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 configure
       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 mul-
       ticast 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 preceding 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 notation. 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 mobilizes 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 mobilizes 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 command of one or more desig-
		       nated 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 qualifier designating the server geographic area such as us or europe.

	       unpeer  This command removes a previously configured association. An address or association ID can be used to identify the associa-
		       tion.  Either  an IP address or DNS name can be used. This command is most useful when supplied via ntpq runtime configura-
		       tion 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 recommended 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;  how-
	       ever,  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 recommended  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 algorithm 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 precision 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 packets. 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 broadcast  mes-
	       sage  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 executed. Note: the novolley option has been deprecated for future enhancements. Note that, in order to
	       avoid accidental or malicious 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
	       authentication.

       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 symmet-
	       ric 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 symmetric 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)