Study of Linux File System and Basic Commands

Study of Linux File System and Basic Commands

  2:39 AM    Dnyaneshwar Kudande

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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