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ntp.conf(5)		      File Formats Manual		   ntp.conf(5)



NAME
       ntp.conf - Server Options


       Following  is  a	 description  of  the configuration commands in NTPv4.
       There are two classes of commands, configuration commands that  config-
       ure  an	association with a remote server, peer or reference clock, and
       auxilliary commands that specify environmental variables	 that  control
       various related operations.

       The  various  modes  described  on  the Association Management page are
       determined by the command keyword and  the  DNS	name  or  IP  address.
       Addresses  are  classed	by  type  as (s) a remote server or peer (IPv4
       class A, B and C), (b) the IP broadcast address of a  local  interface,
       (m)  a  multicast  address  (IPv4  class	 D),  or (r) a reference clock
       address (127.127.x.x). For type m addresses the IANA has	 assigned  the
       multicast  group address IPv4 224.0.1.1 and IPv6 ff05::101 (site local)
       exclusively to NTP, but other nonconflicting addresses can be used.

       If the  Basic  Socket  Interface	 Extensions  for  IPv6	(RFC-2553)  is
       detected,  support for the IPv6 address family is generated in addition
       to the default IPv4 address family. IPv6 addresses can be identified by
       the  presence of colons ":" in the address field. IPv6 addresses can be
       used almost everywhere where IPv4  addresses  can  be  used,  with  the
       exception  of  reference	 clock	addresses, which are always IPv4. Note
       that in contexts where a host name is expected, a -4 qualifier  preced-
       ing  the host name forces DNS resolution to the IPv4 namespace, while a
       -6 qualifier forces DNS resolution to the IPv6 namespace.


CONFIGURATION COMMANDS
       server address [options ...]

       peer address [options ...]

       broadcast address [options ...]

       manycastclient address [options ...]

       pool address [options ...]

       unpeer [address | associd]
	       These commands specify the time server name or  address	to  be
	       used  and  the  mode  in	 which	to operate. The address can be
	       either a DNS name or a IPv4 or IPv6 address in  standard	 nota-
	       tion.  In  general,  multiple commands of each type can be used
	       for different server and peer addresses or multicast groups.

	       server  For type s and r addresses (only), this	command	 mobi-
		       lizes  a	 persistent  client  mode association with the
		       specified remote server or local	 reference  clock.  If
		       the  preempt  flag  is  specified, a preemptable client
		       mode association is mobilized instead.

	       peer    For type s addresses (only), this command  mobilizes  a
		       persistent  symmetric-active  mode association with the
		       specified remote peer.

	       broadcast
		       For type b and m addressees (only), this command	 mobi-
		       lizes  a	 persistent broadcast or multicast server mode
		       association. Note that type b messages go only  to  the
		       interface  specified,  but  type	 m  messages go to all
		       interfaces.

	       manycastclient
		       For type m addresses (only), this command  mobilizes  a
		       manycast	 client	 mode  association  for	 the multicast
		       group address specified. In this mode the address  must
		       match  the address specified on the manycastserver com-
		       mand of one or more designated manycast servers.

	       pool    For type s messages (only)  this	 command  mobilizes  a
		       client  mode  association  for servers implementing the
		       pool automatic server discovery scheme described on the
		       Association  Management page. The address is a DNS name
		       in the form area.pool.ntp.org, where area is  a	quali-
		       fier  designating the server geographic area such as us
		       or europe.

	       unpeer  This command removes a previously  configured  associa-
		       tion. An address or association ID can be used to iden-
		       tify the association. Either an IP address or DNS  name
		       can  be used. This command is most useful when supplied
		       via ntpq runtime	 configuration	commands  :config  and
		       config-from-file.



COMMAND OPTIONS
       autokey Send  and  receive  packets authenticated by the Autokey scheme
	       described in the Authentication Options page.  This  option  is
	       mutually exclusive with the key option.

       burst   When  the  server  is  reachable, send a burst of eight packets
	       instead of the usual one. The packet spacing is normally	 2  s;
	       however,	 the  spacing between the first and second packets can
	       be changed with the calldelay command to allow additional  time
	       for a modem or ISDN call to complete. This option is valid only
	       with the server command and type s addressesa. It is  a	recom-
	       mended  option when the maxpoll option is greater than 10 (1024
	       s).

       iburst  When the server is unreachable, send a burst of	eight  packets
	       instead	of  the usual one. The packet spacing is normally 2 s;
	       however, the spacing between the first and second  packets  can
	       be  changed with the calldelay command to allow additional time
	       for a modem or ISDN call to complete. This option is valid only
	       with  the  server  command and type s addresses. It is a recom-
	       mended option with this command.

       key key Send and receive packets authenticated  by  the	symmetric  key
	       scheme  described  in  the Authentication Options page. The key
	       specifies the key identifier  with  values  from	 1  to	65534,
	       inclusive.  This	 option is mutually exclusive with the autokey
	       option.

       minpoll minpoll

       maxpoll maxpoll
	       These options specify the minimum and  maximum  poll  intervals
	       for  NTP	 messages,  in	seconds as a power of two. The maximum
	       poll interval defaults to 10 (1024 s), but can be increased  by
	       the  maxpoll option to an upper limit of 17 (36 h). The minimum
	       poll interval defaults to 6 (64 s), but can be decreased by the
	       minpoll option to a lower limit of 3 (8 s).

       mode option
	       Pass the option to a reference clock driver, where option is an
	       integer in the range from 0 to 255, inclusive. This  option  is
	       valid only with type r addresses.

       noselect
	       Marks  the  server or peer to be ignored by the selection algo-
	       rithm but visible to the monitoring  program.  This  option  is
	       ignored with the broadcast command.

       preempt Specifies  the  association  as	preemptable  rather  than  the
	       default persistent. This option is ignored with	the  broadcast
	       command	and  is	 most  useful with the manycastclient and pool
	       commands.

       prefer  Mark the server as preferred. All  other	 things	 being	equal,
	       this  host  will	 be  chosen for synchronization among a set of
	       correctly operating hosts. See the  Mitigation  Rules  and  the
	       prefer  Keyword	page  for  further information. This option is
	       valid only with the server and peer commands.

       true    Mark the association to	assume	truechimer  status;  that  is,
	       always  survive	the  selection and clustering algorithms. This
	       option can be used with any association, but is most useful for
	       reference  clocks with large jitter on the serial port and pre-
	       cision pulse-per-second (PPS)  signals.	Caution:  this	option
	       defeats	the  algorithms	 designed to cast out falsetickers and
	       can allow these sources to set the system clock. This option is
	       valid only with the server and peer commands.

       ttl ttl This  option  specifies	the time-to-live ttl for the broadcast
	       command and the maximum ttl for the expanding ring search  used
	       by  the	manycastclient command. Selection of the proper value,
	       which defaults to 127, is something of a black art  and	should
	       be  coordinated	with the network administrator. This option is
	       invalid with type r addresses.

       version version
	       Specifies the version number to be used f or outgoing NTP pack-
	       ets. Versions 1-4 are the choices, with version 4 the default.

       xleave  Operate	in  interleaved	 mode  (symmetric  and broadcast modes
	       only). (see NTP Interleaved Modes)


AUXILLIARY COMMANDS
       broadcastclient
	       Enable reception of broadcast  server  messages	to  any	 local
	       interface (type b address). Ordinarily, upon receiving a broad-
	       cast message for the first time, the broadcast client  measures
	       the   nominal   server	propagation   delay   using   a	 brief
	       client/server exchange, after which it continues in listen-only
	       mode.  If  a  nonzero  value is specified in the broadcastdelay
	       command, the value becomes the delay and the volley is not exe-
	       cuted. Note: the novolley option has been deprecated for future
	       enhancements. Note that, in order to avoid accidental or	 mali-
	       cious  disruption  in  this  mode,  both	 the server and client
	       should operate using symmetric key or public key authentication
	       as  described in the Authentication Options page. Note that the
	       novolley keyword is incompatible with  public  key  authentica-
	       tion.

       manycastserver address [...]
	       Enable  reception  of  manycast	client messages (type m)to the
	       multicast group address(es) (type m) specified.	At  least  one
	       address is required. Note that, in order to avoid accidental or
	       malicious disruption, both the server and client should operate
	       using  symmetric	 key or public key authentication as described
	       in the Authentication Options page.

       multicastclient address [...]
	       Enable reception of multicast server messages to the  multicast
	       group  address(es) (type m) specified. Upon receiving a message
	       for the first time, the multicast client measures  the  nominal
	       server  propagation  delay using a brief client/server exchange
	       with the server, then enters  the  broadcast  client  mode,  in
	       which  it  synchronizes	to succeeding multicast messages. Note
	       that, in order to avoid accidental or malicious	disruption  in
	       this mode, both the server and client should operate using sym-
	       metric key or public key authentication	as  described  in  the
	       Authentication Options page.


BUGS
       The  syntax  checking is not picky; some combinations of ridiculous and
       even hilarious options and modes may not be detected.


SEE ALSO
       ntpd(8), ntp_auth(5), ntp_mon(5), ntp_acc(5), ntp_clock(5), ntp_misc(5)

       The official HTML documentation.

       This file was automatically generated from HTML source.




								   ntp.conf(5)