ntpdate(8)						      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

       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 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 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.

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 authentication 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 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 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 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 unpriv-
	      ileged 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)