- Linux is an operating system that is modeled on UNIX operating system and is advanced version of UNIX.
- Linux was originally developed by Linus Torvalds at the University of Helsinki.
- It was initially developed for Intel 80386 processor based IBM compatible personal computer.
- Over the years Linux has been ported to other platforms based on different processor architectures such as DEC (now HP) Alpha, Sun, SPARC, Motorolla etc.
- Linux is an open source product and its source code is easily available.
- It is a multi user system which means that more than one user can work at the same computer system at the same time.
- It also supports multi - tasking that means more than one program can be made to run at the same time.
- These important characteristics have helped it gain widespread acceptance among a large variety of users.
- The various features of Linux are :-
Portability
The Strong thing about Linux is that it can run successfully on all computers. The reason behind its portability is that it is written in a high level language which has made it easier to read, understand, and change.
Machine Independent
The Linux system does not expose the machine architecture to the user thus, it becomes very easy to write applications that can run on micros, mini's or mainframes.
Multiuser Capability
A multi user system is system in which the same computer resources like hard disk, memory etc. Can be used or accessed by many users simultaneously. Each user is given an terminal. Each terminal is a input and output device for the users. All the terminals are connected to the main computer. So a user sitting at any terminal cannot only use data or the software of the main computer but also the peripherals like printer attached to it.
Multitasking Capability
Linux has the facility to carry out more than one job at the same time. This feature of Linux is called multitasking.
Security
Linux provides a very strong security system. It enforce at three levels. First, each user assigned a login name and a password. Secondly, each file is bound around permission (read, write, execute). Thirdly, file encryption come into picture.
Linux Architecture :
Linux has monolithic architecture that consists of a single layer which performs all the functions of operating system.
The Linux system consists of two major components
1. Kernel
2. Shell
Kernel
1. Kernel is the core of the Linux operating system.
2. It performs functions as controlling devices, executing files and applications and providing network support to user applications.
3. It also monitors files at present on disk, initiates programs.
4. It performs the job of multitasking and allocates memory and other resources to various processes.
5. It also sends and receives packets to and from the network.
6. The various components of kernel are
(i) Process manager : it manages processes. It controls the creation, deletion suspension of processes.
(ii) Memory manager : it performs the task of allocating memory to different processes. It makes use of virtual memory that allows the execution of processes greater in size than physical memory.
(iii) Abstract network services : Linus provides abstract networking services to the organisations via an interface layer called virtual file system.
Virtual file system is implemented using 4. 3BSD (Berkeley software design) and transmission control Protocol / Internet Protocol (TCP/IP). BSD is a combination of Computers IP address and its port number.
(iv) Virtual file system : virtual file system permits Linux to support different file system where each represent a software interface to the virtual file system. The interface translates the details of files system to the program executing in the system.
Shell
1. Shell is a program that serves as a command line interface between the user and the operating system.
2. Shell accepts input in a human understandable language and converts into binary language.
3. It accept command from keyboard or file and send the instructions to CPU for execution and displays the output on the monitor or file.
Linux operating system usually consists of the various shell as : bash (Bourne again shell), pdksh(public domain korn shell), tesh (turbo c shell).
Linux Directory Structure
Linux has a hierarchical directory structure. It is identical to UNIX directory structure.
It consists all the directories present in UNIX. It also contains additional sysuch directories,, such as lost found, proc, sbin, boot, root, and var.
The various additional directories are explained below.
1./lost+found
It contains files that Linux restores after a system failure.
2./proc
It contains information about kernel and processes running on the system.
It also provides information about CPU and RAM.
3./sbin
It stores user applications and systems programs that are required for the efficient working of systems.
It includes system programs, such as fdisk, init and if config that are required for the administration, maintainance, and hardware configuration of systems.
4./boot
It contains the Linux kernel and the system.map file.
It also contains the information that is required during the booting of system.
5./Opt
It contains add on packages and software such as staroffice and KDE. these packages are not required for default system installation.
6./root
It is the home directory of default superuser.
7./var
It contains variable data that is continuously changing during the running of systems.
The /var/main directory stores the incoming and outgoing mails.
The /var/log subdirectory stores system log files that contain information about the problem occurred, if system is not working.
The /var/spool stores information about processes queued up for printing.
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