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+.TH ntpdate 8
+.SH NAME
+ntpdate \- set the date and time via NTP
+.SH SYNOPSIS
+.B ntpdate 
+.RB [\| \-bBdoqsuv \|] 
+.RB [\| \-a 
+.IR key \|] 
+.RB [\| \-e 
+.IR authdelay \|] 
+.RB [\| \-k 
+.IR keyfile \|]
+.RB [\| \-o
+.IR version \|]
+.RB [\| \-p
+.IR samples \|]
+.RB [\| \-t
+.IR timeout \|]
+.IR server
+.RB [\| ... \|]
+.SH DESCRIPTION
+.B ntpdate 
+sets the local date and time by polling the Network Time
+Protocol (NTP) server(s) given as the
+.I server 
+arguments to determine
+the correct time. It must be run as root on the local host (unless the option \fB\-q\fR is used). 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 number 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 discipline
+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() routine. If the
+error is less than 0.5 seconds, it will slew the time by calling the
+system adjtime() 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.
+.SH OPTIONS
+.TP
+.BI \-a \ key
+Enable the authentication function and specify the key
+identifier to be used for authentication as the argument
+keyntpdate. The keys and key identifiers must match in both the
+client and server key files. The default is to disable the
+authentication function.
+.TP
+.B \-B
+Force the time to always be slewed using the adjtime() system
+call, even if the measured offset is greater than +-128 ms. The
+default is to step the time using settimeofday() 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 synchronize clients.
+.TP
+.B \-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.
+.TP
+.B \-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.
+.TP
+.BI \-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.
+.TP
+.BI \-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.
+.TP
+.BI \-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.
+.TP
+.BI \-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.
+.TP
+.B \-q
+Query only - don't set the clock.
+.TP
+.B \-s
+Divert logging output from the standard output (default) to the
+system syslog facility. This is designed primarily for
+convenience of cron scripts.
+.TP
+.BI \-t \ timeout
+Specify the maximum time waiting for a server response as the
+value timeout, in seconds and fraction. The value is is rounded
+to a multiple of 0.2 seconds. The default is 1 second, a value
+suitable for polling across a LAN.
+.TP
+.B \-u
+Direct ntpdate to use an unprivileged port for outgoing packets.
+This is most useful 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.
+.TP
+.B \-v
+Be verbose. This option will cause ntpdate's version
+identification string to be logged.
+.SH DIAGNOSTICS
+\fBntpdate\fP's exit status is zero if it found a server
+and could update the clock, and nonzero otherwise.
+.SH FILES
+.TP
+.I /etc/ntp.keys 
+\- encryption keys used by ntpdate.
+.SH 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.
+.SH AUTHOR
+David L. Mills (mills@udel.edu)
+.br
+This manpage converted from html to roff by 
+Fabrizio Polacco <fpolacco@debian.org>
+.SH "SEE ALSO"
+\fBntpdate\-debian\fR(8)