$FreeBSD: head/usr.sbin/ntp/doc/ntpd.8 61944 2000-06-22 08:45:59Z sheldonh $
.Dd January 10, 2000 .Dt NTPD 8 .Os .Sh NAME .Nm ntpd .Nd Network Time Protocol (NTP) daemon .Sh SYNOPSIS .Nm ntpd .Op Fl aAbdgmx .Op Fl c Ar conffile .Op Fl f Ar driftfile .Op Fl k Ar keyfile .Op Fl l Ar logfile .Op Fl p Ar pidfile .Op Fl r Ar broadcastdelay .Op Fl s Ar statsdir .Op Fl t Ar trustedkey .Op Fl v Ar variable .Op Fl V Ar variable .Sh DESCRIPTION .Nm is an operating system daemon which sets and maintains the system time-of-day in synchronism with Internet standard time servers. .Nm is a complete implementation of the Network Time Protocol (NTP) version 4, but also retains compatibility with version 3, as defined by RFC 1305, and version 1 and 2, as defined by RFC 1059 and RFC 1119, respectively. .Nm does most computations in 64-bit floating point arithmetic and does relatively clumsy 64-bit fixed point operations only when necessary to preserve the ultimate precision, about 232 picoseconds. While the ultimate precision is not achievable with ordinary workstations and networks of today, it may be required with future nanosecond CPU clocks and gigabit LANs.
p The daemon can operate in any of several modes, including symmetric active/passive, client/server broadcast/multicast and manycast. A broadcast/multicast or manycast client can discover remote servers, compute server-client propagation delay correction factors and configure itself automatically. This makes it possible to deploy a fleet of workstations without specifying configuration details specific to the local environment.
p Ordinarily, .Nm reads the .Xr ntp.conf 5 configuration file at startup time in order to determine the synchronization sources and operating modes. It is also possible to specify a working, although limited, configuration entirely on the command line, obviating the need for a configuration file. This may be particularly appropriate when the local host is to be configured as a broadcast/multicast client or manycast client, with all peers being determined by listening to broadcasts at run time.
p If NetInfo support is built into .Nm Ns , then .Nm will attempt to read its configuration from the NetInfo if the default configuration file cannot be read and no file is specified by the .Fl c option.
p Various internal .Nm variables can be displayed and configuration options altered while the daemon is running through use of the .Xr ntpq 8 and .Xr ntpdc 8 programs.
p When .Nm starts it looks at the value of .Xr umask 2 and if it is zero, .Nm will set it to 022.
p The following command line options are available: l -tag -width indent t Fl a Enable authentication mode (default). t Fl A Disable authentication mode. t Fl b Synchronize using NTP broadcast messages. t Fl c Ar conffile Specify the name and path of the configuration file. t Fl d Specify debugging mode. This flag may occur multiple times, with each occurrence indicating greater detail of display. t Fl D Ar level Specify debugging level directly. t Fl f Ar driftfile Specify the name and path of the drift file. t Fl g Normally, the daemon exits if the offset exceeds a 1000 s sanity limit. This option overrides this limit and allows the time to be set to any value without restriction; however, this can happen only once. After that, the daemon will exit if the limit is exceeded. t Fl k Ar keyfile Specify the name and path of the file containing the NTP authentication keys. t Fl l Ar logfile Specify the name and path of the log file. The default is the system log facility. t Fl m Synchronize using NTP multicast messages on the IP multicast group address 224.0.1.1 (requires multicast kernel). t Fl p Ar pidfile Specify the name and path to record the daemon's process ID. t Fl P Override the priority limit set by the operating system. Not recommended for sissies. t Fl r Ar broadcastdelay Specify the default propagation delay between the broadcast/multicast server and this computer. This is necessary only if the delay cannot be computed automatically by the protocol. t Fl s Ar statsdir Specify the directory path for files created by the statistics facility. t Fl t Ar key Add a key number to the trusted key list. t Fl v Ar variable t Fl V Ar variable Add a system variable listed by default. t Fl x Ordinarily, if the time is to be adjusted more than 128 ms, it is stepped, not gradually slewed. This option forces the time to be slewed in all cases. Note: since the slew rate is limited to 0.5 ms/s, each second of adjustment requires an amortization interval of 2000 s. Thus, an adjustment of many seconds can take hours or days to amortize. .El .Ss Variables Most variables used by the NTP protocol can be examined with .Xr ntpdc 8 (mode 7 messages) and .Xr ntpq 8 (mode 6 messages). Currently, very few variables can be modified via mode 6 messages. These variables are either created with the c setvar directive (described in the .Qq Miscellaneous Options section of the .Xr ntp.conf 5 page) or the leap warning bits. The leap warning bits can be set in the .Va leapwarning variable up to one month ahead. Both the .Va leapwarning and .Va leapindication variables have a slightly different encoding than the usual leap bits interpretation:
p l -tag -width indent -compact t 00 The daemon passes the leap bits of its synchronization source (usual mode of operation). t 01 t 10 A leap second is added/deleted (operator forced leap second). t 11 Leap information from the synchronizations source is ignored (thus .Dv LEAP_NOWARNING is passed on). .El .Sh FILES l -tag -width /etc/ntp.drift -compact t Pa /etc/ntp.conf the default name of the configuration file t Pa /etc/ntp.drift the default name of the drift file t Pa /etc/ntp.keys the default name of the key file .El .Sh SEE ALSO .Xr ntp.conf 5 , .Xr ntpdate 8 , .Xr ntpdc 8 , .Xr ntpq 8
p In addition to the manual pages provided, comprehensive documentation is available on the world wide web at .Li http://www.ntp.org/ . A snapshot of this documentation is available in HTML format in
a /usr/share/doc/ntp . .Rs .%A David L. Mills .%T Network Time Protocol (Version 1) .%O RFC1059 .Re .Rs .%A David L. Mills .%T Network Time Protocol (Version 2) .%O RFC1119 .Re .Rs .%A David L. Mills .%T Network Time Protocol (Version 3) .%O RFC1305 .Re .Sh HISTORY Written by .An Dennis Ferguson at the University of Toronto. Text amended by .An David Mills at the University of Delaware. .Sh BUGS .Nm has gotten rather fat. While not huge, it has gotten larger than might be desireable for an elevated-priority daemon running on a workstation, particularly since many of the fancy features which consume the space were designed more with a busy primary server, rather than a high stratum workstation, in mind.