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ntpdate(8)							    ntpdate(8)



NAME
       ntpdate - set the date and time via NTP


       Disclaimer:  The	 functionality of this program is now available in the
       ntpd program. See the -q command line option in the ntpd - Network Time
       Protocol	 (NTP)	daemon	page. After a suitable period of mourning, the
       ntpdate program is to be retired from this distribution


SYNOPSIS
       ntpdate [ -46bBdqsuv ] [ -a key ] [ -e authdelay ] [ -k keyfile ] [  -o
       version ] [ -p samples ] [ -t timeout ] [ -U user_name ] server [ ... ]


DESCRIPTION
       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.

       Note  that  in  contexts	 where a host name is expected, a -4 qualifier
       preceding the host name forces DNS resolution to	 the  IPv4  namespace,
       while a -6 qualifier forces DNS resolution to the IPv6 namespace.

       If  NetInfo  support is compiled into ntpdate, then the server argument
       is optional if ntpdate can find a time server in the NetInfo configura-
       tion for ntpd.


COMMAND LINE OPTIONS
       -4      Force  DNS  resolution  of  following host names on the command
	       line to the IPv4 namespace.

       -6      Force DNS resolution of following host  names  on  the  command
	       line to the IPv6 namespace.

       -a key  Enable  the authentication function and specify the key identi-
	       fier 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() system
	       call, even if the measured offset is greater than +-500 ms. The
	       default	is to step the time using settimeofday() if the offset
	       is greater than +-500 ms. Note that,  if	 the  offset  is  much
	       greater	than  +-500  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 negli-
	       gible 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  4.  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	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	 pack-
	       ets.  This  is  most  useful when behind a firewall that blocks
	       incoming traffic to privileged ports, and you want to  synchro-
	       nize  with  hosts  beyond the firewall. Note that the -d option
	       always uses unprivileged ports.

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

       -U user_name
	       ntpdate	process	 drops	root privileges and changes user ID to
	       user_name and group ID to the primary group of server_user.


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.

SEE ALSO
       ntpd(8)

       Primary source of documentation: /usr/share/doc/ntp-*

       This file was automatically generated from HTML source.




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