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Under GNU General Public License
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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 [ -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 ntp-
date 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 dis-
ruptive 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 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 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 ntpdate. The keys and key iden-
tifiers 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 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 authdelay, in seconds and fraction (see ntpd for details). This num-
ber 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.
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 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 inte-
ger 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 sys-
log facility. This is designed primarily for convenience of cron scripts.
-t timeout
Specify the maximum time waiting for a server response as the value time-
out, 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 privi-
leged 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.
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 vari-
ables tick and tickadj.
SEE ALSO
Primary source of documentation: /usr/share/doc/ntp-*/ntpdate.html
AUTHOR
David L. Mills <mills AT udel.edu>
ntpdate(1)
Generated by $Id: phpMan.php,v 4.49 2006/02/26 13:18:18 chedong Exp $ Author: Che Dong
On Apache/1.3.37 (Unix) mod_throttle/3.1.2 FrontPage/5.0.2.2635 mod_psoft_traffic/0.2 mod_ssl/2.8.28 OpenSSL/0.9.8b
Under GNU General Public License
2008-11-21 07:43 @38.103.63.55 Crawled by CCBot/1.0 (+http://www.commoncrawl.org/bot.html)