Ntp.conf: Things that few people mention

[You can go to ntp.org next NTP server source code, which has the HTML format of the document, the content is very comprehensive. ][ref:http://doc.ntp.org/]comprehensive List of Clock Drivers

Following is a list showing the type and title of each driver currently implemented. The compile-time identifier for each are shown in parentheses. Click on a selected type for specific description and configuration documentation, including the clock address, reference ID, driver ID, device name and serial line speed. For those drivers without specific documentation, please contact the author listed in the Copyright Notice page.

• Type 1 undisciplined local Clock (local)
• ......

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 found in The reference Clock drivers page. Additional information can be found in the pages linked there, including the debugging Hints for Reference Clock Dri Vers and how to Write a Reference Clock driver pages. In addition, support for a PPS signal is available as described in pulse-per-second (PPS) signal Interfacing pag E.

A reference clock would generally (though not always) be a radio timecode receiver which was 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 dependent, but is usually a serial port. A device driver specific to each reference clock must is selected and compiled in the distribution; However, most common radio, satellite and modem clocks is included by default. Note that an attempt to configure a reference clock when the driver have not been compiled or the hardware port have not bee n appropriately configured results in a scalding remark to the system log file, and is otherwise non hazardous.

For the purposes of configuration,  ntpd  treats reference clocks in a manner analogous to normal NTP Peers as much as possible. Reference clocks is identified by a syntactically correct but invalid IP address, in order to distinguish them from Norma L NTP peers. Reference clock addresses is of the form  127.127. T.u , where  T  is An integer denoting the clock type and  u & Nbsp;indicates the unit number in the range 0-3. While it may seem overkill, it's in fact sometimes useful to configure multiple reference clocks of the same type, in WHI CH case The unit numbers must is 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 is 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 is found in the mitigation Rules and the  prefer  keyword&nbs P;page. the  minpoll  and  maxpoll  options has meaning 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 individual clock drivers and normall Y follows immediately after the  server  command. THE&NBSP Address  argument specifies the clock address. the  refid  and  stratum  options control can be used to override the defaults for the Device. There is optional device-dependent time offsets and four flags that can is included in the  Fudge  c Ommand as well.

The stratum number of a reference clock is by default zero. Since the ntpd Daemon adds one to the stratum of each peer, a primary server ordinarily displays an external stra Tum of one. In order to provide engineered backups, it's often useful to specify the reference clock stratum as greater than zero. The stratum option is used for this purpose. Also, in cases involving both a reference clock and a pulse-per-second (PPS) discipline signal, it's useful to specify th e 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 is 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, the this host would be the chosen for synchronization among a set of correctly operating hosts. See the mitigation Rules and the prefer Keyword page for further 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, interpreted As dual logarithms (2 ^ x). For most directly connected reference clocks, both minpoll and maxpoll default to 6 (2^16 = s). For modems reference clocks, minpolldefaults to ten (2^10 = 1024x768 s = 17.1 m) and maxpoll defaults to 1 4 (2^14 = 16384 s = 4.5 h). The allowable range is 4 (+ s) to (36.4 h) inclusive.

Fudge 127.127. t.u [time1 sec] [time2 sec] [stratum int] [refid string] [Flag1 0|1] [flag 2 0|1] [flag3 0|1] [Flag4 0|1]

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

Time1 sec

specifies a constant to is 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 by a particular clock to agree with an external Standard, such as a precision PPS signal. It also provides a-correct a systematic error or bias due to serial port or operating system latencies, different C Able 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 a individual system and driver are available, an approximate correction are noted in the driver doc Umentation pages.

note:in order to facilitate calibration if more than one radio clock or PPS signal is supported, a special CALIBR ation feature is available. It takes the form of a argument to the enable command described in the Miscellaneous Options page and operates As described in thereference Clock Drivers page.

Time2 secs

Specifies a fixed-point decimal number in seconds, which was interpreted in a driver-dependent. 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 a 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.

Flag1 Flag2 Flag3 Flag4

These four flags is 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 are used to enable recording monitoring data to the clockstats file conf Igured with the filegen command. Further information on the Filegen command can is found in the Monitoring Options page.

Ntp.conf: Things that few people mention