ntpdate(8) — Maintenance
Digital
NAME
ntpdate − set the date and time via NTP (Network Time Protocol)
SYNOPSIS
/usr/sbin/ntpdate [ -bdos ] [ -p samples ] [ -t timeout ] server1 server2 server3 ...
FLAGS
-bTells ntpdate to step the system time immediately to match NTP. Use this option only when booting the system.
-dDebug flag.
-oForces ntpdate to poll as a version 1 implementation. By default ntpdate claims to be an NTP version 2 implementation in its outgoing packets. Some older software, including the University of Maryland’s ntpd , will decline to respond to version 2 queries.
-sTells ntpdate to log its actions via the syslog(3) facility rather than to the standard output.
-p samplesAcquires a specified number of samples from each server. This value of samples can be set between 1 and 8, inclusive. The default is 4.
-t timeoutWaits 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
Ntpdate 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. ntpdate is run from /sbin/init.d/settime to set the time of day at boot time, if NTP is configured. (See ntpsetup(8) 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 two ways. If ntpdate determines your clock is off by more than 0.5 seconds it will simply step 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 via a call to adjtime(2) with the offset. The latter technique is less disruptive and more accurate when the offset is small. 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). At boot time, however, it is usually better to always step the time, by using the -b option on the command line.
FILES
/usr/bin/ntpdate
Specifies the command path