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Linux :

Linux is an Operating System(OS), also called as Unix based Operating System(OS) because it is designed using the source code of Unix platform.


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Assembly Language :

An assembly language (or assembler language) is a low-level programming language for a computer, or other programmable device, in which there is a very strong (generally one-to-one) correspondence between the language and the architecture's machine code instructions.

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Operating System(OS) :

An operating system (OS) is system software that manages computer hardware and software resources and provides common services for computer programs. The operating system is a component of the system software in a computer system. Application programs usually require an operating system to function.

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vendor :

It refers to a person or company offering something for sale.

History of Unix :-


  • In 1965, AT&T(American Telephone And Telegraph), GE(General Electric) and MIT(Massachusetts Institute of Technology) started MULTICS(MULTiplexed Information and Computing Service) project to develop the source code of Unix. This project was dropped in 1969 because it written purely on Assembly Language.

  • In the same year 1969, Ken Thompson created UNICS(UNiplexed Information and Computing Service) to develop the source code of Unix. But it written 80% on C Language and 20% on Assembly Language. Hence, again the project was dropped.

  • Later in 1973, Unix project came which is written purely on C Language.

  • The popular vendor used the source code of Unix to designed their own Operating System.

Flavours of Unix :


Different vendors developed different Operating System using Unix platform. Example : AT&T Bell Labs(American Telephone and Telegraph) => SYSIII - SYS V Sun(Stanford University Network) => Solaris IBM(International Business Machines Corporation) => AIX SG(Silicon Graphics) => IRIX SCO(Santa Cruz Operation) => SCO-UNIX BSD(Berkeley Software Distribution) => Free BSD HP(Hewlett-Packard) => HPUX And many more...


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kernel :

The kernel is a computer program that manages input/output requests from software, and translates them into data processing instructions for the central processing unit and other electronic components of a computer.

History of Linux :-


  • In 1990, "Linux Torvalds", a graduate student from University Of Helsinki designed a Unix like kernel called Linux on 386 Intel machine and gave it to Open Source Foundation(OSF).

  • From Open Source Foundation(OSF), multiple vendor took the source code of Linux and designed their own Operating System and given their own name to it. Some vendors are Red Hat, Ubuntu, Suse, Linux Mandrake, Bharat Operating System Solutions(BOSS), etc.

Every Linux distribution has two types of versions :-


  • Non-Commercial (Free) Editions - We can download and install it freely from internet i.e. it is Open Source Operating System.

  • Commercial Editions - We can install it by purchasing the license to provide support from vendor.

Features of Linux :


  • Open Source - Free OS along with source code and documents.

  • Multitasking - Capable of running multiple applications and process it at the same time.

  • Multi-user - Allows multiple users to login and use the resources at the same time.

  • Portability - Can be installed on all hardware architecture.

  • Scalability - Same Operating System can be used as a client edition and as a server edition.

  • Reliability - Large servers have been successfully being running without a single second of down time.

  • Security - Inbuilt firewall(iptables) and SELinux.

Red Hat Linux Versions :


Free Editions Commercial Editions


Red Hat 1 to Red Hat 9 -
Fedora core 1 Red Hat Enterprise Linux RHEL 1
Fedora core 2 RHEL 2
Fedora core 3 RHEL 3 Fedora core 4
Fedora core 5 RHEL 4
Fedora core 6 RHEL 5 Fedora 7
Fedora 8 to Fedora 18 RHEL 6


Note :

CentOS is similar to RHEL but it is open source.


File System Hierarchy Standards :


/ root boot bin var etc media home sbin usr dev opt

/ :


  • This directory is called as 'root' directory.

  • It is at the top of the file system structure.

  • All other directories are placed under it.

/root :


  • This is the default home directory of the root.

  • In Linux/Unix the administrator is called as root.

/home :


  • It contains the home directories of all users(similar to 'Documents and Setting' folder in Windows).

  • When any user logs in the current working directory then by default it is user's home directory.

/boot :


  • It contains the kernel, which is the core of the Operating System.

  • It also contains the files related for booting the OS such as boot loader.

/sbin :


  • It stands for system binary.

  • It contains essential system commands which can only be used by the superuser(root). Example :- fdisk, dump etc.

/bin :


  • It stands for binary.

  • It contains essential commands which can be used by all users. Example :- ping, cat, chmod etc.

/usr :


  • It stands for Unix system resources.

  • It contains the programs and applications which are available for users(similar to program files in Windows).

/var :


  • It stands for variable.

  • It contains variable information, such as logs and print queues.

/dev :


  • It stands for device.

  • It contains information about all hardware devices in the form of character file, block file, link file etc..

/etc :


  • It stands for et cetera.

  • It contains all the configuration files.

/media :


  • It is the default mount point for removable storage media such as CD-ROM/DVD and Pen Drive, etc.

/opt :


  • It stands for optional.

  • It generally contains the third party software's. Example :- Open Office, Kaspersky Antivirus etc.


Desktop :

To access any OS we require login interface with username and password known as desktop.

By default in Linux OS, there are two types of desktop :-

  • Gnome [more user-friendly and easy to manage]




  • KDE




Login Console :

By default in CentOS 7 or RHEL 7, there are six login console.

  • One for GUI(Graphical User Interface)




  • Five for CLI(Command Line Interface)




To change the console GUI mode to CLI mode - Ctrl + Alt + F2 Ctrl + Alt + F3 Ctrl + Alt + F4 Ctrl + Alt + F5 Ctrl + Alt + F6 To change the console CLI mode to GUI mode - Ctrl + Alt + F1