Slackware Linux Essentials
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Chapter 4 System +Configuration

+ +

Table of Contents
4.1 System +Overview
4.2 Selecting a Kernel

+ +

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.

+ +

4.1 System Overview

+ +

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.

+ +

4.1.1 File System Layout

+ +

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 C: 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.

+ +

We call the main directory the root directory, and it's denoted with a single slash +(/). 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 /home 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 +/home. You've now grafted on some more space to your system. +And all without having to move many things around.

+ +

Below, you will find descriptions of the major top level directories under +Slackware.

+ +

bin: +
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 (ls, cp, and so on) are stored +here. The /bin directory usually doesn't receive modification +after installation. If it does, it's usually in the form of package upgrades that we +provide.
+
boot: +
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 / , but common practice is to put the kernel and related files here +to facilitate dual-booting.
+
dev: +
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 /dev directory. You will find this to be true across many Unix-like +operating systems.
+
etc: +
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.
+
home: +
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 /home directory is provided as the default +location for user home directories.
+
lib: +
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.
+
mnt: +
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.
+
opt: +
Optional software packages. The idea behind /opt is that +each software package installs to /opt/software-package, which makes it easy to remove later. +Slackware distributes some things in /opt (such as KDE in /opt/kde), but you are free to add anything you want to /opt.
+
proc: +
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 /proc directory. You can also send information to the kernel +through some of these files. Try doing cat /proc/cpuinfo.
+
root: +
The system administrator is known as root on the system. root's home directory is kept in /root +instead of /home/root. The reason is simple. What if /home was a different partition from / +and it could not be mounted? root 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.
+
sbin: +
Essential programs that are run by root and during the +system bootup process are kept here. Normal users will not run programs in this +directory.
+
tmp: +
The temporary storage location. All users have read and write access to this +directory.
+
usr: +
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.
+
var: +
System log files, cache data, and program lock files are stored here. This is the +directory for frequently-changing data.
+

+ +

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.

+ +

4.1.2 Finding Files

+ +

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.

+ +

4.1.2.1 `which`

+ +

The first is the which(1) command. which is usually used to locate a program quickly. It just searches +your PATH and returns the first instance it finds and the +directory path to it. Take this example:

+ + + + + +

+%  which bash
+/bin/bash
+

+ +

From that you see that bash is in the /bin directory. This is a very limited command for searching, since +it only searches your PATH.

+ +

4.1.2.2 `whereis`

+ +

The whereis(1) command works similar to which, but can also search for man pages and source files. A whereis search for bash should return +this:

+ + + + + +

+%  whereis bash
+bash: /bin/bash /usr/bin/bash /usr/man/man1/bash.1.gz
+

+ +

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 which or +whereis for that.

+ +

4.1.2.3 `find`

+ +

The find(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 xinitrc file on the system, +the following command could be used.

+ + + + + +

+%  find / -name xinitrc
+/var/X11R6/lib/xinit/xinitrc
+

+ +

find 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 root +can see. But find found our file, so that's good. If only it +could be a bit faster...

+ +

4.1.2.4 `slocate`

+ +

The slocate(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 updatedb(1) to update the slocate database (before running updatedb by hand, you must first su to the +root user). Here's an example of slocate in action:

+ + + + + +

+%  slocate xinitrc   # 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
+

+ +

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.

+ +

4.1.3 +The `/etc/rc.d` Directory

+ +

The system initialization files are stored in the /etc/rc.d +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.

+ +

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.

+ +

4.1.3.1 System Startup

+ +

The first program to run under Slackware besides the Linux kernel is init(8). This program reads the /etc/inittab(5) file to see how to run the system. It runs the /etc/rc.d/rc.S script to prepare the system before going into your +desired runlevel. The rc.S 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 rc.S has a lot on +its plate, but here are some scripts in /etc/rc.d that rc.S will call on to complete its work:

+ +

rc.S: +
This is the actual system initialization script.
+
rc.modules: +
Loads kernel modules. Things like your network card, PPP support, and other things are +loaded here. If this script finds rc.netdevice, it will run +that as well.
+
rc.pcmcia: +
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.
+
rc.serial: +
Configures your serial ports by running the appropriate setserial commands.
+
rc.sysvinit: +
Looks for System V init scripts for the desired runlevel and runs them. This is +discussed in more detail below.
+

+ +

4.1.3.2 Runlevel Initialization +Scripts

+ +

After system initialization is complete, init moves on to +runlevel initialization. A runlevel describes the state that your machine will be running +in. Sound redundant? Well, the runlevel tells init 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 agetty(8) to handle logins. The files below define the different +runlevels in Slackware Linux.

+ +

rc.0: +
Halt the system (runlevel 0). By default, this is symlinked to rc.6.
+
rc.4: +
Multiuser startup (runlevel 4), but in X11 with KDM, GDM, or XDM as the login +manager.
+
rc.6: +
Reboot the system (runlevel 6).
+
rc.K: +
Startup in single user mode (runlevel 1).
+
rc.M: +
Multiuser mode (runlevels 2 and 3), but with the standard text-based login. This is +the default runlevel in Slackware.
+

+ +

4.1.3.3 Network Initialization

+ +

Runlevels 2, 3, and 4 will start up the network services. The following files are +responsible for the network initialization:

+ +

rc.inet1: +
Created by netconfig, this file is responsible for +configuring the actual network interface.
+
rc.inet2: +
Runs after rc.inet1 and starts up basic network +services.
+
rc.atalk: +
Starts up AppleTalk services.
+
rc.httpd: +
Starts up the Apache web server. Like a few other rc scripts, this one can also be +used to stop and restart a service. rc.httpd takes arguments of +stop, start, or restart.
+
rc.news: +
Starts up the news server.
+

+ +

4.1.3.4 System V Compatibility

+ +

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.

+ +

The rc.sysvinit script will search for any System V init +scripts you have in /etc/rc.d and run them, if the runlevel is +appropriate. This is useful for certain commercial software packages that install System +V init scripts

+ +

4.1.3.5 Other Files

+ +

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.

+ +

rc.gpm: +
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.
+
rc.font: +
Loads the custom screen font for the console.
+
rc.local: +
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.
+

+ +

To enable a script, all you need to do is add the execute permissions to it with the +chmod command. To disable a script, remove the execute +permissions from it. For more information about chmod, see Section 9.2.

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The `setup` Program		Selecting a Kernel