Overview of the Unix Operating System

UNIX is a multi-user, multitasking, time sharing operating system. It was developed in 1969 in Bell Laboratories by Ken Thompson and Dennis Ritchie. It was the first operating system to be written in C language. That is, why it becomes easy to move it to a new machine-portability. This was an important reason for its large popularity and availability on a wide variety of systems.

Characteristics of UNIX

Portability.

Open system.

Rich and productive programming environment.

Communication.

Multi-user capability.

Multitasking.

Components of UNIX

Kernel

Command Interpreter

File System.

Kernel: - It is known as the base operating system. It controls the computer resources. When the user logs on, the kernel runs init and Getty to check if the user is authorized has the correct password. Kernel provides the following function:

Process scheduling.

Memory management.

Device management.

File management.

System call interface.

Process synchronization (make them show exactly the same time) and inter process communication.

Operator console interface.

The utility programs and UNIX commands are not considered as part of UNIX kernel. Kernel consists of layers closest to the hardware that are the for the most part protected from the user. Kernel communicates directly with hardware. The kernel does not deal directly with a user.

Command Interpreter: - This is a utility program and his called a shell. It interacts with the user and translates the user's request into action on the part of the kernel and other utility programs. Each user opens one shell on logging on. The shell translates typed command in to action; therefore it is termed as command interpreter.

The UNIX File System: - The file system is responsible for storing on disk drives and retrieving and updating this information directed by the user.

Characteristics of UNIX file system:-

Having a hierarchal structure.

Having ability to create and delete files.

Dynamic growth of files.

Consistent treat of file data.

Protection of file data.

The treatment o peripheral devices or files.

Account and Password:-UNIX is security conscious and can be used only by those persons who maintain an account with the computer system. Users using UNIX workstations must set up their own user account. The system administrator will grant the user that authority. The user opens an account with a name, known as login name/username, and enters a secret code password when the system prompts for it.

Logging in:-Logging in procedure tells the UNIX system who the user is. The prompt appear as

Login:-The message indicates that terminal is available for login (connected) and also indicate that the previous user has logged out (disconnected). Enter login name and press key after the string. Login: XYZ

Password:-The system now request the user to enter the secret code(password) allotted by administrator. When the password is entered the terminal does not display it. Then the key is pressed.

Example: login: XYZ Password : ******* The system crosschecks this password and if it is right, the system will allow the user to work.

Shell Commands:-The login efforts end in a prompt, usually a single character, indicating that system is ready to accept the command from you. The prompt is most likely to be dollar sign($) or a percent sign(%), but you can change it. Once you receive the prompt then you can type the commands, which are request that the system do something.