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<title>Debian GNU/Linux System Administrator's Manual (Obsolete Documentation) - Overview of a Debian GNU/Linux System</title>
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<link href="ch-sysadmin-intro.html" rel="chapter" title="1 Introduction">
<link href="ch-sysadmin-overview.html" rel="chapter" title="2 Overview of a Debian GNU/Linux System">
<link href="ch-sysadmin-files.html" rel="chapter" title="3 Files and Devices">
<link href="ch4.html" rel="chapter" title="4 Programs and processes">
<link href="ch-sysadmin-directories.html" rel="chapter" title="5 Directory Structure">
<link href="ch-sysadmin-filesystems.html" rel="chapter" title="6 Filesystems and Storage Media">
<link href="ch-sysadmin-booting.html" rel="chapter" title="7 Boot and Shutdown">
<link href="ch-sysadmin-users.html" rel="chapter" title="8 Managing User Accounts">
<link href="ch-sysadmin-sessions.html" rel="chapter" title="9 Logging In and Out">
<link href="ch-sysadmin-printing.html" rel="chapter" title="10 Printing">
<link href="ch-sysadmin-accounting.html" rel="chapter" title="11 Accounting">
<link href="ch-sysadmin-backup.html" rel="chapter" title="12 Backup and Restore">
<link href="ch-sysadmin-X.html" rel="chapter" title="13 X Windows">
<link href="ch-sysadmin-security.html" rel="chapter" title="14 Security">
<link href="ch-sysadmin-config.html" rel="chapter" title="15 System Configuration">
<link href="ch-sysadmin-time.html" rel="chapter" title="16 Time">
<link href="ch-sysadmin-localisation.html" rel="chapter" title="17 Localisation">
<link href="ch-sysadmin-index.html" rel="chapter" title="18 Index">
<link href="ch-sysadmin-intro.html#s1.1" rel="section" title="1.1 About this manual">
<link href="ch-sysadmin-intro.html#s1.2" rel="section" title="1.2 Where to find newer versions">
<link href="ch-sysadmin-intro.html#s1.3" rel="section" title="1.3 Comments">
<link href="ch-sysadmin-overview.html#s2.1" rel="section" title="2.1 The main components of a system">
<link href="ch-sysadmin-files.html#s3.1" rel="section" title="3.1 Files">
<link href="ch-sysadmin-files.html#s3.2" rel="section" title="3.2 Devices">
<link href="ch4.html#s4.1" rel="section" title="4.1 Programs">
<link href="ch4.html#s4.2" rel="section" title="4.2 Processes">
<link href="ch4.html#s4.3" rel="section" title="4.3 The /proc filesystem">
<link href="ch4.html#s4.4" rel="section" title="4.4 Tools for handling programs and processes">
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<link href="ch-sysadmin-filesystems.html#s6.1" rel="section" title="6.1 Storage devices and media">
<link href="ch-sysadmin-filesystems.html#s6.2" rel="section" title="6.2 Types of filesystem">
<link href="ch-sysadmin-filesystems.html#s6.3" rel="section" title="6.3 Quotas">
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<link href="ch-sysadmin-booting.html#s7.1" rel="section" title="7.1 Boot loaders">
<link href="ch-sysadmin-users.html#s8.1" rel="section" title="8.1 Concepts">
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<link href="ch-sysadmin-printing.html#s10.2" rel="section" title="10.2 Spooler">
<link href="ch-sysadmin-accounting.html#s11.1" rel="section" title="11.1 Concepts">
<link href="ch-sysadmin-backup.html#s12.1" rel="section" title="12.1 Why backup?">
<link href="ch-sysadmin-backup.html#s12.2" rel="section" title="12.2 What to backup?">
<link href="ch-sysadmin-backup.html#s12.3" rel="section" title="12.3 Backup devices and media">
<link href="ch-sysadmin-backup.html#s12.4" rel="section" title="12.4 Backup methods and software">
<link href="ch-sysadmin-backup.html#s12.5" rel="section" title="12.5 Types of backup">
<link href="ch-sysadmin-X.html#s13.1" rel="section" title="13.1 Overview of X">
<link href="ch-sysadmin-security.html#s14.1" rel="section" title="14.1 Threats">
<link href="ch-sysadmin-config.html#s15.1" rel="section" title="15.1 ???">
<link href="ch-sysadmin-time.html#s16.1" rel="section" title="16.1 Setting time, time zones and Daylight Saving">
<link href="ch-sysadmin-time.html#s16.2" rel="section" title="16.2 Setting and showing hardware clock">
<link href="ch-sysadmin-time.html#s-multiboot-with" rel="section" title="16.3 Multiboot with operating systems not understanding timezone">
<link href="ch-sysadmin-time.html#s-syncing-time" rel="section" title="16.4 Syncing time, rdate and NTP">
<link href="ch-sysadmin-time.html#s16.5" rel="section" title="16.5 Setting up an NTP server">
<link href="ch-sysadmin-time.html#s-radio-clocks" rel="section" title="16.6 Radio clocks">
<link href="ch-sysadmin-time.html#s16.7" rel="section" title="16.7 Timestamps">
<link href="ch-sysadmin-time.html#s16.8" rel="section" title="16.8 Time in cron">
<link href="ch-sysadmin-localisation.html#s17.1" rel="section" title="17.1 Environment variables">
<link href="ch-sysadmin-overview.html#s2.1.1" rel="subsection" title="2.1.1 The hardware">
<link href="ch-sysadmin-overview.html#s2.1.2" rel="subsection" title="2.1.2 The Linux kernel">
<link href="ch-sysadmin-overview.html#s2.1.3" rel="subsection" title="2.1.3 Devices">
<link href="ch-sysadmin-overview.html#s2.1.4" rel="subsection" title="2.1.4 Filesystems">
<link href="ch-sysadmin-files.html#s3.1.1" rel="subsection" title="3.1.1 Concepts">
<link href="ch-sysadmin-files.html#s3.1.2" rel="subsection" title="3.1.2 Inodes">
<link href="ch-sysadmin-files.html#s3.1.3" rel="subsection" title="3.1.3 Links">
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<link href="ch-sysadmin-files.html#s3.2.1" rel="subsection" title="3.2.1 Device drivers">
<link href="ch-sysadmin-files.html#s3.2.2" rel="subsection" title="3.2.2 Device nodes">
<link href="ch-sysadmin-files.html#s3.2.3" rel="subsection" title="3.2.3 Kernel modules">
<link href="ch-sysadmin-directories.html#s5.3.1" rel="subsection" title="5.3.1 Hard links">
<link href="ch-sysadmin-directories.html#s5.3.2" rel="subsection" title="5.3.2 Symbolic links">
<link href="ch-sysadmin-users.html#s8.1.1" rel="subsection" title="8.1.1 Usernames and User IDs">
<link href="ch-sysadmin-users.html#s8.1.2" rel="subsection" title="8.1.2 Groups and Group IDs">
<link href="ch-sysadmin-users.html#s8.1.3" rel="subsection" title="8.1.3 Passwords">
<link href="ch-sysadmin-users.html#s8.1.4" rel="subsection" title="8.1.4 Quotas">
<link href="ch-sysadmin-users.html#s8.2.1" rel="subsection" title="8.2.1 Adding new users">
<link href="ch-sysadmin-users.html#s8.2.2" rel="subsection" title="8.2.2 Changing or editing user information and settings">
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<link href="ch-sysadmin-users.html#s8.2.6" rel="subsection" title="8.2.6 Creating groups">
<link href="ch-sysadmin-users.html#s8.2.7" rel="subsection" title="8.2.7 Editing groups">
<link href="ch-sysadmin-users.html#s8.2.8" rel="subsection" title="8.2.8 Deleting groups">
<link href="ch-sysadmin-users.html#s8.2.9" rel="subsection" title="8.2.9 Setting up quotas">
<link href="ch-sysadmin-users.html#s8.2.10" rel="subsection" title="8.2.10 Using shadow passwords">
<link href="ch-sysadmin-users.html#s8.3.1" rel="subsection" title="8.3.1 Command-line tools">
<link href="ch-sysadmin-users.html#s8.3.1.1" rel="subsection" title="8.3.1.1 adduser, addgroup">
<link href="ch-sysadmin-users.html#s8.3.1.2" rel="subsection" title="8.3.1.2 chage">
<link href="ch-sysadmin-users.html#s8.3.1.3" rel="subsection" title="8.3.1.3 chfn">
<link href="ch-sysadmin-users.html#s8.3.1.4" rel="subsection" title="8.3.1.4 chsh">
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<link href="ch-sysadmin-users.html#s8.3.1.7" rel="subsection" title="8.3.1.7 vipw, vigr">
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<link href="ch-sysadmin-users.html#s8.4.1" rel="subsection" title="8.4.1 /etc/passwd">
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<link href="ch-sysadmin-printing.html#s10.2.1" rel="subsection" title="10.2.1 Lp">
<link href="ch-sysadmin-printing.html#s10.2.2" rel="subsection" title="10.2.2 LPrng">
<link href="ch-sysadmin-backup.html#s-sect-floppy" rel="subsection" title="12.3.1 Floppy">
<link href="ch-sysadmin-backup.html#s12.3.1.1" rel="subsection" title="12.3.1.1 Backup example 1, suitable for disk media">
<link href="ch-sysadmin-backup.html#s12.3.1.2" rel="subsection" title="12.3.1.2 Backup example 2, suitable for tape media">
<link href="ch-sysadmin-backup.html#s12.3.1.3" rel="subsection" title="12.3.1.3 Backup example 3, suitable for disk media with DOS file system">
<link href="ch-sysadmin-backup.html#s12.3.2" rel="subsection" title="12.3.2 High Capacity Floppies">
<link href="ch-sysadmin-backup.html#s12.3.3" rel="subsection" title="12.3.3 CD-R and CD-RW">
<link href="ch-sysadmin-backup.html#s12.3.4" rel="subsection" title="12.3.4 Tapes">
<link href="ch-sysadmin-backup.html#s12.4.1" rel="subsection" title="12.4.1 Network backups">
<link href="ch-sysadmin-backup.html#s12.4.1.1" rel="subsection" title="12.4.1.1 Installing EMC NetWorker Client">
<link href="ch-sysadmin-backup.html#s12.4.1.2" rel="subsection" title="12.4.1.2 Setting up and Configuring">
<link href="ch-sysadmin-backup.html#s12.4.2" rel="subsection" title="12.4.2 Tar et al">
<link href="ch-sysadmin-backup.html#s12.4.3" rel="subsection" title="12.4.3 Backup software">
<link href="ch-sysadmin-time.html#s-tzconfig" rel="subsection" title="16.1.1 Changing the timezone after installation">
<link href="ch-sysadmin-time.html#s16.1.2" rel="subsection" title="16.1.2 Setting the TZ environment variable.">
<link href="ch-sysadmin-time.html#s16.4.1" rel="subsection" title="16.4.1 Setting time at system boot">
<link href="ch-sysadmin-time.html#s16.4.2" rel="subsection" title="16.4.2 Setting time using NTP">
<link href="ch-sysadmin-time.html#s16.4.3" rel="subsection" title="16.4.3 Other methods">
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<p><a name="ch-sysadmin-overview"></a></p>
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[ <a href="ch-sysadmin-intro.html">previous</a> ]
[ <a href="index.html#contents">Contents</a> ]
[ <a href="ch-sysadmin-intro.html">1</a> ]
[ 2 ]
[ <a href="ch-sysadmin-files.html">3</a> ]
[ <a href="ch4.html">4</a> ]
[ <a href="ch-sysadmin-directories.html">5</a> ]
[ <a href="ch-sysadmin-filesystems.html">6</a> ]
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[ <a href="ch-sysadmin-users.html">8</a> ]
[ <a href="ch-sysadmin-sessions.html">9</a> ]
[ <a href="ch-sysadmin-printing.html">10</a> ]
[ <a href="ch-sysadmin-accounting.html">11</a> ]
[ <a href="ch-sysadmin-backup.html">12</a> ]
[ <a href="ch-sysadmin-X.html">13</a> ]
[ <a href="ch-sysadmin-security.html">14</a> ]
[ <a href="ch-sysadmin-config.html">15</a> ]
[ <a href="ch-sysadmin-time.html">16</a> ]
[ <a href="ch-sysadmin-localisation.html">17</a> ]
[ <a href="ch-sysadmin-index.html">18</a> ]
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</p>
<hr>
<h1>
Debian GNU/Linux System Administrator's Manual (Obsolete Documentation)
<br>Chapter 2 - Overview of a Debian GNU/Linux System
</h1>
<hr>
<p>
author = Oliver Elphick
</p>
<p>
topics = Linux Kernel, Devices, Filesystems, Users
</p>
<hr>
<h2><a name="s2.1"></a>2.1 The main components of a system</h2>
<p>
A Debian system comprises a computer, with devices to enable it to communicate
with the outside world, temporary and permanent storage, and the software to
make it all work.
</p>
<p>
Linux is available for a number of different types of computer. The original
Linux kernel was written for the Intel 80386, and descendants of this processor
power the majority of Linux systems at present. However, there are also
versions of Linux for DEC Alpha, Motorola, Power PC, ARM, Amiga, MIPS, Sun
SPARC and others.
</p>
<p>
Debian has distributions for x86, DEC Alpha, ARM, Motorola 68k, MIPS,
Motorola/IBM PowerPC, Sun SPARC, Sun UltraSPARC and GNU/Hurd. (The last-named
is not a machine but a new operating system from the Free Software Foundation.)
</p>
<hr>
<h3><a name="s2.1.1"></a>2.1.1 The hardware</h3>
<p>
The minimum needed for any computer system is a <strong>processor</strong> (or
<strong>CPU</strong>), some permanent storage (whether modifiable or not), some
working memory, an input device (usually a keyboard) and an output device
(usually a screen, but it could be a printer or even an array of lights). The
usual configuration of a PC is a box containing a <strong>CPU</strong>, a small
amount of Read Only Memory (<strong>ROM</strong>) and from 4 to 256 Megabytes
of Random Access Memory (<strong>RAM</strong>). These are mounted on a
motherboard, which also contains components such as a clock and interfaces to
various kinds of input and output (<strong>I/O</strong>) devices. The
motherboard also contains a <strong>BIOS</strong> chip which contains the
program which starts the computer working when it is reset or powered up.
</p>
<p>
Inside the computer box, with the motherboard there are usually one or more
disk drives, either removable or permanent, and there may well be a CD/ROM
drive. Special &quot;cards&quot; are plugged into the motherboard to manage
networking, video display, sound and so on. Some motherboards may include
these functions and not need extra cards.
</p>
<p>
Outside the computer box will be peripheral devices of various kinds. These
will almost always include a video monitor and a keyboard. There will probably
also be a mouse. Systems with a soundcard will have speakers. There may be a
modem, printers, graphics pad, music keyboard, scanner, external disk drives,
and so on; the list is almost endless.
</p>
<p>
All these devices are controlled by software; first by the
<strong>BIOS</strong>, then by the boot loader which is run by the
<strong>BIOS</strong> and finally by the <strong>operating system</strong>. In
Debian's case, that operating system is the Linux <strong>kernel</strong>.
</p>
<hr>
<h3><a name="s2.1.2"></a>2.1.2 The Linux kernel</h3>
<p>
The Linux kernel is a program that is running all the time from the moment that
a Debian system is booted. It is responsible for servicing all running
programs when they make `system calls', which are requests to run part of the
kernel code - for instance, reading from a device. No program can operate
without calling on the kernel for some services.
</p>
<p>
The kernel consists of the base kernel itself and a number of modules, which
can be loaded on demand. Once loaded, these modules become part of the kernel
itself, and can be called on in the same way. However, when they are no longer
required they can be unloaded, thus saving memory.
</p>
<p>
Each Debian distribution comes with a pre-built kernel and modules that handle
most devices you are likely to have. However, you can rebuild the kernel to
match your own particular setup, either to accommodate unusual devices or to
save space by removing support for devices you do not have.
</p>
<p>
Linux kernel development is continually in progress. Kernel version numbers
indicate how up-to-date the kernel is. At the time of writing (September
1998), the current stable kernel is 2.0.35 and the development kernel is
2.1.119. Development kernels have an odd number in the second part of their
version numbers. When 2.1 is thought sufficiently stable, it will be renamed
2.2 and will become the new stable release.
</p>
<p>
The current stable Linux kernel should always be available as a Debian package,
and there is also a package called kernel-package which you can use to make
your own customised version of the kernel without conflicting with Debian's
packaging system.
</p>
<hr>
<h3><a name="s2.1.3"></a>2.1.3 Devices</h3>
<p>
Every computer has a number of devices, ranging from its own memory to external
hardware. These devices are controlled by device drivers which are either
built into the kernel or loaded from kernel modules. (It is possible, but
unusual, for device drivers to be user programs rather than kernel code.)
</p>
<p>
Devices are accessed through device nodes, which are stored in the
<samp>/dev</samp> directory. Most operations can be done through these device
nodes. For device-specific actions, <strong><samp>ioctl</samp></strong> calls
can be made to the device driver. Retensioning a tape, for example, is done
through an <strong><samp>ioctl</samp></strong> call.
</p>
<hr>
<h3><a name="s2.1.4"></a>2.1.4 Filesystems</h3>
<p>
Disk devices support filesystems, in which all the information available to the
computer is stored. Filesystems are organised as directory trees.
</p>
<p>
Every Unix computer has at least one filesystem available at all times: this is
the <strong>root</strong> filesystem, which is under the directory
`<strong>/</strong>'. All other filesystems that may be available are mounted
under the root filesystem, so that all the filesystems appear as a unified
whole. Filesystems on other machines can be mounted, and even these appear as
if they were under the root.
</p>
<hr>
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[ <a href="ch-sysadmin-filesystems.html">6</a> ]
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[ <a href="ch-sysadmin-sessions.html">9</a> ]
[ <a href="ch-sysadmin-printing.html">10</a> ]
[ <a href="ch-sysadmin-accounting.html">11</a> ]
[ <a href="ch-sysadmin-backup.html">12</a> ]
[ <a href="ch-sysadmin-X.html">13</a> ]
[ <a href="ch-sysadmin-security.html">14</a> ]
[ <a href="ch-sysadmin-config.html">15</a> ]
[ <a href="ch-sysadmin-time.html">16</a> ]
[ <a href="ch-sysadmin-localisation.html">17</a> ]
[ <a href="ch-sysadmin-index.html">18</a> ]
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</p>
<hr>
<p>
Debian GNU/Linux System Administrator's Manual (Obsolete Documentation)
</p>
<address>
This manual is OBSOLETE and DEPRECATED since 2006, 29 Dezember 2009. Instead see http://www.de.debian.org/doc/user-manuals#quick-reference.<br>
<br>
Ardo van Rangelrooij <code><a href="mailto:ardo.van.rangelrooij@tip.nl">ardo.van.rangelrooij@tip.nl</a></code><br>
Tapio Lehtonen <code><a href="mailto:Tapio.Lehtonen@IKI.FI">Tapio.Lehtonen@IKI.FI</a></code><br>
Oliver Elphick - Previous maintainer<br>
<br>
</address>
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