ntpdate(1M) ntpdate(1M)
NAME
ntpdate - set the date and time via NTP
SYNOPSIS
ntpdate [-bdos] [-a keynum] [-e authdelay] [-k keyfile] [-p samples]
[-t timeout] server ...
DESCRIPTION
The ntpdate command sets the local date and time by polling
the Network Time Protocol server(s) on the host(s) given as
arguments to determine the correct time. A number of samples
are obtained from each of the servers specified and the
standard NTP clock filter and selection algorithms are applied
to select the best of these.
Files
/etc/ntp.keys encryption keys used by ntpdate.
USAGE
ntpdate must be run as a privileged user on the local host.
Typically, ntpdate can be inserted in the /etc/rc.local
startup up script to set the time of day at boot time and/or
can be run from time-to-time via cron(1M).
Time adjustments are made by ntpdate in one of two ways.
If ntpdate determines your clock is off by more than 0.5
seconds, it will simply step the time by calling
settimeofday [see gettimeofday(2)].
If the error is less than 0.5 seconds, ntpdate will, by
default, skew the clock's time via a call to adjtime(2)
with the offset.
The latter technique is less disruptive and more accurate when
the offset is small, and works quite well when ntpdate is run
by cron(1M) every hour or two. The adjustment made in the
latter case is actually 50% larger than the measured offset
since this will tend to keep a badly drifting clock more
accurate (at some expense to stability, though this tradeoff
is usually advantageous).
Note that ntpdate's reliability and precision will improve
dramatically with greater numbers of servers. While a single
server may be used, better performance and greater resistance
to insanity on the part of any one server will be obtained by
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ntpdate(1M) ntpdate(1M)
providing at least three or four servers, if not more.
ntpdate will decline to set the date if an NTP server daemon
[for example, xntpd(1M)] is running on the same host. When
running ntpdate on a regular basis from cron(1M) 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.
Options
ntpdate takes the following options:
-b Force time adjustment at boot time. At boot
time, it is usually better to always step the
time by specifying the -b switch on the command
line.
-d Enable debugging. This flag may be used to
determine what ntpdate will do without it
actually doing it. Information useful for
general debugging will also be printed.
-o By default, ntpdate claims to be an NTP version
2 implementation in its outgoing packets. As
some older software will decline to respond to
version 2 queries, the -o switch can be used to
force the program to poll as a version 1
implementation instead.
-s Log ntpdate activity via the syslog(3G)
facility, rather than to the standard output.
This option is useful when running ntpdate from
cron(1M).
-a keynum Authenticate all packets using the key number
keynum.
-e authdelay Set the authentication processing delay to
authdelay seconds [see xntpd(1M)]. This number
is usually small enough to be negligible for
ntpdate's purposes, though specifying a value
may improve timekeeping on very slow CPU's.
-k keyfile Read authentication keys from the file keyfile,
instead of reading from the default file
/etc/ntp.keys. keyfile should be in the format
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ntpdate(1M) ntpdate(1M)
described in xntpd(1M).
-p samples Set the number of samples ntpdate acquires from
each server to samples, where samples is a
value between 1 and 8 inclusive. The default
is 4.
-t timeout Set the time ntpdate spends waiting for a
response to timeout seconds. The value
specified will be rounded to a multiple of 0.2
seconds. The default is 1 second, a value
suitable for polling across a LAN.
REFERENCES
xntpd(1M)
Copyright 1994 Novell, Inc. Page 3