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ntpdate(8)							    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 [...]

       ntpdate sets the local date and time by polling the Network Time Proto
       col (NTP) server(s) given as the server arguments to determine the cor
       rect time. It must be run as root on the local host. A number  of  sam
       ples  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  sophisti
       cated  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  ntp
       date 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.

       -a key Enable  the  authentication function and specify the key identi
	      fier 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

       -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.

       -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  func
	      tion  as	the value authdelay, in seconds and fraction (see ntpd
	      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 CPUs.

       -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 outgoint packets as the integer ver
	      sion, 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 - dont set the clock.

       -s     Divert logging output from the standard output (default) to  the
	      system  syslog  facility.  This is designed primarily for conve
	      nience 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 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 ntpdates version identifica
	      tion string to be logged.

       ntpdates exit status is zero if it finds  a  server  and  updates  the
       clock, and nonzero otherwise.

	      - 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 tick and tickadj.

       David L. Mills (mills@udel.edu)
       This manpage converted from html to  roff  by  Fabrizio	Polacco  


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