ntpdate



ntpdate(1)                                                          ntpdate(1)




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 [ -bBdoqsuv ] [ -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  Pro-
       tocol  (NTP)  server(s)  given as the server arguments to determine the
       correct time. It must be run as root on the local  host.  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 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.

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


COMMAND LINE OPTIONS

       -a      key Enable the authentication  function  and  specify  the  key
               identifier  to  be  used for authentication as the argument key
               ntpdate . 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 use-
               ful for general debugging will also be printed.

       -e      authdelay Specify the processing delay to perform an  authenti-
               cation  function  as the value authdelay , in seconds and frac-
               tion (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  outgoint  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 inclu-
               sive.  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 or outgoing pack-
               ets. This is most useful when behind  a  firewall  that  blocks
               incoming  traffic to privileged ports, and you want to synchro-
               nise with hosts beyond the firewall. Note that the

       -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.

       -d      always uses unprivileged ports.

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


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

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



AUTHOR

       David L. Mills <mills@udel.edu>



ntp 4.1.1b-r5                                                       ntpdate(1)

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