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.
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.
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 synchronized to the local clock. This command should not be used for type b or m addresses.
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 various 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.
For type b and m addresses (only), this command mobilizes a persistent broadcast mode association. Multiple commands can be used to specify multiple local broadcast interfaces (subnets) and/or multiple multicast groups. Note that local broadcast messages go only to the interface associated with the subnet specified, but multicast messages go to all interfaces. In broadcast mode the local server sends periodic broadcast messages to a client population at the address specified, which is usually the broadcast address on (one of) the local network(s) or a multicast address assigned to NTP. The IANA has assigned the multicast group address 188.8.131.52 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 operation as a broadcast client, see the broadcastclient or multicastclient commands below.
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 184.108.40.206 assigned by the IANA should NOT be used, unless specific means are taken to avoid spraying large areas of the Internet with these messages and causing a possibly massive implosion of replies at the sender. The manycastserver command specifies that the local server is to operate in client mode with the remote servers that are discovered as the result of broadcast/multicast messages. The client broadcasts a request message to the group address associated with the specified address and specifically enabled servers respond to these messages. The client selects the servers providing the best time and continues as with the server command. The remaining servers are discarded as if never heard.
All packets sent to and received from the server or peer are to include authentication fields encrypted using the autokey scheme described in Authentication Options.
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 timekeeping quality with the server command and s addresses.
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.
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).
Marks the server as preferred. All other things being equal, this host will be chosen for synchronization among a set of correctly operating hosts. See the ""Mitigation Rules and the prefer Keyword"" page for further information.
This option is used only with broadcast server and manycast client modes. It specifies the time-to-live ttl to use on broadcast 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.
Specifies the version number to be used for outgoing NTP packets. Versions 1-4 are the choices, with version 4 the default.
This command enables reception of broadcast server messages to any local interface (type b) address. Upon receiving a message for the first time, the broadcast client measures the nominal server propagation delay using a brief client/server exchange with the server, then enters the broadcast client mode, in which it synchronizes to succeeding broadcast messages. Note that, in order to avoid accidental or malicious disruption in this mode, both the server and client should operate using symmetric-key or public-key authentication as described in Authentication Options.
manycastserver address ...
This command enables reception of manycast client messages to the multicast group address(es) (type m) specified. At least one address is required, but the NTP multicast address 220.127.116.11 assigned by the IANA should NOT be used, unless specific means are taken to limit the span of the reply and avoid a possibly massive implosion at the original sender. Note that, in order to avoid accidental or malicious disruption in this mode, both the server and client should operate using symmetric-key or public-key authentication as described in Authentication Options.
multicastclient address ...
This command enables reception of multicast server messages to the multicast group address(es) (type m) specified. Upon receiving a message for the first time, the multicast client measures the nominal server propagation delay using a brief client/server exchange with the server, then enters the broadcast client mode, in which it synchronizes to succeeding multicast messages. Note that, in order to avoid accidental or malicious disruption in this mode, both the server and client should operate using symmetric-key or public-key authentication as described in Authentication Options.
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(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.
This command requires the NTP daemon build process be configured with the RSA library. This command activates public-key cryptography 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:
Specifies the location of the RSA private key file, which otherwise defaults to /usr/local/etc/ntpkey.
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.
Specifies the location of the Diffie-Hellman parameters file, which otherwise defaults to /usr/local/etc/ntpkey_dh.
Specifies the location of the leapsecond table file, which otherwise defaults to /usr/local/etc/ntpkey_leap.
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.
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.
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.
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 of the scheme; 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.
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 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.
Enables writing of statistics records. Currently, four kinds of name statistics are supported.
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 0.013380 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.
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 -0.001605 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.
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.
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 2132.543 18.104.22.168 22.214.171.124 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, transmit and final NTP timestamps in order. The timestamp values are as received and before processing by the various data smoothing and mitigation algorithms.
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.
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(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.
This is the type of the statistics records, as shown in the statistics command.
This is the file name for the statistics records. Filenames of set members are built from three concatenated elements prefix, filename and suffix:
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.
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 file system hierarchy denoted by prefix.
This part is reflects individual elements of a file set. It is generated according to the type of a file set.
A file generation set is characterized by its type. The following types are supported:
The file set is actually a single plain file.
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.
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 .Sm off prefix / filename / 19921210. .Sm on
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.
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.
One generation file element is generated per year. The filename suffix consists of a dot and a 4 digit year number.
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 corresponding 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.
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 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 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:
If access is denied, send a kiss-of-death packet.
Ignore all packets from hosts which match this entry. If this flag is specified neither queries nor time server polls will be responded to.
Ignore all NTP mode 6 and 7 packets (i.e., information queries and configuration requests) from the source. Time service is not affected.
Ignore all NTP mode 6 and 7 packets which attempt to modify the state of the server (i.e., run time reconfiguration). Queries which return information are permitted.
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.
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.
Ignore NTP packets whose mode is other than 6 or 7. In effect, time service is denied, though queries may still be permitted.
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 synchronization partners.
Treat these hosts normally in other respects, but never use them as synchronization sources.
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.
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.
Ignore these hosts if not the current NTP version.
Default restriction list entries, with the flags ignore, interface, ntpport, for each of the local hosts 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 unconfigured; no flags are associated with the default entry (i.e., everything besides your own NTP server is unrestricted).
Set the client_limit variable, which limits the number of simultaneous access-controlled clients. The default value for this variable is 3.
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.
.Sm off 127.127. t. u .Sm on [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:
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 further information.
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.
.Sm off 127.127. t. u .Sm on [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 configures the driver. Note that the same capability is possible at run time using the ntpdc(8) 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 described in Miscellaneous Options page and operates as described in the ""Reference Clock Drivers"" page.
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.
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.
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.
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 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 frequency 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 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(8) must have write permission for the directory the drift file is located in, and that file system links, symbolic or otherwise, should be avoided.
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.
When enabled, this is identical to the broadcastclient command. The default for this flag is disable.
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 kernel discipline signal. See the ""Reference Clock Drivers"" page for further information. The default for this flag is disable.
Enables the precision-time kernel support for the adjtime(2) system call, if implemented. Ordinarily, support 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 development. The default for this flag is enable.
Enables the monitoring facility. See the ntpdc(8) program and the monlist command or further information. The default for this flag is enable.
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 synchronization 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.
Enables the statistics facility. See the ""Monitoring Options"" page for further information. The default for this flag is enable.
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 configuration information. Event messages (events) control logging of events (reachability, synchronization, alarm conditions). Statistical 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 following minimum message configuration could be useful:
logconfig =syncall +clockall
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(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 .Sm off name = value .Sm on is followed 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 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 cannot 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.
All arguments are in floating point seconds or seconds per second. The minpoll argument is an integer in seconds to the power of two. The variables operate as follows:
The argument becomes the new value for the step threshold, 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.
The argument becomes the new value for the panic threshold, normally 1000 s. If set to zero, the panic sanity check is disabled and a clock offset of any value will be accepted.
The argument becomes the new value for the dispersion increase rate, normally .000015.
The argument becomes the new value for the watchdog timeout, normally 900 s.
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).
The argument becomes the new value for the minimum Allan intercept, which is a parameter of the PLL/FLL clock discipline algorithm. The value defaults to 1024 s, which is also the lower limit.
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 reasonable value is 7200 (2 hours). There is no default, since the filter is not enabled unless this command is given.
[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.