1.1.2.2.2 snj .Nm 60 1.1.1.2.2.2 snj will attempt to read its configuration from the 61 1.1.1.2.2.2 snj NetInfo if the default 62 1.1.1.2.2.2 snj .Xr ntp.conf 5 63 1.1.1.2.2.2 snj file cannot be read and no file is 64 1.1.1.2.2.2 snj specified by the 65 1.1.1.2.2.2 snj .Fl c 66 1.1.1.2.2.2 snj option. 67 1.1.1.2.2.2 snj .Pp 68 1.1.1.2.2.2 snj Various internal 69 1.1.1.2.2.2 snj .Nm 70 1.1.1.2.2.2 snj variables can be displayed and 71 1.1.1.2.2.2 snj configuration options altered while the 72 1.1.1.2.2.2 snj .Nm 73 1.1.1.2.2.2 snj is running 74 1.1.1.2.2.2 snj using the 75 1.1.1.2.2.2 snj .Xr ntpq 1ntpqmdoc 76 1.1.1.2.2.2 snj and 77 1.1.1.2.2.2 snj .Xr ntpdc 1ntpdcmdoc 78 1.1.1.2.2.2 snj utility programs. 79 1.1.1.2.2.2 snj .Pp 80 1.1.1.2.2.2 snj When 81 1.1.1.2.2.2 snj .Nm 82 1.1.1.2.2.2 snj starts it looks at the value of 83 1.1.1.2.2.2 snj .Xr umask 2 , 84 1.1.1.2.2.2 snj and if zero 85 1.1.1.2.2.2 snj .Nm 86 1.1.1.2.2.2 snj will set the 87 1.1.1.2.2.2 snj .Xr umask 2 88 1.1.1.2.2.2 snj to 022. 89 1.1.1.2.2.2 snj .Sh "OPTIONS" 90 1.1.1.2.2.2 snj .Bl -tag 91 1.1.1.2.2.2 snj .It Fl 4 , Fl \-ipv4 92 1.1.1.2.2.2 snj Force IPv4 DNS name resolution. 93 1.1.1.2.2.2 snj This option must not appear in combination with any of the following options: 94 1.1.1.2.2.2 snj ipv6. 95 1.1.1.2.2.2 snj .sp 96 1.1.1.2.2.2 snj Force DNS resolution of following host names on the command line 97 1.1.1.2.2.2 snj to the IPv4 namespace. 98 1.1.1.2.2.2 snj .It Fl 6 , Fl \-ipv6 99 1.1.1.2.2.2 snj Force IPv6 DNS name resolution. 100 1.1.1.2.2.2 snj This option must not appear in combination with any of the following options: 101 1.1.1.2.2.2 snj ipv4. 102 1.1.1.2.2.2 snj .sp 103 1.1.1.2.2.2 snj Force DNS resolution of following host names on the command line 104 1.1.1.2.2.2 snj to the IPv6 namespace. 105 1.1.1.2.2.2 snj .It Fl a , Fl \-authreq 106 1.1.1.2.2.2 snj Require crypto authentication. 107 1.1.1.2.2.2 snj This option must not appear in combination with any of the following options: 108 1.1.1.2.2.2 snj authnoreq. 109 1.1.1.2.2.2 snj .sp 110 1.1.1.2.2.2 snj Require cryptographic authentication for broadcast client, 111 1.1.1.2.2.2 snj multicast client and symmetric passive associations. 112 1.1.1.2.2.2 snj This is the default. 113 1.1.1.2.2.2 snj .It Fl A , Fl \-authnoreq 114 1.1.1.2.2.2 snj Do not require crypto authentication. 115 1.1.1.2.2.2 snj This option must not appear in combination with any of the following options: 116 1.1.1.2.2.2 snj authreq. 117 1.1.1.2.2.2 snj .sp 118 1.1.1.2.2.2 snj Do not require cryptographic authentication for broadcast client, 119 1.1.1.2.2.2 snj multicast client and symmetric passive associations. 120 1.1.1.2.2.2 snj This is almost never a good idea. 121 1.1.1.2.2.2 snj .It Fl b , Fl \-bcastsync 122 1.1.1.2.2.2 snj Allow us to sync to broadcast servers. 123 1.1.1.2.2.2 snj .sp 124 1.1.1.2.2.2 snj .It Fl c Ar string , Fl \-configfile Ns = Ns Ar string 125 1.1.1.2.2.2 snj configuration file name. 126 1.1.1.2.2.2 snj .sp 127 1.1.1.2.2.2 snj The name and path of the configuration file, 128 1.1.1.2.2.2 snj \fI/etc/ntp.conf\fP 129 1.1.1.2.2.2 snj by default. 130 1.1.1.2.2.2 snj .It Fl d , Fl \-debug\-level 131 1.1.1.2.2.2 snj Increase debug verbosity level. 132 1.1.1.2.2.2 snj This option may appear an unlimited number of times. 133 1.1.1.2.2.2 snj .sp 134 1.1.1.2.2.2 snj .It Fl D Ar number , Fl \-set\-debug\-level Ns = Ns Ar number 135 1.1.1.2.2.2 snj Set the debug verbosity level. 136 1.1.1.2.2.2 snj This option may appear an unlimited number of times. 137 1.1.1.2.2.2 snj This option takes an integer number as its argument. 138 1.1.1.2.2.2 snj .sp 139 1.1.1.2.2.2 snj .It Fl f Ar string , Fl \-driftfile Ns = Ns Ar string 140 1.1.1.2.2.2 snj frequency drift file name. 141 1.1.1.2.2.2 snj .sp 142 1.1.1.2.2.2 snj The name and path of the frequency file, 143 1.1.1.2.2.2 snj \fI/etc/ntp.drift\fP 144 1.1.1.2.2.2 snj by default. 145 1.1.1.2.2.2 snj This is the same operation as the 146 1.1.1.2.2.2 snj \fBdriftfile\fP \fIdriftfile\fP 147 1.1.1.2.2.2 snj configuration specification in the 148 1.1.1.2.2.2 snj \fI/etc/ntp.conf\fP 149 1.1.1.2.2.2 snj file. 150 1.1.1.2.2.2 snj .It Fl g , Fl \-panicgate 151 1.1.1.2.2.2 snj Allow the first adjustment to be Big. 152 1.1.1.2.2.2 snj This option may appear an unlimited number of times. 153 1.1.1.2.2.2 snj .sp 154 1.1.1.2.2.2 snj Normally, 155 1.1.1.2.2.2 snj \fBntpd\fP 156 1.1.1.2.2.2 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 1.1.1.2.2.2 snj \fBntpd\fP 158 1.1.1.2.2.2 snj will exit with a message to the system log. This option can be used with the 159 1.1.1.2.2.2 snj \fB\-q\fP 160 1.1.1.2.2.2 snj and 161 1.1.1.2.2.2 snj \fB\-x\fP 162 1.1.1.2.2.2 snj options. 163 1.1.1.2.2.2 snj See the 164 1.1.1.2.2.2 snj \fBtinker\fP 165 1.1.1.2.2.2 snj configuration file directive for other options. 166 1.1.1.2.2.2 snj .It Fl i Ar string , Fl \-jaildir Ns = Ns Ar string 167 1.1.1.2.2.2 snj Jail directory. 168 1.1.1.2.2.2 snj .sp 169 1.1.1.2.2.2 snj Chroot the server to the directory 170 1.1.1.2.2.2 snj \fIjaildir\fP 171 1.1.1.2.2.2 snj . 172 1.1.1.2.2.2 snj This option also implies that the server attempts to drop root privileges at startup. 173 1.1.1.2.2.2 snj You may need to also specify a 174 1.1.1.2.2.2 snj \fB\-u\fP 175 1.1.1.2.2.2 snj option. 176 1.1.1.2.2.2 snj This option is only available if the OS supports adjusting the clock 177 1.1.1.2.2.2 snj without full root privileges. 178 1.1.1.2.2.2 snj This option is supported under NetBSD (configure with 179 1.1.1.2.2.2 snj \fB\-\-enable\-clockctl\fP) or Linux (configure with 180 1.1.1.2.2.2 snj \fB\-\-enable\-linuxcaps\fP) or Solaris (configure with \fB\-\-enable\-solarisprivs\fP). 181 1.1.1.2.2.2 snj .It Fl I Ar iface , Fl \-interface Ns = Ns Ar iface 182 1.1.1.2.2.2 snj Listen on an interface name or address. 183 1.1.1.2.2.2 snj This option may appear an unlimited number of times. 184 1.1.1.2.2.2 snj .sp 185 1.1.1.2.2.2 snj Open the network address given, or all the addresses associated with the 186 1.1.1.2.2.2 snj given interface name. This option may appear multiple times. This option 187 1.1.1.2.2.2 snj also implies not opening other addresses, except wildcard and localhost. 188 1.1.1.2.2.2 snj This option is deprecated. Please consider using the configuration file 189 1.1.1.2.2.2 snj \fBinterface\fP command, which is more versatile. 190 1.1.1.2.2.2 snj .It Fl k Ar string , Fl \-keyfile Ns = Ns Ar string 191 1.1.1.2.2.2 snj path to symmetric keys. 192 1.1.1.2.2.2 snj .sp 193 1.1.1.2.2.2 snj Specify the name and path of the symmetric key file. 194 1.1.1.2.2.2 snj \fI/etc/ntp.keys\fP 195 1.1.1.2.2.2 snj is the default. 196 1.1.1.2.2.2 snj This is the same operation as the 197 1.1.1.2.2.2 snj \fBkeys\fP \fIkeyfile\fP 198 1.1.1.2.2.2 snj configuration file directive. 199 1.1.1.2.2.2 snj .It Fl l Ar string , Fl \-logfile Ns = Ns Ar string 200 1.1.1.2.2.2 snj path to the log file. 201 1.1.1.2.2.2 snj .sp 202 1.1.1.2.2.2 snj Specify the name and path of the log file. 203 1.1.1.2.2.2 snj The default is the system log file. 204 1.1.1.2.2.2 snj This is the same operation as the 205 1.1.1.2.2.2 snj \fBlogfile\fP \fIlogfile\fP 206 1.1.1.2.2.2 snj configuration file directive. 207 1.1.1.2.2.2 snj .It Fl L , Fl \-novirtualips 208 1.1.1.2.2.2 snj Do not listen to virtual interfaces. 209 1.1.1.2.2.2 snj .sp 210 1.1.1.2.2.2 snj Do not listen to virtual interfaces, defined as those with 211 1.1.1.2.2.2 snj names containing a colon. This option is deprecated. Please 212 1.1.1.2.2.2 snj consider using the configuration file \fBinterface\fP command, which 213 1.1.1.2.2.2 snj is more versatile. 214 1.1.1.2.2.2 snj .It Fl M , Fl \-modifymmtimer 215 1.1.1.2.2.2 snj Modify Multimedia Timer (Windows only). 216 1.1.1.2.2.2 snj .sp 217 1.1.1.2.2.2 snj Set the Windows Multimedia Timer to highest resolution. This 218 1.1.1.2.2.2 snj ensures the resolution does not change while ntpd is running, 219 1.1.1.2.2.2 snj avoiding timekeeping glitches associated with changes. 220 1.1.1.2.2.2 snj .It Fl n , Fl \-nofork 221 1.1.1.2.2.2 snj Do not fork. 222 1.1.1.2.2.2 snj This option must not appear in combination with any of the following options: 223 1.1.1.2.2.2 snj wait\-sync. 224 1.1.1.2.2.2 snj .sp 225 1.1.1.2.2.2 snj .It Fl N , Fl \-nice 226 1.1.1.2.2.2 snj Run at high priority. 227 1.1.1.2.2.2 snj .sp 228 1.1.1.2.2.2 snj To the extent permitted by the operating system, run 229 1.1.1.2.2.2 snj \fBntpd\fP 230 1.1.1.2.2.2 snj at the highest priority. 231 1.1.1.2.2.2 snj .It Fl p Ar string , Fl \-pidfile Ns = Ns Ar string 232 1.1.1.2.2.2 snj path to the PID file. 233 1.1.1.2.2.2 snj .sp 234 1.1.1.2.2.2 snj Specify the name and path of the file used to record 235 1.1.1.2.2.2 snj \fBntpd\fP's 236 1.1.1.2.2.2 snj process ID. 237 1.1.1.2.2.2 snj This is the same operation as the 238 1.1.1.2.2.2 snj \fBpidfile\fP \fIpidfile\fP 239 1.1.1.2.2.2 snj configuration file directive. 240 1.1.1.2.2.2 snj .It Fl P Ar number , Fl \-priority Ns = Ns Ar number 241 1.1.1.2.2.2 snj Process priority. 242 1.1.1.2.2.2 snj This option takes an integer number as its argument. 243 1.1.1.2.2.2 snj .sp 244 1.1.1.2.2.2 snj To the extent permitted by the operating system, run 245 1.1.1.2.2.2 snj \fBntpd\fP 246 1.1.1.2.2.2 snj at the specified 247 1.1.1.2.2.2 snj \fBsched_setscheduler(SCHED_FIFO)\fP 248 1.1.1.2.2.2 snj priority. 249 1.1.1.2.2.2 snj .It Fl q , Fl \-quit 250 1.1.1.2.2.2 snj Set the time and quit. 251 1.1.1.2.2.2 snj This option must not appear in combination with any of the following options: 252 1.1.1.2.2.2 snj saveconfigquit, wait\-sync. 253 1.1.1.2.2.2 snj .sp 254 1.1.1.2.2.2 snj \fBntpd\fP 255 1.1.1.2.2.2 snj will not daemonize and will exit after the clock is first 256 1.1.1.2.2.2 snj synchronized. This behavior mimics that of the 257 1.1.1.2.2.2 snj \fBntpdate\fP 258 1.1.1.2.2.2 snj program, which will soon be replaced with a shell script. 259 1.1.1.2.2.2 snj The 260 1.1.1.2.2.2 snj \fB\-g\fP 261 1.1.1.2.2.2 snj and 262 1.1.1.2.2.2 snj \fB\-x\fP 263 1.1.1.2.2.2 snj options can be used with this option. 264 1.1.1.2.2.2 snj Note: The kernel time discipline is disabled with this option. 265 1.1.1.2.2.2 snj .It Fl r Ar string , Fl \-propagationdelay Ns = Ns Ar string 266 1.1.1.2.2.2 snj Broadcast/propagation delay. 267 1.1.1.2.2.2 snj .sp 268 1.1.1.2.2.2 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. 269 1.1.1.2.2.2 snj .It Fl \-saveconfigquit Ns = Ns Ar string 270 1.1.1.2.2.2 snj Save parsed configuration and quit. 271 1.1.1.2.2.2 snj This option must not appear in combination with any of the following options: 272 1.1.1.2.2.2 snj quit, wait\-sync. 273 1.1.1.2.2.2 snj .sp 274 1.1.1.2.2.2 snj Cause \fBntpd\fP to parse its startup configuration file and save an 275 1.1.1.2.2.2 snj equivalent to the given filename and exit. This option was 276 1.1.1.2.2.2 snj designed for automated testing. 277 1.1.1.2.2.2 snj .It Fl s Ar string , Fl \-statsdir Ns = Ns Ar string 278 1.1.1.2.2.2 snj Statistics file location. 279 1.1.1.2.2.2 snj .sp 280 1.1.1.2.2.2 snj Specify the directory path for files created by the statistics facility. 281 1.1.1.2.2.2 snj This is the same operation as the 282 1.1.1.2.2.2 snj \fBstatsdir\fP \fIstatsdir\fP 283 1.1.1.2.2.2 snj configuration file directive. 284 1.1.1.2.2.2 snj .It Fl t Ar tkey , Fl \-trustedkey Ns = Ns Ar tkey 285 1.1.1.2.2.2 snj Trusted key number. 286 1.1.1.2.2.2 snj This option may appear an unlimited number of times. 287 1.1.1.2.2.2 snj .sp 288 1.1.1.2.2.2 snj Add the specified key number to the trusted key list. 289 1.1.1.2.2.2 snj .It Fl u Ar string , Fl \-user Ns = Ns Ar string 290 1.1.1.2.2.2 snj Run as userid (or userid:groupid). 291 1.1.1.2.2.2 snj .sp 292 1.1.1.2.2.2 snj Specify a user, and optionally a group, to switch to. 293 1.1.1.2.2.2 snj This option is only available if the OS supports adjusting the clock 294 1.1.1.2.2.2 snj without full root privileges. 295 1.1.1.2.2.2 snj This option is supported under NetBSD (configure with 296 1.1.1.2.2.2 snj \fB\-\-enable\-clockctl\fP) or Linux (configure with 297 1.1.1.2.2.2 snj \fB\-\-enable\-linuxcaps\fP) or Solaris (configure with \fB\-\-enable\-solarisprivs\fP). 298 1.1.1.2.2.2 snj .It Fl U Ar number , Fl \-updateinterval Ns = Ns Ar number 299 1.1.1.2.2.2 snj interval in seconds between scans for new or dropped interfaces. 300 1.1.1.2.2.2 snj This option takes an integer number as its argument. 301 1.1.1.2.2.2 snj .sp 302 1.1.1.2.2.2 snj Give the time in seconds between two scans for new or dropped interfaces. 303 1.1.1.2.2.2 snj For systems with routing socket support the scans will be performed shortly after the interface change 304 1.1.1.2.2.2 snj has been detected by the system. 305 1.1.1.2.2.2 snj Use 0 to disable scanning. 60 seconds is the minimum time between scans. 306 1.1.1.2.2.2 snj .It Fl \-var Ns = Ns Ar nvar 307 1.1.1.2.2.2 snj make ARG an ntp variable (RW). 308 1.1.1.2.2.2 snj This option may appear an unlimited number of times. 309 1.1.1.2.2.2 snj .sp 310 1.1.1.2.2.2 snj .It Fl \-dvar Ns = Ns Ar ndvar 311 1.1.1.2.2.2 snj make ARG an ntp variable (RW|DEF). 312 1.1.1.2.2.2 snj This option may appear an unlimited number of times. 313 1.1.1.2.2.2 snj .sp 314 1.1.1.2.2.2 snj .It Fl w Ar number , Fl \-wait\-sync Ns = Ns Ar number 315 1.1.1.2.2.2 snj Seconds to wait for first clock sync. 316 1.1.1.2.2.2 snj This option must not appear in combination with any of the following options: 317 1.1.1.2.2.2 snj nofork, quit, saveconfigquit. 318 1.1.1.2.2.2 snj This option takes an integer number as its argument. 319 1.1.1.2.2.2 snj .sp 320 1.1.1.2.2.2 snj If greater than zero, alters \fBntpd\fP's behavior when forking to 321 1.1.1.2.2.2 snj daemonize. Instead of exiting with status 0 immediately after 322 1.1.1.2.2.2 snj the fork, the parent waits up to the specified number of 323 1.1.1.2.2.2 snj seconds for the child to first synchronize the clock. The exit 324 1.1.1.2.2.2 snj status is zero (success) if the clock was synchronized, 325 1.1.1.2.2.2 snj otherwise it is \fBETIMEDOUT\fP. 326 1.1.1.2.2.2 snj This provides the option for a script starting \fBntpd\fP to easily 327 1.1.1.2.2.2 snj wait for the first set of the clock before proceeding. 328 1.1.1.2.2.2 snj .It Fl x , Fl \-slew 329 1.1.1.2.2.2 snj Slew up to 600 seconds. 330 1.1.1.2.2.2 snj .sp 331 1.1.1.2.2.2 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. 332 1.1.1.2.2.2 snj This option sets the threshold to 600 s, which is well within the accuracy window to set the clock manually. 333 1.1.1.2.2.2 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. 334 1.1.1.2.2.2 snj Thus, an adjustment as much as 600 s will take almost 14 days to complete. 335 1.1.1.2.2.2 snj This option can be used with the 336 1.1.1.2.2.2 snj \fB\-g\fP 337 1.1.1.2.2.2 snj and 338 1.1.1.2.2.2 snj \fB\-q\fP 339 1.1.1.2.2.2 snj options. 340 1.1.1.2.2.2 snj See the 341 1.1.1.2.2.2 snj \fBtinker\fP 342 1.1.1.2.2.2 snj configuration file directive for other options. 343 1.1.1.2.2.2 snj Note: The kernel time discipline is disabled with this option. 344 1.1.1.2.2.2 snj .It Fl \-usepcc 345 1.1.1.2.2.2 snj Use CPU cycle counter (Windows only). 346 1.1.1.2.2.2 snj .sp 347 1.1.1.2.2.2 snj Attempt to substitute the CPU counter for \fBQueryPerformanceCounter\fP. 348 1.1.1.2.2.2 snj The CPU counter and \fBQueryPerformanceCounter\fP are compared, and if 349 1.1.1.2.2.2 snj they have the same frequency, the CPU counter (RDTSC on x86) is 350 1.1.1.2.2.2 snj used directly, saving the overhead of a system call. 351 1.1.1.2.2.2 snj .It Fl \-pccfreq Ns = Ns Ar string 352 1.1.1.2.2.2 snj Force CPU cycle counter use (Windows only). 353 1.1.1.2.2.2 snj .sp 354 1.1.1.2.2.2 snj Force substitution the CPU counter for \fBQueryPerformanceCounter\fP. 355 1.1.1.2.2.2 snj The CPU counter (RDTSC on x86) is used unconditionally with the 356 1.1.1.2.2.2 snj given frequency (in Hz). 357 1.1.1.2.2.2 snj .It Fl m , Fl \-mdns 358 1.1.1.2.2.2 snj Register with mDNS as a NTP server. 359 1.1.1.2.2.2 snj .sp 360 1.1.1.2.2.2 snj Registers as an NTP server with the local mDNS server which allows 361 1.1.1.2.2.2 snj the server to be discovered via mDNS client lookup. 362 1.1.1.2.2.2 snj .It Fl \&? , Fl \-help 363 1.1.1.2.2.2 snj Display usage information and exit. 364 1.1.1.2.2.2 snj .It Fl \&! , Fl \-more\-help 365 1.1.1.2.2.2 snj Pass the extended usage information through a pager. 366 1.1.1.2.2.2 snj .It Fl \-version Op Brq Ar v|c|n 367 1.1.1.2.2.2 snj Output version of program and exit. The default mode is `v', a simple 368 1.1.1.2.2.2 snj version. The `c' mode will print copyright information and `n' will 369 1.1.1.2.2.2 snj print the full copyright notice. 370 1.1.1.2.2.2 snj .El 371 1.1.1.2.2.2 snj .Sh "OPTION PRESETS" 372 1.1.1.2.2.2 snj Any option that is not marked as \fInot presettable\fP may be preset 373 1.1.1.2.2.2 snj by loading values from environment variables named: 374 1.1.1.2.2.2 snj .nf 375 1.1.1.2.2.2 snj \fBNTPD_<option\-name>\fP or \fBNTPD\fP 376 1.1.1.2.2.2 snj .fi 377 1.1.1.2.2.2 snj .ad 378 1.1.1.2.2.2 snj .Sh USAGE 379 1.1.1.2.2.2 snj .Ss "How NTP Operates" 380 1.1.1.2.2.2 snj The 381 1.1.1.2.2.2 snj .Nm 382 1.1.1.2.2.2 snj utility operates by exchanging messages with 383 1.1.1.2.2.2 snj one or more configured servers over a range of designated poll intervals. 384 1.1.1.2.2.2 snj When 385 1.1.1.2.2.2 snj started, whether for the first or subsequent times, the program 386 1.1.1.2.2.2 snj requires several exchanges from the majority of these servers so 387 1.1.1.2.2.2 snj the signal processing and mitigation algorithms can accumulate and 388 1.1.1.2.2.2 snj groom the data and set the clock. 389 1.1.1.2.2.2 snj In order to protect the network 390 1.1.1.2.2.2 snj from bursts, the initial poll interval for each server is delayed 391 1.1.1.2.2.2 snj an interval randomized over a few seconds. 392 1.1.1.2.2.2 snj At the default initial poll 393 1.1.1.2.2.2 snj interval of 64s, several minutes can elapse before the clock is 394 1.1.1.2.2.2 snj set. 395 1.1.1.2.2.2 snj This initial delay to set the clock 396 1.1.1.2.2.2 snj can be safely and dramatically reduced using the 397 1.1.1.2.2.2 snj .Cm iburst 398 1.1.1.2.2.2 snj keyword with the 399 1.1.1.2.2.2 snj .Ic server 400 1.1.1.2.2.2 snj configuration 401 1.1.1.2.2.2 snj command, as described in 402 1.1.1.2.2.2 snj .Xr ntp.conf 5 . 403 1.1.1.2.2.2 snj .Pp 404 1.1.1.2.2.2 snj Most operating systems and hardware of today incorporate a 405 1.1.1.2.2.2 snj time\-of\-year (TOY) chip to maintain the time during periods when 406 1.1.1.2.2.2 snj the power is off. 407 1.1.1.2.2.2 snj When the machine is booted, the chip is used to 408 1.1.1.2.2.2 snj initialize the operating system time. 409 1.1.1.2.2.2 snj After the machine has 410 1.1.1.2.2.2 snj synchronized to a NTP server, the operating system corrects the 411 1.1.1.2.2.2 snj chip from time to time. 412 1.1.1.2.2.2 snj In the default case, if 413 1.1.1.2.2.2 snj .Nm 414 1.1.1.2.2.2 snj detects that the time on the host 415 1.1.1.2.2.2 snj is more than 1000s from the server time, 416 1.1.1.2.2.2 snj .Nm 417 1.1.1.2.2.2 snj assumes something must be terribly wrong and the only 418 1.1.1.2.2.2 snj reliable action is for the operator to intervene and set the clock 419 1.1.1.2.2.2 snj by hand. 420 1.1.1.2.2.2 snj (Reasons for this include there is no TOY chip, 421 1.1.1.2.2.2 snj or its battery is dead, or that the TOY chip is just of poor quality.) 422 1.1.1.2.2.2 snj This causes 423 1.1.1.2.2.2 snj .Nm 424 1.1.1.2.2.2 snj to exit with a panic message to 425 1.1.1.2.2.2 snj the system log. 426 1.1.1.2.2.2 snj The 427 1.1.1.2.2.2 snj .Fl g 428 1.1.1.2.2.2 snj option overrides this check and the 429 1.1.1.2.2.2 snj clock will be set to the server time regardless of the chip time 430 1.1.1.2.2.2 snj (up to 68 years in the past or future \(em 431 1.1.1.2.2.2 snj this is a limitation of the NTPv4 protocol). 432 1.1.1.2.2.2 snj However, and to protect against broken hardware, such as when the 433 1.1.1.2.2.2 snj CMOS battery fails or the clock counter becomes defective, once the 434 1.1.1.2.2.2 snj clock has been set an error greater than 1000s will cause 435 1.1.1.2.2.2 snj .Nm 436 1.1.1.2.2.2 snj to exit anyway. 437 1.1.1.2.2.2 snj .Pp 438 1.1.1.2.2.2 snj Under ordinary conditions, 439 1.1.1.2.2.2 snj .Nm 440 1.1.1.2.2.2 snj adjusts the clock in 441 1.1.1.2.2.2 snj small steps so that the timescale is effectively continuous and 442 1.1.1.2.2.2 snj without discontinuities. 443 1.1.1.2.2.2 snj Under conditions of extreme network 444 1.1.1.2.2.2 snj congestion, the roundtrip delay jitter can exceed three seconds and 445 1.1.1.2.2.2 snj the synchronization distance, which is equal to one\-half the 446 1.1.1.2.2.2 snj roundtrip delay plus error budget terms, can become very large. 447 1.1.1.2.2.2 snj The 448 1.1.1.2.2.2 snj .Nm 449 1.1.1.2.2.2 snj algorithms discard sample offsets exceeding 128 ms, 450 1.1.1.2.2.2 snj unless the interval during which no sample offset is less than 128 451 1.1.1.2.2.2 snj ms exceeds 900s. 452 1.1.1.2.2.2 snj The first sample after that, no matter what the 453 1.1.1.2.2.2 snj offset, steps the clock to the indicated time. 454 1.1.1.2.2.2 snj In practice this 455 1.1.1.2.2.2 snj reduces the false alarm rate where the clock is stepped in error to 456 1.1.1.2.2.2 snj a vanishingly low incidence. 457 1.1.1.2.2.2 snj .Pp 458 1.1.1.2.2.2 snj As the result of this behavior, once the clock has been set it 459 1.1.1.2.2.2 snj very rarely strays more than 128 ms even under extreme cases of 460 1.1.1.2.2.2 snj network path congestion and jitter. 461 1.1.1.2.2.2 snj Sometimes, in particular when 462 1.1.1.2.2.2 snj .Nm 463 1.1.1.2.2.2 snj is first started without a valid drift file 464 1.1.1.2.2.2 snj on a system with a large intrinsic drift 465 1.1.1.2.2.2 snj the error might grow to exceed 128 ms, 466 1.1.1.2.2.2 snj which would cause the clock to be set backwards 467 1.1.1.2.2.2 snj if the local clock time is more than 128 s 468 1.1.1.2.2.2 snj in the future relative to the server. 469 1.1.1.2.2.2 snj In some applications, this behavior may be unacceptable. 470 1.1.1.2.2.2 snj There are several solutions, however. 471 1.1.1.2.2.2 snj If the 472 1.1.1.2.2.2 snj .Fl x 473 1.1.1.2.2.2 snj option is included on the command line, the clock will 474 1.1.1.2.2.2 snj never be stepped and only slew corrections will be used. 475 1.1.1.2.2.2 snj But this choice comes with a cost that 476 1.1.1.2.2.2 snj should be carefully explored before deciding to use 477 1.1.1.2.2.2 snj the 478 1.1.1.2.2.2 snj .Fl x 479 1.1.1.2.2.2 snj option. 480 1.1.1.2.2.2 snj The maximum slew rate possible is limited 481 1.1.1.2.2.2 snj to 500 parts\-per\-million (PPM) as a consequence of the correctness 482 1.1.1.2.2.2 snj principles on which the NTP protocol and algorithm design are 483 1.1.1.2.2.2 snj based. 484 1.1.1.2.2.2 snj As a result, the local clock can take a long time to 485 1.1.1.2.2.2 snj converge to an acceptable offset, about 2,000 s for each second the 486 1.1.1.2.2.2 snj clock is outside the acceptable range. 487 1.1.1.2.2.2 snj During this interval the 488 1.1.1.2.2.2 snj local clock will not be consistent with any other network clock and 489 1.1.1.2.2.2 snj the system cannot be used for distributed applications that require 490 1.1.1.2.2.2 snj correctly synchronized network time. 491 1.1.1.2.2.2 snj .Pp 492 1.1.1.2.2.2 snj In spite of the above precautions, sometimes when large 493 1.1.1.2.2.2 snj frequency errors are present the resulting time offsets stray 494 1.1.1.2.2.2 snj outside the 128\-ms range and an eventual step or slew time 495 1.1.1.2.2.2 snj correction is required. 496 1.1.1.2.2.2 snj If following such a correction the 497 1.1.1.2.2.2 snj frequency error is so large that the first sample is outside the 498 1.1.1.2.2.2 snj acceptable range, 499 1.1.1.2.2.2 snj .Nm 500 1.1.1.2.2.2 snj enters the same state as when the 501 1.1.1.2.2.2 snj .Pa ntp.drift 502 1.1.1.2.2.2 snj file is not present. 503 1.1.1.2.2.2 snj The intent of this behavior 504 1.1.1.2.2.2 snj is to quickly correct the frequency and restore operation to the 505 1.1.1.2.2.2 snj normal tracking mode. 506 1.1.1.2.2.2 snj In the most extreme cases 507 1.1.1.2.2.2 snj (the host 508 1.1.1.2.2.2 snj .Cm time.ien.it 509 1.1.1.2.2.2 snj comes to mind), there may be occasional 510 1.1.1.2.2.2 snj step/slew corrections and subsequent frequency corrections. 511 1.1.1.2.2.2 snj It 512 1.1.1.2.2.2 snj helps in these cases to use the 513 1.1.1.2.2.2 snj .Cm burst 514 1.1.1.2.2.2 snj keyword when 515 1.1.1.2.2.2 snj configuring the server, but 516 1.1.1.2.2.2 snj ONLY 517 1.1.1.2.2.2 snj when you have permission to do so from the owner of the target host. 518 1.1.1.2.2.2 snj .Pp 519 1.1.1.2.2.2 snj Finally, 520 1.1.1.2.2.2 snj in the past many startup scripts would run 521 1.1.1.2.2.2 snj .Xr ntpdate 1ntpdatemdoc 522 1.1.1.2.2.2 snj to get the system clock close to correct before starting 523 1.1.1.2.2.2 snj .Xr ntpd 1ntpdmdoc , 524 1.1.1.2.2.2 snj but this was never more than a mediocre hack and is no longer needed. 525 1.1.1.2.2.2 snj If you are following the instructions in 526 1.1.1.2.2.2 snj .Sx "Starting NTP (Best Current Practice)" 527 1.1.1.2.2.2 snj and you still need to set the system time before starting 528 1.1.1.2.2.2 snj .Nm , 529 1.1.1.2.2.2 snj please open a bug report and document what is going on, 530 1.1.1.2.2.2 snj and then look at using 531 1.1.1.2.2.2 snj .Xr sntp 1sntpmdoc . 532 1.1.1.2.2.2 snj .Pp 533 1.1.1.2.2.2 snj There is a way to start 534 1.1.1.2.2.2 snj .Xr ntpd 1ntpdmdoc 535 1.1.1.2.2.2 snj that often addresses all of the problems mentioned above. 536 1.1.1.2.2.2 snj .Ss "Starting NTP (Best Current Practice)" 537 1.1.1.2.2.2 snj First, use the 538 1.1.1.2.2.2 snj .Cm iburst 539 1.1.1.2.2.2 snj option on your 540 1.1.1.2.2.2 snj .Cm server 541 1.1.1.2.2.2 snj entries. 542 1.1.1.2.2.2 snj .Pp 543 1.1.1.2.2.2 snj If you can also keep a good 544 1.1.1.2.2.2 snj .Pa ntp.drift 545 1.1.1.2.2.2 snj file then 546 1.1.1.2.2.2 snj .Xr ntpd 1ntpdmdoc 547 1.1.1.2.2.2 snj will effectively "warm\-start" and your system's clock will 548 1.1.1.2.2.2 snj be stable in under 11 seconds' time. 549 1.1.1.2.2.2 snj .Pp 550 1.1.1.2.2.2 snj As soon as possible in the startup sequence, start 551 1.1.1.2.2.2 snj .Xr ntpd 1ntpdmdoc 552 1.1.1.2.2.2 snj with at least the 553 1.1.1.2.2.2 snj .Fl g 554 1.1.1.2.2.2 snj and perhaps the 555 1.1.1.2.2.2 snj .Fl N 556 1.1.1.2.2.2 snj options. 557 1.1.1.2.2.2 snj Then, 558 1.1.1.2.2.2 snj start the rest of your "normal" processes. 559 1.1.1.2.2.2 snj This will give 560 1.1.1.2.2.2 snj .Xr ntpd 1ntpdmdoc 561 1.1.1.2.2.2 snj as much time as possible to get the system's clock synchronized and stable. 562 1.1.1.2.2.2 snj .Pp 563 1.1.1.2.2.2 snj Finally, 564 1.1.1.2.2.2 snj if you have processes like 565 1.1.1.2.2.2 snj .Cm dovecot 566 1.1.1.2.2.2 snj or database servers 567 1.1.1.2.2.2 snj that require 568 1.1.1.2.2.2 snj monotonically\-increasing time, 569 1.1.1.2.2.2 snj run 570 1.1.1.2.2.2 snj .Xr ntp\-wait 1ntp\-waitmdoc 571 1.1.1.2.2.2 snj as late as possible in the boot sequence 572 1.1.1.2.2.2 snj (perhaps with the 573 1.1.1.2.2.2 snj .Fl v 574 1.1.1.2.2.2 snj flag) 575 1.1.1.2.2.2 snj and after 576 1.1.1.2.2.2 snj .Xr ntp\-wait 1ntp\-waitmdoc 577 1.1.1.2.2.2 snj exits successfully 578 1.1.1.2.2.2 snj it is as safe as it will ever be to start any process that require 579 1.1.1.2.2.2 snj stable time. 580 1.1.1.2.2.2 snj .Ss "Frequency Discipline" 581 1.1.1.2.2.2 snj The 582 1.1.1.2.2.2 snj .Nm 583 1.1.1.2.2.2 snj behavior at startup depends on whether the 584 1.1.1.2.2.2 snj frequency file, usually 585 1.1.1.2.2.2 snj .Pa ntp.drift , 586 1.1.1.2.2.2 snj exists. 587 1.1.1.2.2.2 snj This file 588 1.1.1.2.2.2 snj contains the latest estimate of clock frequency error. 589 1.1.1.2.2.2 snj When the 590 1.1.1.2.2.2 snj .Nm 591 1.1.1.2.2.2 snj is started and the file does not exist, the 592 1.1.1.2.2.2 snj .Nm 593 1.1.1.2.2.2 snj enters a special mode designed to quickly adapt to 594 1.1.1.2.2.2 snj the particular system clock oscillator time and frequency error. 595 1.1.1.2.2.2 snj This takes approximately 15 minutes, after which the time and 596 1.1.1.2.2.2 snj frequency are set to nominal values and the 597 1.1.1.2.2.2 snj .Nm 598 1.1.1.2.2.2 snj enters 599 1.1.1.2.2.2 snj normal mode, where the time and frequency are continuously tracked 600 1.1.1.2.2.2 snj relative to the server. 601 1.1.1.2.2.2 snj After one hour the frequency file is 602 1.1.1.2.2.2 snj created and the current frequency offset written to it. 603 1.1.1.2.2.2 snj When the 604 1.1.1.2.2.2 snj .Nm 605 1.1.1.2.2.2 snj is started and the file does exist, the 606 1.1.1.2.2.2 snj .Nm 607 1.1.1.2.2.2 snj frequency is initialized from the file and enters normal mode 608 1.1.1.2.2.2 snj immediately. 609 1.1.1.2.2.2 snj After that the current frequency offset is written to 610 1.1.1.2.2.2 snj the file at hourly intervals. 611 1.1.1.2.2.2 snj .Ss "Operating Modes" 612 1.1.1.2.2.2 snj The 613 1.1.1.2.2.2 snj .Nm 614 1.1.1.2.2.2 snj utility can operate in any of several modes, including 615 1.1.1.2.2.2 snj symmetric active/passive, client/server broadcast/multicast and 616 1.1.1.2.2.2 snj manycast, as described in the 617 1.1.1.2.2.2 snj .Qq Association Management 618 1.1.1.2.2.2 snj page 619 1.1.1.2.2.2 snj (available as part of the HTML documentation 620 1.1.1.2.2.2 snj provided in 621 1.1.1.2.2.2 snj .Pa /usr/share/doc/ntp ) . 622 1.1.1.2.2.2 snj It normally operates continuously while 623 1.1.1.2.2.2 snj monitoring for small changes in frequency and trimming the clock 624 1.1.1.2.2.2 snj for the ultimate precision. 625 1.1.1.2.2.2 snj However, it can operate in a one\-time 626 1.1.1.2.2.2 snj mode where the time is set from an external server and frequency is 627 1.1.1.2.2.2 snj set from a previously recorded frequency file. 628 1.1.1.2.2.2 snj A 629 1.1.1.2.2.2 snj broadcast/multicast or manycast client can discover remote servers, 630 1.1.1.2.2.2 snj compute server\-client propagation delay correction factors and 631 1.1.1.2.2.2 snj configure itself automatically. 632 1.1.1.2.2.2 snj This makes it possible to deploy a 633 1.1.1.2.2.2 snj fleet of workstations without specifying configuration details 634 1.1.1.2.2.2 snj specific to the local environment. 635 1.1.1.2.2.2 snj .Pp 636 1.1.1.2.2.2 snj By default, 637 1.1.1.2.2.2 snj .Nm 638 1.1.1.2.2.2 snj runs in continuous mode where each of 639 1.1.1.2.2.2 snj possibly several external servers is polled at intervals determined 640 1.1.1.2.2.2 snj by an intricate state machine. 641 1.1.1.2.2.2 snj The state machine measures the 642 1.1.1.2.2.2 snj incidental roundtrip delay jitter and oscillator frequency wander 643 1.1.1.2.2.2 snj and determines the best poll interval using a heuristic algorithm. 644 1.1.1.2.2.2 snj Ordinarily, and in most operating environments, the state machine 645 1.1.1.2.2.2 snj will start with 64s intervals and eventually increase in steps to 646 1.1.1.2.2.2 snj 1024s. 647 1.1.1.2.2.2 snj A small amount of random variation is introduced in order to 648 1.1.1.2.2.2 snj avoid bunching at the servers. 649 1.1.1.2.2.2 snj In addition, should a server become 650 1.1.1.2.2.2 snj unreachable for some time, the poll interval is increased in steps 651 1.1.1.2.2.2 snj to 1024s in order to reduce network overhead. 652 1.1.1.2.2.2 snj .Pp 653 1.1.1.2.2.2 snj In some cases it may not be practical for 654 1.1.1.2.2.2 snj .Nm 655 1.1.1.2.2.2 snj to run continuously. 656 1.1.1.2.2.2 snj A common workaround has been to run the 657 1.1.1.2.2.2 snj .Xr ntpdate 1ntpdatemdoc 658 1.1.1.2.2.2 snj or 659 1.1.1.2.2.2 snj .Xr sntp 1sntpmdoc 660 1.1.1.2.2.2 snj programs from a 661 1.1.1.2.2.2 snj .Xr cron 8 662 1.1.1.2.2.2 snj job at designated 663 1.1.1.2.2.2 snj times. 664 1.1.1.2.2.2 snj However, these programs do not have the crafted signal 665 1.1.1.2.2.2 snj processing, error checking or mitigation algorithms of 666 1.1.1.2.2.2 snj .Nm . 667 1.1.1.2.2.2 snj The 668 1.1.1.2.2.2 snj .Fl q 669 1.1.1.2.2.2 snj option is intended for this purpose. 670 1.1.1.2.2.2 snj Setting this option will cause 671 1.1.1.2.2.2 snj .Nm 672 1.1.1.2.2.2 snj to exit just after 673 1.1.1.2.2.2 snj setting the clock for the first time. 674 1.1.1.2.2.2 snj The procedure for initially 675 1.1.1.2.2.2 snj setting the clock is the same as in continuous mode; most 676 1.1.1.2.2.2 snj applications will probably want to specify the 677 1.1.1.2.2.2 snj .Cm iburst 678 1.1.1.2.2.2 snj keyword with the 679 1.1.1.2.2.2 snj .Ic server 680 1.1.1.2.2.2 snj configuration command. 681 1.1.1.2.2.2 snj With this 682 1.1.1.2.2.2 snj keyword a volley of messages are exchanged to groom the data and 683 1.1.1.2.2.2 snj the clock is set in about 10 s. 684 1.1.1.2.2.2 snj If nothing is heard after a 685 1.1.1.2.2.2 snj couple of minutes, the daemon times out and exits. 686 1.1.1.2.2.2 snj After a suitable 687 1.1.1.2.2.2 snj period of mourning, the 688 1.1.1.2.2.2 snj .Xr ntpdate 1ntpdatemdoc 689 1.1.1.2.2.2 snj program will be 690 1.1.1.2.2.2 snj retired. 691 1.1.1.2.2.2 snj .Pp 692 1.1.1.2.2.2 snj When kernel support is available to discipline the clock 693 1.1.1.2.2.2 snj frequency, which is the case for stock Solaris, Tru64, Linux and 694 1.1.1.2.2.2 snj .Fx , 695 1.1.1.2.2.2 snj a useful feature is available to discipline the clock 696 1.1.1.2.2.2 snj frequency. 697 1.1.1.2.2.2 snj First, 698 1.1.1.2.2.2 snj .Nm 699 1.1.1.2.2.2 snj is run in continuous mode with 700 1.1.1.2.2.2 snj selected servers in order to measure and record the intrinsic clock 701 1.1.1.2.2.2 snj frequency offset in the frequency file. 702 1.1.1.2.2.2 snj It may take some hours for 703 1.1.1.2.2.2 snj the frequency and offset to settle down. 704 1.1.1.2.2.2 snj Then the 705 1.1.1.2.2.2 snj .Nm 706 1.1.1.2.2.2 snj is 707 1.1.1.2.2.2 snj stopped and run in one\-time mode as required. 708 1.1.1.2.2.2 snj At each startup, the 709 1.1.1.2.2.2 snj frequency is read from the file and initializes the kernel 710 1.1.1.2.2.2 snj frequency. 711 1.1.1.2.2.2 snj .Ss "Poll Interval Control" 712 1.1.1.2.2.2 snj This version of NTP includes an intricate state machine to 713 1.1.1.2.2.2 snj reduce the network load while maintaining a quality of 714 1.1.1.2.2.2 snj synchronization consistent with the observed jitter and wander. 715 1.1.1.2.2.2 snj There are a number of ways to tailor the operation in order enhance 716 1.1.1.2.2.2 snj accuracy by reducing the interval or to reduce network overhead by 717 1.1.1.2.2.2 snj increasing it. 718 1.1.1.2.2.2 snj However, the user is advised to carefully consider 719 1.1.1.2.2.2 snj the consequences of changing the poll adjustment range from the 720 1.1.1.2.2.2 snj default minimum of 64 s to the default maximum of 1,024 s. 721 1.1.1.2.2.2 snj The 722 1.1.1.2.2.2 snj default minimum can be changed with the 723 1.1.1.2.2.2 snj .Ic tinker 724 1.1.1.2.2.2 snj .Cm minpoll 725 1.1.1.2.2.2 snj command to a value not less than 16 s. 726 1.1.1.2.2.2 snj This value is used for all 727 1.1.1.2.2.2 snj configured associations, unless overridden by the 728 1.1.1.2.2.2 snj .Cm minpoll 729 1.1.1.2.2.2 snj option on the configuration command. 730 1.1.1.2.2.2 snj Note that most device drivers 731 1.1.1.2.2.2 snj will not operate properly if the poll interval is less than 64 s 732 1.1.1.2.2.2 snj and that the broadcast server and manycast client associations will 733 1.1.1.2.2.2 snj also use the default, unless overridden. 734 1.1.1.2.2.2 snj .Pp 735 1.1.1.2.2.2 snj In some cases involving dial up or toll services, it may be 736 1.1.1.2.2.2 snj useful to increase the minimum interval to a few tens of minutes 737 1.1.1.2.2.2 snj and maximum interval to a day or so. 738 1.1.1.2.2.2 snj Under normal operation 739 1.1.1.2.2.2 snj conditions, once the clock discipline loop has stabilized the 740 1.1.1.2.2.2 snj interval will be increased in steps from the minimum to the 741 1.1.1.2.2.2 snj maximum. 742 1.1.1.2.2.2 snj However, this assumes the intrinsic clock frequency error 743 1.1.1.2.2.2 snj is small enough for the discipline loop correct it. 744 1.1.1.2.2.2 snj The capture 745 1.1.1.2.2.2 snj range of the loop is 500 PPM at an interval of 64s decreasing by a 746 1.1.1.2.2.2 snj factor of two for each doubling of interval. 747 1.1.1.2.2.2 snj At a minimum of 1,024 748 1.1.1.2.2.2 snj s, for example, the capture range is only 31 PPM. 749 1.1.1.2.2.2 snj If the intrinsic 750 1.1.1.2.2.2 snj error is greater than this, the drift file 751 1.1.1.2.2.2 snj .Pa ntp.drift 752 1.1.1.2.2.2 snj will 753 1.1.1.2.2.2 snj have to be specially tailored to reduce the residual error below 754 1.1.1.2.2.2 snj this limit. 755 1.1.1.2.2.2 snj Once this is done, the drift file is automatically 756 1.1.1.2.2.2 snj updated once per hour and is available to initialize the frequency 757 1.1.1.2.2.2 snj on subsequent daemon restarts. 758 1.1.1.2.2.2 snj .Ss "The huff\-n'\-puff Filter" 759 1.1.1.2.2.2 snj In scenarios where a considerable amount of data are to be 760 1.1.1.2.2.2 snj downloaded or uploaded over telephone modems, timekeeping quality 761 1.1.1.2.2.2 snj can be seriously degraded. 762 1.1.1.2.2.2 snj This occurs because the differential 763 1.1.1.2.2.2 snj delays on the two directions of transmission can be quite large. 764 1.1.1.2.2.2 snj In 765 1.1.1.2.2.2 snj many cases the apparent time errors are so large as to exceed the 766 1.1.1.2.2.2 snj step threshold and a step correction can occur during and after the 767 1.1.1.2.2.2 snj data transfer is in progress. 768 1.1.1.2.2.2 snj .Pp 769 1.1.1.2.2.2 snj The huff\-n'\-puff filter is designed to correct the apparent time 770 1.1.1.2.2.2 snj offset in these cases. 771 1.1.1.2.2.2 snj It depends on knowledge of the propagation 772 1.1.1.2.2.2 snj delay when no other traffic is present. 773 1.1.1.2.2.2 snj In common scenarios this 774 1.1.1.2.2.2 snj occurs during other than work hours. 775 1.1.1.2.2.2 snj The filter maintains a shift 776 1.1.1.2.2.2 snj register that remembers the minimum delay over the most recent 777 1.1.1.2.2.2 snj interval measured usually in hours. 778 1.1.1.2.2.2 snj Under conditions of severe 779 1.1.1.2.2.2 snj delay, the filter corrects the apparent offset using the sign of 780 1.1.1.2.2.2 snj the offset and the difference between the apparent delay and 781 1.1.1.2.2.2 snj minimum delay. 782 1.1.1.2.2.2 snj The name of the filter reflects the negative (huff) 783 1.1.1.2.2.2 snj and positive (puff) correction, which depends on the sign of the 784 1.1.1.2.2.2 snj offset. 785 1.1.1.2.2.2 snj .Pp 786 1.1.1.2.2.2 snj The filter is activated by the 787 1.1.1.2.2.2 snj .Ic tinker 788 1.1.1.2.2.2 snj command and 789 1.1.1.2.2.2 snj .Cm huffpuff 790 1.1.1.2.2.2 snj keyword, as described in 791 1.1.1.2.2.2 snj .Xr ntp.conf 5 . 792 1.1.1.2.2.2 snj .Sh "ENVIRONMENT" 793 1.1.1.2.2.2 snj See \fBOPTION PRESETS\fP for configuration environment variables. 794 1.1.1.2.2.2 snj .Sh FILES 795 1.1.1.2.2.2 snj .Bl -tag -width /etc/ntp.drift -compact 796 1.1.1.2.2.2 snj .It Pa /etc/ntp.conf 797 1.1.1.2.2.2 snj the default name of the configuration file 798 1.1.1.2.2.2 snj .It Pa /etc/ntp.drift 799 1.1.1.2.2.2 snj the default name of the drift file 800 1.1.1.2.2.2 snj .It Pa /etc/ntp.keys 801 1.1.1.2.2.2 snj the default name of the key file 802 1.1.1.2.2.2 snj .El 803 1.1.1.2.2.2 snj .Sh "EXIT STATUS" 804 1.1.1.2.2.2 snj One of the following exit values will be returned: 805 1.1.1.2.2.2 snj .Bl -tag 806 1.1.1.2.2.2 snj .It 0 " (EXIT_SUCCESS)" 807 1.1.1.2.2.2 snj Successful program execution. 808 1.1.1.2.2.2 snj .It 1 " (EXIT_FAILURE)" 809 1.1.1.2.2.2 snj The operation failed or the command syntax was not valid. 810 1.1.1.2.2.2 snj .It 70 " (EX_SOFTWARE)" 811 1.1.1.2.2.2 snj libopts had an internal operational error. Please report 812 1.1.1.2.2.2 snj it to autogen\-users (a] lists.sourceforge.net. Thank you. 813 1.1.1.2.2.2 snj .El 814 1.1.1.2.2.2 snj .Sh "SEE ALSO" 815 1.1.1.2.2.2 snj .Xr ntp.conf 5 , 816 1.1.1.2.2.2 snj .Xr ntpdate 1ntpdatemdoc , 817 1.1.1.2.2.2 snj .Xr ntpdc 1ntpdcmdoc , 818 1.1.1.2.2.2 snj .Xr ntpq 1ntpqmdoc , 819 1.1.1.2.2.2 snj .Xr sntp 1sntpmdoc 820 1.1.1.2.2.2 snj .Pp 821 1.1.1.2.2.2 snj In addition to the manual pages provided, 822 1.1.1.2.2.2 snj comprehensive documentation is available on the world wide web 823 1.1.1.2.2.2 snj at 824 1.1.1.2.2.2 snj .Li http://www.ntp.org/ . 825 1.1.1.2.2.2 snj A snapshot of this documentation is available in HTML format in 826 1.1.1.2.2.2 snj .Pa /usr/share/doc/ntp . 827 1.1.1.2.2.2 snj .Rs 828 1.1.1.2.2.2 snj .%A David L. Mills 829 1.1.1.2.2.2 snj .%T Network Time Protocol (Version 1) 830 1.1.1.2.2.2 snj .%O RFC1059 831 1.1.1.2.2.2 snj .Re 832 1.1.1.2.2.2 snj .Rs 833 1.1.1.2.2.2 snj .%A David L. Mills 834 1.1.1.2.2.2 snj .%T Network Time Protocol (Version 2) 835 1.1.1.2.2.2 snj .%O RFC1119 836 1.1.1.2.2.2 snj .Re 837 1.1.1.2.2.2 snj .Rs 838 1.1.1.2.2.2 snj .%A David L. Mills 839 1.1.1.2.2.2 snj .%T Network Time Protocol (Version 3) 840 1.1.1.2.2.2 snj .%O RFC1305 841 1.1.1.2.2.2 snj .Re 842 1.1.1.2.2.2 snj .Rs 843 1.1.1.2.2.2 snj .%A David L. Mills 844 1.1.1.2.2.2 snj .%A J. Martin, Ed. 845 1.1.1.2.2.2 snj .%A J. Burbank 846 1.1.1.2.2.2 snj .%A W. Kasch 847 1.1.1.2.2.2 snj .%T Network Time Protocol Version 4: Protocol and Algorithms Specification 848 1.1.1.2.2.2 snj .%O RFC5905 849 1.1.1.2.2.2 snj .Re 850 1.1.1.2.2.2 snj .Rs 851 1.1.1.2.2.2 snj .%A David L. Mills 852 1.1.1.2.2.2 snj .%A B. Haberman, Ed. 853 1.1.1.2.2.2 snj .%T Network Time Protocol Version 4: Autokey Specification 854 1.1.1.2.2.2 snj .%O RFC5906 855 1.1.1.2.2.2 snj .Re 856 1.1.1.2.2.2 snj .Rs 857 1.1.1.2.2.2 snj .%A H. Gerstung 858 1.1.1.2.2.2 snj .%A C. Elliott 859 1.1.1.2.2.2 snj .%A B. Haberman, Ed. 860 1.1.1.2.2.2 snj .%T Definitions of Managed Objects for Network Time Protocol Version 4: (NTPv4) 861 1.1.1.2.2.2 snj .%O RFC5907 862 1.1.1.2.2.2 snj .Re 863 1.1.1.2.2.2 snj .Rs 864 1.1.1.2.2.2 snj .%A R. Gayraud 865 1.1.1.2.2.2 snj .%A B. Lourdelet 866 1.1.1.2.2.2 snj .%T Network Time Protocol (NTP) Server Option for DHCPv6 867 1.1.1.2.2.2 snj .%O RFC5908 868 1.1.1.2.2.2 snj .Re 869 1.1.1.2.2.2 snj .Sh "AUTHORS" 870 1.1.1.2.2.2 snj The University of Delaware 871 1.1.1.2.2.2 snj .Sh "COPYRIGHT" 872 1.1.1.2.2.2 snj Copyright (C) 1970\-2014 The University of Delaware all rights reserved. 873 1.1.1.2.2.2 snj This program is released under the terms of the NTP license, <http://ntp.org/license>. 874 1.1.1.2.2.2 snj .Sh BUGS 875 1.1.1.2.2.2 snj The 876 1.1.1.2.2.2 snj .Nm 877 1.1.1.2.2.2 snj utility has gotten rather fat. 878 1.1.1.2.2.2 snj While not huge, it has gotten 879 1.1.1.2.2.2 snj larger than might be desirable for an elevated\-priority 880 1.1.1.2.2.2 snj .Nm 881 1.1.1.2.2.2 snj running on a workstation, particularly since many of 882 1.1.1.2.2.2 snj the fancy features which consume the space were designed more with 883 1.1.1.2.2.2 snj a busy primary server, rather than a high stratum workstation in 884 1.1.1.2.2.2 snj mind. 885 1.1.1.2.2.2 snj .Pp 886 1.1.1.2.2.2 snj Please send bug reports to: http://bugs.ntp.org, bugs (a] ntp.org 887 1.1.1.2.2.2 snj .Sh NOTES 888 1.1.1.2.2.2 snj Portions of this document came from FreeBSD. 889 1.1.1.2.2.2 snj .Pp 890 1.1.1.2.2.2 snj This manual page was \fIAutoGen\fP\-erated from the \fBntpd\fP 891 1.1.1.2.2.2 snj option definitions. 892
Indexes created Sun Aug 23 00:25:02 UTC 2026