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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
     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 fil-ter filter
     ter and selection algorithms are applied to select the best of these.  Note that the accuracy and reli-ability reliability
     ability 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 off-set offset
             set 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 function as the value authdelay, in
             seconds and fraction (see ntpd(8) for details).  This number is usually small enough to be neg-ligible negligible
             ligible 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 val-ues values
             ues 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 convenience 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 identification 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 ini-tially initially
     tially 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 daemon, which uses sophisticated algorithms to maximize accuracy and reliability while min-imizing minimizing
     imizing 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).

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

SEE ALSO
     ntpd(8)

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 kern.clockrate.tick and kern.clockrate.tickadj.

BSD                             January 6, 2000                            BSD