ntpdate(1M) System Administration Commands ntpdate(1M)NAMEntpdate - set the date and time by way of NTP
SYNOPSIS
/usr/sbin/ntpdate [-bBdoqsuv] [-a key#] [-e authdelay]
[-k keyfile] [-m] [-o version] [-p samples]
[-t timeout] [-w] server...
DESCRIPTION
The ntpdate utility sets the local date and time. To determine the cor‐
rect time, it polls the Network Time Protocol (NTP) servers on the
hosts given as arguments. This utility must be run as root on the local
host. It obtains a number of samples from each of the servers and
applies the standard NTP clock filter and selection algorithms to
select the best of these.
The reliability and precision of ntpdate improve dramatically with a
greater number of servers. While a single server may be used, better
performance and greater resistance to inaccuracy on the part of any one
server can be obtained by providing at least three or four servers, if
not more.
The ntpdate utility makes time adjustments in one of two ways. If it
determines that your clock is off by more than 0.5 seconds it simply
steps the time by calling gettimeofday(3C). If the error is less than
0.5 seconds, by default, it slews the clock's time with the offset, by
way of a call to adjtime(2). The latter technique is less disruptive
and more accurate when the offset is small; it 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. This
adjustment tends to keep a badly drifting clock more accurate, at some
expense to stability. This tradeoff is usually advantageous. At boot
time, however, it is usually better to step the time. This can be
forced in all cases by specifying the -b option on the command line.
The ntpdate utility declines to set the date if an NTP server daemon
like xntpd(1M) is running on the same host. It can be run on a regular
basis from cron(1M) as an alternative to running a daemon. Doing so
once every one to two hours results in precise enough timekeeping to
avoid stepping the clock.
OPTIONS
The following options are supported:
-a key# Authenticate transactions, using the key number, key#.
-b Step the time by calling gettimeofday(3C).
-B Force the time to always be slewed using the adjtime(2)
system call, even if the measured offset is greater
than +-128 ms. The default is to step the time using
settimeofday(3C) if the offset is greater than +-128
ms. If this option is used and the offset is much
greater than +-128 ms, 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.
-d Display what will be done without actually doing it.
Information useful for general debugging is also
printed.
-e authdelay Specify an authentication processing delay, authdelay
in seconds. See xntpd(1M) for details. This number is
usually small enough to be negligible for purposes of
ntpdate. However, specifying a value may improve time‐
keeping on very slow CPU's.
-k keyfile Read keys from the file keyfile instead of the default
file, /etc/inet/ntp.keys. keyfile should be in the for‐
mat described in xntpd(1M).
-m Join multicast group specified in server and synchro‐
nize to multicast NTP packets. The standard NTP group
is 224.0.1.1.
-o version Force the program to poll as a version 1 or version 2
implementation. By default ntpdate claims to be an NTP
version 3 implementation in its outgoing packets. How‐
ever, some older software declines to respond to ver‐
sion 3 queries. This option can be used in these cases.
-p samples Set the number of samples ntpdate acquires from each
server. samples can be between 1 and 8 inclusive. The
default is 4.
-q Query only. Do not set the clock.
-s Log actions by way of the syslog(3C) facility rather
than to the standard output — a useful option when run‐
ning the program from cron(1M).
-t timeout Set the time ntpdate spends, waiting for a response.
timeout is rounded to a multiple of 0.2 seconds. The
default is 1 second, a value suitable for polling
across a LAN.
-u Use an unprivileged port to send the packets from. This
option is useful when you are behind a firewall that
blocks incoming traffic to privileged ports, and you
want to synchronize with hosts beyond the firewall. The
-d option always uses unprivileged ports.
-v Be verbose. This option causes ntpdate's version iden‐
tification string to be logged.
-w Wait until able to synchronize with a server. When the
-w option is used together with -m, ntpdate waits until
able to join the group and synchronize.
FILES
/etc/inet/ntp.keys Contains the encryption keys used by ntpdate.
ATTRIBUTES
See attributes(5) for descriptions of the following attributes:
┌─────────────────────────────┬─────────────────────────────┐
│ ATTRIBUTE TYPE │ ATTRIBUTE VALUE │
├─────────────────────────────┼─────────────────────────────┤
│Availability │SUNWntpu │
└─────────────────────────────┴─────────────────────────────┘
SEE ALSOcron(1M), xntpd(1M), adjtime(2), gettimeofday(3C), settimeofday(3C)sys‐
log(3C), attributes(5)NOTES
The technique of compensating for clock oscillator errors to improve
accuracy is inadequate. However, to further improve accuracy would
require the program to save state from previous runs.
SunOS 5.10 29 Sep 1999 ntpdate(1M)
