NAME

       ntpdate - set the date and time via NTP

SYNOPSIS

       ntpdate [-46bBdqsuv] [-a key] [-k keyfile] [-o version] [-t timeout] server [...]

DESCRIPTION

       ntpdate  sets the local date and time by polling the Network Time Protocol (NTP) server(s)
       given as the server argument(s) 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,  if the -u flag was not specified, 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.

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 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.  This is the
              default.

       -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  and  using  an unprivileged port. Information useful for
              general debugging will also be printed.

       -k keyfile
              Specify the path for the authentication key file as the string keyfile. The default
              is /etc/ntpsec/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, 2, 3 or 4. The default is 4. This allows ntpdate  to  be  used  with  older  NTP
              versions.

       -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  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  updates  the  clock,  and  nonzero
       otherwise.

FILES

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

AUTHOR

       David L. Mills (mills@udel.edu)
       This man page was converted from HTML to roff by Fabrizio Polacco <fpolacco@debian.org>

SEE ALSO

       ntpdate-debian(8)

                                                                                       ntpdate(8)