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ntpdate(8)                  System Manager's Manual                 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.

DIAGNOSTICS
       ntpdate's exit status is zero if it finds  a  server  and  updates  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.
SEE ALSO
       ntpd(8)
       The official HTML documentation.
       This file was automatically generated from HTML source.


                                                                    ntpdate(8)