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Linux 2.6 - man page for ntpdate (linux section 8)

ntpdate(8)									       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 (unless the option -q 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  ntp-
       date 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  maxi-
       mize  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  lim-
       ited.

       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  set-
       timeofday() routine. If the error is less than 0.5 seconds, it will slew the time by call-
       ing the system adjtime() routine. The latter technique is less disruptive and  more  accu-
       rate  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 run-
       ning a daemon, doing so once every hour or two will result in precise  enough  timekeeping
       to avoid stepping the clock.

OPTIONS
       -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 authentica-
	      tion function.

       -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 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  sam-
	      ples, 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
	      facility. 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 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's version identification string to be
	      logged.

DIAGNOSTICS
       ntpdate's exit status is zero if it found a server and could update the clock, and nonzero
       otherwise.

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

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.

AUTHOR
       David L. Mills (mills@udel.edu)
       This manpage converted from html to roff by Fabrizio Polacco <fpolacco@debian.org>

SEE ALSO
       ntpdate-debian(8)

										       ntpdate(8)


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