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 Protocol (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 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 ntpdate 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  ntp-
       date  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 configuration 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 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
               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 adj-
               time() 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. Infor-
               mation 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 frac-
               tion (see ntpd for details). This number is usually small enough to be negligible for most purposes, though spec-
               ifying 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  primar-
               ily 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 synchronize with hosts beyond the firewall. Note
               that the -d option always uses unprivileged ports.

       -v      Be verbose. This option will cause ntpdate's version identification 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 ker-
       nel variables tick and tickadj.

SEE ALSO
       ntpd(8)

       HTML documentation in ntp-doc package.

       This file was automatically generated from HTML source.




                                                                                                                      ntpdate(8)