ntpd.8

ftam等标准协议服务器和客户端的源代码。

.\" $Header: /xtel/isode/isode/others/ntp/RCS/ntpd.8,v 9.0 1992/06/16 12:42:48 isode Rel $
.\"
.\" $Log: ntpd.8,v $
.\" Revision 9.0  1992/06/16  12:42:48  isode
.\" Release 8.0
.\"
.\"
.TH NTPD 8 "15 June 1989"
.SH NAME
ntpd \- time synchronization daemon implementing NTP
.SH SYNOPSIS
.B /usr/local/etc/ntpd
[-a threshold] [-c file] [-d] [-D level] [-l] [-n] [-s] [-t] [-p port]
.SH OPTIONS
.B -a 
.I threshold
is used to set the threshold which limits how far 
.B ntpd
will change the system clock.  Its used as a sort of ultimate sanity check to
prevent your system time from being changed a great deal.  By default, the
threshold is 1000 seconds. 
.I threshold
is to be specified in units of seconds, or the string
.B any
to defeat the sanity check.
.PP
.B -c 
.I config-file
can be used to specify the location of the
.I ntpd
configuration file. By default, /etc/ntp.conf is used.
.PP
.B -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 
.I ntpd
has not been compiled with 
.B DEBUG
defined.
.PP
.B -D
.I level
will set the debug level to the value specified.
.PP
.B -l
will cause
.I ntpd
to log a message each time the logical clock is changed.  Normally, you would
not specify this option  unless you wanted to gather statistical information
to analyze the logical clock behavior.  If the
.B -l 
option is specified, a message will be logged approximately every 2 minutes.
.PP
.B -n
will, on Ultrix systems, inhibit the
.I ntpd
program from being swapped.  This is a desirable thing to do when in the
diskless workstation environment.
.PP
.B -s
will cause
.I ntpd
to
.B never
adjust the the local clock.
.PP
.B -t
will cause
.I ntpd
to modify the value of
.I tickadj
in your kernel.  This will have no effect unless 
.I ntpd
was compiled with
.B SETTICKADJ
defined.  This is an ugly thing to do, and idealy you should set the value
of
.B tickadj
in your kernel configuration to the correct value.
.PP
.B -p
will specify a UDP port to use for ntp. This will override the default.
.PP
.SH DESCRIPTION
.I NTPD
is the network time synchronization daemon and is normally invoked at 
boot time from the
.IR /etc/rc (8)
file.  It implements a new revision of the
.B Network Time Protocol
first described in RFC-958.
It maintains the host's time synchronized 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. 
.PP
.I Ntpd
uses the
.IR adjtime (2)
system call to slew the clock of the host by small amount in order to keep the
clock synchronized.  If the local clock exceeds the ``correct'' time by some
threshold, then 
.IR settimeofday (2)
is used to make a step adjustment of the local clock.
.PP
When
.IR ntpd (8)
is started on the machine, it reads configuration information from
.I /etc/ntpd.conf
which contains information about other 
.I ntp
time servers and host specific information.  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:
.in +2m
.nf
#
# 		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
#
tickadj 5
#
peer       INET:foo.umd.edu
peer       INET:192.5.39.94
peer       OSI:Internet=foo.bar.edu
peer       OSI:Janet=000021000018+PID+03030101
server     INET:bogon.umd.edu
passive    INET:bozo.umd.edu
#
# Configure a reference clock.  
#           device      refid  stratum  precision  type
#          -------     -----   -------  ---------  ----
refclock   /dev/tty03   WWV      1        -5       psti
# refclock       /dev/null    LOCL     1        -5       local

.DT
.fi
.PP
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 timekeeping machinary, such
as 
.B precision
and
.BR tickadj .
The remote time server specifications give details of the ntp clients
and server to synchronise with.
.PP
The possible configuration file options are as follows:-
.PP
.TP
.B precision
a number which describes the resolution of the local clock, as a power
of two.  For example, a 
.I VAX
system typically has a 100 HZ clock and thus a 
.I precision 
of -7.  If the symbol
.B _hz
is defined in the namelist of /vmunix, this value is automatically set based
on the value of hz.
.TP
.B tickadj
is used to specify the granularity of clock adjustment done by the
.IR adjtime(2)
system call.  If the 
.B \-t
option is specified when ntpd is invoked, the kernel variable _tickadj is
modified via
.IR /dev/kmem.
The preferred method of setting 
.B tickadj
is by changing the value in the kernel file
.I 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
.B tickadj
on various hardware platforms.
.TP
.B driftfile
can be used to specify the name of the file that the drift compensation
register will be loaded from at initialization time and that updated values
will be written into.  The drift compensation value describes the intrinsic
drift of your host's clock.  By default, the file
.B /etc/ntp.drift
will be used.
.TP
.B peer
.TP
.B passive
.TP
.B server
Currently three time server specifications are supported.  
Each command takes an address. If the address starts with the letters
.I OSI:
then it is assumed to be an OSI address, 
.I INET:
implies internet addressing and neither prefix currently defaults to
internet.  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
.B peer
and
.B server
commands create an active polling situation; in the case of 
.B peer,
the NTP packets are sourced in 
.I Symmetric-Active
mode, while using
.B server
causes the packets to be in
.I 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
.B 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.
.br
It is recommended that the bulk of the peers configured should be specified
with the
.I 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
.I 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
.I peers
in your NTP configuration;
.I client
specifications are more appropriate.
.TP
.B refclock
To configure a 
.B reference
clock, you should use something like the example above.  The first
field after the
.B refclock
keyword is the name of the file that the clock is connected to.  This must be
a complete path name with a leading
.B /
character.  The next field is the 
.I reference-id
that will be inserted into the packets generated from this NTP daemon.  For
a PSTI clock, this should be
.B WWV.
The next field is the 
.B stratum
of the clock.  Actually, it is really the 
stratum that will be placed in the packet if this clock is selected by the
local NTP daemon as the reference clock.  Following that is the 
.B precision
that will be inserted into the packet when this clock is selected.  The
final field is the
.B type
of the clock.  Currently, two types are supported:
.B psti
for the Precision Standard Time, Inc WWV clock (RIP) and
.B local
for the local time of the system.  The
.B local
type of clock can be used to declare one host in an isolated network as
having the "correct" time and then the other hosts on that network can
synchronized to it.
.br
The reference clock feature is new and will probably be enhanced in the future.
.TP
.B maxpeers
sets the maximum number of peers allowed (currently not used).
.TP
.B trusting
allows clocks not mentioned in your configuration file to be eligle to
synchronise your clock if they appear suitable.
.TP
.B osilisten
This is an OSI address specification that
.I ntpd 
listens on for incoming connections.
.TP
.B logclock
sets the variable which logs all clock changes.
.TP
.B driftfile
specifies the localtion of the drift file (defaults to 
.IR /etc/ntp.drift ).
.TP
.B waytoobig
.TP
.B setthreshold
either of these sets a variable which is the maximum clock change that
will be considered. Setting this to
.I any
allows any change. Otherwise this value should be a floating point
number.
.TP
.B debuglevel
Another way to set the debug level.
.TP
.B settickadj
this specifies whether to set the kernels tickadj parameter if required.
.TP
.B noswap
On machines that support it (ultrix) this will allow the process to be
locked in memory, which helps.
.TP 
.B broadcast
this specifies an interface which will allow broadcast mode ntp actions.
.TP
.B logfile
This specifies a log file that will receive the tracing and monitoring
output of the ntp daemon.
.TP
.B priority
The priority for the
.I ntpd
process to run at (defaults to -10).
.SH NOTES
.B Please choose your NTP peers carefully; 
.B send mail to
.IR [e-mail]
.B for assitance.
.SH BUGS
No doubt.
.SH FILES
.nf
/etc/ntp.conf  NTP daemon configuration file
.fi
.SH "SEE ALSO"
adjtime(2), settimeofday(2), RFC-958, 
.I Network Time Protocol (Version 2) Specification and Implementation, 
.I Revised 15 April 1988,
David L. Mills, University of Delaware
.SH "AUTHORS"
Original Code
.br
Louis A. Mamakos,
.I [e-mail]
.br
Michael G. Petry,
.I [e-mail]
.br
The University of Maryland, Computer Science Center.
.sp
OSI support and various gratuitous changes
.br
Julian Onions,
.I [e-mail]
.br
Nottingham University