ntpdate
ntpdate(8) ntpdate(8)
NAME
ntpdate - set the date and time via NTP
Disclaimer: The functionality of this program is now available in the
ntpd program. See the -q command line option in the ntpd - Network
Time Protocol (NTP) daemon page. After a suitable period of mourning,
the ntpdate program is to be retired from this distribution
SYNOPSIS
ntpdate [ -46bBdqsuv ] [ -a key ] [ -e authdelay ] [ -k keyfile ] [ -o
version ] [ -p samples ] [ -t timeout ] [ -U user_name ] server [ ...
]
DESCRIPTION
ntpdate sets the local date and time by polling the Network Time Pro-
tocol (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 start-
ing the NTP daemon ntpd. It is also possible to run ntpdate from a
cron script. However, it is important to note that ntpdate with con-
trived 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 ntp-
date 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.
Note that in contexts where a host name is expected, a -4 qualifier
preceding the host name forces DNS resolution to the IPv4 namespace,
while a -6 qualifier forces DNS resolution to the IPv6 namespace.
If NetInfo support is compiled into ntpdate, then the server argument
is optional if ntpdate can find a time server in the NetInfo configu-
ration for ntpd.
COMMAND LINE OPTIONS
-4 Force DNS resolution of following host names on the command
line to the IPv4 namespace.
-6 Force DNS resolution of following host names on the command
line to the IPv6 namespace.
-a key Enable the authentication function and specify the key identi-
fier to be used for authentication as the argument key. 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 +-500 ms.
The default is to step the time using settimeofday() if the
offset is greater than +-500 ms. Note that, if the offset is
much greater than +-500 ms in this case, that it can take a
long time (hours) to slew the clock to the correct value. Dur-
ing 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 4. 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 pack-
ets. This is most useful when behind a firewall that blocks
incoming traffic to privileged ports, and you want to synchro-
nize with hosts beyond the firewall. Note that the -d option
always uses unprivileged ports.
-v Be verbose. This option will cause ntpdate’s version identifi-
cation string to be logged.
-U user_name
ntpdate process drops root privileges and changes user ID to
user_name and group ID to the primary group of server_user.
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 trou-
bling hunt for some values of the kernel variables tick and tickadj.
SEE ALSO
ntpd(8)
Primary source of documentation: /usr/share/doc/ntp-*
This file was automatically generated from HTML source.
ntpdate(8)
