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diff --git a/sag-0.6.1-www/sag-0.6.1.html/c63.html b/sag-0.6.1-www/sag-0.6.1.html/c63.html new file mode 100644 index 0000000..215276b --- /dev/null +++ b/sag-0.6.1-www/sag-0.6.1.html/c63.html @@ -0,0 +1,264 @@ +<!DOCTYPE HTML PUBLIC "-//Norman Walsh//DTD DocBook HTML 1.0//EN"> +<HTML +><HEAD +><TITLE +>Overview of a Linux System</TITLE +><META +NAME="GENERATOR" +CONTENT="Modular DocBook HTML Stylesheet"><LINK +REL="HOME" +TITLE="The Linux System Administrators' Guide" +HREF="book1.html"><LINK +REL="PREVIOUS" +TITLE="Introduction" +HREF="c31.html"><LINK +REL="NEXT" +TITLE="Important parts of the kernel" +HREF="x83.html"></HEAD +><BODY +BGCOLOR="#FFFFFF" +TEXT="#000000" +><DIV +CLASS="NAVHEADER" +><TABLE +WIDTH="100%" +BORDER="0" +CELLPADDING="0" +CELLSPACING="0" +><TR +><TH +COLSPAN="3" +ALIGN="center" +>The Linux System Administrators' Guide</TH +></TR +><TR +><TD +WIDTH="10%" +ALIGN="left" +VALIGN="bottom" +><A +HREF="c31.html" +>Prev</A +></TD +><TD +WIDTH="80%" +ALIGN="center" +VALIGN="bottom" +></TD +><TD +WIDTH="10%" +ALIGN="right" +VALIGN="bottom" +><A +HREF="x83.html" +>Next</A +></TD +></TR +></TABLE +><HR +ALIGN="LEFT" +WIDTH="100%"></DIV +><DIV +CLASS="CHAPTER" +><H1 +><A +NAME="AEN63" +>Chapter 2. Overview of a Linux System</A +></H1 +><DIV +CLASS="TOC" +><DL +><DT +><B +>Table of Contents</B +></DT +><DT +><A +HREF="c63.html#AEN69" +>Various parts of an operating system</A +></DT +><DT +><A +HREF="x83.html" +>Important parts of the kernel</A +></DT +><DT +><A +HREF="x94.html" +>Major services in a UNIX system</A +></DT +></DL +></DIV +><BLOCKQUOTE +><P +>“God looked over everything he + had made, and saw that it was very good. ” (Genesis + 1:31)</P +></BLOCKQUOTE +><P +>This chapter gives an overview of a Linux system. First, + the major services provided by the operating system are described. + Then, the programs that implement these services are described + with a considerable lack of detail. The purpose of this chapter + is to give an understanding of the system as a whole, so that + each part is described in detail elsewhere.</P +><DIV +CLASS="SECT1" +><H1 +CLASS="SECT1" +><A +NAME="AEN69" +>Various parts of an operating system</A +></H1 +><P +>A UNIX operating system consists + of a <I +CLASS="GLOSSTERM" +>kernel</I +> and some + <I +CLASS="GLOSSTERM" +>system programs</I +>. There are also some + <I +CLASS="GLOSSTERM" +>application</I +> programs} for doing work. + The kernel is the heart of the operating system. + + <A +NAME="AEN75" +HREF="#FTN.AEN75" +>[1]</A +> + + It keeps track of files on the disk, starts programs and runs + them concurrently, assigns memory and other resources to various + processes, receives packets from and sends packets to the network, + and so on. The kernel does very little by itself, but it provides + tools with which all services can be built. It also prevents + anyone from accessing the hardware directly, forcing everyone + to use the tools it provides. This way the kernel provides + some protection for users from each other. The tools provided + by the kernel are used via <I +CLASS="GLOSSTERM" +>system calls<I +CLASS="GLOSSTERM" +>; + see manual page section 2 for more information on these. </I +></I +></P +><P +>The system programs use the tools provided by the kernel to + implement the various services required from an operating system. + System programs, and all other programs, run `on top of the + kernel', in what is called the <I +CLASS="GLOSSTERM" +>user mode</I +>. + The difference between system and application programs is + one of intent: applications are intended for getting useful + things done (or for playing, if it happens to be a game), + whereas system programs are needed to get the system working. + A word processor is an application; <B +CLASS="COMMAND" +>telnet</B +> + is a system program. The difference is often somewhat blurry, + however, and is important only to compulsive categorizers.</P +><P +>An operating system can also contain compilers and their + corresponding libraries (GCC and the C library in particular under + Linux), although not all programming languages need be part of + the operating system. Documentation, and sometimes even games, + can also be part of it. Traditionally, the operating system has + been defined by the contents of the installation tape or disks; + with Linux it is not as clear since it is spread all over the + FTP sites of the world.</P +></DIV +></DIV +><H3 +>Notes</H3 +><TABLE +BORDER="0" +CLASS="FOOTNOTES" +WIDTH="100%" +><TR +><TD +ALIGN="LEFT" +VALIGN="TOP" +WIDTH="5%" +><A +NAME="FTN.AEN75" +HREF="c63.html#AEN75" +>[1]</A +></TD +><TD +ALIGN="LEFT" +VALIGN="TOP" +WIDTH="95%" +><P +>In fact, it is often mistakenly considered + to be the operating system itself, but it is not. + An operating system provides many more services than a + plain kernel.</P +></TD +></TR +></TABLE +><DIV +CLASS="NAVFOOTER" +><HR +ALIGN="LEFT" +WIDTH="100%"><TABLE +WIDTH="100%" +BORDER="0" +CELLPADDING="0" +CELLSPACING="0" +><TR +><TD +WIDTH="33%" +ALIGN="left" +VALIGN="top" +><A +HREF="c31.html" +>Prev</A +></TD +><TD +WIDTH="34%" +ALIGN="center" +VALIGN="top" +><A +HREF="book1.html" +>Home</A +></TD +><TD +WIDTH="33%" +ALIGN="right" +VALIGN="top" +><A +HREF="x83.html" +>Next</A +></TD +></TR +><TR +><TD +WIDTH="33%" +ALIGN="left" +VALIGN="top" +>Introduction</TD +><TD +WIDTH="34%" +ALIGN="center" +VALIGN="top" +> </TD +><TD +WIDTH="33%" +ALIGN="right" +VALIGN="top" +>Important parts of the kernel</TD +></TR +></TABLE +></DIV +></BODY +></HTML +>
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