ntpdate
set the date and time via NTP
see also :
ntpdate-debian
Synopsis
ntpdate
[-bBdoqsuv] [-a key]
[-e authdelay] [-k
keyfile] [-o version]
[-p samples] [-t
timeout] server [...]
add an example, a script, a trick and tips
examples
source
ntpdate europe.pool.ntp.org
source
ntpdate pool.ntp.org
ntpdate stdtime.gov.hk
hwclock -w
source
sudo ntpdate time.nist.gov
source
ntpdate[3912]: no server suitable for synchronization found
You need to configure your firewall to allow UDP replies on port
123.
source
System time wrong after running ntpdate because DST ignored
IIRC EST is short for Eastern Standard Time, and not subject to DST. I'm
guessing what you really want to use is
/usr/share/zoneinfo/America/New_York, but my guess
as to where you are might be off.
Edit:
Kyle Jones suggests to use EST5EDT, which is quite possibly a
better choice. I'm coloured by familiarity with cases where
national capitals are suitable, unambiguous references for the
time zone in the country.
source
ntpdate command not found [only when using with cron]
Use full path!
/usr/sbin/ntpdate $NTPSERVER
cron doesn't include any ~/.bashrc,
~/.zshrc, etc., so the $PATH maybe
unset.
source
linux "date -s" command not working to change date on a server
http://www.linuxforum.com/threads/2154-Linux-ntp-time-Offset-on-Xen-VM-incorrect
After a lot of searching I found that by default, the VM's
clocks are synchronized to the HOST clock running on the
control domain, and cannot be independently changed. This was
surprising to me because NTP was still configured and appeared
able to synchronize the clocks.
add the following line to your /etc/sysctl.conf file
# Allow the VM to update it's own clock, and do not use the DOM host clock.
xen.independent_wallclock=1
then restart the network service
/etc/init.d/network restart #for redhat, centos, fedora
/etc/init.d/networking restart #debian, ubuntu
now you can set the date with date -s ...
Here is a link to the official xen docs
Here is a link to the ntp docs
description
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 (unless the option -q is
used). 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() routine. If the error is less than 0.5
seconds, it will slew the time by calling the system
adjtime() 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.
options
-a key
Enable the authentication
function and specify the key identifier to be used for
authentication as the argument 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
Force the time to always be slewed using the adjtime()
system call, even if the measured offset is greater than
+-128 ms. The default is to step the time using
settimeofday() if the offset is greater than +-128 ms. Note
that, 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.
-b
Force the time to be stepped using the settimeofday()
system call, rather than slewed (default) using the
adjtime() system call. This option should be used when
called from a startup file at boot time.
-d
Enable the debugging mode, in which ntpdate will go
through all the steps, but not adjust the local clock.
Information useful for general debugging will also be
printed.
-e authdelay
Specify the processing delay to
perform an authentication function as the value authdelay,
in seconds and fraction (see ntpd for details). This number
is usually small enough to be negligible for most purposes,
though specifying a value may improve timekeeping on very
slow CPU’s.
-k keyfile
Specify the path for the
authentication key file as the string keyfile. The default
is /etc/ntp.keys. This file should be in the format
described in ntpd.
-o version
Specify the NTP version for
outgoing packets as the integer version, which can be 1 or
2. The default is 3. This allows ntpdate to be used with
older NTP versions.
-p samples
Specify the number of samples
to be acquired from each server as the integer samples, with
values from 1 to 8 inclusive. The default is 4.
-q
Query only - don’t set the clock.
-s
Divert logging output from the standard output (default)
to the system syslog facility. This is designed primarily
for convenience of cron scripts.
-t timeout
Specify the maximum time
waiting for a server response as the value timeout, in
seconds and fraction. The value is is rounded to a multiple
of 0.2 seconds. The default is 1 second, a value suitable
for polling across a LAN.
-u
Direct 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
Be verbose. This option will cause ntpdate’s
version identification string to be logged.
diagnostics
ntpdate’s exit status is zero if it found a server and
could update the clock, and nonzero otherwise.
files
/etc/ntp.keys
- encryption keys used by ntpdate.
bugs
The slew
adjustment is actually 50% larger than the measured offset,
since this (it is argued) will tend to keep a badly drifting
clock more accurate. This is probably not a good idea and
may cause a troubling hunt for some values of the kernel
variables tick and tickadj.
see also
ntpdate-debian
author
David L. Mills
(mills[:at:]udel[:dot:]edu)
This manpage converted from html to roff by Fabrizio Polacco
<fpolacco[:at:]debian[:dot:]org>