ntpdate(8) - phpMan

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ntpdate(8)                                                          ntpdate(8)

       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

       ntpdate [ -46bBdqsuv ] [ -a key ] [ -e authdelay ] [ -k keyfile ] [ -o version ]  [
       -p samples ] [ -t timeout ] [ -U user_name ] 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 ntp-
       date 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 dis-
       ruptive 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 run-
       ning 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 configuration for ntpd.

       -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 dis-
               able 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.  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  num-
               ber  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

       -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  inte-
               ger 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 sys-
               log facility. This is designed primarily for convenience of cron scripts.

       -t timeout
               Specify the maximum time waiting for a server response as the  value  time-
               out,  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

       -u      Direct  ntpdate  to  use an unprivileged port for outgoing packets. This is
               most useful when behind a firewall that blocks incoming traffic  to  privi-
               leged  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.

       ntpdate's exit status is zero if it finds a  server  and  updates  the  clock,  and
       nonzero otherwise.

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

       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 vari-
       ables tick and tickadj.


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