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ntpdate(8) System Manager's Manual ntpdate(8) NAME ntpdate - 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 ... FLAGS Tells ntpdate to step the system time immediately to match NTP. Use this option only when booting the system. Prints configuration and de- bugging information. Queries the server(s) and prints the information received; the date and time are not set. Tells ntpdate to log its ac- tions 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 au- thentication 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 de- fault ntpdate claims to be an NTP version 3 implementation in its out- going packets. Some older software will decline to respond to version 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 se- lect 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 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 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. 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 au- thentication key 1. /usr/sbin/ntpdate -a 1 host2.dec.com 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 FILES Specifies the command path Contains the encryption keys used by ntp- date. RELATED INFORMATION Commands: ntpq(8), ntpsetup(8), xntpd(8), xntpdc(8) Files: ntp.conf(4) delim off ntpdate(8)