HP-UX Reference (11i v2 03/08) - 1M System Administration Commands N-Z (vol 4)

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ntpdate(1M) ntpdate(1M)
NAME
ntpdate - set the date and time via NTP
SYNOPSIS
ntpdate [ -Bbdpqsuv ][-a key# ][
-e authdelay ][-k keyfile ]
[
-o version ][-p samples ][
-t timeout ] server[ ... ]
DESCRIPTION
ntpdate sets the local date and time by polling those 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 the
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 xntpd.
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 dis-
cipline the host clock frequency as does xntpd, 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 seconds, it will simply step the time by calling the clock_settime
(see clocks(2))
system routine. If the error is less than 0.5 seconds, it will slew the time by calling the
adjtime (see adj-
time(2)) system 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 (see cron(1M)) every hour or two.
ntpdate will decline to set the date if an NTP server daemon (e.g., xntpd) 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.
COMMAND LINE OPTIONS
ntpdate supports the following options:
-a Enable the authentication function and specify the key identifier to be used for authenti-
cation. 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 the
clock_settime system call if the offset is greater than +-128 ms. Note that, if the
offset is much greater than +-128 ms 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 clock_settime 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 function as the value authde-
lay, in seconds and fraction (see xntpd(1M) for details). This number is usually small
enough to be negligible for most purposes, though specifying a value may improve time-
keeping 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 xntpd.
-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.
Section 1M−−566 Hewlett-Packard Company − 1 − HP-UX 11i Version 2: August 2003