Operating System What is an Operating System? A program that acts as an intermediary between a user of a computer and the computer hardware. An operating System is a collection of system programs that together control the operations of a computer system. Some examples of operating systems are UNIX, Mach, MS-DOS, MS- Windows, Windows/NT, Chicago, OS/2, MacOS, VMS, MVS, and VM. Operating system goals: Execute user programs and make solving user problems easier. Make the computer system convenient to use. Use the computer hardware in an efficient manner.

Computer System Components 1. Hardware – provides basic computing resources (CPU, memory, I/O devices). 2. Operating system – controls and coordinates the use of the hardware among the various application programs for the various users. 3. Applications programs – Define the ways in which the system resources are used to solve the computing problems of the users (compilers, database systems, video games, business programs). 4. Users (people, machines, other computers).

Abstract View of System Components

Components of OS OS has two parts. (1)Kernel.(2)Shell. (1)Kernel is an active part of an OS i.e., it is the part of OS running at all times. It is a programs which can interact with the hardware. Ex: Device driver, dll files, system files etc. (2) Shell is called as the command interpreter. It is a set of programs used to interact with the application programs. It is responsible for execution of instructions given to OS (called commands).

Introduction to Linux Linux is one of popular version of UNIX operating System. It is open source as its source code is freely available. It is free to use. Linux was designed considering UNIX compatibility. It's functionality list is quite similar to that of UNIX.

Components of Linux System Linux Operating System has primarily three components Kernel - Kernel is the core part of Linux. It is responsible for all major activities of this operating system. It is consists of various modules and it interacts directly with the underlying hardware. Kernel provides the required abstraction to hide low level hardware details to system or application programs. System Library - System libraries are special functions or programs using which application programs or system utilities accesses Kernel's features. These libraries implements most of the functionalities of the operating system and do not requires kernel module's code access rights. System Utility - System Utility programs are responsible to do specialized, individual level tasks.

Components of Linux…..

Basic Features Portable - Portability means softwares can works on different types of hardwares in same way.Linux kernel and application programs supports their installation on any kind of hardware platform. Open Source - Linux source code is freely available and it is community based development project. Multiple teams works in collaboration to enhance the capability of Linux operating system and it is continuously evolving. Multi-User - Linux is a multiuser system means multiple users can access system resources like memory/ ram/ application programs at same time. Multiprogramming - Linux is a multiprogramming system means multiple applications can run at same time. Hierarchical File System - Linux provides a standard file structure in which system files/ user files are arranged. Shell - Linux provides a special interpreter program which can be used to execute commands of the operating system. It can be used to do various types of operations, call application programs etc. Security - Linux provides user security using authentication features like password protection/ controlled access to specific files/ encryption of data.

Architecture

Layers in Linux Hardware layer - Hardware consists of all peripheral devices (RAM/ HDD/ CPU etc). Kernel - Core component of Operating System, interacts directly with hardware, provides low level services to upper layer components. Shell - An interface to kernel, hiding complexity of kernel's functions from users. Takes commands from user and executes kernel's functions. Utilities - Utility programs giving user most of the functionalities of an operating systems.

Directory Structure

Directory Related Commands Command: mkdir creates a new directory creates two entries: dot(.) current directory and dot dot (..) parent directory Use : man mkdir for options Syntax: mkdir directory_name

Directory commands….. Command: cd Used to change to the respective directory cd.. Used to go to parent directory cd / Used to go to root cd path Used to go to a specific directory Syntax: cd directory_name/path

Directory Commands…. Command : pwd Displays the path of the present working directory Syntax/Example: pwd

Absolute/ Relative Path A path starting from root (/) to reach the directory is called absolute path Example:

Example Absolute path of d will be /a/d Relative path represents a manner in which we can move from current directory to a destination directory Example: If we are present in d and want to change to c, we write./../../c

Directory command… Command: rmdir Used to delete an EMPTY directory ONLY [if a directory is not empty, first delete the contents of the directory, then go to its parent, and delete the directory] Syntax: rmdir dir_name [before using rmdir, make sure that you are present in the parent]

Directory commands.. Command: ls Used to display contents of the present directory/ a specific directory. For options on ls use: man ls. >