Administrator Linux Step By Step Form – Fill Out and Use This PDF

Excerpted from:

The Accidental Administrator:

Linux Server Step-by-Step

Configuration Guide

First Edition

by Don R. Crawley

Linux+ and CCNA Security

Provided courtesy of

Seattle, Washington

www.soundtraining.net

SBN-10: 1-4536-8992-3

ISBN-13: 978-1-4536-8992-9

©2010, Don R. Crawley. All rights reserved.

Chapter Two:

Linux Administration

"If you want to travel around the world and be invited to speak at a lot of different places, just write a Unix operating system."

--Linus Torvalds

GUI vs. CLI

Since the first graphical user interface (GUI) was created in the Xerox Palo Alto Research Center in the early 1970s, those of us who work in information systems and technology have debated its merits and liabilities.

The real issue is not whether to use a GUI or a command-line interface (CLI); it is about choosing a

tool that works for you and helps you work most effectively. For most of us, that means that sometimes we‟ll use a GUI and sometimes we‟ll use a CLI.

I once had a student in a Linux workshop who said his nickname was “No GUI Louie”. While I remember Louie as a very knowledgeable and capable IT pro, I have also had students who avoid the CLI because of its complexity without considering the power it affords an administrator. I think we limit ourselves when we arbitrarily limit the tools at our disposal by eliminating GUI or CLI tools.

In my own work, I find that I use both the CLI and GUI, depending on the task at hand and my personal familiarity with the tools in question. (Okay, I use the command-line most often, but I‟m

very grateful for the GUI when performing unfamiliar tasks!)

	GUI Pros			GUI Cons
Faster				Farther away from the “road”
Fewer typing errors				Less control
Less minutia				Java and other issues might make GUI unavailable
Safer (harder to make mistakes)				Some of the names and labels it creates are strange
Can help teach you CLI commands				Some people are more familiar with the CLI

Linux Directories

Everything in Linux/UNIX is based on the file system. The file system is comprised of various directories (Windows calls them “folders”.) The root directory (“/”) is at the base of the file system.

Some directories may be on different partitions or drives, but they are still a part of the file system. Some directories may even be on completely different computers, perhaps running a completely different operating system, but they are still part of the file system. What follows is a list of some of the more commonly found directories in the Linux file system (all directories are not included on all systems):

/ is the root directory

/bin/ and /usr/bin/ store user commands.

/boot/ contains files used for system startup including the kernel.

/dev/ contains device files

/etc/ is where configuration files and directories are located.

/home/ is the default location for users‟ home directories.

/initrd/ is used to load required device modules and mount the initrd.img image file during system startup.

/lib/ and /usr/lib/ hold library files used by programs in /bin/ and /sbin/.

/lost+found/ holds orphaned files (files without names) found by fsck

/mnt/ holds the mount points for file systems that were mounted after boot.

/opt/ is used primarily for installation and unintallation of third-party software. Holds optional files and programs.

/proc/ is a virtual directory (not actually stored on the disk) which holds system information required by certain programs.

/root/ is the home directory of the superuser “root”

/sbin/ and /usr/sbin/ store system commands.

/tmp/ is the system temporary directory. All users have read+write access to /tmp/.

/usr/ contains files related to users such as application files and related library files (“usr” is an acronym that stands for UNIX system resources).

/var/ (as in “variable”) holds files and directories that are constantly changing such as printer spools and log files.

The above is a brief overview of Linux/UNIX directories. For a more complete discussion of

Linux/UNIX directory structures, search on “Filesystem Hierarchy Standard” at

www.wikipedia.com.

Soundthinking point: Customizing the Desktop Background

Customize the Gnome or KDE background by right-clicking on the background and choosing Change Desktop Background.

Starting and Stopping Services

In Linux, the various services that together make up the entire operating system are called daemons

(pronounced DEE-muns). There are daemons for the DNS name server (named), the Web server (httpd), DHCP (dhcpd), and so on. When you see odd names ending with the letter “d”, you‟re most

likely looking at a daemon name. Most of the daemons can be controlled through scripts located at

/etc/init.d/. For example, to start the Web server from a terminal window, you would execute the command “/etc/init.d/httpd start”. To stop it, you would execute the command “/etc/init.d/httpd stop”.

Different Linux distros might place the scripts in slightly different locations. Later in the book, you‟ll learn how to use the find command to locate such scripts as well as other files and directories.

The Red Hat System-Config and System-Control Utilities

Red Hat-based systems include the system-config and system-control utility, a text and graphics- based utility to help you configure and manage various aspects of your system. You can see the available utilities by opening a terminal window and, as root, typing the following command:

#system-

Do not hit enter, but instead touch the tab key twice and you‟ll see a listing of options.

Figure 1 The Red Hat system utility

The Shell

The shell is the interface between the user and the operating system. It acts as a keyboard interpreter, taking the keyboard input from the user and delivering it to the operating system. You can think of the shell as being the part of the operating system that allows you to interact with the kernel. The shell is the program that executes Linux or UNIX commands.

There are several shells available for use in the Linux and UNIX. The one most commonly used in Linux is the bash shell (Bourne Again Shell). Other shells include sh (Bourne Shell), csh (CShell), tcsh, csh, and ksh (Korn Shell).

You can change the shell by typing the shell‟s name at a command prompt.

For the purpose of this document, we‟ll focus on the bash shell.

The shell is not only a command interpreter, it is also a scripting language. Experienced Linux administrators often write scripts to automate frequently conducted system tasks.

Linux, like all multi-user operating systems, has an administrator account which is used for system

configurations and operations. In Linux/UNIX, the administrator account is called “root” (equivalent to “admin”, “administrator”, or “supervisor” in other operating systems). “root” is often referred to as the “superuser” because of the account‟s unrestricted access to every area of the system and every aspect of the system‟s configuration.

When logged on as root using the bash shell, the prompt is a pound sign (#). When logged on as a regular user using the bash shell, the prompt is a dollar sign ($).

Shell commands in the Linux/UNIX world are usually case sensitive.

You can see your default shell with this command:

#echo $SHELL

Linux Profiles

There are two types of Linux profiles: system-wide and user-specific. System-wide configurations affect all users, while user-specific configurations affect only a single user. Normally, you must be root to change system-wide configurations.

User-Specific Profiles

User-specific profile settings are found in the user‟s home directory (/home/donc), but they‟re hidden by prepending a “.” to the filename. Examples of profile files include:

.bashrc

.bash_profile

.bash_history

There are many others. You can view the hidden files in any directory by using “ls -a”.

System-Wide Configurations

System-wide configuration settings are almost entirely found in /etc. This is where you find files for configuring Apache, BIND DNS, and nearly any other aspect of Linux. For example, in Debian Linux, if you want to modify settings of your Apache web server, you would probably modify /etc/apache2/apache2.conf. If you are working with a Red Hat product, the file most likely is /etc/httpd/conf/httpd.conf. (The reason for using tentative language is because everything is configurable in Linux and the person who built your Linux system might have chosen to place the configuration files elsewhere.)

Administration Tools and Techniques

Working in Terminal

Most Linux systems configured as servers are managed in a command-line interface (CLI) and many Linux power-users prefer to manager even their desktop system in the CLI. Although the graphical user interface (GUI) tools available for use in many Linux distros have improved considerably over past versions, the CLI continues to provide the greatest power and flexibility for configuring and

managing a Linux system. The other benefit to working in a CLI is that each Linux distro is much more similar in the CLI than in the GUI. For the purpose of this workshop, you will do most of your configurations in the CLI, thus allowing you to make smoother and simpler transitions from Debian to other distros such as SuSE, Ubuntu, RedHat, Slackware, or even traditional UNIX systems.

soundthinking Point: Desktop Environments

The default desktop environment in CentOS 5.x, Debian 4.0r5, and many other Linux distros is Gnome. The desktop environment is what provides the buttons, backgrounds, effects, and applications. Desktop environments will be covered later in the workshop, but for now understand that different desktop environments may have slightly different to significantly different menu locations than those described here.

Student Exercise 2.1: Commonly-Used Shell Commands

When you first logon to a Linux system, you may be in a GUI or in a command-line shell. If you are in a GUI, you can open a terminal window (a command-line shell) by clicking on Applications in the menu at the top of your desktop, then mouse over Accessories, and click on Terminal. Once you are in a command-line shell, you are

placed in your home directory (/home/[username]). You can navigate to other directories by using the “cd” command, followed by the path to the desired destination.

1.If you are not already using the root account, use the su (switch user) command with the “-“ switch to change to the root account and profile:

$su -

Password: p@ss5678

2.#cd changes the working directory. Enter the following command (bearing in mind that the “#” represents your prompt:

#cd /home

Notice that the prompt changes to display the current directory (home).

3.To return to your own home directory, type the following command:

#cd ~

You can also type “cd” to return to your home directory, but you should know that the tilde (~) represents your home directory. The tilde is often used in path statements to represent your home directory.

4.Now, enter the “pwd” command to print your working directory to your screen (output directed to the screen is known as standard output or stdout):

#pwd

5.You can go up one level in the directory hierarchy by using the command:

#cd ..

The “..” indicates the parent directory. All directories except for the root (/) directory have a parent.

6.Once again, enter the “pwd” command to print your working directory:

#pwd

7.Once again, return to your own home directory. This time, simply enter “cd” with no tilde:

#cd

8.Now issue an “ls” command to see the contents of the current directory. “ls” lists the contents of a directory.

#ls

There are a variety of switches available for use with “ls”:

	Some commonly used options
				Results
	with “ls”
	ls –a			Lists all files including hidden files
	ls –l			Long listing, includes permissions, owners,
				groups, etc.
	ls –R			Lists sub-directories recursively
	ls –sh			Shows file size (s) in human-readable
				format (h)
	ls -1 (the number “1”)			Displays one file per line
	ls –d			Tells “ls” to list directory names, but not
				their contents

You can also use common shell metacharacters with “ls”:

* is the string wildcard

? is the character wildcard

[] encloses a character set

[-] is a character range

{} is a string set

When you issue the “cd” command with no parameters, you will be returned to your home directory.

#mkdir creates directories.

Student Exercise 2.2: Creating Directories and Files

In this exercise, you will create a working directory which you will use for upcoming exercises. You will work with several commands to become familiar with some of the important tools related to directory and file management.

Student Exercise 2.2.1: Working with Directories

1.Log on to your system as the regular user you created during the installation process.

2.Click on the Applications menu, move your mouse over Accessories, and on the submenu that appears, click on Terminal.

3.In the terminal window, enter the following commands (remember that the “$” and the “#” are prompts and you should not type them at the beginning of the command):

$su –

Password: P@SS5678

#mkdir /demo

You have just created a directory called “demo” which is a subdirectory under the root directory (/).

Note: You can create multiple directories at the same time simply by separating their names with a space.

4.Display the contents of your working directory with the following command:

#ls

Notice that /demo is not displayed. The reason is that /demo is a subdirectory of the room directory. You are presently in a different directory.

5.Print your working directory to stdout (your screen) with the following command:

#pwd

Notice that you‟re in the super user root‟s home directory which is not where you created /demo.

6.Display the contents of the root directory with the following command:

#ls /

Notice that you now see the demo directory, along with several other directories that are all child directories under the parent /.

7.Enter the following command to change your working directory to /demo:

#cd /demo

#pwd You should now see that /demo is your working directory.

8.Enter the following commands:

#mkdir demo1 demo2 demo3 You have just created three sub-directories in /demo called demo1, demo2, and demo3.

9.Now, list the contents of /demo with the following command:

#ls

You should now see the three subdirectories you just created.

To remove a directory, use the command “rmdir”:

10.While still in /demo, remove the three directories you just created with the following command:

#rmdir demo1 demo2 demo3

11.Use the “ls” command again to confirm that the three directories are removed:

#ls

The /demo directory should be empty.

12.You can also use wildcards to simplify file and directory management. Touch the

up arrow on your keyboard several times. Notice that it repeats the last several commands. Stop when you see the command “mkdir demo1 demo2 demo3”.