199 lines
4.0 KiB
HTML
199 lines
4.0 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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>An overview of boots and shutdowns</TITLE
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NAME="GENERATOR"
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REL="HOME"
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TITLE="Linux System Administrators Guide"
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TITLE="Boots And Shutdowns"
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TITLE="Boots And Shutdowns"
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TITLE="The boot process in closer look"
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HREF="boot-process.html"></HEAD
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><TR
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>Linux System Administrators Guide: </TH
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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 8. Boots And Shutdowns</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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CLASS="SECT1"
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><H1
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CLASS="SECT1"
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><A
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NAME="BOOT-OVERVIEW"
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></A
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>8.1. An overview of boots and shutdowns</H1
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><P
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>The act of turning on a computer system and causing its
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operating system to be loaded
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is called <I
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CLASS="GLOSSTERM"
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>booting</I
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>. The name comes from
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an image of the computer pulling itself up from its bootstraps,
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but the act itself slightly more realistic.</P
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><P
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>During bootstrapping, the computer first loads a small piece
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of code called the <I
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CLASS="GLOSSTERM"
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>bootstrap loader</I
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>, which
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in turn loads and starts the operating system. The bootstrap
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loader is usually stored in a fixed location on a hard disk
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or a floppy. The reason for this two step process is that
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the operating system is big and complicated, but the first
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piece of code that the computer loads must be very small (a
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few hundred bytes), to avoid making the firmware unnecessarily
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complicated.</P
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><P
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>Different computers do the bootstrapping differently.
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For PCs, the computer (its BIOS) reads in the first sector
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(called the <I
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CLASS="GLOSSTERM"
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>boot sector</I
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>) of a floppy or
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hard disk. The bootstrap loader is contained within this sector.
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It loads the operating system from elsewhere on the disk (or
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from some other place).</P
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><P
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>After Linux has been loaded, it initializes the hardware and
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device drivers, and then runs <B
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CLASS="COMMAND"
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>init</B
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>.
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<B
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CLASS="COMMAND"
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>init</B
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>
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starts other processes to allow users to log in, and do things.
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The details of this part will be discussed below.</P
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><P
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>In order to shut down a Linux system, first all processes
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are told to terminate (this makes them close any files and
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do other necessary things to keep things tidy), then filesystems
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and swap areas are unmounted, and finally a message is printed
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to the console that the power can be turned off. If the proper
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procedure is not followed, terrible things can and will happen;
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most importantly, the filesystem buffer cache might not be flushed,
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which means that all data in it is lost and the filesystem on
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disk is inconsistent, and therefore possibly unusable.
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</P
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ACCESSKEY="P"
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>Prev</A
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WIDTH="33%"
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VALIGN="top"
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>Boots And Shutdowns</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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>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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>The boot process in closer look</TD
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></TR
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></TABLE
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> |