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

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

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

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

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

For type s messages (only) this command mobilizes a client mode association for servers implementing the pool automatic server discovery scheme described on the Association Management page at file:///usr/share/doc/ntp/assoc.html. The address is a DNS name in the form area.pool.ntp.org, where area is a qualifier designating the server geographic area such as us or europe.

autokey

burst

iburst

key key

minpoll minpoll

maxpoll maxpoll

mode option

noselect

preempt

prefer

true

ttl ttl

version version

broadcastclient [novolley]

manycastserver address [...]

multicastclient address [...]

server 127.127.t.u [prefer] [mode int] [minpoll int] [maxpoll int]

prefer

mode int

minpoll int

These options specify the minimum and maximum polling interval for reference clock messages in seconds, interpreted as dual logarithms (2 ^ x). For most directly connected reference clocks, both minpoll and maxpoll default to 6 (2^16 = 64 s). For modem reference clocks, minpoll defaults to 10 (2^10 = 1024 s = 17.1 m) and maxpoll defaults to 14 (2^14 = 16384 s = 4.25 h). The allowable range is 4 (16 s) to 17 (36.4 h) inclusive.

This command can be used to configure reference clocks in special ways. It must immediately follow the server command which configures the driver. Note that the same capability is possible at run time using the ntpdc program. The options are interpreted as follows:

Specifies a constant to be added to the time offset produced by the driver, a fixed-point decimal number in seconds. 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 signal. 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 propagation delay provided by other means, such as internal DIPswitches. Where a calibration for an individual system 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 and operates as described in the Reference Clock Drivers page at file:///usr/share/doc/ntp/refclock.html.

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 at file:///usr/share/doc/ntp/refclock.html.

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.

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.

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.

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.

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.

Specifies the key identifier to use with the ntpq 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 65,534, inclusive.

This command requires the OpenSSL library. It activates public key cryptography and loads the required public/private encryption and sign kyes and public certificat. If one or more files are left unspecified, the default names are used as described below. Unless the complete path and name of the file are specified, the location of a file is relative to the keys directory specified in the keysdir command or default /etc/inet. Following are the subcommands.

Specifies the host name used in the host key link ntpkey_host_name, sign key link ntpkey_sign_name and certificate link ntpkey_cert_name. The ntp-keygen program automatically installs these links to the most recently generated files.

Specifies the group name used in the identity key link ntpkey_key_name, where key identifies the key type described on the ntp-keygen page. The ntp-keygen program automatically installs these links to the most recently generated files.

Specifies the password to decrypt files previously encrypted by the ntp-keygen program.

Specifies the location of the random seed file used by the OpenSSL library. The defaults are described on the ntp-keygen(8) man page.

Specifies the complete path to the MD5 key file containing the keys and key identifiers used by ntpd, ntpq and ntpdc when operating with symmetric key cryptography. This is the same operation as the -k command line option.

This command specifies the default directory path for cryptographic keys, parameters and certificates. The default is /etc/inet/.

Specifies the key identifier to use with the ntpdc utility program, which uses a proprietary protocol specific to this implementation of ntpd. The key argument is a key identifier for the trusted key, where the value can be in the range 1 to 65,534, inclusive.

Specifies the interval between re-randomization of certain cryptographic 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; however, 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.

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 and ntpdc programs. The authentication 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 arguments are 32-bit unsigned integers with values from 1 to 65,534.

Set the parameters of the limited facility which protects the server from client abuse. The average subcommand specifies the minimum average packet spacing, while the minimum subcommand specifies the minimum packet spacing. Packets that violate these minima are discarded and a kiss-o'-death packet returned if enabled. The default minimum average and minimum are 5 and 2, respectively. The monitor subcommand specifies the probability of discard for packets that overflow the rate-control window.

The address argument expressed in dotted-quad form is the address of a host or network. Alternatively, the address argument can be a valid host DNS name. The mask argument expressed in dotted-quad form defaults to 255.255.255.255, meaning that the 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 is always the first entry in the list. Note that text string default, with no mask option, may be used to indicate the default entry.

In the current 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 catagories, 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:

Deny packets of all kinds, including ntpq and ntpdc queries.

If this flag is set when an access violation occurs, a kiss-o'-death (KoD) packet is sent. KoD packets are rate limited to no more than one per second. If another KoD packet occurs within one second after the last one, the packet is dropped

Deny service if the packet spacing violates the lower limits specified in the discard command. A history of clients is kept using the monitoring capability of ntpd. Thus, monitoring is always active as long as there is a restriction entry with the limited flag.

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.

Deny ntpq and ntpdc queries which attempt to modify the state of the server (i.e., run time reconfiguration). Queries which return information are permitted.

Deny ntpq and ntpdc queries. Time service is not affected.

Deny packets which would result in mobilizing a new association.  This includes broadcast, symmetric-active and manycast client packets when a configured association does not exist.

Deny all packets except ntpq and ntpdc queries.

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

Deny packets unless the packet is cryptographically authenticated.

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.

Deny packets that do not match the current NTP version.

Enables writing of statistics records. Currently, six kinds of namestatistics are supported.

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 notation, 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 information can be gathered and displayed as well. See information specific to each clock for further details.

This option requires the OpenSSL cryptographic software library. It enables recording of cryptographic public key protocol information. Each message received by the protocol module appends a line of the following form to the file generation set named cryptostats:

49213 525.624 127.127.4.1 message

The first two fields show the date (Modified Julian Day) and time (seconds and fraction past UTC midnight). The next field shows the peer address in dotted-quad notation, The final message field includes the message type and certain ancillary information. See the Authentication Options page at file:///usr/share/doc/ntp/authopt.html for further information.

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

50935 75440.031 0.000006019 13.778190 0.000351733 0.0133806 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.

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 peerstats:

48773 10847.650 127.127.4.1 9714 -0.001605376 0.000000000 0.001424877 0.000958674

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 B of the NTP specification RFC 1305. The final four fields show the offset, delay, dispersion and RMS jitter, all in seconds.

Enables recording of raw-timestamp statistics information. This includes statistics records of all peers of a NTP server and of special signals, where present and configured. 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 2132.2543 128.4.1.1 128.4.1.20 3102453281.2584327000 3102453281.258622800031 02453332.2540806000 3102453332.2541458000

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, transmit and final NTP timestamps in order. The timestamp values are as received and before processing by the various data smoothing and mitigation algorithms.

Enables recording of ntpd statistics counters on a periodic basis. Each hour a line of the following form is appended to the file generation set named sysstats:

50928 2132.2543 36000 81965 0 9546 56 71793 512 540 10 147

The first two fields show the date (Modified Julian Day) and time (seconds and fraction past UTC midnight). The remaining ten fields show the statistics counter values accumulated since the last generated line.

Time since restart 36000: Time in hours since the system was last rebooted.

Packets received 81965: Total number of packets received.

Packets processed 0: Number of packets received in response to previous packets sent

Current version 9546: Number of packets matching the current NTP version.

Previous version 56: Number of packets matching the previous NTP version.

Bad version 71793: Number of packets matching neither NTP version.

Access denied 512: Number of packets denied access for any reason.

Bad length or format 540: Number of packets with invalid length, format or port number.

Bad authentication 10: Number of packets not verified as authentic.

Rate exceeded 147: Number of packets discarded due to rate limitation.

Indicates the full path of a directory where statistics files should be created (see below). This keyword allows the (otherwise constant) filegen filename prefix to be modified for file generation sets, which is useful for handling statistics logs. This directory must be writable by the user "daemon" and all files in it must be writable by that user.

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 administrational operations without the risk of disturbing the operation of ntpd. (Most important: they can be removed to free space for new data produced.) Note that this command can be sent from the ntpdc 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. Filenames of set members are built from three concatenated elements prefix, filename and suffix:

prefix This is a constant filename path. It is not subject to modifications via the filegen option. It is defined by the server, usually specified as a compile-time constant. It may, however, be configurable 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 prefix 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 filesystem hierarchy 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:

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 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.

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 Ethernet), a number between 0.003 and 0.007 seconds is appropriate. The default when this command is not used is 0.004 seconds.

This option controls the delay in seconds between the first and second packets sent in burst or iburst mode to allow additional time for a modem or ISDN call to complete.

This command specifies the complete path and name of the file used to record the frequency of the local clock oscillator. This is the same operation as the -f command linke option. If the file exists, it is read at startup in order to set the initial frequency and then updated once per hour with the current frequency computed by the daemon. If the file name is specified, but the file itself does not exist, the starts with an initial frequency of zero and creates the file when writing it for the first time. If this command is not given, the daemon will always start with an initial frequency of zero. This file must be in a directory writable by the user "daemon".

The file format consists of a single line containing a single floating point number, which records the frequency offset measured 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 must have write permission for the directory the drift file is located in, and that file system links, symbolic or otherwise, should be avoided.

The parameter tolerance is the wander threshold to skip writing the new value. If the value of wander computed from recent frequency changes is greater than this threshold the file will be updated once per hour. If below the threshold, the file will not be written.

Provides a way to enable or disable various system options. Flags not mentioned are unaffected. Note that all of these flags can be controlled remotely using the ntpdc utility program.

Enables the server to synchronize with unconfigured peers only if the peer has been correctly authenticated using either public key or private key cryptography. The default for this flag is enable.

Enables the server to listen for a message from a broadcast or multicast server, as in the multicastclient command with default address. The default for this flag is disable.

Enables the calibrate feature for reference clocks. The default for this flag is disable.

Enables the kernel time discipline, if available. The default for this flag is enable if support is available, otherwise disable.

Enables the monitoring facility. See the ntpdc program and the monlist command or further information. The default for this flag is enable.

Enables time and frequency discipline. In effect, this switch opens and closes the feedback loop, which is useful for testing. The default for this flag is enable.

Enables the pulse-per-second (PPS) signal when frequency and time is disciplined by the precision time kernel modifications. See the Kernel Model for Precision Timekeeping page at file:///usr/share/doc/ntp/kern.html for further information. The default for this flag is disable.

Enables the statistics facility. The default for this flag is disable

This command allows additional configuration commands to be included from a separate file. Include files may be nested to a depth of five; upon reaching the end of any include file, command processing resumes in the previous configuration file. This option is useful for sites that run ntpd on multiple hosts, with (mostly) common options (e.g., a restriction list). The include file must be in a file readable by the user "daemon".

This command controls the amount and type of output written to the system syslog facility or the alternate logfile log file. All configkeyword keywords can be prefixed with =, + and -, where = sets the syslogmask, + adds and - removes messages. syslog 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), event messages (events), statistics messages (statistics) and status messages (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. By default, logconfig output is set to allsync.

Thus, a minimal log configuration could look like this:

logconfig =syncstatus +sysevents

This would just list the synchronizations state of ntpd and the major system events. For a simple reference server, the following minimum message configuration could be useful:

logconfig =allsync +allclock

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

This command specifies the location of an alternate log file to be used instead of the default system syslog facility. This is the same operation as the -l command line option. This file must be writable by the user "daemon" and be in a directory writable by that user.

This command is used in conjunction with the ACTS modem driver (type 18). The arguments consist of a maximum of 10 telephone numbers used to dial USNO, NIST or European time services. The Hayes command ATDT is normally prepended to the number, which can contain other modem control codes as well.

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 followed by the default keyword, the variable will be listed as part of the default system variables (ntpq 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 variables 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.

This command can be used to alter several system variables in very exceptional circumstances. It should occur in the configuration 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 command is for them. Emphasis added: twisters are on their own and can expect no help from the support group.

The variables operate as follows:

allan allan

dispersion dispersion

freq freq

huffpuff huffpuff

panic panic

step step

stepout stepout

This command affects the clock selection and clustering algorithms. It can be used to select the quality and quantity of peers used to synchronize the system clock and is most useful in manycast mode. The variables operate as follows:

beacon beacon

ceiling ceiling

cohort { 0 | 1 }

floor floor

orphan stratum

mindist mindistance

maxdist maxdistance

minclock minclock

minsane minsane

This command specifies a list of TTL values in increasing order. up to 8 values can be specified. In manycast mode these values are used in turn in an expanding-ring search. The default is eight multiples of 32 starting at 31.

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.

This command specifies a list of TTL values in increasing order. up to 8 values can be specified. In manycast mode these values are used in turn in an expanding-ring search. The default is eight multiples of 32 starting at 31.