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 (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.

AUTHOR

       David L. Mills (mills@udel.edu)
       This manpage converted from html to roff by Fabrizio Polacco <fpolacco@debian.org>

SEE ALSO

       ntpdate-debian(8)

                                                                                                      ntpdate(8)