Tuesday, August 30, 2011

Basics of Unix Commands

Unix is a command line based operating system. Unix commands can be combined to perform complex tasks.To perform these tasks repeatedly these commands can be placed in files called shell scripts and these shell scripts can be executed to provide the required output.

Unix users and processes:

Unix has two basic concepts : files have places and processes have life . All files are placed at some location and each process travels  in a life cycle from birth to death.

Each user in unix is identified by uniquely by an  identification number,name and group identification.A user is able to access  a unix system only after being given a login name and password by the system administrator. When a user tries to access a unix system it displays a  login  prompt where the users types in the login name and password. If the user is a valid user , a shell prompt($) appears on the screen where unix commands can be typed..

A user can end a unix session by pressing < ctrl+d >.  Ctrl+d kills a process.

Command Line is defined as the line on which the shell prompt occurs and a command with its arguments is  entered  and is considered complete only when the enter key is pressed.
The command may spill over multiple lines shown by a secondary prompt (>). The complete line is then fed to the shell as its input for interpretation and execution.

Unix is CASE SENSITIVE. All unix commands must be typed in LOWER CASE.

The next post would be concerning shell commands- the syntax and the  actual commands.


Saturday, August 27, 2011

The Unix System Architecture

An operating system(OS) is an intricately woven fabric of programs.The programs are usually coded in the assembly language and are  specific to the processor around which the computer is built. The unix OS ,on the contrary, is written largely in the 'C' language which is not processor dependent. However, part of the unix os is written on the Assembler. This makes Unix highly portable- which means that it can run on various processors with little modification.
The structure of the Unix OS makes it a better OS as compared to other conventional operating systems.

The responsibilities of an OS include command interpretation,I/O control, communications and a lot more .To perform these tasks a large number of simple as well as complicated programs are needed. These programs can be independent or interdependent. In conventional operating systems, all these programs are put  together forming one large program that occupies a large amount of memory. Therefore the system response is very slow. Unix with a fresh structural approach does not slow down the system.

The Unix system can be divided into four major units. These units work together but are still separate so that one large portion of the memory does not get blocked and slow the system down.
The four units are:-

1. Kernel- A core unit that interacts with the hardware for low-level functions. The kernel is  a program that constitutes the nucleus of the operating system. It co-ordinates the internal functions of the computer, such as allocating system resources. The kernel works invisibly. The user will never be aware of it while working on the system.

2.Shell- An outer unit that interacts with the user to perform functions desired by the user. The shell is a program that acts as a liason between the user  and the kernel by interpreting and executing user commands. As it reads user input and sends messages to the user it is described as interactive.

3.Commands - Commands  are compiled C programs that perform a specific operating system job. These commands are invoked by name through the shell. Unix has very few in- built commands(internal commands) like 'echo'and 'pwd'. For these no separate C compiled programs are required. These are the shell's inbuilt features and the  shell is able to interpret them itself. Unix commands  perform  a range of functions like editing, copying , erasing files, sending and receiving emails etc.

4.File System- The file system is a collection of all the files available on the computer. It allows you to store and retrieve information easily.

Thursday, August 25, 2011


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Unix is an operating system that was developed at AT&T's Bell Laboratories in the early 1970's by Ken Thompson ,Dennis Ritchie and others. The unix system has become quite popular since its inception, running on machines of varying processing power from microprocessors to mainframes and providing a common execution environment across them. Unix systems usually offer the best performanceand support for the most concurrent users of any computer configuration. It was designed to be a multi-user, time sharing operating system that can efficiently handle a large number of user stations running different programs simultaneously.

Unix supports many programming languages,databases and program development tools. it is an open system, so it runs on many different hardware systems. Today, Windows  systems are being networked together to provide the multi-user capability that unix provides. Unix can also support graphic applications by using special X  Windows stations.

This blog aims at giving you an insight into the intricacies of the Unix operating system.