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Table Of Contents  CertiGuide to A+ (A+ 4 Real)
 9  Chapter 5: The Linux Operating System
      9  The Major Components and Interfaces of Linux and Their Functions

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According to the file system hierarchy standard, this directory contains the configuration files and directories that are specific to the system. We will spend a little time looking at a few key sub-directories and files within this directory. Let’s start with Table 10, which contains a summary description of the key subdirectories within /etc.

Table 10: Key Linux Files / Subdirectories under /etc

File/Directory (indicated by *)



The system-wide configurations file for the Bourne Again Shell. Defines functions and aliases for all users.

crontab and the cron.d* directories

Configuration of tasks that need to be executed periodically, backups, updates of the system databases, cleaning of the system, rotating logs etc.


Default options for certain commands, such as useradd.


Known file systems: ext3, vfat, iso9660 etc.


Lists partitions and their mount points.

ftpaccess, ftphost, ftpuser

Configuration of the ftp-server: who can connect, what parts of the system are accessible etc.


Configuration file for user groups. The shadow utilities groupadd, groupmod and groupdel are used to edit this file. Edit manually only if you really know what you are doing.


Boot information.


A list of machines that can be contacted using the network, but without the need for a domain name service. This has nothing to do with the system“s network configuration, which is usually done in /etc/sysconfig.


Config files for the Apache web server.


Information for booting: mode, number of text consoles etc.


Information about the distribution (release version and/or kernel info).

Locations of library files.

lilo.conf, silo.conf, aboot.conf etc.

Boot information for the LInux LOader, the system for booting that was in use before Lilo changed to GRUB.


Rotation of the logs, a system preventing the collection of huge amounts of log files.


Directory containing instructions for the behavior of the mail server.


Configuration of modules that enable special features (drivers).


Message Of The Day: Shown to everyone who connects to the system (in text mode), may be used by the system administrator to announce system services/maintenance etc.


Currently mounted file systems. It is advised to never edit this file.


Order in which to contact the name resolvers when a process demands resolving of a host name.


Configuration of authentication modules.


Lists local users. Use the shadow utilities useradd, usermod and userdel to edit this file. Edit manually only when you really know what you are doing.


System wide configuration of the shell environment: variables, default properties of new files, limitation of resources etc.


Directories defining active services for each run level.

init.d - contains startup scripts
rc0.d-rc6.d - directories for startup run levels
rc.local -


Order in which to contact DNS servers (Domain Name Servers only).

Main config file for the Sendmail server.


Connections accepted by this machine (open ports).

sndconfig and sound

Configuration of the sound card and sound events.


Directory containing the config files for secure shell client and server.


Directory containing the system configuration files: mouse, keyboard, network, desktop, system clock, power management, etc. Not all distributions use this directory.


Settings for the graphical server, X. Name of the main configuration file, XF86Config (created by a tool like Xconfigurator). Also contains the general directions for the window managers available on the system, for example gdm, fvwm, twm, etc.


Configuration files for Internet services that are run from the system“s (extended) Internet services daemon (servers that don“t run an independent daemon).

The following subsections provide more details about some of the main subdirectories and files under /etc.

Quick navigation to subsections and regular topics in this section

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CertiGuide to A+ (A+ 4 Real) ( on
Version 1.0 - Version Date: March 29, 2005

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