184 lines
7.7 KiB
HTML
184 lines
7.7 KiB
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<HTML><HEAD><TITLE>
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<TT>ntpd</TT> - Network Time Protocol (NTP) daemon
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</TITLE></HEAD><BODY><H3>
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<TT>ntpd</TT> - Network Time Protocol (NTP) daemon
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</H3><HR>
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<H4>Synopsis</H4>
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<TT>ntpd [ -aAbdm ] [ -c <I>conffile</I> ] [ -f <I>driftfile</I> ] [ -g
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] [ -k <I>keyfile</I> ] [ -l <I>logfile</I> ] [ -p <I>pidfile</I> ] [ -r
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<I>broadcastdelay</I> ] [ -s <I>statsdir</I> ] [ -t <I>key</I> ] [ -v
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<I>variable</I> ] [ -V <I>variable</I> ] [ -x ]</TT>
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<H4>Description</H4>
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<TT>ntpd</TT> is an operating system daemon which sets and maintains the
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system time-of-day in synchronism with Internet standard time servers.
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<TT>ntpd</TT> is a complete implementation of the Network Time Protocol
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(NTP) version 4, but also retains compatibility with version 3, as
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defined by RFC-1305, and version 1 and 2, as defined by RFC-1059 and
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RFC-1119, respectively. <TT>ntpd</TT> does most computations in 64-bit
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floating point arithmetic and does relatively clumsy 64-bit fixed point
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operations only when necessary to preserve the unltimate precision,
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about 232 picoseconds. While the ultimate precision, is not achievable
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with ordinary workstations and networks of today, it may be required
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with future nanosecond CPU clocks and gigabit LANs.
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<P>The daemon can operate in any of several modes, including symmetric
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active/passive, client/server broadcast/multicast and manycast. A
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broadcast/multicast or manycast client can discover remote servers,
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compute server-client propagation delay correction factors and configure
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itself automatically. This makes it possible to deploy a fleet of
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workstations without specifying configuration details specific to the
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local environment.
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<P>Ordinarily, <TT>ntpd</TT> reads the <TT>ntp.conf</TT> configuration
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file at startup time in order to determine the synchronization sources
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and operating modes. It is also possible to specify a working, although
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limited, configuration entirely on the command line, obviating the need
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for a configuration file. This may be particularly appropriate when the
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local host is to be configured as a broadcast/multicast client or
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manycast client, with all peers being determined by listening to
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broadcasts at run time.
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<P>If NetInfo support is built into <TT>ntpd</TT>, then <TT>ntpd</TT>
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will attempt to read its configuration from the NetInfo if the default
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ntp.conf file cannot be read and no file is specified by the <TT>-c</TT>
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option.
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<P>Various internal <TT>ntpd</TT> variables can be displayed and
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configuration options altered while the daemon is running using the
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<TT><A HREF="ntpq.htm">ntpq</A></TT> and <TT><A
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HREF="ntpdc.htm">ntpdc</A></TT> utility programs.
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<P>When <TT>ntpd</TT> starts it looks at the value of <TT>umask</TT>,
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and if it's zero <TT>ntpd</TT> will set the <TT>umask</TT> to
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<TT>022</TT>.
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<H4>Command Line Options</H4>
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<DL>
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<DT><TT>-a</TT></DT>
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<DD>Enable authentication mode (default).</DD>
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<DT><TT>-A</TT></DT>
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<DD>Disable authentication mode.</DD>
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<DT><TT>-b</TT></DT>
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<DD>Synchronize using NTP broadcast messages.</DD>
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<DT><TT>-c <I>conffile</I></TT></DT>
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<DD>Specify the name and path of the configuration file.</DD>
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<DT><TT>-d</TT></DT>
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<DD>Specify debugging mode. This flag may occur multiple times, with
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each occurrence indicating greater detail of display.</DD>
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<DT><TT>-D <I>level</I></TT></DT>
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<DD>Specify debugging level directly.</DD>
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<DT><TT>-f <I>driftfile</I></TT></DT>
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<DD>Specify the name and path of the drift file.</DD>
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<DT><TT>-g</TT></DT>
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<DD>Normally, the daemon exits if the offset exceeds a 1000-s sanity
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limit. This option overrides this limit and allows the time to be set to
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any value without restriction; however, this can happen only once. After
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that, the daemon will exit of the limit is exceeded.
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<DT><TT>-k <I>keyfile</I></TT></DT>
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<DD>Specify the name and path of the file containing the NTP
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authentication keys.</DD>
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<DT><TT>-l <I>logfile</I></TT></DT>
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<DD>Specify the name and path of the log file. The default is the system
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log facility.</DD>
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<DT><TT>-m</TT></DT>
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<DD>Synchronize using NTP multicast messages on the IP multicast group
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address 224.0.1.1 (requires multicast kernel).</DD>
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<DT><TT>-p <I>pidfile</I></TT></DT>
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<DD>Specify the name and path to record the daemon's process ID.</DD>
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<DT><TT>-P</TT></DT>
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<DD>Override the priority limit set by the operating system. Not
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recommended for sissies.</DD>
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<DT><TT>-r <I>broadcastdelay</I></TT></DT>
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<DD>Specify the default propagation delay from the broadcast/multicast
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server and this computer. This is necessary only if the delay cannot be
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computed automatically by the protocol.</DD>
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<DT><TT>-s <I>statsdir</I></TT></DT>
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<DD>Specify the directory path for files created by the statistics
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facility.</DD>
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<DT><TT>-t <I>key</I></TT></DT>
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<DD>Add a key number to the trusted key list.</DD>
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<DT><TT>-v <I>variable</I></TT></DT>
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<DT><TT>-V <I>variable</I></TT></DT>
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<DD>Add a system variable listed by default.</DD>
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<DT><TT>-x</TT></DT>
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<DD>Ordinarily, if the time is to be adjusted more than 128 ms, it is
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stepped, not gradually slewed. This option forces the time to be slewed
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in all cases. Note: Since the slew rate is limited to 0.5 ms/s, each
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second of adjustment requires an amortization interval of 2000 s. Thus,
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an adjustment of many seconds can take hours or days to amortize.</DD>
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</DL>
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<H4>The Configuration File</H4>
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The <TT>ntpd</TT> configuration file is read at initial startup in order
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to specify the synchronization sources, modes and other related
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information. Usually, it is installed in the <TT>/etc</TT> directory,
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but could be installed elsewhere (see the <TT>-c <I>conffile</I></TT>
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command line option). The file format is similar to other Unix
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configuration files - comments begin with a <TT>#</TT> character and
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extend to the end of the line; blank lines are ignored. Configuration
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commands consist of an initial keyword followed by a list of arguments,
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some of which may be optional, separated by whitespace. Commands may not
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be continued over multiple lines. Arguments may be host names, host
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addresses written in numeric, dotted-quad form, integers, floating
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point numbers (when specifying times in seconds) and text strings.
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Optional arguments are delimited by <TT>[ ]</TT> in the following
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descriptions, while alternatives are separated by <TT>|</TT>. The
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notation <TT>[ ... ]</TT> means an optional, indefinite repetition of
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the last item before the <TT>[ ... ]</TT>.
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<P>See the following pages for configuration and control options. While
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there is a rich set of options available, the only required option is
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one or more <TT>server, peer,</TT> <TT>broadcast</TT> or
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<TT>manycastclient </TT>commands described in the Configuration Options
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page. The <A HREF="notes.htm">Notes on Configuring NTP and Setting up a
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NTP Subnet </A>page contains an extended discussion of these options.
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<P><A HREF="confopt.htm">Configuration Options</A>
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<BR><A HREF="authopt.htm">Authentication Options</A>
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<BR><A HREF="monopt.htm">Monitoring Options</A>
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<BR><A HREF="accopt.htm">Access Control Options</A>
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<BR><A HREF="clockopt.htm">Reference Clock Options</A>
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<BR><A HREF="miscopt.htm">Miscellaneous Options</A>
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<H4>Files</H4>
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<TT>/etc/ntp.conf</TT> - the default name of the configuration file
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<BR><TT>/etc/ntp.drift</TT> - the default name of the drift file
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<BR><TT>/etc/ntp.keys</TT> - the default name of the key file
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<H4>Bugs</H4>
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<TT>ntpd</TT> has gotten rather fat. While not huge, it has gotten
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larger than might be desireable for an elevated-priority daemon running
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on a workstation, particularly since many of the fancy features which
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consume the space were designed more with a busy primary server, rather
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than a high stratum workstation, in mind.
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<hr><a href=index.htm><img align=left src=pic/home.gif></a><address><a
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href=mailto:mills@udel.edu> David L. Mills <mills@udel.edu></a>
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</address></a></body></html>
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