System Administration Commands ntpdate(1M)
NAME
ntpdate - 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 deter-
mine the correct 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 dramati-
cally with a greater number of servers. While a single
server may be used, better performance and greater resis-
tance 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 dis-
ruptive 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 alterna-
tive to running a daemon. Doing so once every one to two
hours results in precise enough timekeeping to avoid step-
ping 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
the offset is much greater than +-128 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.
-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
timekeeping on very slow CPU's.
-k keyfile Read keys from the file keyfile instead of
the default file, /etc/inet/ntp.keys. key-
file should be in the format described in
xntpd(1M).
-m Join multicast group specified in server and
synchronize 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. However, 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) facil-
ity rather than to the standard output - a
useful option when running 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 identification 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 attri-
butes:
____________________________________________________________
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
|_____________________________|_____________________________|
| Availability | SUNWntpu |
|_____________________________|_____________________________|
SEE ALSO
cron(1M), xntpd(1M), adjtime(2), gettimeofday(3C),
settimeofday(3C)syslog(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 previ-
ous runs.
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