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xntpd- Network Time Protocol (NTP) daemon
xntpd [ -aAbdm ] [ -c conffile ] [ -f
driftfile ] [ -k keyfile ] [ -l logfile ] [
-p pidfile ] [ -r broadcastdelay ] [ -s
statsdir ] [ -t key ] [ -v variable ] [ -V
xntpd is an operating system daemon which sets and
maintains the system time-of-day in synchronism with Internet
standard time servers.
xntpd is a complete
implementation of the Network Time Protocol (NTP) version 3, as
defined by RFC-1305, but also retains compatibility with version 1
and 2 servers as defined by RFC- 1059 and RFC-1119,
xntpd does all computations in 64-bit
fixed point arithmetic and requires no floating point
support. While the ultimate precision of this design, about 232
picoseconds, is not achievable with ordinary workstations and
networks of today, it may be required with future nanosecond CPU
clocks and gigabit LANs.
The daemon can operate in any of several modes, including symmetric active/passive, client/server and broadcast/multicast, as described in RFC-1305. A broadcast/multicast 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.
xntpd reads the
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 or multicast client, with all
peers being determined by listening to broadcasts at run time.
xntpd variables can be displayed
and configuration options altered while the daemon is running
xntpdc utility programs.
xntpd starts it looks at the value of
umask, and if it's zero
xntpd will set
xntpd configuration file is read at initial startup
in order to specify the synchronization sources, modes and other related
information. Usually, it is installed in the
directory, but could be installed elsewhere (see the
conffile command line option). The file format is similar
to other Unix configuration files - comments begin with a
character and extend to the end of the line; blank lines are ignored.
Configuration commands consist of an initial keyword followed by a list
of arguments, some of which may be optional, separated by whitespace.
Commands may not be continued over multiple lines. Arguments may be host
names, host addresses written in numeric, dotted-quad form, integers,
floating point numbers (when specifying times in seconds) and text
strings. Optional arguments are delimited by
[ ] in the
following descriptions, while alternatives are separated by
|. The notation [ ... ] means an optional, indefinite
repetition of the last item before the [ ... ].
See the following pages for configuration and control options. While
there is a rich set of options available, the only required option is
one or more
server, peer or
described in the Configuration Options page. The
Notes on Configuring NTP and Setting up a NTP Subnet page contains
an extended discussion of these options.
Access Control Options
Reference Clock Options
/etc/ntp.conf - the default name of the configuration
/etc/ntp.drift - the default name of the drift file
/etc/ntp.keys - the default name of the key file
xntpd 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.