ntpdate(8)ntpdate(8)NAMEntpdate - set the date and time via NTP (Network Time Protocol)
SYNOPSIS
/usr/sbin/ntpdate [-bdqsuv] [-a key#] [-e authdelay] [-k keyfile] [-o
version] [-p samples] [-t timeout] server1 server2 server3...
OPTIONS
Tells ntpdate to step the system time immediately to match NTP. Use
this option only when booting the system. Prints configuration and
debugging information. Queries the server(s) and prints the informa‐
tion received; the date and time are not set. Tells ntpdate to log its
actions through the syslog(3) facility rather than to the standard out‐
put. This is useful when running the program from cron(8). Tells ntp‐
date to use an unprivileged port to send the packets from. This is use‐
ful when you are 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. Runs
in verbose mode. Specifies that all packets should be authenticated
using the key number provided. Specifies an authentication processing
delay, in seconds (see xntpd(8) for details). 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. Specifies that
authentication keys will be read from keyfile instead of the default
/etc/ntp.keys file. This file should be in the format described in
xntpd(8). Forces ntpdate to poll as a version implementation. By
default ntpdate claims to be an NTP version 3 implementation in its
outgoing packets. Some older software will decline to respond to ver‐
sion 3 queries. Acquires a specified number of samples from each
server. The range of values for samples is from 1 and 8, inclusive.
The default is 4. Waits timeout seconds for a response. Any value
entered will be rounded to a multiple of 0.2 seconds. The default is 1
second, a value suitable for polling across a LAN.
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. It must be run as root on the local host. 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. The ntpdate command is run from
/sbin/init.d/settime to set the time of day at boot time, if NTP is
configured. (See Network Administration: Services for information on
configuring NTP.) 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 integrity will be obtained
by providing at least three or four servers, if not more.
Time adjustments are made by ntpdate in one of the following ways: If
ntpdate determines your clock is off by more than 0.5 seconds, it steps
the time by calling settimeofday(2). If the error is less than 0.5
seconds, however, it will by default slew the clock's time by a call to
adjtime(2) with the offset.
The latter technique is less disruptive and more accurate when the off‐
set is small, and works quite well when ntpdate is run by cron 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).
Ntpdate will decline to set the date if an NTP server daemon (for exam‐
ple, xntpd(8)) is running on the same host. When running ntpdate on a
regular basis from cron(8) 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
Because of significant changes in NTP version 3, you should check all
scripts that use the ntpdate command for correct usage and output.
ERRORS
A common problem is polling a server using the wrong query version num‐
ber or wrong authentication key. If either occurs, ntpdate prints the
following error message: 18 Apr 10:20:28 ntpdate(1192]: no server
suitable for synchronization found
At boot time, if NTP is not configured, the ntpdate prints the follow‐
ing message: WARNING: ntpdate cannot succeed, please check your
NTP configuration
EXAMPLES
The following command line sets the date and time after polling server
host1.dec.com as a version 2 implementation: /usr/sbin/ntpdate -o 2
host1.dec.com The following command line sets the date and time after
polling server host2.dec.com. All packets are authenticated using
authentication key 1. /usr/sbin/ntpdate -a 1 host2.dec.com
FILES
Specifies the command path Contains the encryption keys used by ntpdateSEE ALSO
Commands: ntpq(8), xntpd(8), xntpdc(8)
Files: ntp.conf(4)ntpdate(8)
