manpagez: man (manual) pages & more
man ntp.conf(5)
Home | html | info | man
ntp.conf(5)                 BSD 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 Support, 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] [noselect] [preempt]

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

     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 mes-
             sages 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
             nonconflicting 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 discov-
             ered 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 remain-
             ing 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 Support.

     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).

     noselect
             Marks the server as unused, except for display purposes. The
             server is discarded by the selection algorithm. This option is
             valid only with the server and peer commands.

     preempt
             Specifies the association as preemptable rather than the default
             persistent. This option is valied only with the server command.

     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.

     true    Force 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 preci-
             sion 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.  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 Support.

     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 Support.

     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 Support.


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 corresponding 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 con-
     structed 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.

BSD                              June 8, 2006                              BSD

Mac OS X 10.6 - Generated Thu Sep 17 20:25:12 CDT 2009