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<div class="CHAPTER">
<h1><a id="SYSTEM-CONFIGURATION" name="SYSTEM-CONFIGURATION"></a>Chapter 4 System
Configuration</h1>
<div class="TOC">
<dl>
<dt><b>Table of Contents</b></dt>
<dt>4.1 <a href="system-configuration.html#SYSTEM-CONFIGURATION-OVERVIEW">System
Overview</a></dt>
<dt>4.2 <a href="system-configuration-kernel.html">Selecting a Kernel</a></dt>
</dl>
</div>
<p>Before you can configure the more advanced parts of your system, it's a good idea to
learn how the system is organized and what commands can be used to search for files and
programs. It's also good to know if you need to compile a custom kernel and what the
steps for doing that are. This chapter will familiarize you with system organization and
configuration files. Then, you can move on to configuring the more advanced parts of the
system.</p>
<div class="SECT1">
<h1 class="SECT1"><a id="SYSTEM-CONFIGURATION-OVERVIEW"
name="SYSTEM-CONFIGURATION-OVERVIEW">4.1 System Overview</a></h1>
<p>It's important to understand how a Linux system is put together before diving into the
various configuration aspects. A Linux system is significantly different from a DOS,
Windows, or Macintosh system (with the exception of the Unix-based Mac OS X), but these
sections will help you get acquainted with the layout so that you can easily configure
your system to meet your needs.</p>
<div class="SECT2">
<h2 class="SECT2"><a id="SYSTEM-CONFIGURATION-LAYOUT"
name="SYSTEM-CONFIGURATION-LAYOUT">4.1.1 File System Layout</a></h2>
<p>The first noticeable difference between Slackware Linux and a DOS or Windows system is
the filesystem. For starters, we do not use drive letters to denote different partitions.
Under Linux, there is one main directory. You can relate this to the <tt
class="DEVICENAME">C:</tt> drive under DOS. Each partition on your system is mounted to a
directory on the main directory. It's kind of like an ever-expanding hard disk.</p>
<p>We call the main directory the root directory, and it's denoted with a single slash
(<tt class="FILENAME">/</tt>). This concept may seem strange, but it actually makes life
easy for you when you want to add more space. For example, let's say you run out of space
on the drive that has <tt class="FILENAME">/home</tt> on it. Most people install
Slackware and make one big root drive. Well, since a partition can be mounted to any
directory, you can simply go to the store and pick up a new hard drive and mount it to
<tt class="FILENAME">/home</tt>. You've now grafted on some more space to your system.
And all without having to move many things around.</p>
<p>Below, you will find descriptions of the major top level directories under
Slackware.</p>
<div class="VARIABLELIST">
<dl>
<dt><tt class="FILENAME">bin</tt></dt>
<dd>
<p>Essential user programs are stored here. These represent the bare minimum set of
programs required for a user to use the system. Things like the shell and the filesystem
commands (<tt class="COMMAND">ls</tt>, <tt class="COMMAND">cp</tt>, and so on) are stored
here. The <tt class="FILENAME">/bin</tt> directory usually doesn't receive modification
after installation. If it does, it's usually in the form of package upgrades that we
provide.</p>
</dd>
<dt><tt class="FILENAME">boot</tt></dt>
<dd>
<p>Files that are used by the Linux Loader (LILO). This directory also receives little
modification after an installation. The kernel is stored here as of Slackware 8.1. In
earlier releases of Slackware, the kernel was simply stored under <tt
class="FILENAME">/</tt> , but common practice is to put the kernel and related files here
to facilitate dual-booting.</p>
</dd>
<dt><tt class="FILENAME">dev</tt></dt>
<dd>
<p>Everything in Linux is treated as a file, even hardware devices like serial ports,
hard disks, and scanners. In order to access these devices, a special file called a
device node has to be present. All device nodes are stored in the <tt
class="FILENAME">/dev</tt> directory. You will find this to be true across many Unix-like
operating systems.</p>
</dd>
<dt><tt class="FILENAME">etc</tt></dt>
<dd>
<p>This directory holds system configuration files. Everything from the X Window
configuration file, the user database, to the system startup scripts. The system
administrator will become quite familiar with this directory over time.</p>
</dd>
<dt><tt class="FILENAME">home</tt></dt>
<dd>
<p>Linux is a multiuser operating system. Each user on the system is given an account and
a unique directory for personal files. This directory is called the user's home
directory. The <tt class="FILENAME">/home</tt> directory is provided as the default
location for user home directories.</p>
</dd>
<dt><tt class="FILENAME">lib</tt></dt>
<dd>
<p>System libraries that are required for basic operation are stored here. The C library,
the dynamic loader, the ncurses library, and kernel modules are among the things stored
here.</p>
</dd>
<dt><tt class="FILENAME">mnt</tt></dt>
<dd>
<p>This directory contains temporary mount points for working on hard disks or removable
drives. Here you'll find mount points for your CD-ROM and floppy drives.</p>
</dd>
<dt><tt class="FILENAME">opt</tt></dt>
<dd>
<p>Optional software packages. The idea behind <tt class="FILENAME">/opt</tt> is that
each software package installs to <tt class="FILENAME">/opt/<var
class="REPLACEABLE">software-package</var></tt>, which makes it easy to remove later.
Slackware distributes some things in <tt class="FILENAME">/opt</tt> (such as KDE in <tt
class="FILENAME">/opt/kde</tt>), but you are free to add anything you want to <tt
class="FILENAME">/opt</tt>.</p>
</dd>
<dt><tt class="FILENAME">proc</tt></dt>
<dd>
<p>This is a unique directory. It's not really part of the filesystem, but a virtual
filesystem that provides access to kernel information. Various pieces of information that
the kernel wants you to know are conveyed to you through files in the <tt
class="FILENAME">/proc</tt> directory. You can also send information to the kernel
through some of these files. Try doing <tt class="COMMAND">cat /proc/cpuinfo</tt>.</p>
</dd>
<dt><tt class="FILENAME">root</tt></dt>
<dd>
<p>The system administrator is known as <tt class="USERNAME">root</tt> on the system. <tt
class="USERNAME">root</tt>'s home directory is kept in <tt class="FILENAME">/root</tt>
instead of <tt class="FILENAME">/home/root</tt>. The reason is simple. What if <tt
class="FILENAME">/home</tt> was a different partition from <tt class="FILENAME">/</tt>
and it could not be mounted? <tt class="USERNAME">root</tt> would naturally want to log
in and repair the problem. If his home directory was on the damaged filesystem, it would
make it difficult for him to log in.</p>
</dd>
<dt><tt class="FILENAME">sbin</tt></dt>
<dd>
<p>Essential programs that are run by <tt class="USERNAME">root</tt> and during the
system bootup process are kept here. Normal users will not run programs in this
directory.</p>
</dd>
<dt><tt class="FILENAME">tmp</tt></dt>
<dd>
<p>The temporary storage location. All users have read and write access to this
directory.</p>
</dd>
<dt><tt class="FILENAME">usr</tt></dt>
<dd>
<p>This is the big directory on a Linux system. Everything else pretty much goes here,
programs, documentation, the kernel source code, and the X Window system. This is the
directory to which you will most likely be installing programs.</p>
</dd>
<dt><tt class="FILENAME">var</tt></dt>
<dd>
<p>System log files, cache data, and program lock files are stored here. This is the
directory for frequently-changing data.</p>
</dd>
</dl>
</div>
<p>You should now have a good feel for which directories contain what on the filesystem.
More detailed information about the filesystem layout is available in the hier(7) man
page. The next section will help you find specific files easily, so you don't have to do
it by hand.</p>
</div>
<div class="SECT2">
<h2 class="SECT2"><a id="SYSTEM-CONFIGURATION-FINDING"
name="SYSTEM-CONFIGURATION-FINDING">4.1.2 Finding Files</a></h2>
<p>You now know what each major directory holds, but it still doesn't really help you
find things. I mean, you could go looking through directories, but there are quicker
ways. There are four main file search commands available in Slackware.</p>
<div class="SECT3">
<h3 class="SECT3"><a id="AEN1329" name="AEN1329">4.1.2.1 <tt
class="COMMAND">which</tt></a></h3>
<p>The first is the <tt class="COMMAND">which</tt>(1) command. <tt
class="COMMAND">which</tt> is usually used to locate a program quickly. It just searches
your <tt class="ENVAR">PATH</tt> and returns the first instance it finds and the
directory path to it. Take this example:</p>
<table border="0" bgcolor="#E0E0E0" width="100%">
<tr>
<td>
<pre class="SCREEN">
<samp class="PROMPT">%</samp> <kbd class="USERINPUT">which bash</kbd>
/bin/bash
</pre>
</td>
</tr>
</table>
<p>From that you see that <tt class="COMMAND">bash</tt> is in the <tt
class="FILENAME">/bin</tt> directory. This is a very limited command for searching, since
it only searches your <tt class="ENVAR">PATH</tt>.</p>
</div>
<div class="SECT3">
<h3 class="SECT3"><a id="AEN1347" name="AEN1347">4.1.2.2 <tt
class="COMMAND">whereis</tt></a></h3>
<p>The <tt class="COMMAND">whereis</tt>(1) command works similar to <tt
class="COMMAND">which</tt>, but can also search for man pages and source files. A <tt
class="COMMAND">whereis</tt> search for <tt class="COMMAND">bash</tt> should return
this:</p>
<table border="0" bgcolor="#E0E0E0" width="100%">
<tr>
<td>
<pre class="SCREEN">
<samp class="PROMPT">%</samp> <kbd class="USERINPUT">whereis bash</kbd>
bash: /bin/bash /usr/bin/bash /usr/man/man1/bash.1.gz
</pre>
</td>
</tr>
</table>
<p>This command not only told us where the actual program is located, but also where the
online documentation is stored. Still, this command is limited. What if you wanted to
search for a specific configuration file? You can't use <tt class="COMMAND">which</tt> or
<tt class="COMMAND">whereis</tt> for that.</p>
</div>
<div class="SECT3">
<h3 class="SECT3"><a id="AEN1363" name="AEN1363">4.1.2.3 <tt
class="COMMAND">find</tt></a></h3>
<p>The <tt class="COMMAND">find</tt>(1) command allows the user to search the filesystem
with a rich collection of search predicates. Users may specify a search with filename
wildcards, ranges of modification or creation times, or other advanced properties. For
example, to search for the default <tt class="FILENAME">xinitrc</tt> file on the system,
the following command could be used.</p>
<table border="0" bgcolor="#E0E0E0" width="100%">
<tr>
<td>
<pre class="SCREEN">
<samp class="PROMPT">%</samp> <kbd class="USERINPUT">find / -name xinitrc</kbd>
/var/X11R6/lib/xinit/xinitrc
</pre>
</td>
</tr>
</table>
<p><tt class="COMMAND">find</tt> will take a while to run, since it has to traverse the
entire root directory tree. And if this command is run as a normal user, there will be
permission denied error messages for directories that only <tt class="USERNAME">root</tt>
can see. But <tt class="COMMAND">find</tt> found our file, so that's good. If only it
could be a bit faster...</p>
</div>
<div class="SECT3">
<h3 class="SECT3"><a id="AEN1378" name="AEN1378">4.1.2.4 <tt
class="COMMAND">slocate</tt></a></h3>
<p>The <tt class="COMMAND">slocate</tt>(1) command searches the entire filesystem, just
like the find command can do, but it searches a database instead of the actual
filesystem. The database is set to automatically update every morning, so you have a
somewhat fresh listing of files on your system. You can manually run <tt
class="COMMAND">updatedb</tt>(1) to update the slocate database (before running <tt
class="COMMAND">updatedb</tt> by hand, you must first <tt class="COMMAND">su</tt> to the
<tt class="USERNAME">root</tt> user). Here's an example of <tt
class="COMMAND">slocate</tt> in action:</p>
<table border="0" bgcolor="#E0E0E0" width="100%">
<tr>
<td>
<pre class="SCREEN">
<samp class="PROMPT">%</samp> <kbd
class="USERINPUT">slocate xinitrc</kbd> # we don't have to go to the root
/var/X11R6/lib/xinit/xinitrc
/var/X11R6/lib/xinit/xinitrc.fvwm2
/var/X11R6/lib/xinit/xinitrc.openwin
/var/X11R6/lib/xinit/xinitrc.twm
</pre>
</td>
</tr>
</table>
<p>We got more than what we were looking for, and quickly too. With these commands, you
should be able to find whatever you're looking for on your Linux system.</p>
</div>
</div>
<div class="SECT2">
<h2 class="SECT2"><a id="SYSTEM-CONFIGURATION-RCD" name="SYSTEM-CONFIGURATION-RCD">4.1.3
The <tt class="FILENAME">/etc/rc.d</tt> Directory</a></h2>
<p>The system initialization files are stored in the <tt class="FILENAME">/etc/rc.d</tt>
directory. Slackware uses the BSD-style layout for its initialization files as opposed to
System V init scripts, which tend to make configuration changes much more difficult
without using a program specifically designed for that purpose. In BSD-init scripts, each
runlevel is given a single rc file. In System V, each runlevel is given its own
directory, each containing numerous init scripts. This provides an organized structure
that is easy to maintain.</p>
<p>There are several categories of initialization files. These are system startup,
runlevels, network initialization, and System V compatibility. As per tradition, we'll
lump everything else into another category.</p>
<div class="SECT3">
<h3 class="SECT3"><a id="AEN1406" name="AEN1406">4.1.3.1 System Startup</a></h3>
<p>The first program to run under Slackware besides the Linux kernel is <tt
class="COMMAND">init</tt>(8). This program reads the <tt
class="FILENAME">/etc/inittab</tt>(5) file to see how to run the system. It runs the <tt
class="FILENAME">/etc/rc.d/rc.S</tt> script to prepare the system before going into your
desired runlevel. The <tt class="FILENAME">rc.S</tt> file enables your virtual memory,
mounts your filesystems, cleans up certain log directories, initializes Plug and Play
devices, loads kernel modules, configures PCMCIA devices, sets up serial ports, and runs
System V init scripts (if found). Obviously <tt class="FILENAME">rc.S</tt> has a lot on
its plate, but here are some scripts in <tt class="FILENAME">/etc/rc.d</tt> that <tt
class="FILENAME">rc.S</tt> will call on to complete its work:</p>
<div class="VARIABLELIST">
<dl>
<dt><tt class="FILENAME">rc.S</tt></dt>
<dd>
<p>This is the actual system initialization script.</p>
</dd>
<dt><tt class="FILENAME">rc.modules</tt></dt>
<dd>
<p>Loads kernel modules. Things like your network card, PPP support, and other things are
loaded here. If this script finds <tt class="FILENAME">rc.netdevice</tt>, it will run
that as well.</p>
</dd>
<dt><tt class="FILENAME">rc.pcmcia</tt></dt>
<dd>
<p>Probes for and configures any PCMCIA devices that you might have on your system. This
is most useful for laptop users, who probably have a PCMCIA modem or network card.</p>
</dd>
<dt><tt class="FILENAME">rc.serial</tt></dt>
<dd>
<p>Configures your serial ports by running the appropriate <tt
class="COMMAND">setserial</tt> commands.</p>
</dd>
<dt><tt class="FILENAME">rc.sysvinit</tt></dt>
<dd>
<p>Looks for System V init scripts for the desired runlevel and runs them. This is
discussed in more detail below.</p>
</dd>
</dl>
</div>
</div>
<div class="SECT3">
<h3 class="SECT3"><a id="AEN1454" name="AEN1454">4.1.3.2 Runlevel Initialization
Scripts</a></h3>
<p>After system initialization is complete, <tt class="COMMAND">init</tt> moves on to
runlevel initialization. A runlevel describes the state that your machine will be running
in. Sound redundant? Well, the runlevel tells <tt class="COMMAND">init</tt> if you will
be accepting multiuser logins or just a single user, whether or not you want network
services, and if you will be using the X Window System or <tt
class="COMMAND">agetty</tt>(8) to handle logins. The files below define the different
runlevels in Slackware Linux.</p>
<div class="VARIABLELIST">
<dl>
<dt><tt class="FILENAME">rc.0</tt></dt>
<dd>
<p>Halt the system (runlevel 0). By default, this is symlinked to <tt
class="FILENAME">rc.6</tt>.</p>
</dd>
<dt><tt class="FILENAME">rc.4</tt></dt>
<dd>
<p>Multiuser startup (runlevel 4), but in X11 with KDM, GDM, or XDM as the login
manager.</p>
</dd>
<dt><tt class="FILENAME">rc.6</tt></dt>
<dd>
<p>Reboot the system (runlevel 6).</p>
</dd>
<dt><tt class="FILENAME">rc.K</tt></dt>
<dd>
<p>Startup in single user mode (runlevel 1).</p>
</dd>
<dt><tt class="FILENAME">rc.M</tt></dt>
<dd>
<p>Multiuser mode (runlevels 2 and 3), but with the standard text-based login. This is
the default runlevel in Slackware.</p>
</dd>
</dl>
</div>
</div>
<div class="SECT3">
<h3 class="SECT3"><a id="AEN1493" name="AEN1493">4.1.3.3 Network Initialization</a></h3>
<p>Runlevels 2, 3, and 4 will start up the network services. The following files are
responsible for the network initialization:</p>
<div class="VARIABLELIST">
<dl>
<dt><tt class="FILENAME">rc.inet1</tt></dt>
<dd>
<p>Created by <tt class="COMMAND">netconfig</tt>, this file is responsible for
configuring the actual network interface.</p>
</dd>
<dt><tt class="FILENAME">rc.inet2</tt></dt>
<dd>
<p>Runs after <tt class="FILENAME">rc.inet1</tt> and starts up basic network
services.</p>
</dd>
<dt><tt class="FILENAME">rc.atalk</tt></dt>
<dd>
<p>Starts up AppleTalk services.</p>
</dd>
<dt><tt class="FILENAME">rc.httpd</tt></dt>
<dd>
<p>Starts up the Apache web server. Like a few other rc scripts, this one can also be
used to stop and restart a service. <tt class="FILENAME">rc.httpd</tt> takes arguments of
stop, start, or restart. </p>
</dd>
<dt><tt class="FILENAME">rc.news</tt></dt>
<dd>
<p>Starts up the news server.</p>
</dd>
</dl>
</div>
</div>
<div class="SECT3">
<h3 class="SECT3"><a id="AEN1534" name="AEN1534">4.1.3.4 System V Compatibility</a></h3>
<p>System V init compatibility was introduced in Slackware 7.0. Many other Linux
distributions make use of this style instead of the BSD style. Basically each runlevel is
given a subdirectory for init scripts, whereas BSD style gives one init script to each
runlevel.</p>
<p>The <tt class="FILENAME">rc.sysvinit</tt> script will search for any System V init
scripts you have in <tt class="FILENAME">/etc/rc.d</tt> and run them, if the runlevel is
appropriate. This is useful for certain commercial software packages that install System
V init scripts</p>
</div>
<div class="SECT3">
<h3 class="SECT3"><a id="AEN1546" name="AEN1546">4.1.3.5 Other Files</a></h3>
<p>The scripts described below are the other system initialization scripts. They are
typically run from one of the major scripts above, so all you need to do is edit the
contents.</p>
<div class="VARIABLELIST">
<dl>
<dt><tt class="FILENAME">rc.gpm</tt></dt>
<dd>
<p>Starts up general purpose mouse services. Allows you to copy and paste at the Linux
console. Occasionally, gpm will cause problems with the mouse when it is used under X
windows. If you experience problems with the mouse under X, try taking away the
executable permission from this file and stopping the gpm server.</p>
</dd>
<dt><tt class="FILENAME">rc.font</tt></dt>
<dd>
<p>Loads the custom screen font for the console.</p>
</dd>
<dt><tt class="FILENAME">rc.local</tt></dt>
<dd>
<p>Contains any specific startup commands for your system. This is empty after a fresh
install, as it is reserved for local administrators. This script is run after all other
initialization has taken place.</p>
</dd>
</dl>
</div>
<p>To enable a script, all you need to do is add the execute permissions to it with the
<tt class="COMMAND">chmod</tt> command. To disable a script, remove the execute
permissions from it. For more information about <tt class="COMMAND">chmod</tt>, see <a
href="filesystem-structure-permissions.html">Section 9.2</a>.</p>
</div>
</div>
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