# 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
           #

    Printed 4/11/100	27 November 1996			1

    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.

    Printed 4/11/100	27 November 1996			2

    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.

    Printed 4/11/100	27 November 1996			3

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