Skip site navigation (1)Skip section navigation (2)

FreeBSD Man Pages

Man Page or Keyword Search:
Man Architecture
Apropos Keyword Search (all sections) Output format
home | help
NTP.CONF(5)		  FreeBSD File Formats Manual		   NTP.CONF(5)

NAME
     ntp.conf -- Network Time Protocol (NTP) daemon configuration file

SYNOPSIS
     /etc/ntp.conf

DESCRIPTION
     The ntp.conf configuration	file is	read at	initial	startup	by the ntpd(8)
     daemon in order to	specify	the synchronization sources, modes and other
     related information.  Usually, it is installed in the /etc	directory, but
     could be installed	elsewhere (see the daemon's -c command line option).

     The file format is	similar	to other UNIX configuration files.  Comments
     begin with	a `#' character	and extend to the end of the line; blank lines
     are ignored.  Configuration commands consist of an	initial	keyword	fol-
     lowed by a	list of	arguments, some	of which may be	optional, separated by
     whitespace.  Commands may not be continued	over multiple lines.  Argu-
     ments may be host names, host addresses written in	numeric, dotted-quad
     form, integers, floating point numbers (when specifying times in seconds)
     and text strings.

     The rest of this page describes the configuration and control options.
     The "Notes	on Configuring NTP and Setting up a NTP	Subnet"	page (avail-
     able as part of the HTML documentation provided in	/usr/share/doc/ntp)
     contains an extended discussion of	these options.	In addition to the
     discussion	of general Configuration Options, there	are sections describ-
     ing the following supported functionality and the options used to control
     it:

	   +o   Authentication Support

	   +o   Monitoring Support

	   +o   Access Control Support

	   +o   Reference Clock Support

     Following these is	a section describing Miscellaneous Options.  While
     there is a	rich set of options available, the only	required option	is one
     or	more server, peer, broadcast or	manycastclient commands.

Configuration Support
     Following is a description	of the configuration commands in NTPv4.	 These
     commands have the same basic functions as in NTPv3	and in some cases new
     functions and new arguments.  There are two classes of commands, configu-
     ration commands that configure a persistent association with a remote
     server or peer or reference clock,	and auxiliary commands that specify
     environmental variables that control various related operations.

   Configuration Commands
     The various modes are determined by the command keyword and the type of
     the required IP address.  Addresses are classed by	type as	(s) a remote
     server or peer (IP	class A, B and C), (b) the broadcast address of	a
     local interface, (m) a multicast address (IP class	D), or (r) a reference
     clock address (127.127.x.x).  Note	that only those	options	applicable to
     each command are listed below.  Use of options not	listed may not be
     caught as an error, but may result	in some	weird and even destructive
     behavior.

     server address [key key | autokey]	[burst]	[iburst] [version version]
	     [prefer] [minpoll minpoll]	[maxpoll maxpoll]

     peer address [key key | autokey] [version version]	[prefer] [minpoll
	     minpoll] [maxpoll maxpoll]

     broadcast address [key key	| autokey] [version version] [prefer] [minpoll
	     minpoll] [ttl ttl]

     manycastclient address [key key | autokey]	[version version] [prefer]
	     [minpoll minpoll] [maxpoll	maxpoll] [ttl ttl]

     These four	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	an IP address in dotted-quad notation.	Additional information on
     association behavior can be found in the "Association Management" page.

     server  For type s	and r addresses, this command mobilizes	a persistent
	     client mode association with the specified	remote server or local
	     radio clock.  In this mode	the local clock	can synchronized to
	     the remote	server,	but the	remote server can never	be synchro-
	     nized to the local	clock.	This command should not	be used	for
	     type b or m addresses.

     peer    For type s	addresses (only), this command mobilizes a persistent
	     symmetric-active mode association with the	specified remote peer.
	     In	this mode the local clock can be synchronized to the remote
	     peer or the remote	peer can be synchronized to the	local clock.
	     This is useful in a network of servers where, depending on	vari-
	     ous failure scenarios, either the local or	remote peer may	be the
	     better source of time.  This command should NOT be	used for type
	     b,	m or r addresses.

     broadcast
	     For type b	and m addresses	(only),	this command mobilizes a per-
	     sistent broadcast mode association.  Multiple commands can	be
	     used to specify multiple local broadcast interfaces (subnets)
	     and/or multiple multicast groups.	Note that local	broadcast mes-
	     sages go only to the interface associated with the	subnet speci-
	     fied, but multicast messages go to	all interfaces.	 In broadcast
	     mode the local server sends periodic broadcast messages to	a
	     client population at the address specified, which is usually the
	     broadcast address on (one of) the local network(s)	or a multicast
	     address assigned to NTP.  The IANA	has assigned the multicast
	     group address 224.0.1.1 exclusively to NTP, but other noncon-
	     flicting addresses	can be used to contain the messages within
	     administrative boundaries.	 Ordinarily, this specification
	     applies only to the local server operating	as a sender; for oper-
	     ation as a	broadcast client, see the broadcastclient or
	     multicastclient commands below.

     manycastclient
	     For type m	addresses (only), this command mobilizes a manycast
	     client mode association for the multicast address specified.  In
	     this case a specific address must be supplied which matches the
	     address used on the manycastserver	command	for the	designated
	     manycast servers.	The NTP	multicast address 224.0.1.1 assigned
	     by	the IANA should	NOT be used, unless specific means are taken
	     to	avoid spraying large areas of the Internet with	these messages
	     and causing a possibly massive implosion of replies at the
	     sender.  The manycastserver command specifies that	the local
	     server is to operate in client mode with the remote servers that
	     are discovered as the result of broadcast/multicast messages.
	     The client	broadcasts a request message to	the group address
	     associated	with the specified address and specifically enabled
	     servers respond to	these messages.	 The client selects the
	     servers providing the best	time and continues as with the server
	     command.  The remaining servers are discarded as if never heard.

     Options:

     autokey
	     All packets sent to and received from the server or peer are to
	     include authentication fields encrypted using the autokey scheme
	     described in Authentication Options.

     burst   when the server is	reachable and at each poll interval, send a
	     burst of eight packets instead of the usual one packet.  The
	     spacing between the first and the second packets is about 16s to
	     allow a modem call	to complete, while the spacing between the
	     remaining packets is about	2s.  This is designed to improve time-
	     keeping quality with the server command and s addresses.

     iburst  When the server is	unreachable and	at each	poll interval, send a
	     burst of eight packets instead of the usual one.  As long as the
	     server is unreachable, the	spacing	between	packets	is about 16s
	     to	allow a	modem call to complete.	 Once the server is reachable,
	     the spacing between packets is about 2s.  This is designed	to
	     speed the initial synchronization acquisition with	the server
	     command and s addresses and when ntpd(8) is started with the -q
	     option.

     key key
	     All packets sent to and received from the server or peer are to
	     include authentication fields encrypted using the specified key
	     identifier	with values from 1 to 65534, inclusive.	 The default
	     is	to include no encryption field.

     minpoll minpoll

     maxpoll maxpoll
	     These options specify the minimum and maximum poll	intervals for
	     NTP messages, in seconds to the power of two.  The	maximum	poll
	     interval defaults to 10 (1,024 s),	but can	be increased by	the
	     maxpoll option to an upper	limit of 17 (36.4 h).  The minimum
	     poll interval defaults to 6 (64 s), but can be decreased by the
	     minpoll option to a lower limit of	4 (16 s).

     prefer  Marks the server as preferred.  All other things being equal,
	     this host will be chosen for synchronization among	a set of cor-
	     rectly operating hosts.  See the "Mitigation Rules	and the	prefer
	     Keyword" page for further information.

     ttl ttl
	     This option is used only with broadcast server and	manycast
	     client modes.  It specifies the time-to-live ttl to use on	broad-
	     cast server and multicast server and the maximum ttl for the
	     expanding ring search with	manycast client	packets.  Selection of
	     the proper	value, which defaults to 127, is something of a	black
	     art and should be coordinated with	the network administrator.

     version version
	     Specifies the version number to be	used for outgoing NTP packets.
	     Versions 1-4 are the choices, with	version	4 the default.

   Auxiliary Commands
     broadcastclient
	     This command enables reception of broadcast server	messages to
	     any local interface (type b) address.  Upon receiving a message
	     for the first time, the broadcast 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 broadcast 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 Authentication Options.

     manycastserver address ...
	     This command enables reception of manycast	client messages	to the
	     multicast group address(es) (type m) specified.  At least one
	     address is	required, but the NTP multicast	address	224.0.1.1
	     assigned by the IANA should NOT be	used, unless specific means
	     are taken to limit	the span of the	reply and avoid	a possibly
	     massive implosion at the original sender.	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	Authentication Options.

     multicastclient address ...
	     This command enables reception of multicast server	messages to
	     the multicast group address(es) (type m) specified.  Upon receiv-
	     ing 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
	     Authentication Options.

Authentication Support
     Authentication support allows the NTP client to verify that the server is
     in	fact known and trusted and not an intruder intending accidentally or
     on	purpose	to masquerade as that server.  The NTPv3 specification
     RFC-1305 defines a	scheme which provides cryptographic authentication of
     received NTP packets.  Originally,	this was done using the	Data Encryp-
     tion Standard (DES) algorithm operating in	Cipher Block Chaining (CBC)
     mode, commonly called DES-CBC.  Subsequently, this	was augmented by the
     RSA Message Digest	5 (MD5)	algorithm using	a private key, commonly	called
     keyed-MD5.	 Either	algorithm computes a message digest, or	one-way	hash,
     which can be used to verify the server has	the correct private key	and
     key identifier.

     NTPv4 retains the NTPv3 schemes, properly described as symmetric-key
     cryptography and, in addition, provides a new Autokey scheme based	on
     public-key	cryptography.  Public-key cryptography is generally considered
     more secure than symmetric-key cryptography, since	the security is	based
     on	a private value	which is generated by each server and never revealed.
     With Autokey all key distribution and management functions	involve	only
     public values, which considerably simplifies key distribution and stor-
     age.

     Authentication is configured separately for each association using	the
     key or autokey subcommands	on the peer, server, broadcast and
     manycastclient commands as	described in Configuration Options.  The
     authentication options described below specify the	suite of keys, select
     the key for each configured association and manage	the configuration
     operations.

     The auth flag controls whether new	associations or	remote configuration
     commands require cryptographic authentication.  This flag can be set or
     reset by the enable and disable configuration commands and	also by	remote
     configuration commands sent by a ntpdc(8) program running in another
     machine.  If this flag is enabled,	which is the default case, new broad-
     cast client and symmetric passive associations and	remote configuration
     commands must be cryptographically	authenticated using either symmetric-
     key or public-key schemes.	 If this flag is disabled, these operations
     are effective even	if not cryptographic authenticated.  It	should be
     understood	that operating in the latter mode invites a significant	vul-
     nerability	where a	rogue hacker can seriously disrupt client timekeeping.

     In	networks with firewalls	and large numbers of broadcast clients it may
     be	acceptable to disable authentication, since that avoids	key distribu-
     tion and simplifies network maintenance.  However,	when the configuration
     file contains host	names, or when a server	or client is configured
     remotely, host names are resolved using the DNS and a separate name reso-
     lution process.  In order to protect against bogus	name server messages,
     name resolution messages are authenticated	using an internally generated
     key which is normally invisible to	the user.  However, if cryptographic
     support is	disabled, the name resolution process will fail.  This can be
     avoided either by specifying IP addresses instead of host names, which is
     generally inadvisable, or by enabling the flag for	name resolution	and
     disabled it once the name resolution process is complete.

     An	attractive alternative where multicast support is available is many-
     cast mode,	in which clients periodically troll for	servers.  Crypto-
     graphic authentication in this mode uses public-key schemes as described
     below.  The principle advantage of	this manycast mode is that potential
     servers need not be configured in advance,	since the client finds them
     during regular operation, and the configuration files for all clients can
     be	identical.

     In	addition to the	default	symmetric-key cryptographic support, support
     for public-key cryptography is available if the requisite rsaref20	soft-
     ware distribution has been	installed before building the distribution.
     Public-key	cryptography provides secure authentication of servers without
     compromising accuracy and stability.  The security	model and protocol
     schemes for both symmetric-key and	public-key cryptography	are described
     below.

   Symmetric-Key Scheme
     The original RFC-1305 specification allows	any one	of possibly 65,534
     keys, each	distinguished by a 32-bit key identifier, to authenticate an
     association.  The servers and clients involved must agree on the key and
     key identifier to authenticate their messages.  Keys and related informa-
     tion are specified	in a key file, usually called ntp.keys,	which should
     be	exchanged and stored using secure procedures beyond the	scope of the
     NTP protocol itself.  Besides the keys used for ordinary NTP associa-
     tions, additional keys can	be used	as passwords for the ntpq(8) and
     ntpdc(8) utility programs.

     When ntpd(8) is first started, it reads the key file specified in the
     keys command and installs the keys	in the key cache.  However, the	keys
     must be activated with the	trusted	command	before use.  This allows, for
     instance, the installation	of possibly several batches of keys and	then
     activating	or deactivating	each batch remotely using ntpdc(8).  This also
     provides a	revocation capability that can be used if a key	becomes	com-
     promised.	The requestkey command selects the key used as the password
     for the ntpdc(8) utility, while the controlkey command selects the	key
     used as the password for the ntpq(8) utility.

   Public-Key Scheme
     The original NTPv3	authentication scheme described	in RFC-1305 continues
     to	be supported; however, in NTPv4	an additional authentication scheme
     called Autokey is available.  It uses MD5 message digest, RSA public-key
     signature and Diffie-Hellman key agreement	algorithms available from sev-
     eral sources, but not included in the NTPv4 software distribution.	 In
     order to be effective, the	rsaref20 package must be installed as
     described in the README.rsa file.	Once installed,	the configure and
     build process automatically detects it and	compiles the routines
     required.	The Autokey scheme has several modes of	operation correspond-
     ing to the	various	NTP modes supported.  RSA signatures with timestamps
     are used in all modes to verify the source	of cryptographic values.  All
     modes use a special cookie	which can be computed independently by the
     client and	server.	 In symmetric modes the	cookie is constructed using
     the Diffie-Hellman	key agreement algorithm.  In other modes the cookie is
     constructed from the IP addresses and a private value known only to the
     server.  All modes	use in addition	a variant of the S-KEY scheme, in
     which a pseudo-random key list is generated and used in reverse order.
     These schemes are described along with an executive summary, current sta-
     tus, briefing slides and reading list, in the "Autonomous Authentication"
     page.

     The cryptographic values used by the Autokey scheme are incorporated as a
     set of files generated by the ntp-genkeys(8) program, including the sym-
     metric private keys, public/private key pair, and the agreement parame-
     ters.  See	the ntp.keys(5)	page for a description of the formats of these
     files.  They contain cryptographic	values generated by the	algorithms of
     the rsaref20 package and are in printable ASCII format.  All file names
     include the timestamp, in NTP seconds, following the default names	given
     below.  Since the file data are derived from random values	seeded by the
     system clock and the file name includes the timestamp, every generation
     produces a	different file and different file name.

     The ntp.keys file contains	the DES/MD5 private keys.  It must be distrib-
     uted by secure means to other servers and clients sharing the same	secu-
     rity compartment and made visible only to root.  While this file is not
     used with the Autokey scheme, it is needed	to authenticate	some remote
     configuration commands used by the	ntpdc(8), ntpq(8) utilities.  The
     ntpkey file contains the RSA private key.	It is useful only to the
     machine that generated it and never shared	with any other daemon or
     application program, so must be made visible only to root.

     The ntp_dh	file contains the agreement parameters,	which are used only in
     symmetric (active and passive) modes.  It is necessary that both peers
     beginning a symmetric-mode	association share the same parameters, but it
     does not matter which ntp_dh file generates them.	If one of the peers
     contains the parameters, the other	peer obtains them using	the Autokey
     protocol.	If both	peers contain the parameters, the most recent copy is
     used by both peers.  If a peer does not have the parameters, they will be
     requested by all associations, either configured or not; but, none	of the
     associations can proceed until one	of them	has received the parameters.
     Once loaded, the parameters can be	provided on request to other clients
     and servers.  The ntp_dh file can be also be distributed using insecure
     means, since the data are public values.

     The ntpkey_host file contains the RSA public key, where host is the name
     of	the host.  Each	host must have its own ntpkey_host file, which is nor-
     mally provided to other hosts using the Autokey protocol.	Each server or
     peer association requires the public key associated with the particular
     server or peer to be loaded either	directly from a	local file or indi-
     rectly from the server using the Autokey protocol.	 These files can be
     widely distributed	and stored using insecure means, since the data	are
     public values.

     The optional ntpkey_certif_host file contains the PKI certificate for the
     host.  This provides a binding between the	host hame and RSA public key.
     In	the current implementation the certificate is obtained by a client, if
     present, but the contents are ignored.

     Due to the	widespread use of interface-specific naming, the host names
     used in configured	and mobilized associations are determined by the UNIX
     gethostname(3) library routine.  Both the ntp-genkeys(8) program and the
     Autokey protocol derive the name of the public key	file using the name
     returned by this routine.	While every server and client is required to
     load their	own public and private keys, the public	keys for each client
     or	peer association can be	obtained from the server or peer using the
     Autokey protocol.	Note however, that at the current stage	of development
     the authenticity of the server or peer and	the cryptographic binding of
     the server	name, address and public key is	not yet	established by a cer-
     tificate authority	or web of trust.

   Leapseconds Table
     The NIST provides a table showing the epoch for all historic occasions of
     leap second insertion since 1972.	The leapsecond table shows each	epoch
     of	insertion along	with the offset	of International Atomic	Time (TAI)
     with respect to Coordinated Universal Time	(UTC), as disseminated by NTP.
     The table can be obtained directly	from NIST national time	servers	using
     FTP as the	ASCII file pub/leap-seconds.

     While not strictly	a security function, the Autokey scheme	provides means
     to	securely retrieve the leapsecond table from a server or	peer.  Servers
     load the leapsecond table directly	from the file specified	in the crypto
     command, while clients can	load the table indirectly from the servers
     using the Autokey protocol.  Once loaded, the table can be	provided on
     request to	other clients and servers.

   Key Management
     All key files are installed by default in /usr/local/etc, which is	nor-
     mally in a	shared file system in NFS-mounted networks and avoids
     installing	them in	each machine separately.  The default can be overrid-
     den by the	keysdir	configuration command.	However, this is not a good
     place to install the private key file, since each machine needs its own
     file.  A suitable place to	install	it is in /etc, which is	normally not
     in	a shared file system.

     The recommended practice is to keep the timestamp extensions when
     installing	a file and to install a	link from the default name (without
     the timestamp extension) to the actual file.  This	allows new file	gener-
     ations to be activated simply by changing the link.  However, ntpd(8)
     parses the	link name when present to extract the extension	value and
     sends it along with the public key	and host name when requested.  This
     allows clients to verify that the file and	generation time	are always
     current.  However,	the actual location of each file can be	overridden by
     the crypto	configuration command.

     All cryptographic keys and	related	parameters should be regenerated on a
     periodic and automatic basis, like	once per month.	 The ntp-genkeys(8)
     program uses the same timestamp extension for all files generated at one
     time, so each generation is distinct and can be readily recognized	in
     monitoring	data.  While a public/private key pair must be generated by
     every server and client, the public keys and agreement parameters do not
     need to be	explicitly copied to all machines in the same security com-
     partment, since they can be obtained automatically	using the Autokey pro-
     tocol.  However, it is necessary that all primary servers have the	same
     agreement parameter file.	The recommended	way to do this is for one of
     the primary servers to generate that file and then	copy it	to the other
     primary servers in	the same compartment using the UNIX rdist(1) command.
     Future versions of	the Autokey protocol are to contain provisions for an
     agreement protocol	to do this automatically.

     Servers and clients can make a new	generation in the following way.  All
     machines have loaded the old generation at	startup	and are	operating nor-
     mally.  At	designated intervals, each machine generates a new public/pri-
     vate key pair and makes links from	the default file names to the new file
     names.  The ntpd(8) is then restarted and loads the new generation, with
     result clients no longer can authenticate correctly.  The Autokey proto-
     col is designed so	that after a few minutes the clients time out and
     restart the protocol from the beginning, with result the new generation
     is	loaded and operation continues as before.  A similar procedure can be
     used for the agreement parameter file, but	in this	case precautions must
     be	take to	be sure	that all machines with this file have the same copy.

   Authentication Commands
     autokey [logsec]
	     Specifies the interval between regenerations of the session key
	     list used with the	Autokey	protocol.  Note	that the size of the
	     key list for each association depends on this interval and	the
	     current poll interval.  The default value is 12 (4096 s or	about
	     1.1 hours).  For poll intervals above the specified interval, a
	     session key list with a single entry will be regenerated for
	     every message sent.

     controlkey	key
	     Specifies the key identifier to use with the ntpq(8) utility,
	     which uses	the standard protocol defined in RFC-1305.  The	key
	     argument is the key identifier for	a trusted key, where the value
	     can be in the range 1 to 65534, inclusive.

     crypto [flags flags] [privatekey file] [publickey file] [dhparms file]
	     [leap file]
	     This command requires the NTP daemon build	process	be configured
	     with the RSA library.  This command activates public-key cryptog-
	     raphy and loads the required RSA private and public key files and
	     the optional Diffie-Hellman agreement parameter file, if present.
	     If	one or more files are left unspecified,	the default names are
	     used as described below.  Following are the subcommands:

	     privatekey	file
		     Specifies the location of the RSA private key file, which
		     otherwise defaults	to /usr/local/etc/ntpkey.

	     publickey file
		     Specifies the location of the RSA public key file,	which
		     otherwise defaults	to /usr/local/etc/ntpkey_host, where
		     host is the name of the generating	machine.

	     dhparms file
		     Specifies the location of the Diffie-Hellman parameters
		     file, which otherwise defaults to
		     /usr/local/etc/ntpkey_dh.

	     leap file
		     Specifies the location of the leapsecond table file,
		     which otherwise defaults to /usr/local/etc/ntpkey_leap.

     keys keyfile
	     Specifies the location of the DES/MD5 private key file containing
	     the keys and key identifiers used by ntpd(8), ntpq(8) and
	     ntpdc(8) when operating in	symmetric-key mode.

     keysdir path
	     This command requires the NTP daemon build	process	be configured
	     with the RSA library.  It specifies the default directory path
	     for the private key file, agreement parameters file and one or
	     more public key files.  The default when this command does	not
	     appear in the configuration file is /usr/local/etc.

     requestkey	key
	     Specifies the key identifier to use with the ntpdc(8) utility
	     program, which uses a proprietary protocol	specific to this
	     implementation of ntpd(8).	 The key argument is a key identifier
	     for the trusted key, where	the value can be in the	range 1	to
	     65534, inclusive.

     revoke logsec
	     Specifies the interval between re-randomization of	certain	cryp-
	     tographic values used by the Autokey scheme, as a power of	2 in
	     seconds.  These values need to be updated frequently in order to
	     deflect brute-force attacks on the	algorithms of the scheme; how-
	     ever, updating some values	is a relatively	expensive operation.
	     The default interval is 16	(65,536	s or about 18 hours).  For
	     poll intervals above the specified	interval, the values will be
	     updated for every message sent.

     trustedkey	key ...
	     Specifies the key identifiers which are trusted for the purposes
	     of	authenticating peers with symmetric-key	cryptography, as well
	     as	keys used by the ntpq(8) and ntpdc(8) programs.	 The authenti-
	     cation procedures require that both the local and remote servers
	     share the same key	and key	identifier for this purpose, although
	     different keys can	be used	with different servers.	 The key argu-
	     ments are 32-bit unsigned integers	with values from 1 to 65,534.

Monitoring Support
     ntpd(8) includes a	comprehensive monitoring facility suitable for contin-
     uous, long	term recording of server and client timekeeping	performance.
     See the statistics	command	below for a listing and	example	of each	type
     of	statistics currently supported.	 Statistic files are managed using
     file generation sets and scripts in the ./scripts directory of this dis-
     tribution.	 Using these facilities	and UNIX cron(8) jobs, the data	can be
     automatically summarized and archived for retrospective analysis.

   Monitoring Commands
     statistics	name ...
	     Enables writing of	statistics records.  Currently,	four kinds of
	     name statistics are supported.

	     loopstats
		     Enables recording of loop filter statistics information.
		     Each update of the	local clock outputs a line of the fol-
		     lowing form to the	file generation	set named loopstats:

		     50935 75440.031 0.000006019 13.778190 0.000351733 0.013380	6

		     The first two fields show the date	(Modified Julian Day)
		     and time (seconds and fraction past UTC midnight).	 The
		     next five fields show time	offset (seconds), frequency
		     offset (parts per million - PPM), RMS jitter (seconds),
		     Allan deviation (PPM) and clock discipline	time constant.

	     peerstats
		     Enables recording of peer statistics information.	This
		     includes statistics records of all	peers of a NTP server
		     and of special signals, where present and configured.
		     Each valid	update appends a line of the following form to
		     the current element of a file generation set named	peer-
		     stats:

		     48773 10847.650 127.127.4.1 9714 -0.001605	0.00000	0.00142

		     The first two fields show the date	(Modified Julian Day)
		     and time (seconds and fraction past UTC midnight).	 The
		     next two fields show the peer address in dotted-quad
		     notation and status, respectively.	 The status field is
		     encoded in	hex in the format described in Appendix	A of
		     the NTP specification RFC 1305.  The final	three fields
		     show the offset, delay and	RMS jitter, all	in seconds.

	     clockstats
		     Enables recording of clock	driver statistics information.
		     Each update received from a clock driver appends a	line
		     of	the following form to the file generation set named
		     clockstats:

		     49213 525.624 127.127.4.1 93 226 00:08:29.606 D

		     The first two fields show the date	(Modified Julian Day)
		     and time (seconds and fraction past UTC midnight).	 The
		     next field	shows the clock	address	in dotted-quad nota-
		     tion.  The	final field shows the last timecode received
		     from the clock in decoded ASCII format, where meaningful.
		     In	some clock drivers a good deal of additional informa-
		     tion can be gathered and displayed	as well.  See informa-
		     tion specific to each clock for further details.

	     rawstats
		     Enables recording of raw-timestamp	statistics informa-
		     tion.  This includes statistics records of	all peers of a
		     NTP server	and of special signals,	where present and con-
		     figured.  Each NTP	message	received from a	peer or	clock
		     driver appends a line of the following form to the	file
		     generation	set named rawstats:

		     50928 2132.543 128.4.1.1 128.4.1.20 3102453281.584327000 3102453281.58622800031 02453332.540806000	3102453332.541458000
		     The first two fields show the date	(Modified Julian Day)
		     and time (seconds and fraction past UTC midnight).	 The
		     next two fields show the remote peer or clock address
		     followed by the local address in dotted-quad notation.
		     The final four fields show	the originate, receive,	trans-
		     mit and final NTP timestamps in order.  The timestamp
		     values are	as received and	before processing by the vari-
		     ous data smoothing	and mitigation algorithms.

     statsdir directory_path
	     Indicates the full	path of	a directory where statistics files
	     should be created (see below).  This keyword allows the (other-
	     wise constant) filegen filename prefix to be modified for file
	     generation	sets, which is useful for handling statistics logs.

     filegen name [file	filename] [type	typename] [link	| nolink] [enable |
	     disable]
	     Configures	setting	of generation file set name.  Generation file
	     sets provide a means for handling files that are continuously
	     growing during the	lifetime of a server.  Server statistics are a
	     typical example for such files.  Generation file sets provide
	     access to a set of	files used to store the	actual data.  At any
	     time at most one element of the set is being written to.  The
	     type given	specifies when and how data will be directed to	a new
	     element of	the set.  This way, information	stored in elements of
	     a file set	that are currently unused are available	for adminis-
	     trational operations without the risk of disturbing the operation
	     of	ntpd(8).  (Most	important: they	can be removed to free space
	     for new data produced.)  Note that	this command can be sent from
	     the ntpdc(8) program running at a remote location.

	     name    This is the type of the statistics	records, as shown in
		     the statistics command.

	     file filename
		     This is the file name for the statistics records.	File-
		     names of set members are built from three concatenated
		     elements prefix, filename and suffix:

		     prefix  This is a constant	filename path.	It is not sub-
			     ject to modifications via the filegen option.  It
			     is	defined	by the server, usually specified as a
			     compile-time constant.  It	may, however, be con-
			     figurable for individual file generation sets via
			     other commands.  For example, the prefix used
			     with loopstats and	peerstats generation can be
			     configured	using the statsdir option explained
			     above.

		     filename
			     This string is directly concatenated to the pre-
			     fix mentioned above (no intervening `/' (slash)).
			     This can be modified using	the file argument to
			     the filegen statement.  No	`..' elements are
			     allowed in	this component to prevent filenames
			     referring to parts	outside	the file system	hier-
			     archy denoted by prefix.

		     suffix  This part is reflects individual elements of a
			     file set.	It is generated	according to the type
			     of	a file set.

	     type typename
		     A file generation set is characterized by its type.  The
		     following types are supported:

		     none    The file set is actually a	single plain file.

		     pid     One element of file set is	used per incarnation
			     of	a ntpd(8) server.  This	type does not perform
			     any changes to file set members during runtime,
			     however it	provides an easy way of	separating
			     files belonging to	different ntpd(8) server
			     incarnations.  The	set member filename is built
			     by	appending a `.'	(dot) to concatenated prefix
			     and filename strings, and appending the decimal
			     representation of the process ID of the ntpd(8)
			     server process.

		     day     One file generation set element is	created	per
			     day.  A day is defined as the period between
			     00:00 and 24:00 UTC.  The file set	member suffix
			     consists of a `.' (dot) and a day specification
			     in	the form YYYYMMdd.  YYYY is a 4-digit year
			     number (e.g., 1992).  MM is a two digit month
			     number.  dd is a two digit	day number.  Thus, all
			     information written at 10 December	1992 would end
			     up	in a file named	~prefix/filename/19921210.

		     week    Any file set member contains data related to a
			     certain week of a year.  The term week is defined
			     by	computing day-of-year modulo 7.	 Elements of
			     such a file generation set	are distinguished by
			     appending the following suffix to the file	set
			     filename base: A dot, a 4-digit year number, the
			     letter Ql W , and a 2-digit week number.  For
			     example, information from January,	10th 1992
			     would end up in a file with suffix	.1992W1.

		     month   One generation file set element is	generated per
			     month.  The file name suffix consists of a	dot, a
			     4-digit year number, and a	2-digit	month.

		     year    One generation file element is generated per
			     year.  The	filename suffix	consists of a dot and
			     a 4 digit year number.

		     age     This type of file generation sets changes to a
			     new element of the	file set every 24 hours	of
			     server operation.	The filename suffix consists
			     of	a dot, the letter `a', and an 8-digit number.
			     This number is taken to be	the number of seconds
			     the server	is running at the start	of the corre-
			     sponding 24-hour period.  Information is only
			     written to	a file generation by specifying
			     enable; output is prevented by specifying
			     disable.

	     link | nolink
		     It	is convenient to be able to access the current element
		     of	a file generation set by a fixed name.	This feature
		     is	enabled	by specifying link and disabled	using nolink.
		     If	link is	specified, a hard link from the	current	file
		     set element to a file without suffix is created.  When
		     there is already a	file with this name and	the number of
		     links of this file	is one,	it is renamed appending	a dot,
		     the letter	`C', and the pid of the	ntpd(8)	server
		     process.  When the	number of links	is greater than	one,
		     the file is unlinked.  This allows	the current file to be
		     accessed by a constant name.

	     enable | disable
		     Enables or	disables the recording function.

Access Control Support
     ntpd(8) implements	a general purpose address-and-mask based restriction
     list.  The	list is	sorted by address and by mask, and the list is
     searched in this order for	matches, with the last match found defining
     the restriction flags associated with the incoming	packets.  The source
     address of	incoming packets is used for the match,	with the 32- bit
     address being and'ed with the mask	associated with	the restriction	entry
     and then compared with the	entry's	address	(which has also	been and'ed
     with the mask) to look for	a match.  Additional information and examples
     can be found in the "Notes	on Configuring NTP and Setting up a NTP
     Subnet" page.

     The restriction facility was implemented in conformance with the access
     policies for the original NSFnet backbone time servers.  While this
     facility may be otherwise useful for keeping unwanted or broken remote
     time servers from affecting your own, it should not be considered an
     alternative to the	standard NTP authentication facility.  Source address
     based restrictions	are easily circumvented	by a determined	cracker.

   The Kiss-of-Death Packet
     Ordinarily, packets denied	service	are simply dropped with	no further
     action except incrementing	statistics counters.  Sometimes	a more proac-
     tive response is needed, such as a	server message that explicitly
     requests the client to stop sending and leave a message for the system
     operator.	A special packet format	has been created for this purpose
     called the	kiss-of-death packet.  If the kod flag is set and either ser-
     vice is denied or the client limit	is exceeded, the server	returns	the
     packet and	sets the leap bits unsynchronized, stratum zero	and the	ASCII
     string "DENY" in the reference source identifier field.  If the kod flag
     is	not set, the server simply drops the packet.

     A client or peer receiving	a kiss-of-death	packet performs	a set of san-
     ity checks	to minimize security exposure.	If this	is the first packet
     received from the server, the client assumes an access denied condition
     at	the server.  It	updates	the stratum and	reference identifier peer
     variables and sets	the access denied (test	4) bit in the peer flash vari-
     able.  If this bit	is set,	the client sends no packets to the server.  If
     this is not the first packet, the client assumes a	client limit condition
     at	the server, but	does not update	the peer variables.  In	either case, a
     message is	sent to	the system log.

   Access Control Commands
     restrict numeric_address [mask numeric_mask] [flag	...]
	     The numeric_address argument, expressed in	dotted-quad form, is
	     the address of a host or network.	The mask, also expressed in
	     dotted-quad form, defaults	to 255.255.255.255, meaning that the
	     numeric_address is	treated	as the address of an individual	host.
	     A default entry (address 0.0.0.0, mask 0.0.0.0) is	always
	     included and, given the sort algorithm, is	always the first entry
	     in	the list.  Note	that, while numeric_address is normally	given
	     in	dotted-quad format, the	text string `default', with no mask
	     option, may be used to indicate the default entry.	 In the	cur-
	     rent implementation, flag always restricts	access,	i.e., an entry
	     with no flags indicates that free access to the server is to be
	     given.  The flags are not orthogonal, in that more	restrictive
	     flags will	often make less	restrictive ones redundant.  The flags
	     can generally be classed into two categories, those which
	     restrict time service and those which restrict informational
	     queries and attempts to do	run-time reconfiguration of the
	     server.  One or more of the following flags may be	specified:

	     kod     If	access is denied, send a kiss-of-death packet.

	     ignore  Ignore all	packets	from hosts which match this entry.  If
		     this flag is specified neither queries nor	time server
		     polls will	be responded to.

	     noquery
		     Ignore all	NTP mode 6 and 7 packets (i.e. information
		     queries and configuration requests) from the source.
		     Time service is not affected.

	     nomodify
		     Ignore all	NTP mode 6 and 7 packets which attempt to mod-
		     ify the state of the server (i.e. run time	reconfigura-
		     tion).  Queries which return information are permitted.

	     notrap  Decline to	provide	mode 6 control message trap service to
		     matching hosts.  The trap service is a subsystem of the
		     mode 6 control message protocol which is intended for use
		     by	remote event logging programs.

	     lowpriotrap
		     Declare traps set by matching hosts to be low priority.
		     The number	of traps a server can maintain is limited (the
		     current limit is 3).  Traps are usually assigned on a
		     first come, first served basis, with later	trap
		     requestors	being denied service.  This flag modifies the
		     assignment	algorithm by allowing low priority traps to be
		     overridden	by later requests for normal priority traps.

	     noserve
		     Ignore NTP	packets	whose mode is other than 6 or 7.  In
		     effect, time service is denied, though queries may	still
		     be	permitted.

	     nopeer  Provide stateless time service to polling hosts, but do
		     not allocate peer memory resources	to these hosts even if
		     they otherwise might be considered	useful as future syn-
		     chronization partners.

	     notrust
		     Treat these hosts normally	in other respects, but never
		     use them as synchronization sources.

	     limited
		     These hosts are subject to	limitation of number of
		     clients from the same net.	 Net in	this context refers to
		     the IP notion of net (class A, class B, class C, etc.).
		     Only the first client_limit hosts that have shown up at
		     the server	and that have been active during the last
		     client_limit_period seconds are accepted.	Requests from
		     other clients from	the same net are rejected.  Only time
		     request packets are taken into account.  Query packets
		     sent by the ntpq(8) and ntpdc(8) programs are not subject
		     to	these limits.  A history of clients is kept using the
		     monitoring	capability of ntpd(8).	Thus, monitoring is
		     always active as long as there is a restriction entry
		     with the limited flag.

	     ntpport
		     This is actually a	match algorithm	modifier, rather than
		     a restriction flag.  Its presence causes the restriction
		     entry to be matched only if the source port in the	packet
		     is	the standard NTP UDP port (123).  Both ntpport and
		     non-ntpport may be	specified.  The	ntpport	is considered
		     more specific and is sorted later in the list.

	     version
		     Ignore these hosts	if not the current NTP version.

	     Default restriction list entries, with the	flags ignore,
	     interface,	ntpport, for each of the local host's interface
	     addresses are inserted into the table at startup to prevent the
	     server from attempting to synchronize to its own time.  A default
	     entry is also always present, though if it	is otherwise unconfig-
	     ured; no flags are	associated with	the default entry (i.e.,
	     everything	besides	your own NTP server is unrestricted).

     clientlimit limit
	     Set the client_limit variable, which limits the number of simul-
	     taneous access-controlled clients.	 The default value for this
	     variable is 3.

     clientperiod period
	     Set the client_limit_period variable, which specifies the number
	     of	seconds	after which a client is	considered inactive and	thus
	     no	longer is counted for client limit restriction.	 The default
	     value for this variable is	3600 seconds.

Reference Clock	Support
     The NTP Version 4 daemon supports some three dozen	different radio,
     satellite and modem reference clocks plus a special pseudo-clock used for
     backup or when no other clock source is available.	 Detailed descriptions
     of	individual device drivers and options can be found in the "Reference
     Clock Drivers" page (available as part of the HTML	documentation provided
     in	/usr/share/doc/ntp).  Additional information can be found in the pages
     linked there, including the "Debugging Hints for Reference	Clock Drivers"
     and "How To Write a Reference Clock Driver" pages.	 In addition, support
     for a PPS signal is available as described	in the "Pulse-per-second (PPS)
     Signal Interfacing" page.	Many drivers support special line disci-
     pline/streams modules which can significantly improve the accuracy	using
     the driver.  These	are described in the "Line Disciplines and Streams
     Drivers" page.

     A reference clock will generally (though not always) be a radio timecode
     receiver which is synchronized to a source	of standard time such as the
     services offered by the NRC in Canada and NIST and	USNO in	the US.	 The
     interface between the computer and	the timecode receiver is device	depen-
     dent, but is usually a serial port.  A device driver specific to each
     reference clock must be selected and compiled in the distribution;	how-
     ever, most	common radio, satellite	and modem clocks are included by
     default.  Note that an attempt to configure a reference clock when	the
     driver has	not been compiled or the hardware port has not been appropri-
     ately configured results in a scalding remark to the system log file, but
     is	otherwise non hazardous.

     For the purposes of configuration,	ntpd(8)	treats reference clocks	in a
     manner analogous to normal	NTP peers as much as possible.	Reference
     clocks are	identified by a	syntactically correct but invalid IP address,
     in	order to distinguish them from normal NTP peers.  Reference clock
     addresses are of the form 127.127.t.u, where t is an integer denoting the
     clock type	and u indicates	the unit number	in the range 0-3.  While it
     may seem overkill,	it is in fact sometimes	useful to configure multiple
     reference clocks of the same type,	in which case the unit numbers must be
     unique.

     The server	command	is used	to configure a reference clock,	where the
     address argument in that command is the clock address.  The key, version
     and ttl options are not used for reference	clock support.	The mode
     option is added for reference clock support, as described below.  The
     prefer option can be useful to persuade the server	to cherish a reference
     clock with	somewhat more enthusiasm than other reference clocks or	peers.
     Further information on this option	can be found in	the "Mitigation	Rules
     and the prefer Keyword" page.  The	minpoll	and maxpoll options have mean-
     ing only for selected clock drivers.  See the individual clock driver
     document pages for	additional information.

     The fudge command is used to provide additional information for individ-
     ual clock drivers and normally follows immediately	after the server com-
     mand.  The	address	argument specifies the clock address.  The refid and
     stratum options can be used to override the defaults for the device.
     There are two optional device-dependent time offsets and four flags that
     can be included in	the fudge command as well.

     The stratum number	of a reference clock is	by default zero.  Since	the
     ntpd(8) daemon adds one to	the stratum of each peer, a primary server
     ordinarily	displays an external stratum of	one.  In order to provide
     engineered	backups, it is often useful to specify the reference clock
     stratum as	greater	than zero.  The	stratum	option is used for this	pur-
     pose.  Also, in cases involving both a reference clock and	a pulse-per-
     second (PPS) discipline signal, it	is useful to specify the reference
     clock identifier as other than the	default, depending on the driver.  The
     refid option is used for this purpose.  Except where noted, these options
     apply to all clock	drivers.

   Reference Clock Commands
     server 127.127.t.u	[prefer] [mode int] [minpoll int] [maxpoll int]
	     This command can be used to configure reference clocks in special
	     ways.  The	options	are interpreted	as follows:

	     prefer  Marks the reference clock 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	fur-
		     ther information.

	     mode int
		     Specifies a mode number which is interpreted in a device-
		     specific fashion.	For instance, it selects a dialing
		     protocol in the ACTS driver and a device subtype in the
		     parse drivers.

	     minpoll int

	     maxpoll int
		     These options specify the minimum and maximum polling
		     interval for reference clock messages, in seconds to the
		     power of two.  For	most directly connected	reference
		     clocks, both minpoll and maxpoll default to 6 (64 s).
		     For modem reference clocks, minpoll defaults to 10	(17.1
		     m)	and maxpoll defaults to	14 (4.5	h).  The allowable
		     range is 4	(16 s) to 17 (36.4 h) inclusive.

     fudge 127.127.t.u [time1 sec] [time2 sec] [stratum	int] [refid string]
	     [mode int]	[flag1 0 | 1] [flag2 0 | 1] [flag3 0 | 1] [flag4 0 |
	     1]
	     This command can be used to configure reference clocks in special
	     ways.  It must immediately	follow the server command which	con-
	     figures the driver.  Note that the	same capability	is possible at
	     run time using the	ntpdc(8) program.  The options are interpreted
	     as	follows:

	     time1 sec
		     Specifies a constant to be	added to the time offset pro-
		     duced by the driver, a fixed-point	decimal	number in sec-
		     onds.  This is used as a calibration constant to adjust
		     the nominal time offset of	a particular clock to agree
		     with an external standard,	such as	a precision PPS	sig-
		     nal.  It also provides a way to correct a systematic
		     error or bias due to serial port or operating system
		     latencies,	different cable	lengths	or receiver internal
		     delay.  The specified offset is in	addition to the	propa-
		     gation delay provided by other means, such	as internal
		     DIPswitches.  Where a calibration for an individual sys-
		     tem and driver is available, an approximate correction is
		     noted in the driver documentation pages.  Note: in	order
		     to	facilitate calibration when more than one radio	clock
		     or	PPS signal is supported, a special calibration feature
		     is	available.  It takes the form of an argument to	the
		     enable command described in Miscellaneous Options page
		     and operates as described in the "Reference Clock
		     Drivers" page.

	     time2 secs
		     Specifies a fixed-point decimal number in seconds,	which
		     is	interpreted in a driver-dependent way.	See the
		     descriptions of specific drivers in the "reference	clock
		     drivers" page.

	     stratum int
		     Specifies the stratum number assigned to the driver, an
		     integer between 0 and 15.	This number overrides the
		     default stratum number ordinarily assigned	by the driver
		     itself, usually zero.

	     refid string
		     Specifies an ASCII	string of from one to four characters
		     which defines the reference identifier used by the
		     driver.  This string overrides the	default	identifier
		     ordinarily	assigned by the	driver itself.

	     mode int
		     Specifies a mode number which is interpreted in a device-
		     specific fashion.	For instance, it selects a dialing
		     protocol in the ACTS driver and a device subtype in the
		     parse drivers.

	     flag1 0 | 1

	     flag2 0 | 1

	     flag3 0 | 1

	     flag4 0 | 1
		     These four	flags are used for customizing the clock
		     driver.  The interpretation of these values, and whether
		     they are used at all, is a	function of the	particular
		     clock driver.  However, by	convention flag4 is used to
		     enable recording monitoring data to the clockstats	file
		     configured	with the filegen command.  Further information
		     on	the filegen command can	be found in Monitoring
		     Options.

Miscellaneous Options
     broadcastdelay seconds
	     The broadcast and multicast modes require a special calibration
	     to	determine the network delay between the	local and remote
	     servers.  Ordinarily, this	is done	automatically by the initial
	     protocol exchanges	between	the client and server.	In some	cases,
	     the calibration procedure may fail	due to network or server
	     access controls, for example.  This command specifies the default
	     delay to be used under these circumstances.  Typically (for Eth-
	     ernet), a number between 0.003 and	0.007 seconds is appropriate.
	     The default when this command is not used is 0.004	seconds.

     driftfile driftfile
	     This command specifies the	name of	the file used to record	the
	     frequency offset of the local clock oscillator.  If the file
	     exists, it	is read	at startup in order to set the initial fre-
	     quency offset and then updated once per hour with the current
	     frequency offset computed by the daemon.  If the file does	not
	     exist or this command is not given, the initial frequency offset
	     is	assumed	zero.  In this case, it	may take some hours for	the
	     frequency to stabilize and	the residual timing errors to subside.

	     The file format consists of a single line containing a single
	     floating point number, which records the frequency	offset mea-
	     sured in parts-per-million	(PPM).	The file is updated by first
	     writing the current drift value into a temporary file and then
	     renaming this file	to replace the old version.  This implies that
	     ntpd(8) must have write permission	for the	directory the drift
	     file is located in, and that file system links, symbolic or oth-
	     erwise, should be avoided.

     enable [auth | bclient | calibrate	| kernel | monitor | ntp | stats]

     disable [auth | bclient | calibrate | kernel | monitor | ntp | stats]
	     Provides a	way to enable or disable various server	options.
	     Flags not mentioned are unaffected.  Note that all	of these flags
	     can be controlled remotely	using the ntpdc(8) utility program.

	     bclient
		     When enabled, this	is identical to	the broadcastclient
		     command.  The default for this flag is disable.

	     calibrate
		     Enables the calibration facility, which automatically
		     adjusts the time1 values for each clock driver to display
		     the same offset as	the currently selected source or ker-
		     nel discipline signal.  See the "Reference	Clock Drivers"
		     page for further information.  The	default	for this flag
		     is	disable.

	     kernel  Enables the precision-time	kernel support for the
		     adjtime(2)	system call, if	implemented.  Ordinarily, sup-
		     port for this routine is detected automatically when the
		     NTP daemon	is compiled, so	it is not necessary for	the
		     user to worry about this flag.  It	is provided primarily
		     so	that this support can be disabled during kernel	devel-
		     opment.  The default for this flag	is enable.

	     monitor
		     Enables the monitoring facility.  See the ntpdc(8)	pro-
		     gram and the monlist command or further information.  The
		     default for this flag is enable.

	     ntp     Enables the server	to adjust its local clock by means of
		     NTP.  If disabled,	the local clock	free-runs at its
		     intrinsic time and	frequency offset.  This	flag is	useful
		     in	case the local clock is	controlled by some other
		     device or protocol	and NTP	is used	only to	provide	syn-
		     chronization to other clients.  In	this case, the local
		     clock driver can be used to provide this function and
		     also certain time variables for error estimates and leap-
		     indicators.  See the "Reference Clock Drivers" page for
		     further information.  The default for this	flag is
		     enable.

	     stats   Enables the statistics facility.  See the "Monitoring
		     Options" page for further information.  The default for
		     this flag is enable.

     logconfig configkeyword
	     This command controls the amount and type of output written to
	     the system	syslog(3) facility or the alternate logfile log	file.
	     By	default, all output is turned on.  All configkeyword keywords
	     can be prefixed with `=', `+' and `-', where `=' sets the
	     syslog(3) priority	mask, `+' adds and `-' removes messages.
	     syslog(3) messages	can be controlled in four classes (clock,
	     peer, sys and sync).  Within these	classes	four types of messages
	     can be controlled.	 Informational messages	(info) control config-
	     uration information.  Event messages (events) control logging of
	     events (reachability, synchronization, alarm conditions).	Sta-
	     tistical output is	controlled with	the statistics keyword.	 The
	     final message group is the	status messages.  This describes
	     mainly the	synchronizations status.  Configuration	keywords are
	     formed by concatenating the message class with the	event class.
	     The all prefix can	be used	instead	of a message class.  A message
	     class may also be followed	by the all keyword to enable/disable
	     all messages of the respective message class.  Thus, a minimal
	     log configuration could look like this:

	     logconfig=syncstatus +sysevents

	     This would	just list the synchronizations state of	ntpd(8)	and
	     the major system events.  For a simple reference server, the fol-
	     lowing minimum message configuration could	be useful:

	     logconfig=syncall +clockall

	     This configuration	will list all clock information	and synchro-
	     nization information.  All	other events and messages about	peers,
	     system events and so on is	suppressed.

     logfile logfile
	     This command specifies the	location of an alternate log file to
	     be	used instead of	the default system syslog(3) facility.

     setvar variable [default]
	     This command adds an additional system variable.  These variables
	     can be used to distribute additional information such as the
	     access policy.  If	the variable of	the form name=value is fol-
	     lowed by the default keyword, the variable	will be	listed as part
	     of	the default system variables (ntpq(8) rv command)).  These
	     additional	variables serve	informational purposes only.  They are
	     not related to the	protocol other that they can be	listed.	 The
	     known protocol variables will always override any variables
	     defined via the setvar mechanism.	There are three	special	vari-
	     ables that	contain	the names of all variable of the same group.
	     The sys_var_list holds the	names of all system variables.	The
	     peer_var_list holds the names of all peer variables and the
	     clock_var_list holds the names of the reference clock variables.

     tinker [step step | panic panic | dispersion dispersion | stepout stepout
	     | minpoll minpoll | allan allan | huffpuff	huffpuff]
	     This command can be used to alter several system variables	in
	     very exceptional circumstances.  It should	occur in the configu-
	     ration file before	any other configuration	options.  The default
	     values of these variables have been carefully optimized for a
	     wide range	of network speeds and reliability expectations.	 In
	     general, they interact in intricate ways that are hard to predict
	     and some combinations can result in some very nasty behavior.
	     Very rarely is it necessary to change the default values; but,
	     some folks	can't resist twisting the knobs	anyway and this	com-
	     mand is for them.	Emphasis added:	twisters are on	their own and
	     can expect	no help	from the support group.

	     All arguments are in floating point seconds or seconds per	sec-
	     ond.  The minpoll argument	is an integer in seconds to the	power
	     of	two.  The variables operate as follows:

	     step step
		     The argument becomes the new value	for the	step thresh-
		     old, normally 0.128 s.  If	set to zero, step adjustments
		     will never	occur.	In general, if the intent is only to
		     avoid step	adjustments, the step threshold	should be left
		     alone and the -x command line option be used instead.

	     panic panic
		     The argument becomes the new value	for the	panic thresh-
		     old, normally 1000	s.  If set to zero, the	panic sanity
		     check is disabled and a clock offset of any value will be
		     accepted.

	     dispersion	dispersion
		     The argument becomes the new value	for the	dispersion
		     increase rate, normally .000015.

	     stepout stepout
		     The argument becomes the new value	for the	watchdog time-
		     out, normally 900 s.

	     minpoll minpoll
		     The argument becomes the new value	for the	minimum	poll
		     interval used when	configuring multicast client, manycast
		     client and	, symmetric passive mode association.  The
		     value defaults to 6 (64 s)	and has	a lower	limit of 4 (16
		     s).

	     allan allan
		     The argument becomes the new value	for the	minimum	Allan
		     intercept,	which is a parameter of	the PLL/FLL clock dis-
		     cipline algorithm.	 The value defaults to 1024 s, which
		     is	also the lower limit.

	     huffpuff huffpuff
		     The argument becomes the new value	for the	experimental
		     huff-n'-puff filter span, which determines	the most
		     recent interval the algorithm will	search for a minimum
		     delay.  The lower limit is	900 s (15 m), but a more rea-
		     sonable value is 7200 (2 hours).  There is	no default,
		     since the filter is not enabled unless this command is
		     given.

     trap host_address [port port_number] [interface interface_address]
	     This command configures a trap receiver at	the given host address
	     and port number for sending messages with the specified local
	     interface address.	 If the	port number is unspecified, a value of
	     18447 is used.  If	the interface address is not specified,	the
	     message is	sent with a source address of the local	interface the
	     message is	sent through.  Note that on a multihomed host the
	     interface used may	vary from time to time with routing changes.

	     The trap receiver will generally log event	messages and other
	     information from the server in a log file.	 While such monitor
	     programs may also request their own trap dynamically, configuring
	     a trap receiver will ensure that no messages are lost when	the
	     server is started.

FILES
     /etc/ntp.conf   the default name of the configuration file
     ntp.keys	     private MD5 keys
     ntpkey	     RSA private key
     ntpkey_host     RSA public	key
     ntp_dh	     Diffie-Hellman agreement parameters

SEE ALSO
     ntpd(8), ntpdc(8),	ntpq(8)

     In	addition to the	manual pages provided, comprehensive documentation is
     available on the world wide web at	http://www.ntp.org/.  A	snapshot of
     this documentation	is available in	HTML format in /usr/share/doc/ntp.

     David L. Mills, Network Time Protocol (Version 3),	RFC1305.

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

     The ntpkey_host files are really digital certificates.  These should be
     obtained via secure directory services when they become universally
     available.

FreeBSD	10.1		       January 13, 2000			  FreeBSD 10.1

NAME | SYNOPSIS | DESCRIPTION | Configuration Support | Authentication Support | Monitoring Support | Access Control Support | Reference Clock Support | Miscellaneous Options | FILES | SEE ALSO | BUGS

Want to link to this manual page? Use this URL:
<http://www.freebsd.org/cgi/man.cgi?query=ntp.conf&sektion=5&manpath=FreeBSD+5.2-RELEASE>

home | help