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Tuesday, June 2, 2009


Starting a Linux Session: Logging in

A user of a Linux based system works at a user terminal. After you connect to the Linux system, a message similar to the one shown below appears at the terminal.

Red Hat Linux release 6.0 (Hedwig)
Kernel 2.2.5 - 15 on an i586
login: _

Each user has an identification name called the user name or the login name, which has to be entered when the login: prompt appears. At the login: prompt, after you enter your login name, you are asked to enter your password.

Linux keeps track of all the user names and the information about users in special files (the shadow and passwd files under the /etc directory). When you enter the login name and password, these are checked in the above mentioned files.

If the login name entered does not match any of the user names in the file, the login message is displayed again. This ensures that only authorised users can access the machine. When a valid user name is entered at the terminal, the [user_name@localhostcurrent_directory_name] $ symbol is displayed on the screen.

This is the shell prompt, in which user_name is the user' s login name and current_directory_name is the user' s current working directory.

The administrator assigns each user a HOME directory when a new login account is created. When you log in, you are taken directly into your HOME directory. In Linux, login names (usernames) are usually the names of the users, and their HOME directory usually, although not necessarily, has the same time.

For instance, if your user name is tom and your HOME directory name is also tom, after logging in, you will see the following prompt on the screen.

[tom@localhost tom] $

You can now start working on Linux.

You have to be careful while typing your Login name and password, as this are case-sensitive. The entire login process appears like the one shown below:

Red Hat Linux release 6.0 (Hedwig)
Kernel 2.2.5 - 15 on an i586
password: [user enters password here]
Last login: Sat Sep 18 12:18:02 from
[tom@localhost tom] $

A Sample Linux Login Screen

Ending a Linux Session: Logging Out

Once you have logged on to the system, your work session continues until you instruct the shell to terminal the session.

Typing exit or logout at the command prompt ends your current Linux session.

The system then displays the login: prompt on the screen.

In order to maintain the security of files, you should NEVER leave the terminal without logging out.

Features of Linux Operating System

Features of Linux Operating System


Linux allows many programs to be executed simultaneously by different users. This feature is called multi-programming.


Multi-programming is made possible on the Linux system by the concept of time-sharing. The operating system has to manage the various programs to be executed. The programs are queued and CPU time is shraed among them. Each program gets CPU time for a sepcific period and is then put back in the queue to wait its turn again as the next program in the queue is attended to.


A program in Linux is broken down into tasks, each task being something like reading from or writing to the disk, or waiting for input from a user. The ability of an OS to handle the execution of multiple tasks is kn own as multi-tasking.

When a task is waiting for the completion of an activity, the CPU, instead of wasting time, starts executing the next task. Therefore, while one task is waiting for input from the user, another program could be reading from the hard disk.

To explain the concept of multi-taskign, let's make a simple example. You are having a cup of coffee, reading a book, and talking to your friend over the phone. You are actually performing more than one task simultaneously.

However, at a given point in time, you would be either sipping coffee, reading the book, or speaking over the phone. As you notice, you divide your time into smaller units and in each unit of time.

you would be doing only one of the tasks. Similarly, the CPU divides the time between all the active task.
The kernel is responsible for scheduling the tasks.

Linux Compared to Unix

Linux was developed keeping unix as preference model. Hence, the basics architechture and most of the features of Linux and Unix are the same. In fact, Linux is also considered another version of Unix. The main difference between Linux and Unix is that Linux is Free. Various distributors pf Linux do not charge a price.

but the price is quite low compared to other operating systems. What you get is a full-blown server operating system-- with NO licensing issues. Linux comes with all the development tools you could possibly require-- C, C++, FORTRAN, Pascal, and lot of scripting languages like awk, Perl, and Python, most of which are free . Also, Web servers like Apache, amd browsers such as Netscape provide their versions for Linux, again free.

The Unix operating system requires atleast 500 mb of hard disk space., whereas Linux can be installed on a computer with a little as 150 mb of hard disk space and can run on 8 MB of RAM.

Features Linux Unix
Shells available bash, pdksh, tcsh, zsh, ash Bourne, Kom, C
Variants Red hat, Calders, Debian, LinuxPPC, SUSE AT & T, MULTICS, TICS, BSD, SCO, HP-Ux, IRIX, Ultrix, XENIX Sun Solaris


Freely distributed

Expensive licensing

The Advantages of Linux

The Advantages of Linux


Linux is a stable operating system. Linux servers are nto shut down for years together . This means tht users on the Linux operating system work consistensly with the Linux server, without reporting any operating system failures.

Backwadrd Compatibility

Linux is siad toe be backward compatible. This implies that Linux has excellent support for older hardware. It can run on different types of processors, not just Intel. It can run on 386 and 486 Intel processors. It also runs well on DEC' s Alpha processor, Sun' s SPARC machine, PowerPc and SGI MIPS.

Simple Upgrade and Installation Process

The installation procedure of most Linux versions is menu-driven and easy. It includes the ability to upgrade from prior versions. The upgrade process preserves the exisitign configuration files and maintains a list of its actions during installations.

Low Total Cost of Owership (TCO)

Linux and most of the packages that come with it are free therefore the total cost of ownership in procuring a Linux server software is low. Also, there are a lot of people and organizations providing free support for Linux, so the cost of support can also reduce. The system configurations reuirements for installing a Linux machines is less, hence the hardware cost goes down.

Support for Legacy Devcies

Linux can run on a machine with low configuration , such as 386 DX/ Users who have low and configuration machines prefer to use Linux compared to other PSs that require configuration.

GUI InterFace

The graphical interface for Linux is the X Window system. It is didvided into two web systems consisting if a server and client. Linux has a number of graphical user interfaces called desktop Environments , such as k desktop Enironment (GNOME), both of which are versions of the X Window system. They run in the x sever.

when u start in KDEM the desktop is organised into folders such as an autoshart, trashcnn
CD-ROM , Printer, and floopy drive. all these folders are simbolized pictorially by icons. When u click on an icon the k manager pops up a browser windw.

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