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System Administration Commands                           ntpd(1M)

     ntpd - Network Time Protocol daemon Version 4

     /usr/lib/inet/ntpd [-46aAbdDgLmnNqvx] [-c conffile]
         [-f driftfile] [-k keyfile] [-l logfile] [-p pidfile]
         [-P priority] [-r broadcastdelay] [-s statsdir]
         [-t trustedkey] [-U interface_update_time]

     The ntpd program is an operating  system  daemon  that  syn-
     chronises  the  system clock with remote NTP time servers or
     local reference clocks. It is a complete  implementation  of
     the  Network Time Protocol (NTP) version 4, but also retains
     compatibility with version 3, as defined by  RFC  1305,  and
     versions  1  and  2,  as  defined  by RFC 1059 and RFC 1119,

  How NTP Operates
     The ntpd program operates by exchanging messages with one or
     more configured servers at designated intervals ranging from
     about one minute to about 17 minutes. When started, the pro-
     gram requires several exchanges while the algorithms accumu-
     late and groom the data before setting the clock.  The  ini-
     tial  delay to set the clock can be reduced using options as
     described    in    the    server    options     page      at

     When the machine is booted, the hardware time of  day  (TOD)
     chip  is used to initialize the operating system time. After
     the machine has synchronized to a NTP server, the  operating
     system  corrects  the  chip  from  time  to time. During the
     course of operation if for some reason the  system  time  is
     more  than  1000s  offset from the server time, ntpd assumes
     something must be terribly wrong and exits with a panic mes-
     sage  to  the system log. If it was started via SMF, the ntp
     service is placed into maintenance mode and must be  cleared
     manually.  The -g option overrides this check at startup and
     allows ntpd to set the clock to the server  time  regardless
     of the chip time, but only once.

     Under ordinary conditions, ntpd slews the clock so that  the
     time  is effectively continuous and never runs backwards. If
     due to extreme network congestion an error spike exceeds the
     step  threshold  (128ms by default), the spike is discarded.
     However, if the error persists for  more  than  the  stepout
     threshold  (900s  by default) the system clock is stepped to
     the correct value. In  practice  the  need  for  a  step  is
     extremely  rare  and  almost always the result of a hardware
     failure. With the -x option the step threshold is  increased
     to  600s.  Other  options  are  available  using  the tinker

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System Administration Commands                           ntpd(1M)

     command as described in the miscellaneous  options  page  at

     The issues should be carefully considered before using these
     options.  The  maximum  slew rate possible is limited to 500
     parts-per-million (PPM) by the Unix kernel. As a result, the
     clock  can  take  2000s for each second the clock is outside
     the acceptable range. During this interval  the  clock  will
     not  be consistent with any other network clock and the sys-
     tem cannot be used for distributed applications that require
     correctly synchronized network time.

  Frequency Discipline
     The frequency file, usually called ntp.drift,  contains  the
     latest  estimate  of  clock frequency. If this file does not
     exist when  ntpd  is  started,  it  enters  a  special  mode
     designed  to  measure the particular frequency directly. The
     measurement takes 15 minutes, after which the  frequency  is
     set  and  ntpd  resumes  normal mode where the time and fre-
     quency are continuously  adjusted.  The  frequency  file  is
     updated  at  intervals  of  an hour or more depending on the
     measured clock stability.

  Operating Modes
     The ntpd daemon can operate in any of several modes, includ-
     ing       symmetric       active/passive,      client/server
     broadcast/multicast and manycast, as described in the  Asso-
     ciation             Management            page            at
     file:///usr/share/doc/ntp/assoc.html. It  normally  operates
     continuously while monitoring for small changes in frequency
     and trimming the clock for the ultimate precision.  However,
     it can operate in a one-time mode where the time is set from
     an external server and frequency is set  from  a  previously
     recorded  frequency  file. A broadcast/multicast or manycast
     client can discover remote  servers,  compute  server-client
     propagation  delay  correction  factors and configure itself
     automatically. This makes it possible to deploy a  fleet  of
     workstations   without   specifying   configuration  details
     specific to the local environment.

     By default, ntpd runs in continuous mode where each of  pos-
     sibly several external servers is polled at intervals deter-
     mined by an intricate  phase/frequency-lock  feedback  loop.
     The  feedback  loop  measures the incidental roundtrip delay
     jitter and oscillator frequency wander  and  determines  the
     best  poll interval using a heuristic algorithm. Ordinarily,
     and in most operating environments, the state  machine  will
     start with 64s intervals and eventually increase in steps to
     1024s. A small amount of random variation is  introduced  in
     order  to avoid bunching at the servers. In addition, should
     a server become unreachable for some time, the poll interval
     is  increased  in  steps to 1024s in order to reduce network

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System Administration Commands                           ntpd(1M)

     overhead. In general it is best not to  force  ntpd  to  use
     specific  poll  intervals,  allowing  it  to choose the best
     intervals based its current needs and  the  quality  of  the
     available servers and the clock.

     In some cases it may not be practical for ntpd to  run  con-
     tinuously.  In  the past a common workaround has been to run
     the ntpdate program from a cron  job  at  designated  times.
     However,  ntpdate  does not have the crafted signal process-
     ing, error checking and mitigation algorithms of  ntpd.  The
     ntpd  daemon  with  -q option is intended to replace ntpdate
     when used in this manner. Setting  this  option  will  cause
     ntpd  to  exit  just  after  setting the clock for the first
     time. The procedure for initially setting the clock  is  the
     same  as in continuous mode; most applications will probably
     want to specify the iburst keyword with  the  server  confi-
     guration command. With this keyword a volley of messages are
     exchanged to groom the data and the clock is  set  in  about
     10s. If nothing is heard after a couple of minutes, the dae-
     mon times out and exits. Eventually the ntpdate program  may
     be retired.

  Kernel Clock Discipline
     The kernel supports a method specific to ntpd to  discipline
     the  clock  frequency. First, ntpd is run in continuous mode
     with selected servers in order to  measure  and  record  the
     intrinsic  clock  frequency offset in the frequency file. It
     may take some hours for the frequency and offset  to  settle
     down.  Then  ntpd is run in normal mode as required. At each
     startup, the frequency is read from the file and initializes
     the  kernel  frequency,  thus  avoiding the settling period.
     When the kernel discipline is in use, the system's clock  is
     adjusted  at  each  system tick and thus the system clock is
     always as accurate as possible. When the  kernel  discipline
     is  not  used  the clock is adjusted once each second. It is
     important to delete the ntp.drift file before starting  ntpd
     if  the intrinsic frequency might have changed, such as by a
     motherboard swap.

  Poll Interval Control
     The ntpd program includes an intricate clock  discipline  to
     reduce  the network load while maintaining a quality of syn-
     chronization consistent with the observed jitter and wander.
     There  are a number of ways to tailor the operation in order
     to enhance accuracy by reducing the interval  or  to  reduce
     network  overhead  by  increasing  it.  However, the user is
     advised to carefully consider the consequences  of  changing
     the  poll  adjustment  range from the default. It is not the
     case that shorter poll intervals will  necessarily  lead  to
     more accuracy. Most device drivers will not operate properly
     if the poll interval is less than 64 s and that  the  broad-
     cast  server  and manycast client associations will also use

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System Administration Commands                           ntpd(1M)

     the default, unless overridden. In general, it  is  best  to
     let ntpd determine the best polling interval.

     In some cases involving dial up or toll services, it may  be
     useful  to  increase  the  minimum interval to a few tens of
     minutes and maximum interval to a day or  so.  Under  normal
     operation  conditions,  once  the  clock discipline loop has
     stabilized the interval will be increased in steps from  the
     minimum  to the maximum. However, this assumes the intrinsic
     clock frequency error is small  enough  for  the  discipline
     loop correct it. The capture range of the loop is 500 PPM at
     an interval of 64s decreasing by a factor of  two  for  each
     doubling  of interval. At a minimum of 1,024 s, for example,
     the capture range is only 31 PPM.

  The Huff-n'-Puff Filter
     In scenarios where a considerable amount of data are  to  be
     downloaded  or  uploaded over bandwidth limited links, time-
     keeping quality can be seriously degraded due  to  the  dif-
     ferent  delays  in  the  two  directions.  In many cases the
     apparent time errors are so large  as  to  exceed  the  step
     threshold  and  a step correction can occur during and after
     the data transfer is in progress.

     The huff-n'-puff filter is designed to correct the  apparent
     time  offset  in these cases. It depends on knowledge of the
     propagation delay when no  other  traffic  is  present.  The
     filter maintains a shift register that remembers the minimum
     delay over the most  recent  interval  measured  usually  in
     hours. Under conditions of severe delay, the filter corrects
     the apparent offset using the sign of  the  offset  and  the
     difference between the apparent delay and minimum delay. The
     name of the filter reflects the negative (huff) and positive
     (puff) correction, which depends on the sign of the offset.

     The filter is activated by the tinker command  and  huffpuff
     keyword,  as  described in the Miscellaneous Options page at

  Leap Second Processing
     As provided by international agreement, an extra  second  is
     sometimes  inserted  in  Coordinated Universal Time (UTC) at
     the end of a selected month, usually June or  December.  The
     National  Institutes of Standards and Technology (NIST) pro-
     vides an historic  leapseconds  file  at  time.nist.gov  for
     retrieval   via   FTP.   This   file,  usually  called  ntp-
     leapseconds.list, is copied into the /etc/inet directory and
     the  leapfile  configuration command then specifies the path
     to this file. At startup,  ntpd  reads  it  and  initializes
     three  leapsecond  values:  the NTP seconds at the next leap
     event, the offset of UTC relative  to  International  Atomic
     Time  (TAI)  after  the  leap  and  the NTP seconds when the

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System Administration Commands                           ntpd(1M)

     leapseconds file expires and should be retrieved again.

     If a host does not have the leapsecond values, they  can  be
     obtained  over  the net using the Autokey security protocol.
     Ordinarily, the leapseconds file is installed on the primary
     servers  and the values flow from them via secondary servers
     to the clients. When  multiple  servers  are  involved,  the
     values with the latest expiration time are used.

     If the latest leap is in the past, nothing further  is  done
     other  than to install the TAI offset. If the leap is in the
     future less than 28 days, the leap warning bits are set.  If
     in  the  future  less  than 23 hours, the kernel is armed to
     insert one second at the end of the current day.  Additional
     details  are in the The NTP Timescale and Leap Seconds white
     paper at http://www.eecis.udel.edu/~mills/leap.html.

     If none of the above provisions  are  available,  dsependent
     servers and clients tally the leap warning bits of surviving
     servers and reference clocks. When a majority  of  the  sur-
     vivors  show warning, a leap is programmed at the end of the
     current month. During the month and day of  insertion,  they
     operate  as  above. In this way the leap is is propagated at
     all dependent servers and clients.

     -4, --ipv4
          Force DNS resolution of following  host  names  on  the
          command line to the IPv4 namespace. Cannot be used with
          the --ipv6 option.

     -6, --ipv6
          Force DNS resolution of following  host  names  on  the
          command line to the IPv6 namespace. Cannot be used with
          the --ipv6 option.

     -a, --authreq
          Require  cryptographic  authentication  for   broadcast
          client, multicast client and symmetric passive associa-
          tions.  This is the  default.   This  option  must  not
          appear with authnoreq option.

     -A, --authnoreq
          Do not require cryptographic authentication for  broad-
          cast  client,  multicast  client  and symmetric passive
          associations.  This is almost never a good  idea.  This
          option must not appear with the authreq option.

     -b, --bcastsync
          Enable the client to sync to broadcast servers.

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System Administration Commands                           ntpd(1M)

     -c string, --configfile=string
          The  name  and  path   of   the   configuration   file,
          /etc/inet/ntp.conf by default.

     -d, --debug-level
          Increase output debug message level.  This  option  may
          appear an unlimited number of times.

     -D string, --set-debug-level=string
          Set the output debugging level.  Can be supplied multi-
          ple times, but each overrides the previous value(s).

     -f string, --driftfile=string
          The   name   and   path   of   the   frequency    file,
          /var/ntp/ntp.drift by default.

     -g, --panicgate
          Allow the first adjustment to exceed the panic limit.

          Normally, ntpd exits with a message to the  system  log
          if  the  offset  exceeds  the panic threshold, which is
          1000s by default. This option allows the time to be set
          to  any  value  without  restriction; however, this can
          happen only once. If the threshold  is  exceeded  after
          that,  ntpd will exit with a message to the system log.
          This option can be used with the  -q  and  -x  options.
          See  the  tinker configuration file directive for other

     -k string, --keyfile=string
          Specify the name and path of the  symmetric  key  file.
          /etc/inet/ntp.keys is the default.

     -l string, --logfile=string
          Specify the name and path of the log file.  The default
          is the system log file.

     -L, --novirtualips
          Do not listen to virtual IPs. The default is to listen.

     -m, --mdns
          Register as a NTP server with mDNS system. Implies that
          you are willing to serve time to others.

     -n, --nofork
          Do not fork.

     -N, --nice
          To the extent permitted by the  operating  system,  run
          ntpd at the highest priority.

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System Administration Commands                           ntpd(1M)

     -p string, --pidfile=string
          Specify the name and path of the file  used  to  record
          ntpd's process ID.

     -P number, --priority=number
          To the extent permitted by the  operating  system,  run
          ntpd  at  the  specified sched_setscheduler(SCHED_FIFO)

     -q, --quit
          Set the time and quit.  ntpd will exit just  after  the
          first  time the clock is set. This behavior mimics that
          of the ntpdate program, which is to be retired.  The -g
          and -x options can be used with this option.  Note: The
          kernel time discipline is disabled with this option.

     -r string, --propagationdelay=string
          Specify  the  default  propagation   delay   from   the
          broadcast/multicast  server  to  this  client.  This is
          necessary only if the delay cannot be computed automat-
          ically by the protocol.

     -s string, --statsdir=string
          Specify the directory path for  files  created  by  the
          statistics  facility. This is the same operation as the
          statsdir statsdir command.

     -t number, --trustedkey=number
          Add a key number to the trusted key list.  This  option
          can occur more than once. This is the same operation as
          the trustedkey key command.

     -U number, --updateinterval=number
          interval in seconds between scans for  new  or  dropped
          interfaces.  This option takes an integer number as its

          Give the time in seconds between two scans for  new  or
          dropped  interfaces.   For  systems with routing socket
          support the scans will be performed shortly  after  the
          interface  change has been detected by the system.  Use
          0 to disable scanning. 60 seconds is the  minimum  time
          between scans.

          make ARG an ntp variable (RW).  This option may  appear
          an unlimited number of times.

          make ARG an ntp variable  (RW|DEF).   This  option  may
          appear an unlimited number of times.

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System Administration Commands                           ntpd(1M)

     -x, --slew
          Slew up to 600 seconds.

          Normally, the time is slewed if the offset is less than
          the  step  threshold,  which  is 128 ms by default, and
          stepped if above the threshold.  This option  sets  the
          threshold  to  600 s, which is well within the accuracy
          window to set the clock manually.  Note: Since the slew
          rate  of  typical  Unix kernels is limited to 0.5 ms/s,
          each second  of  adjustment  requires  an  amortization
          interval of 2000 s.  Thus, an adjustment as much as 600
          s will take almost 14 days to  complete.   This  option
          can be used with the -g and -q options.  See the tinker
          configuration file directive for other options.   Note:
          The  kernel  time  discipline  is  disabled  with  this

     -?, --help
          Display usage information and exit.

     -!, --more-help
          Extended usage information passed thru pager.

          Output version of program and exit.

Option Presets
     All of the above options except the last three may be preset
     by loading values from environment variables named:
       NTPD_<option-name> or NTPD
     The environmental presets  take  precedence  (are  processed
     later  than) the configuration files. The option-name should
     be in all capital letters.  For example, to set  the  --quit
     option, you would set the NTPD_QUIT environment variable.

Automatic Service Management (smf)
     NTP on Solaris is managed via the service management  facil-
     ity  described  in  smf(5).  There  are several options con-
     trolled by services properties which can be set by the  sys-
     tem  administrator.  The  available options can be listed by
     executing the following command:
          svccfg -s svc:/network/ntp:default listprop config
     Each of these properties can be set using this command:
          svccfg -s  svc:/network/ntp:default setprop propname = value
     The available options and there meaning are as follows:

          A boolean which when false, prevents ntpd from allowing
          step larger than 17 minutes except once when the system
          boots. The default is true, which allows such  a  large
          step once each time ntpd starts.

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System Administration Commands                           ntpd(1M)

          An integer specifying the level of debugging requested.
          A zero means no debugging. The default is zero.

          A string specifying the location of the file  used  for
          log output. The default is /var/ntp/ntp.log

          A boolean which when  true,  specifies  that  anonymous
          servers  such  as broadcast, multicast and active peers
          can be accepted without any pre-configured  keys.  This
          is  very insecure and should only be used if the nework
          is secure and all the systems on it  are  trusted.  The
          default is false.

          A boolean which when true, instructs ntpd to  slew  the
          clock  as  much  as  possible,  instead of stepping the
          clock. It does not prevent all stepping, but  increases
          the  threshold  above  which  stepping is used. It also
          disables the use of the kernel NTP facility,  which  is
          incompatible  with  long  slew  times.  The  default is

          A boolean which when true, causes the  NTP  service  to
          delay  coming  completely on-line until after the first
          time the system clock is synchronized. This  can  pote-
          tially  delay  the  system  start  up  by a significant
          amount. The default is false.

          A boolean which when true, will  cause  the  daemon  to
          register  with  the network mDNS system. The default is

          A boolean which when true, cause the  daemon  to  issue
          logging messages. The default is false.

     See attributes(5) for descriptions of the  following  attri-

     box; cbp-1 | cbp-1 l | l .  ATTRIBUTE TYPE ATTRIBUTE VALUE =
     Availability   service/network/ntp = Stability Uncommitted

     The system clock must be set  to  within  68  years  of  the
     actual time before ntpd is started.

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System Administration Commands                           ntpd(1M)

     The ntpd service is managed by the service management facil-
     ity, smf(5), under the service identifier:


     Administrative actions on this service,  such  as  enabling,
     disabling,  or  requesting  restart,  can be performed using
     svcadm(1M). The service's status can be  queried  using  the
     svcs(1) command.

     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.

     Various internal ntpd variables can be displayed and  confi-
     guration options altered while the ntpd is running using the
     ntpq and ntpdc utility programs.

     When ntpd starts it looks at the value of umask, and if zero
     ntpd will set the umask to 022.

     The documentation available at  /usr/share/doc/ntp  is  pro-
     vided as is from the NTP distribution and may contain infor-
     mation that is not applicable to the software as provided in
     this particular distribution.

See Also
     svcs(1), sntp(1M),  ntp-keygen(1M),  ntpdate(1m),  ntpq(1M),
     ntptrace(1M), ntptime(1M), svcadm(1M), ntpdc(1M), rename(2),
     attributes(5), smf(5)

     This  software  was   built   from   source   available   at
     https://java.net/projects/solaris-userland.    The  original
     community       source       was       downloaded       from

     Further information about this software can be found on  the
     open source community website at http://www.ntp.org/.

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