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NetBSD 6.1.5 - man page for ntpdate (netbsd section 8)

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NTPDATE(8)			   BSD System Manager's Manual			       NTPDATE(8)

NAME
     ntpdate -- set the date and time via NTP

SYNOPSIS
     ntpdate [-bBdoqsuv] [-a key] [-e authdelay] [-k keyfile] [-o version] [-p samples]
	     [-t timeout] [server ...]

DESCRIPTION
     ntpdate sets the local date and time by polling the Network Time Protocol (NTP) server(s)
     given as the server arguments to determine the correct time. It must be run as root on the
     local host. A number of samples are obtained from each of the servers specified and a subset
     of the NTP clock filter and selection algorithms are applied to select the best of these.
     Note that the accuracy and reliability of ntpdate depends on the number of servers, the num-
     ber of polls each time it is run and the interval between runs.

     ntpdate can be run manually as necessary to set the host clock, or it can be run from the
     host startup script to set the clock at boot time. This is useful in some cases to set the
     clock initially before starting the NTP daemon ntpd.  It is also possible to run ntpdate
     from a cron script. However, it is important to note that ntpdate with contrived cron
     scripts is no substitute for the NTP daemon, which uses sophisticated algorithms to maximize
     accuracy and reliability while minimizing resource use. Finally, since ntpdate does not dis-
     cipline the host clock frequency as does ntpd, the accuracy using ntpdate is limited.

     Time adjustments are made by ntpdate in one of two ways. If ntpdate determines the clock is
     in error more than 0.5 second it will simply step the time by calling the system
     settimeofday(2) routine. If the error is less than 0.5 seconds, it will slew the time by
     calling the system adjtime(2) routine. The latter technique is less disruptive and more
     accurate when the error is small, and works quite well when ntpdate is run by cron every
     hour or two.

     ntpdate will decline to set the date if an NTP server daemon (e.g., ntpd ) is running on the
     same host. When running ntpdate on a regular basis from cron as an alternative to running a
     daemon, doing so once every hour or two will result in precise enough timekeeping to avoid
     stepping the clock.

     If NetInfo support is compiled into ntpdate, then the server argument is optional if ntpdate
     can find a time server in the NetInfo configuration for ntpd

COMMAND LINE OPTIONS
     -a key  Enable the authentication function and specify the key identifier to be used for
	     authentication as the argument key ntpdate.  The keys and key identifiers must match
	     in both the client and server key files.  The default is to disable the authentica-
	     tion function.

     -B      Force the time to always be slewed using the adjtime() system call, even if the mea-
	     sured offset is greater than +-128 ms. The default is to step the time using set-
	     timeofday() if the offset is greater than +-128 ms. Note that, if the offset is much
	     greater than +-128 ms in this case, that it can take a long time (hours) to slew the
	     clock to the correct value. During this time. the host should not be used to syn-
	     chronize clients.

     -b      Force the time to be stepped using the settimeofday() system call, rather than
	     slewed (default) using the adjtime() system call. This option should be used when
	     called from a startup file at boot time.

     -d      Enable the debugging mode, in which ntpdate will go through all the steps, but not
	     adjust the local clock. Information useful for general debugging will also be
	     printed.

     -e authdelay
	     Specify the processing delay to perform an authentication function as the value
	     authdelay , in seconds and fraction (see ntpd for details). This number is usually
	     small enough to be negligible for most purposes, though specifying a value may
	     improve timekeeping on very slow CPU's.

     -k keyfile
	     Specify the path for the authentication key file as the string keyfile The default
	     is /etc/ntp.keys.	This file should be in the format described in ntpd

     -o version
	     Specify the NTP version for outgoing packets as the integer version , which can be 1
	     or 2. The default is 3. This allows ntpdate to be used with older NTP versions.

     -p samples
	     Specify the number of samples to be acquired from each server as the integer samples
	     , with values from 1 to 8 inclusive. The default is 4.

     -q      Query only - don't set the clock.

     -s      Divert logging output from the standard output (default) to the system syslog facil-
	     ity. This is designed primarily for convenience of cron scripts.

     -t timeout
	     Specify the maximum time waiting for a server response as the value timeout , in
	     seconds and fraction. The value is rounded to a multiple of 0.2 seconds.  The
	     default is 1 second, a value suitable for polling across a LAN.

     -u      Direct ntpdate to use an unprivileged port for outgoing packets.  This is most use-
	     ful when behind a firewall that blocks incoming traffic to privileged ports, and you
	     want to synchronise with hosts beyond the firewall. Note that the -d option always
	     uses unprivileged ports.

     -v      Be verbose. This option will cause ntpdate string to be logged.

FILES
     /etc/ntp.keys  encryption keys used by ntpdate.

AUTHORS
     David L. Mills (mills@udel.edu)

BUGS
     The slew adjustment is actually 50% larger than the measured offset, since this (it is
     argued) will tend to keep a badly drifting clock more accurate.  This is probably not a good
     idea and may cause a troubling hunt for some values of the kernel variables tick and
     tickadj.

BSD					 January 28, 2010				      BSD
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