ntpdate(8) - NetBSD Manual Pages

NTPDATE(8)              NetBSD System Manager's Manual              NTPDATE(8)


NAME

     ntpdate -- set the date and time via NTP


SYNOPSIS

     ntpdate [-bBdoqsuv] [-a key] [-e authdelay] [-k keyfile] [-o version]
             [-p samples] [-t timeout] [server ...]


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. 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


COMMAND LINE OPTIONS

     -a key  Enable the authentication function and specify the key identifier
             to be used for authentication as the argument key ntpdate.  The
             keys and key identifiers must match in both the client and server
             key files.  The default is to disable the authentication func-
             tion.

     -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 func-
             tion as the value authdelay , in seconds and fraction (see ntpd
             for details). This number is usually small enough to be negligi-
             ble 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 conve-
             nience 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 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 string to be logged.


FILES

     /etc/ntp.keys  encryption keys used by ntpdate.


AUTHORS

     David L. Mills (mills@udel.edu)


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.

NetBSD 8.1                     January 28, 2010                     NetBSD 8.1