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ntpdate(8)                                     System Manager's Manual                                     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 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 ntp‐
       date  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.

       Note that in contexts where a host name is expected, a -4 qualifier preceding the host name forces DNS resolu‐
       tion 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 configuration 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 identifier 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
               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 packets. This is most useful when behind a
               firewall that blocks incoming traffic to privileged ports, and you  want  to  synchronize  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.

       -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.


DIAGNOSTICS
       ntpdate's exit status is zero if it finds a server and updates 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
       ntpd(8)

       The official HTML documentation.