man pages section 1M: System Administration Commands

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Updated: July 2014

ntpdate (1m)


ntpdate - set the date and time with NTP


/usr/sbin/ntpdate  [-46bBdqsuv]  [-a key] [-e Authdelay] [-k
keyfile] [-o version] [-p samples] [-t timeout] server [ ...


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System Administration Commands                        ntpdate(1M)

     ntpdate - set the date and time with NTP

     /usr/sbin/ntpdate  [-46bBdqsuv]  [-a key] [-e Authdelay] [-k
     keyfile] [-o version] [-p samples] [-t timeout] server [ ...

     -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 authentication and specify the key identifier 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 authen-

     -B   Force  the time to always be slewed using the adjtime()
          system call, even if the  measured  offset  is  greater
          than 0.5 seconds. The default is to step the time using
          settimeofday() if the offset is  greater  than  +-0.5s.
          Note that, if the offset is much greater than +-0.5s 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

     -e authdelay
          Specify the processing delay to perform an  authentica-
          tion  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

     -k keyfile
          Specify the path for the authentication key file as the
          string keyfile. The default is /etc/inet/ntp.keys. This

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System Administration Commands                        ntpdate(1M)

          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.

     -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
          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 unprivileged ports.

     -v   Print ntpdate's version  identification  string  during
          program startup.

     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 unless
     the -d or -q options are  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 relia-
     bility of ntpdate depends on the number of servers, the num-
     ber  of  polls  each time it is run and the interval between

     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. 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.

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System Administration Commands                        ntpdate(1M)

     Finally,  since  ntpdate  does not discipline the host clock
     frequency as does ntpd, the accuracy using ntpdate  is  lim-

     Time  adjustments are made by ntpdate in one of two ways. If
     ntpdate determines the clock is in error more than 0.5  sec-
     ond  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 calling the system adjtime() rou-
     tine. The latter technique is less disruptive and more accu-
     rate 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 run-
     ning 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 con-
     texts where a host name is expected, a -4 qualifier  preced-
     ing  the  host name forces DNS resolution to the IPv4 names-
     pace, while a -6 qualifier forces DNS resolution to the IPv6

     See   attributes(5)   for   descriptions  of  the  following

     |Availability   | service/network/ntp  |
     |Stability      | Uncommitted obsolete |
     Disclaimer: The functionality of this program is now  avail-
     able  in the ntpd program. See the -q command line option in
     the ntpd - Network Time Protocol (NTP) daemon man page.  The
     ntpdate program is to be retired from this distribution.

     ntpd(1M), ntpdc(1M), attributes(5)

     This   software   was   built   from   source  available  at   The   original
     community    source    was   downloaded   from    http://ar-

     Further information about this software can be found on  the
     open source community website at

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