2.11BSD#431 - /usr/man/cat8/ntpd.0

NTPD(8)         Clockwatcher's Programming Manual	  NTPD(8)


NAME
     ntpd - time synchronization daemon implementing NTP

SYNOPSIS
     ntpd [-d] [-s] [-t]

OPTIONS
     -d will bump the debug level by one.  May be specified more
     than once to increment debug level by one each time.  Has no
     effect if ntpd has not been compiled with DEBUG defined.

     -s will cause ntpd to not adjust the the local clock.

     -t will cause ntpd to modify the value of tickadj in your
     kernel.  This will have no effect unless ntpd was compiled
     with SETTICKADJ defined.

DESCRIPTION
     NTPD is the network time synchronization daemon and is nor-
     mally invoked at boot time from the /etc/rc(8) file.  It
     implements a new revision of the Network Time Protocol first
     described in RFC-958.  It maintains the host's time syn-
     chronized with a set of distributed time servers, each with
     varying accurracy and reliability.  Multiple time server
     masters may exist, but there is no requirement for election
     of a single master.

     Ntpd uses the adjtime(2) system call to slew the clock of
     the host by small amount in order to keep the clock syn-
     chronized.  If the local clock exceeds the ``correct'' time
     by some threshold, then settimeofday(2) is used to make a
     step adjustment of the local clock.

     When ntpd(8) is started on the machine, it reads configura-
     tion information from /etc/ntp.conf which contains informa-
     tion about other ntp time servers and host specific informa-
     tion.  Configuration information is listed one entry per
     line, with fields separated by whitespace.  Lines which
     begin with a ``#'' character are treated as comments.  Here
     is a sample configuration file:
       #
       #	 Local clock parameters
       #
       #    Precision of the local clock to the nearest power of 2
       #	 ex.
       #	      60-HZ   = 2**-6
       #	      100-HZ  = 2**-7
       #	      1000-HZ = 2**-10
       precision -7
       #
       # intrinsic drift of local clock
       #


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NTPD(8)         Clockwatcher's Programming Manual	  NTPD(8)


       tickadj 1
       #
       #    Peers	   Type Name
       #
       peer	  foo.umd.edu
       peer	  192.5.39.94
       peer	  bar.arpa
       server	  bogon.umd.edu
       passive	  bozo.umd.edu


     There are two major types of information specified in the
     configuration file: local host information, and remote timer
     server specification.  The local host information is used to
     describe the intrinsic properties of the local host's time-
     keeping machinary.  The commands in this group are preci-
     sion, and tickadj.

     The precision command takes a number which describes the
     resolution of the local clock, as a power of two.	For exam-
     ple, a VAX system typically has a 100 HZ clock and thus a
     precision of -7.  If the symbol _hz is defined in the namel-
     ist of /vmunix, this value is automatically set based on the
     value of hz.

     The tickadj command is used to specify the granularity of
     clock adjustment done by the adjtime(2) system call.  If the
     -s option is specified when ntpd is invoked, the kernel
     variable _tickadj is modified via /dev/kmem.  The preferred
     method of setting tickadj is by changing the value in the
     kernel file conf.c instead of having ntpd set in this rude
     fashion.  On a VAX, a value of 1 is usually used. See the
     README file for typical values of tickadj on various
     hardware platforms.

     Currently three timer server specifications are supported.
     They are peer, server and passive. Each command takes either
     a dotted-quad internet address or a host name.  Each host
     specified in any one of the three commands is elligable to
     be synchronized to, while random hosts which set up a peer
     relationship are not.  The peer and server commands create
     an active polling situation; in the case of peer, the NTP
     packets are sourced in Symmetric-Active mode, while using
     server causes the packets to be in Client mode.  When
     reachability is lost with a configured host in either of
     these two cases, the daemon will continue to poll to re-
     acquire that host.  A host specified in the passive command
     will not continue to be polled.  If that host begins to poll
     us, it will be eligable as to be synchronized but will not
     be polled if reachability is lost.


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NTPD(8)         Clockwatcher's Programming Manual	  NTPD(8)


     It is recommended that the bulk of the peers configured
     should be specified with the client keyword; this will
     minimize resource usage on the remote NTP server.	If your
     host will be serving as a redistribution point for a cluster
     of hosts,	you should set up peer relationships with higher
     quality clocks (lower stratums) and other equal stratum
     clocks.  In other words, if you are not redistributing time
     to others, you shouldn't need to configure any peers in your
     NTP configuration; client specifications are more appropri-
     ate.

NOTES
     Please choose your NTP peers carefully; send mail to
     ntp@TRANTOR.UMD.EDU for assitance.

     There exists a broadcast command which will exercise com-
     pletely untested code.  Use at your own risk.

     There is no reason to believe that the hpux code which was
     added still works.  In general, this code and adaptations of
     the NTPD to platforms without the adjtime(2) system call are
     not likely to be very satisfying.

BUGS
     No doubt.

FILES
     /etc/ntp.conf  NTP daemon configuration file

SEE ALSO
     adjtime(2), settimeofday(2), RFC-958, Network Time Protocol
     (Version 1) Specification Revised 17 September 1988

AUTHORS
     Louis A. Mamakos, louie@TRANTOR.UMD.EDU
     Michael G. Petry, petry@TRANTOR.UMD.EDU
     The University of Maryland, Computer Science Center.


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