RedHat Linux Essentials

This guide is designed to bring newcomers up to speed with Linux basics. We base this guide on the RedHat Linux Essentials (RH033) course outline. As the main RedHat course outline seemed a little thin, we searched for more detailed specifications for their course and came across PTR's, Global Knowledge's and Pragati Software's more detailed definitions of the course outline. Global Knowledge seemed to have the most detailed outline so we are basing this guide on their course outline.

Unit 1: Overview

Unix History and Principles

Unix was developed in the 1960's. It's main purpose was to allow users to operate in a multi user environment. Although UNIX was developed by programmers for programmers, it provides an environment so powerful and flexible that it is found in businesses, sciences, academia, and industry. Many telecommunications switches and transmission systems also are controlled by administration and maintenance systems based on UNIX. The principle of Unix is that it uses kernel to control all the hardware of the machine. The Kernel manages; all the running processes, memory, network connections, etc.

References

GNU Project, FSF and GPL

In the 1980's the Free Software Foundation began the GNU project. The idea behind this was to create an operating system that users could modify re-write and distribute freely under a General Public Licence (GPL). GNU was made up of entirely free software packages developed by multiple programmers brought together to create a variety of packages however there was a problem. The problem that GNU had was developing the Kernel, with out the Kernel the vision of a free o/s could not be realized.
GPL - The licenses for most software and other practical works are designed to take away your freedom to share and change the works. By contrast, the GNU General Public License is intended to guarantee your freedom to share and change all versions of a program--to make sure it remains free software for all its users

References

Linux Origins and Benefits

In 1991 Linus Torvalds the a student began developing an operating system kernel, which he named "Linux". The success of this allowed FSF to finally create their operating systems. As there were so many freely available components, different organizations complied different packages thus Linux distributions were born. The main players are Red Hat, Mandrake, SuSE, Caldera, Corel, and Debian, all based on the Linux Kernel and all using GNU library's

References

Red Hat Linux Offerings

Red Hat currently offers a wide product range from operating systems for Desktop computers to servers. Red Hat Enterprise Linux 5.1 Red Hat Enterprise Linux 5 Red Hat Enterprise Linux AS, ES, WS and Red Hat Desktop (version 4) (not to mention Fedora)

References

Recommended Hardware

Hardware for Red Hat depends on the version. There are over 320 certified hardware versions. Details can be found on the Redhat website. Under the installation guide for the product. The current system requirements are found on this table.

Red Hat Linux GUI Environments

GUI Environments for Red Hat are commonly GNOME, KDE, and X Windows. There are also command language interpreters such as the bash shell (default shell), sh, csh and ksh (among others), but they're text based so not really a true GUI like the others.

GNOME
GNU Object Model Environment, an intuitive and attractive desktop for users, and the GNOME development platform, an extensive framework for building applications that integrate into the rest of the desktop. You can liken this to the way Microsoft (eghh no) provide windows and all the libraries you can use to develop windows applications. So as windows has libraries you can utilize to quickly make windows applications, GNOME provides similar libraries to create applications within it's environment.
Start GNOME by typing BLAH at the local shell.
KDE
K Desktop Environment aims to work across all UNIX variants, UNIX, BSD, LINUX... as a direct replacement for Microsoft Windows GUI.
Start KDE by typing BLAH at the local shell.
X Windows
X Windows is probably the most common GUI across Unix based systems.
Start X Windows by typing startx at the local shell.

Unit 2: A quick tour of RedHat Linux

Components of the Red Hat Linux User Interface

You have the 3 GUI's mentioned in the previous section, and several console shells, most notably Bash and SH. Bash is the default shell that the console will drop into. Bash is an sh-compatible shell that incorporates useful features from the Korn shell (ksh) and C shell (csh).

References

Local Logins and Users

Users are defined in the file /etc/passwd, if they have a password, then it's saved in /etc/shadow using 1 way encryption (encryption with no known unencryption method). This file also defines their default shell (if they have one), such as /bin/bash. Users without a valid shell will not be able to login to a console, they are generally used for programs such as SendMail or BIND allowing you to give their files more secure permissions.

root is the master user account on all Linux systems. When logged in as root you can change all aspects of the system.

References

Examining the Filesystem

The filesystem is laid out with the main directories being:-

The filesystem mounts are defined in the /etc/fstab file. File partitions on the local disk(s) (including swap) must be added to this file so that they are automatically mounted on bootup. This file also defines if user quotas are enabled on the partition.

Commands used to navigate and alter the filesystem.

Files and directories have an owner, a group and set permissions. Files and directories whose name starts with a '.' are hidden files.

References

Command Line Shells

BASH
Bourne Again SHell, this is the default shell. Designed to offer all the best features from other shells such as sh, csh and ksh. Scriptable, useful tab file finishing and unlimited command history accessible with the arrow keys.
SH
Bourne Shell was the default UNIX shell and is also available in Linux.
KSH
Korn Shell is much more than a command interpreter, it takes the scripting capabilities much further, provide a high level programming language that is quick and easy making it ideal for prototyping.
CSH
C SHell is a command interpreter that also provides scripting abilities based on the C programming language.

References

Running Commands, Command Options and Help

From a shell you can just type in commands to execute them. Command options are generally typed directly after the command, flags are often (but not always, ie. 'ps') proceeded by a dash -. Usually you can get help for commands by typing --help after the command. You can view the man pages by 'man COMMAND'. HTML documentation for programs can often be found in /usr/share/doc.

Changing Your Password

You can change your password by typing 'passwd'. You will be prompted to enter your new password. If you are logged in as root you can change other users passwords by typing 'passwd USERNAME' substituting USERNAME for the user that you want to change.

Virtual Consoles

When in your default command shell you can open other console shells by typing the shells binary. Such as 'bash' for bash, 'sh' for bourne shell... etc. You can then close and return to the previous shell by typing 'exit'.

Unit 3: File and Shell Basics

The Current Working Directory

The current working directory is the directory that your shell has currently navigated to. When you first enter the shell you will be put in your users home directory. You can access your users home directory by using tilde, simply typing 'cd ~'.

File Names

Filenames in Linux are case sensitive and can contain a wider variety of characters than windows systems.

Absolute and Relative Pathnames

Absolute pathnames begin with a / and provide the full path to the file or directory, such as /usr/local/bin. So you could type 'cd /usr/local/bin' to change the current working directory to /usr/local/bin. If your current working directory was /usr, you could use a Relative path and type 'cd local/bin' (note no proceeding slash /). You can also use '.' and '..' that allow you to reference the current directory and it's parent directory respectively. So 'cd .' would change to the current directory (rather pointless), and 'cd ..' would change to the parent working directory. '..' can be very useful, if you current working directory was /usr/local/bin, and you wanted to access /usr/local/share all you'd need to type is 'cd ../share'.

The Home Directory and System Directories

'cd ~' allows you to quickly access the current users home directory. 'cd /' allows you to quickly access the system directories.

Changing Directories

cd

Listing Directory Contents

'ls' is used to list the contents of the directory. 'ls -l' is used to display more detailed information. 'ls -a' is used to display all files including those that are hidden (starting with a '.').

Checking Free Space

'df' displays hard disk usage, mount points and free space.
'free' displays RAM memory and SWAP memory usage and amounts free.

Copying, Moving and Renaming Files and Directories

'cp' is used to copy files. Alone it'll copy files without maintaining ownership, permissions or directories. The following flags (proceeded by a '-') are most useful:-

f - force the copy operation (will not prompt to replace files, etc)
p - preserve ownerships, permissions, timestamps, etc.
r or R - recursive, follow directories.
l - link files rather than copy the data.
s - make symbolic links rather than copy the data or create hard links.

'mv' is used to move and also rename files.

Creating and Removing Files Directories

'mkdir' make a directory.
'rm' remove a file or directory. Useful flags are -f force and -r recursive.

Determining File Type

'file' can be used to determine a files type. For example 'file somescript.cgi' returns 'somescript.cgi: perl script text executable'.

Viewing and Editing Text Files

'vi' is the most common Linux text editor, although not the easiest to use (unless you know what you are doing).
'nano' is an easy to use text editor, similar to DOS' edit.

Filename Pattern Matching

Wildcards are usable for filename pattern matching, much as they are in DOS. 'ls a*' will display all files that start with 'a'. 'ls a?c' will match filenames like 'abc', 'aac', 'acc', etc.

Hands-on Lab: File and Directory Operations

Practice all the before mentioned commands and navigate around the system to get used to it!

Unit 4: Users, Groups, and System Information

Users and Groups

Users and groups are used for all programs and not use human logins. Users have a private group that all files they create will default to. They can also be a member of any number of other groups, allowing them to modify files of that group with group permissions enabled.

User and group commands:-

'useradd' - 'useradd -u USERNAME -g GROUP', etc.
'useradd -d' - gives info on how the user will be added.
'usermod' - modify a users details (I find editing /etc/passwd with root a lot easier)
'userdel' - delete a user, but will leave their files (email, etc) behind.
'userdel -r' - delete a user and all their files.
'passwd' - change user password.
'groupadd' - can be used to create a new group.
'groupmod' - modify group details (or edit /etc/group).
'groupdel' - remove a group.
'gpasswd -a USERNAME GROUPNAME' can be used to add a group to a user. A user can be a member or multiple groups.

As mentioned before users can be found in /etc/passwd, their encrypted passwords in /etc/shadow and group information can be found in /etc/group.

References

The Red Hat Linux Security Model

The core of Linux security is the file permission system. This is covered in more detail later.

SELinux can be enabled with policies.

Regular package updates.

lokkit can be used to quickly setup IPTables.

References

The root user and other system users and groups

root is the main administrative user on all RedHat Linux systems. When logged in as root you are unrestricted in what you can do on the system. A user with an ID number below 500 is a system user. Systems users generally have more privilages in the system and usually have no shell access (shell set to /sbin/nologin) to make them more secure. They are used for processes such as BIND and CRON, allowing files to have more secure permissions.

User and System Information Commands

User and group commands were covered earlier. Useful commands for system information are:-

arch
Gives information on the CPU architecture, such as x86_64.
date
Gives the systems date, can also be used to set the date.
cal
Displays calander information.
dnsdomainname
Displays the domain name for the server.
env
Displays a list of the systems (a current users) environment variables.
fdisk -l /dev/sda or hda
Displays partition information, can also be used to create partitions.
hostname -i
Displays hostname and IP.
lsmod
Shows kernel modules that have been loaded.
nslookup DOMAIN
Shows the name and address for a domain.
pwd
Shows the present working directory.
swapon -s
Displays swap partition information.
uname -a
Displays a long line full of system information.
w or who
Shows all current users with some details.
du -h
Displays disk usage (the -h makes it human readable, so you get K and MB rather than blocks).
df
Displays whole disk usage (disk free).
free -m
Shows RAM and swap usage.
ps aux
Shows all processes with info, the filesystem represents processes in the /proc folder.
pstree
Lists child processes under their parent.
fuser -a
Lists users and processes that are accessing a file or resource. Such as 'fuser 80/tcp' to see processes that are listening on port 80 (probably apache).
top
Processes that are using the most system resources.
finger USER
Display information on the current user, or a specific user.
groups USER
Displays groups that a user belongs to.
id USER
Displays ID number information for a user.
whoami
Not the Jackie Chan film, but a program that tells you what user you are currently logged in as.
cat /etc/redhat-release
uname -a wont show you what version of redhat you are on, this will.
cat /proc/cpuinfo
Gives you detailed information on your CPU(s).
/proc
Have a look in here, there is a lot of useful information BUT BE CAREFUL NOT TO EDIT ANY OF THE FILES!!!
/var/log
Check the logs to see what's happened when there is a problem. To skip to the end of a log I use 'nano +100000000 logname.log'.

References

Changing Your Identity

'su USER' allows you to open a new shell as another user. 'login USER' allows you to login as another user in your current shell. 'sudo' allows you to run individual commands as a different user.

Hands-on Lab: Examining User Information

Unit 5: File Access Permissions

Red Hat Linux File Security

This is the core of the Linux security model. Every file or directory has an owner and belongs to a group. The file has separate permissions for the owner, group members, and others (everyone else). These permissions are made up of read access (denoted by an r or 4), write access (denoted by a w or 2) and execute access (denoted by an x or 1).

Examining Permissions on Files and Directories

The 'ls -l' command will allow you to view a files owner, group and also list it's permissions.

Example:-

-rw-r--r-- 1 root root 72942 Nov 14 12:26 backups
drwxr-xr-x 4 root root 4096 Nov 22 14:00 unixstuff

The first character denotes the file type, such as - for a regular file and d for a directory. The next 3 the owners permissions, the next 3 the groups, and the last 3 everyones.

File Permission Types

r - read
w - write
x - execute
s - setuid
- - dash, no permissions in this field

Files types can be:-

- - normal files
d - directory
l - symbolic link
s - socket
p - named pipe
c - character (unbuffered) device file special
b - block (buffered) device file special

File permissions are also defined by individual numbers that represent the various combinations of rwx. These numbers are octal (0-7).

0 - no permissions
1 - execute only (x)
2 - write only (w)
3 - execute/write (wx)
4 - read only (r)
5 - read/execute (rx)
6 - read/write (rw)
7 - read/write/execute (rwx)

References

User Categories

Owner - the owner or the file or directory.
Group - the group the file or directory is attached to. There may be any number of users in a group.
Everyone - all users.

Default File Permissions

The user file-creation mode mask (umask) is use to determine the file permission for newly created files. It can be used to control the default file permission for new files. It is a four-digit octal number. You can find your default umask by typing 'umask'. The default for umask is 0022. For now ignore the first number, let's concentrate on 022. The 0 is for the owner, 2 for the group, 2 for everyone. This means the owner permissions will not be effected by the umask, but the group and everyone permissions will be minus write permisson (remember that 2 is for w).

Changing Access Permissions

Permissions are changed using the 'chmod' command. 'chmod' can be used with 2 main methods to change a files permissions. You can use the r, w and x symbols to update permissions. Such as 'chmod u+rwx FILE ' would add read write and execute permissions to the user (owner) of FILE. 'chmod g-w FILE ' would remove execute permissions from the group and 'chmod o-wx FILE ' would remove execute and write permissions from other (everyone).

The main (and easier once you get the hang of it) is to use the octal values. You can use just 3 numbers to change the user, group, other permissions. Or 4 to change the special permission as well. Some common permission are:-
chmod 0777 FILE - open to everyone to read, write and execute.
chmod 0755 FILE - used for scripts to be executable by everyone, writable by user (owner).
chmod 0666 FILE - read/write all round.
chmod 0444 FIEL - read only.

Special Permission Types

Now we'll look at that first number. It's used to define special permissions.

1 - Sticky. When applied to a folder that is writeable by groups or everyone, that users cannot delete each others files. Thus the files they create are stick to their username. Others can view their files, but not delete, rename or edit them.
2 - Setguid. When applied to an executable file it's always executed as the group ID. When applied to a directory that has writeable permissions to other (everyone) files they create will automatically be assigned to the folders group.
3 - Setguid and sticky.
4 - Setuid. When applied to an executable file it's always executed as the users ID. When applied to a directory that has writeable permissions to other (everyone) files they create will automatically be assigned to the folders user (owner).
5 - Setuid and sticky.
6 - setguid and sticky.
7 - setguid, setuid and sticky.

References

Hands-on Lab: File Permissions

Try out all the commands and permissions mentioned to get used to it!

Unit 6: The Red Hat Linux Filesystem

Red Hat Linux File Hierarchy Concepts

 

ext2/ext3 Filesystem Details

Hard and Soft Links

Mounting Removable Media

Finding and Processing Files

File Compression and Archiving Utilities

Hands-on Lab: Red Hat Linux Filesystem Essentials

Unit 7: The bash Shell

System Variables and Environment

Shell Variables

Shell vs. Environment Variables

Common Environment Variables

Which Command is Executed?

Command Recall

Command-Line Expansion

Protecting from Expansion

Command Return Values

Aliases

Shell Functions

Startup and Shutdown Scripts

Login Shells

History Tricks

Command Completion and Editing Tricks

Hands-on Lab: The bash Shell

Unit 8: Standard I/O and Pipes

Redirecting Input and Output

Overwriting and Appending

Redirecting Standard Error

Redirecting Both Standard Output and Error

Using Pipes to Connect Processes

Unit 9: String Processing

Counting Words, Lines and Characters

Printing Lines That Match a Pattern

Regular Expressions

Sorting Files

Printing Unique Lines of Files

Printing Selected Columns and Fields

Rearranging Columns and Fields

Determining Differences Between Files

Character Translation

Spell-checking and Reformatting Text

Hands-on Lab: String Processing, Standard I/O, and Pipes

Unit 10: Introduction to Processes

What is a Process?

How Processes Are Started

Process Ancestry and States

Viewing and Terminating Processes

Sending Signals to Processes

Altering Process Scheduling Priority

Running a Process in the Foreground and Background

Suspending a Process

Listing and Resuming Background and Suspended Jobs

Continuing Command Execution After Logout

Compound Commands

Hands-on Lab: Process Control

Unit 11: X / GNOME / KDE

The X Window System

The X Protocol

The GNOME and KDE Desktop Environment

Original X Environment

Window Managers

Switching Desktop Environments

Mouse Configuration

Copying and Pasting in X

Starting XFree86

GUI Terminals and Editors

Nautilus: the GNOME File Browser

GNOME Desktop Applications

Web Browsers and Mail Clients

Office Applications

Image Utilities

Audio Applications

KDE Applications

X Customization

Hands-on Lab: Customizing the Graphical Environment

Unit 12: Printing and Mailing

Printing in Red Hat Linux

Printer Control

Printing From Applications

Printing Utilities

Email Topology

Email Clients

Email Delivery via POP and IMAP

Email Filtering

Fetchmail

Hands-on Lab: Print Preprocessing

Unit 13: Basic Networking

Determining Connectivity to a Host

Getting Information About Routes and Interfaces

Listing the Route to a Particular Host

Translating Between Hostnames and IP Addresses

Listing DNS Records

Listing Domain Contacts

Transferring Files Across the Network

Checking the Status of Network Ports

Secure Shell

Hands-on Lab: Basic Network Clients

Unit 14: Using the vi Editor

Starting vi

Modes

Cursor Movement

Saving and Exiting

Cut, Copy and Paste

Undoing Changes

Searching For Text

Searching With Regular Expressions

Miscellaneous Commands

Hands-on Lab: vi

Unit 15: bash Shell Scripting

Scripting Basics

Creating Shell Scripts

Making Scripts Executable

Generating Output

Handling Input

Conditional Execution

Loops

Using Positional Parameters

Unit 16: sed, awk, and Other Languages

sed Addresses

Scripting sed

A sed Example

awk Programs

awk Rules

Running awk Programs

Awk Examples

When To Use awk

Where To Learn More

Other Languages

Unit 17: System Tools

Terminal Configuration

Getting Information About Your System

Scheduling a Process to Execute Later

Scheduling Periodic Processes

RPM Package Manager Queries

System Administrator Duties

Hands-on Lab: System Tools