jammy (8) ntpdate.8.gz

Provided by: ntpsec-ntpdate_1.2.1+dfsg1-4_amd64 bug

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)