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


     ntpdate -- set the date and time via NTP


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


     Note: The functionality of this program is now available in the ntpd(8)
     program.  See the -q command line option in the ntpd(8) page.  After a
     suitable period of mourning, the ntpdate utility is to be retired from
     this distribution.

     The ntpdate utility 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 number of polls each time it is run and the
     interval between runs.

     The following options are available:

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

     -B      Force the time to always be slewed using the adjtime(2) system
             call, even if the measured offset is greater than +-128 ms.  The
             default is to step the time using settimeofday(2) if the offset
             is greater than +-128 ms.  Note that, if the offset is much
             greater than +-128 ms in this case, 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.

     -b      Force the time to be stepped using the settimeofday(2) system
             call, rather than slewed (default) using the adjtime(2) 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 func-
             tion as the value authdelay, in seconds and fraction (see ntpd(8)
             for details).  This number is usually small enough to be negligi-
             ble 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(8).

     -o version
             Specify the NTP version for outgoint 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(3) facility.  This is designed primarily for conve-
             nience of cron(8) 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 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.

     -v      Be verbose.  This option will cause ntpdate's version identifica-
             tion string to be logged.

     The ntpdate utility 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(8).  It is also possible to run
     ntpdate from a cron(8) script.  However, it is important to note that
     ntpdate with contrived cron(8) scripts is no substitute for the NTP dae-
     mon, which uses sophisticated algorithms to maximize accuracy and relia-
     bility while minimizing resource use.  Finally, since ntpdate does not
     discipline the host clock frequency as does ntpd(8), 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(8) every hour or two.

     The ntpdate utility will decline to set the date if an NTP server daemon
     (e.g., ntpd(8)) is running on the same host.  When running ntpdate on a
     regular basis from cron(8) 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.  ntpd(8).


     /etc/ntp.keys  contains the encryption keys used by ntpdate.




     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 kern.clockrate.tick and

BSD                             January 6, 2000                            BSD

Mac OS X 10.7 - Generated Tue Sep 6 06:04:09 CDT 2011
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