173 lines
3.4 KiB
HTML
173 lines
3.4 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
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<HTML
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><HEAD
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><TITLE
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>The hardware and software clocks</TITLE
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><META
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NAME="GENERATOR"
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CONTENT="Modular DocBook HTML Stylesheet Version 1.7"><LINK
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REL="HOME"
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TITLE="Linux System Administrators Guide"
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HREF="index.html"><LINK
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REL="UP"
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TITLE="Keeping Time"
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HREF="keeping-time.html"><LINK
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REL="PREVIOUS"
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TITLE="The concept of localtime"
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HREF="localtime.html"><LINK
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REL="NEXT"
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TITLE="Showing and setting time"
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HREF="showing-setting-time.html"></HEAD
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><BODY
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CLASS="SECT1"
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BGCOLOR="#FFFFFF"
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TEXT="#000000"
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LINK="#0000FF"
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VLINK="#840084"
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ALINK="#0000FF"
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><DIV
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CLASS="NAVHEADER"
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><TABLE
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SUMMARY="Header navigation table"
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WIDTH="100%"
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BORDER="0"
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CELLSPACING="0"
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><TR
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><TH
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COLSPAN="3"
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ALIGN="center"
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>Linux System Administrators Guide: </TH
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></TR
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><TR
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><TD
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WIDTH="10%"
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ALIGN="left"
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VALIGN="bottom"
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><A
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HREF="localtime.html"
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ACCESSKEY="P"
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>Prev</A
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></TD
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><TD
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WIDTH="80%"
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ALIGN="center"
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VALIGN="bottom"
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>Chapter 14. Keeping Time</TD
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><TD
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WIDTH="10%"
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ALIGN="right"
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VALIGN="bottom"
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><A
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HREF="showing-setting-time.html"
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ACCESSKEY="N"
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>Next</A
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></TD
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></TR
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></TABLE
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><HR
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ALIGN="LEFT"
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WIDTH="100%"></DIV
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><DIV
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CLASS="SECT1"
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><H1
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CLASS="SECT1"
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><A
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NAME="HW-SW-CLOCKS"
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></A
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>14.2. The hardware and software clocks</H1
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><P
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> A personal computer has a battery driven hardware clock.
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The battery ensures that the clock will work even if the rest of
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the computer is without electricity. The hardware clock can be
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set from the BIOS setup screen or from whatever operating system
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is running. </P
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><P
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> The Linux kernel keeps track of time independently from
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the hardware clock. During the boot, Linux sets its own clock
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to the same time as the hardware clock. After this, both clocks
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run independently. Linux maintains its own clock because looking
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at the hardware is slow and complicated. </P
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><P
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> The kernel clock always shows universal time. This way,
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the kernel does not need to know about time zones at all. The
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simplicity results in higher reliability and makes it easier
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to update the time zone information. Each process handles time
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zone conversions itself (using standard tools that are part of
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the time zone package). </P
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><P
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> The hardware clock can be in local time or in universal
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time. It is usually better to have it in universal time,
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because then you don't need to change the hardware clock when
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daylight savings time begins or ends (UTC does not have DST).
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Unfortunately, some PC operating systems, including MS-DOS,
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Windows, and OS/2, assume the hardware clock shows local time.
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Linux can handle either, but if the hardware clock shows local
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time, then it must be modified when daylight savings time begins
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or ends (otherwise it wouldn't show local time). </P
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></DIV
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><DIV
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CLASS="NAVFOOTER"
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><HR
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ALIGN="LEFT"
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WIDTH="100%"><TABLE
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SUMMARY="Footer navigation table"
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WIDTH="100%"
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BORDER="0"
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CELLPADDING="0"
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CELLSPACING="0"
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><TR
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><TD
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WIDTH="33%"
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ALIGN="left"
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VALIGN="top"
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><A
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HREF="localtime.html"
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ACCESSKEY="P"
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>Prev</A
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></TD
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><TD
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WIDTH="34%"
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ALIGN="center"
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VALIGN="top"
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><A
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HREF="index.html"
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ACCESSKEY="H"
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>Home</A
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></TD
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><TD
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WIDTH="33%"
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ALIGN="right"
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VALIGN="top"
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><A
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HREF="showing-setting-time.html"
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ACCESSKEY="N"
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>Next</A
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></TD
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></TR
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><TR
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><TD
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WIDTH="33%"
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ALIGN="left"
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VALIGN="top"
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>The concept of localtime</TD
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><TD
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WIDTH="34%"
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ALIGN="center"
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VALIGN="top"
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><A
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HREF="keeping-time.html"
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ACCESSKEY="U"
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>Up</A
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></TD
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><TD
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WIDTH="33%"
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ALIGN="right"
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VALIGN="top"
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>Showing and setting time</TD
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></TR
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></TABLE
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></DIV
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></BODY
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></HTML
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> |