NTPDATE(8) | System Manager's Manual | NTPDATE(8) |
ntpdate
—
ntpdate |
[-bBdoqsuv ] [-a
key] [-e
authdelay] [-k
keyfile] [-o
version] [-p
samples] [-t
timeout] [server ...] |
ntpdate
sets the local date and time by polling the
Network Time Protocol (NTP) server(s) given as the
server 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 a subset of the NTP clock filter and selection
algorithms are applied to select the best of these. Note that the accuracy and
reliability of ntpdate
depends on the number of
servers, the number of polls each time it is run and the interval between
runs.
ntpdate
can be run manually as necessary
to set the host clock, or it can be run from the host startup script to set
the clock at boot time. This is useful in some cases to set the clock
initially before starting the NTP daemon ntpd. It is
also possible to run ntpdate
from a
cron script. However, it is important to note that
ntpdate
with contrived cron
scripts is no substitute for the NTP daemon, which uses sophisticated
algorithms to maximize accuracy and reliability while minimizing resource
use. Finally, since ntpdate
does not discipline the
host clock frequency as does ntpd, the accuracy
using ntpdate
is limited.
Time adjustments are made by ntpdate
in
one of two ways. If ntpdate
determines the clock is
in error more than 0.5 second it will simply step the time by calling the
system settimeofday(2)
routine. If the error is less than 0.5 seconds, it will slew the time by
calling the system adjtime(2)
routine. The latter technique is less disruptive and more accurate when the
error is small, and works quite well when ntpdate
is
run by cron every hour or two.
ntpdate
will decline to set the date if an
NTP server daemon (e.g., ntpd ) is running on the
same host. When running ntpdate
on a regular basis
from cron 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.
If NetInfo support is compiled into
ntpdate
, then the server
argument is optional if ntpdate
can find a time
server in the NetInfo configuration for ntpd
-a
keyntpdate
. The keys and key identifiers must match
in both the client and server key files. The default is to disable the
authentication function.-B
-b
-d
ntpdate
will
go through all the steps, but not adjust the local clock. Information
useful for general debugging will also be printed.-e
authdelay-k
keyfile-o
versionntpdate
to be used with older NTP
versions.-p
samples-q
-s
-t
timeout-u
ntpdate
to use an unprivileged port for
outgoing packets. This is most useful when 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.-v
ntpdate
string
to be logged.ntpdate
.January 28, 2010 | NetBSD 9.4 |