121 lines
5.3 KiB
HTML
121 lines
5.3 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN">
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<HTML>
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<HEAD>
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<META NAME="GENERATOR" CONTENT="SGML-Tools 1.0.9">
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<TITLE>The Clock Mini-HOWTO: Introduction</TITLE>
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<LINK HREF="Clock-2.html" REL=next>
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<LINK HREF="Clock.html#toc1" REL=contents>
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</HEAD>
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<BODY>
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<A HREF="Clock-2.html">Next</A>
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Previous
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<A HREF="Clock.html#toc1">Contents</A>
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<HR>
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<H2><A NAME="s1">1. Introduction</A></H2>
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<H2><A NAME="ss1.1">1.1 Does Anybody Really Know What Time It Is?</A>
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</H2>
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<P>The Real-Time-Clock (RTC) chips used on PC motherboards are
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notoriously inaccurate, usually gaining or losing the same
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amount of time each day. Linux provides a simple way to correct
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for this in software, which can make the clock <EM>*very*</EM>
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accurate, even without an external time source. But most people
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don't know how to set it up, for several reasons:
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<P>
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<UL>
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<LI>It's not mentioned in most of the general documentation
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on how to set up linux, and it can't be set up
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automatically (unless you have an external time source),
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so the default is not to use it.</LI>
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<LI>If you type "<CODE>man clock</CODE>" you may get
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the man page for <CODE>clock(3)</CODE>, which is not what you
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want. Try "<CODE>man 8 clock</CODE>" or
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"<CODE>man 8 hwclock</CODE>" (some distributions
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search the man pages in numerical order if you don't give
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a section number, others search in the order specified in
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<CODE>/etc/man.config</CODE>).</LI>
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<LI>Most people don't seem to care what time it is anyway.</LI>
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<LI>Those few who do care often want to sync the system clock
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to an external time source, such as a network time server
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or radio clock. This makes the accuracy of the RTC
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(mostly) irrelevant.</LI>
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</UL>
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<P>This mini-HOWTO describes the low-tech approach (which can be
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very accurate by itself), and provides pointers to several more
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sophisticated options. In most cases the documentation is well
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written, so I'm not going to repeat that information here.
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<P>Previous versions included detailed instructions for the old
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<CODE>clock(8)</CODE> program for anyone still running an older
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system, but I've dropped that section because most distributions
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now use <CODE>hwclock(8)</CODE> instead, which has much better
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documentation. If you still want a copy of the <CODE>clock(8)</CODE>
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instructions I can email them to you, but read the section on
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<CODE>hwclock(8)</CODE> first.
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<P>
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<DL>
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<DT><B>Note</B><DD><P>You must be logged in as "<B>root</B>" to run
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any program that affects the RTC or the system time, which
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includes most of the programs described here. If you
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normally use a graphical interface for everything, you may
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also need to learn some basic unix shell commands.
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</DL>
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<P>
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<DL>
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<DT><B>Note</B><DD><P>If you run more than one OS on your machine, you should
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only let one of them set the RTC, so they don't
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confuse each other. The exception is the twice-a-year
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adjustment for Daylight Saving(s) Time (see the section on
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DST for details).
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</DL>
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<P>If you run a dual-boot system that spends a lot of time running
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Windows, you may want to check out some of the clock software
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available for that OS instead. Follow the links on the NTP
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website at
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<A HREF="http://www.eecis.udel.edu/~ntp/software.html">http://www.eecis.udel.edu/~ntp/software.html</A>.
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Many of the radio clocks mentioned here include software for Windows.
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<H2><A NAME="ss1.2">1.2 Where to Find Stuff: "The Usual Places"</A>
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</H2>
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<P>In some places I've mentioned that software can be downloaded
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from "the usual places", which means any place you
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could download a complete Linux system if you didn't get it on a
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CD-ROM. In the old days that meant the ftp archive at
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sunsite.unc.edu, and various mirror sites around the world. That
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site has been renamed
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<A HREF="http://metalab.unc.edu/linux/">http://metalab.unc.edu/linux/</A>
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(since Sun no longer sponsors it). Some distributions also have
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their own websites, which may include a lot of this stuff.
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<P>I assume most people get Linux on CD these days, and those CDs
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often include software that is not part of the default
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installation, so you may already have some of the programs
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mentioned here without knowing it.
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<P>The latest version of this mini-HOWTO can be found at the home of
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the Linux Documentation Project, which is currently
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<A HREF="http://www.linuxdoc.org/">http://www.linuxdoc.org/</A> (and is also reachable from
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the metalab site mentioned above). I think all the old links are
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now forwarded to this one.
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<P>All HOWTOs are written in SGML and converted to various other
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formats by standardized conversion programs. Most people seem to
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want the HTML version, which is at
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<A HREF="http://www.linuxdoc.org/HOWTO/mini/Clock.html">http://www.linuxdoc.org/HOWTO/mini/Clock.html</A>.
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Revision history can be found as comments in the SGML source.
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Most Linux distributions install a complete set of HOWTO's in
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<CODE>/usr/doc/HOWTO/</CODE> and
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<CODE>/usr/doc/HOWTO/mini</CODE>.
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<H2><A NAME="ss1.3">1.3 Acknowledgements</A>
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</H2>
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<P>This mini-HOWTO has been greatly improved thanks to various
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people who have sent me email since the first version in 1996.
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In some cases they wrote with questions but ended up giving me as
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much information as I gave them. Unfortunately I haven't compiled
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a list of names (maybe next time). You know who you are <CODE>:-)</CODE>.
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<HR>
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<A HREF="Clock-2.html">Next</A>
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Previous
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<A HREF="Clock.html#toc1">Contents</A>
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</BODY>
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</HTML>
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