This blog includes subject like Computer Organization, Microprocessor, Digital Electronics, System Programming

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This blog includes subject like Computer Organization, Microprocessor, Digital Electronics, System Programming

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Monday, August 19, 2019

Study of Linux File System and Basic Commands



TITLE: Study of basic Linux Commands

OBJECTIVE:

1.      To identify the origins of UNIX and how LINUX is related to UNIX.

2.      To interpret various OS functions used in LINUX / Ubuntu by learning basic commands.

THEORY:

UNIX, which is not an acronym, was developed by some of the members of the Multics team at the bell labs starting in the late 1960's by many of the same people who helped create the C programming language. The UNIX today, however, is not just the work of a couple of programmers. Other organizations, institutes, and other individuals contributed significant additions to the system we now know today.

Salient features of UNIX:-

The UNIX OS offers several salient features, the important of which are discussed below.

1.      Multi user capability

2.      Multitasking capability

3.      Communication

4.      Security

5.      Portability

Linux is a free version of UNIX (or UN*X). The free part is not meat in money terms but rather that the source code for Linux is freely available for inspection, modification and what you feel you can do.

Developed by Linus Torvalds and further elaborated by a number of developers throughout the world, Linux is a freely available multitasking and multiuser operating system. From the outset, Linux was placed under General Public License (GPL). The system can be distributed, used, and expanded free of charge. In this way, developers have access to all the source codes, thus being able to integrate new functions or to find and eliminate programming bugs quickly. Thereby drivers for new adapters (SCSI controller, graphics cards, etc.) can be integrated very rapidly.

Linux is a multitask and multiuser operating system. An operating system is a collection of programs that run in a computer so that a person can easily access the hardware and all resources of the computers. In this operating system is the big program that makes your computer life easy (or difficult, if the operating system is a bad one).

Linux is portable to any hardware platform. Linux is secure and versatile. The security model used in Linux is based on the UNIX idea of security, which is known to be robust and of proven quality. But Linux is not only fit for use as a fort against enemy attacks from the Internet: it will adapt equally to other situations, utilizing the same high standards for security. Your development machine or control station will be as secure as your firewall.

A multitask operating system is capable of doing several tasks at the same time. A multiuser operating system has a concept of "user quote” a way to identify the person that is using the system, and can allow different users to perform different task in the computer, and protect one user's tasks from interfering with another user's programs.


Some terminology:

Shell: this is a program in the system that allows you to give the commands you want toexecute. It is the basic programs that connect you to the operating system.

Process: any task that you run in the system is called a process (again, a process is somethinga little more complex than just a task, but that definition is good enough to start).
File: a part of the hard disk that contains data owned by a user of the system. X-windows (or simply windows): this is a mode of Linux where your screen (monitor) can besplit in small "parts" called windows, that allow you to do several things at the same time (or rather change from one task to another easily) and view graphics in a nice way.
Text terminal: a monitor that has only the capability to display text stuff, no graphics (orperhaps a very basic graphics display).

Session: the time you spend between logging on in the system and logging out of the system.

The LINUX file system:-

"On a LINUX system, everything is a file; if something is not a file, it is a process." LINUX treats everything it knows and understands as a file. All utilities,applications, data in LINUX is stored as files. The LINUX file system resembles an upside down tree. Thus, the file system begins with a directory called root. The root directory is denoted as slash (/). Branching from the root there are several other directories called bin, lib, user, etc, temp and dev. The root directory also contains a file called LINUX which is LINUX kernel itself. These directories are called sub- directories, their parent being the root directory. Each of these sub-directories contains several files and directories called sub- sub- directories.


LINUX basic commands:

      

        

Command          Description

    Example













 ls



List information about file(s)

$ ls













 date



Display or change the date & time

$ date












 cal




Display a calendar

$ cal





















 pwd



Print Working Directory

$ pwd





















 uname



Print system information

$ uname











 clear



Clear terminal screen

$ clear











 man



Help manual

$ man gedit





















$  cd  directoryname  –  into


 cd



Change working directory

directory





















$ cd .. – out of directory











 mkdir



Create new folder(s)

$ mkdir newfolder











 rmdir



Remove folder(s)

$ rmdir unwantedfolder












 cp



Copy  one  or  more  files  to  another

$ cp sourcefile newfile





location























 rm



Remove files

$ rm unwanted file











 ps



Process status

$ ps











 who



Print all usernames currently logged in

$ who












 whoami



Print the current user id and name (`id -

$ whoami





un')























 adduser



Add a new user

$ sudo adduser student











 useradd



Create new user account

$ sudo useradd user1











 expr



Evaluate expressions

$ expr c = $ (( $a + $b ))











 echo



Display message on screen

$ echo “ HELLO ”











 read



To get input from keboard

$ read a





















$   mount   -t   type   device


 mount



Mount a file system

destination_dir










$ mount /dev/fd0 /mnt/floppy













 umount



Unmount a device

$ umount [options] filesystem






$ umount /dir1






















 chmod



Change the access permissions of files

$ chmod 755 hello.c





and directories























 man



read man pages on command

$man pwd











 info



read Info pages on command

$info ls