Introduction to Linux

LINUX BASICS CDAC Mumbai 1

Introduction to Linux The Linux operating system (OS) was

first coded by a Finnish computer

programmer called Linus Benedict

Torvalds in 1991, when he was just

21! He had got a new 386, and he

found the existing DOS and UNIX too

expensive and inadequate.

As a hobby he decided to build his own tiny OS

In those days, a UNIX-like tiny, free OS called Minix was extensively used for

academic purposes. Since its source

code was available, Linus decided to

take Minix as a model.

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GNU PROJECT

Established in 1984 by Richard Stallman, who believes that

software should be free from restrictions against copying or

modification in order to make better and efficient computer

programs

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GNU is a recursive acronym for GNU's Not Unix

Aim at developing a complete Unix-like operating system which is free for copying and modification Companies make their money by maintaining and distributing the software, e.g. optimally packaging the software with different tools (Redhat, Slackware, Mandrake, SuSE, etc)

Stallman built the first free GNU C Compiler in 1991. But still, an OS was yet to be developed

Introduction to Linux Linus liked the endeavours of the Free Software Foundation and released his kernel under the GNU GPL

The Linux kernel and GNU tools made a complete, free operating system: the GNU/Linux operating system

Linux most commonly distributed with the toolset & collection of application called as distributions.(Redhat, Fedora, Ubuntu, Mandrake etc)

The largest part of the work on Linux is performed by the community: the thousands of programmers around the world that

use Linux and send their suggested improvements to the

maintainers.

Various companies have also helped not only with the development of the Kernels, but also with the writing of the body

of auxiliary software, which is distributed with Linux. 4

WHY LINUX ?

A Linux distribution has software worth thousands of dollars, for

virtually no cost

Linux operating system is reliable, stable, and very powerful

Linux comes with a complete development environment, including

compilers, toolkits, and scripting languages

Linux comes with networking facilities, allowing you to share

hardware

Linux utilizes your memory, CPU, and other hardware to the fullest

A wide variety of commercial software is also available

Linux is very easily upgradeable

Supports multiple processors as standard

True multitasking. So many apps, all at once 5

FILE SYSTEM OF LINUX

The Linux File system is organized

hierarchically.

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LINUX FILE SYSTEM

Some important directories are

/bin contains commonly used commands.

/usr/bin contains less commonly used commands.

/mnt provides a location for mounting devices.

/etc contains system administration commands.

/dev contains device files.

/usr contains users directories

/opt addon application software packages.

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LINUX FILE SYSTEM

/proc processor related files.

/home This is where user home directories are stored.

/root This is the root (administrator) user's home directory

/sbin Binaries which are only expected to be used by the

super user.

/tmp Temporary files.

/boot Has the bootable Linux kernel and boot loader

configuration files(GRUB).

/var This directory is used to store files which change

frequently

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BASIC LINUX COMMANDS

File Handling

Text Processing

System Administration

Process Management

Archival

File Systems

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SOURCES TO LEARN COMMANDS??

Primary man(manual) pages. man shows all information about the

command help shows the available options for that

command Secondary Books and Internet

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FILE HANDLING COMMANDS

mkdir make directories

Usage: mkdir [OPTION] DIRECTORY...

eg. mkdir prabhat

rmdir remove directory

eg. rmdir prabhat

ls list directory contents

Usage: ls [OPTION]... [FILE]...

eg. ls, ls l, ls prabhat

cd changes directories

Usage: cd [DIRECTORY]

eg. cd prabhat

pwd print name of current working directory

Usage: pwd

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FILE HANDLING COMMANDS(CONTD)

cp copy files and directories

Usage: cp [OPTION]... SOURCE DEST

eg. cp sample.txt sample_copy.txt

cp sample_copy.txt target_dir

mv move (rename) files

Usage: mv [OPTION]... SOURCE DEST

eg. mv source.txt target_dir

mv old.txt new.txt

rm remove files or directories

Usage: rm [OPTION]... FILE...

eg. rm file1.txt , rm -rf some_dir

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FILE HANDLING COMMANDS(CONTD)

find search for files in a directory hierarchy

Usage: find [OPTION] [path] [pattern]

eg. find file1.txt find name file1.txt

history prints recently used commands

Usage: history

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TEXT PROCESSING COMMANDS

cat concatenate files and print on the standard output

Usage: cat [OPTION] [FILE]...

eg. cat file1.txt file2.txt

cat -n file1.txt

echo display a line of text

Usage: echo [OPTION] [string] ...

eg. echo I love India

echo $HOME

grep print lines matching a pattern

Usage: grep [OPTION] PATTERN [FILE]...

eg. grep i apple sample.txt

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TEXT PROCESSING COMMANDS (CONTD)

wc print the number of newlines, words, and bytes in files

Usage: wc [OPTION]... [FILE]...

eg. wc file1.txt

wc -l file1.txt

sort sort lines of text files

Usage: sort [OPTION]... [FILE]...

eg. sort file1.txt

sort r file1.txt

-r reverses the result

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LINUX FILE PERMISSIONS

3 types of file permissions read, write, execute

10 bit format from 'ls -l command

1 2 3 4 5 6 7 8 9 10

file type owner group others

eg. drwxrw-r--

means owner has all three permissions, group has

read and write, others have only read permission

read permission 4, write 2, execute 1

eg. rwxrw-r-- = 764

673 = rw-rwx-wx

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SYSTEM ADMINISTRATION

chmod change file access permissions

Usage: chmod [OPTION] [MODE] [FILE]

eg. chmod 744 calculate.sh

chown change file owner and group

Usage: chown [OPTION]... OWNER[:[GROUP]] FILE...

eg. chown remo myfile.txt

su change user ID or become superuser

Usage: su [OPTION] [LOGIN]

eg. su remo, su

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SYSTEM ADMINISTRATION( CONTD)

passwd update a users authentication tokens(s)

Usage: passwd [OPTION]

eg. passwd

who show who is logged on

Usage: who [OPTION]

eg. who

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PROCESS MANAGEMENT

ps report a snapshot of the current processes

Usage: ps [OPTION]

eg. ps, ps el

Top - Show system usage statistics

kill to kill a process(using signal mechanism)

Usage: kill [OPTION] pid

eg. kill -9 2275

killall - Stop a program. The program is specified by

command name.

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ARCHIVAL COMMANDS

tar to archive a file

Usage: tar [OPTION] DEST SOURCE

eg. tar -cvf /home/archive.tar /home/original

tar -xvf /home/archive.tar

zip package and compress (archive) files

Usage: zip [OPTION] DEST SOURSE

eg. zip original.zip original

unzip list, test and extract compressed files in a ZIP archive

Usage: unzip filename

eg. unzip original.zip 20

FILE SYSTEM COMMANDS

fdisk partition manipulator

eg. sudo fdisk -l

mount mount a file system

Usage: mount -t type device dir

eg. mount /dev/sda5 /media/target

umount unmount file systems

Usage: umount [OPTIONS] dir | device...

eg. umount /media/target

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FILE SYSTEM COMMANDS(CONTD)

du estimate file space usage

Usage: du [OPTION]... [FILE]...

eg. du

df report filesystem disk space usage

Usage: df [OPTION]... [FILE]...

eg. df

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LINUX COMMAND SUMMARY

Command Function Example

ls To see the files in the directory ls

ls -l display details of the files such as permissions, size date of last update

ls -l

ls -a To list hidden files ls -a

cat To display contens of one or more files

cat hello

cp Copy file1 to file2 cp file1 file2i

rm or rm-i To delete a file rm hello

mv To rename a file mv hello mytextfile

head To display top 10 lines of the file Head hello

tail To display bottom 10 lines of file tail hello

wc To display number of lines,words & characters in a file

wc hello

nl To display file with line numbers nl hello

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LINUX COMMAND SUMMARY

Command Function Example

pwd To know the present working directory pwd

cd To change directory, you can specify either relative or absolute path

cd /etc , cd .. cd ./cprograms

mkdir To create a new directory mkdir hello, mkdir /usr/prasad/hello

rmdir To delete a directory rmdir hello

find To search for file find hello

du To know the directory size in number of blocks

du prasad

df To know the disk space occupied by the total file system

df

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INPUT / OUTPUT REDIRECTION

In linux all devices are considered as files, hence we have three standard files Stdin file desc. 0

Stdout file desc. 1

Stderr file desc. 2

Input is given through the keyboard, called standard i/p: stdin

Output is displayed on the monitor, called standard o/p: stdout

The error messages are also displayed on the monitor, called standard error: stderr

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INPUT / OUTPUT REDIRECTION Instead of taking input from the keyboard, you can

take the i/p from a file known as input indirection.

$wc < filename (< input indirection)

Similarly, the o/p can be redirected to a file instead of

monitor.

$ls -l > filelist (> output redirection)

$cat filelist

you can combine both input indirection & o/p

redirection in one command

$wc file2

$cat file2>>file1 (can append a file to another file)

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VI EDITOR

To create text files or C/C++ programs, you need a text editor.

The most commonly used editors are ed , Vi, vim etc.

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STARTING VIM

You may use vim to open an already existing file by typing

vim filename

vim has three modes:

command mode

insert mode

Colon mode(Ex Command Mode)

In command mode, the letters of the keyboard perform editing

functions (like moving the cursor, deleting text, etc.).

To enter command mode, press the escape key. In

insert mode, the letters you type form words and sentences.

To enter Ex-command mode Press esc and :

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Entering Text

In order to begin entering text in this empty file, you must

change from command mode to insert mode. To do this,

type i

Deleting Words

To delete a word, move the cursor to the first letter of the

word, and type

dw

This command deletes the word and the space following it.

To delete three words type

3dw

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Deleting Lines

To delete a whole line, type

dd

Typing dd deletes the entire line containing the cursor

and places the cursor at the start of the next line.

To delete two lines, type

2dd

To delete from the cursor position to the end of the line, type

D (uppercase)

Moving around in a file

H to top line of screen

M to middle line of screen

L to last line of screen

G to last line of file

1G to first line of file

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Moving by Searching

To move quickly by searching for text, while in

command mode:

Type / (slash).

Enter the text to search for.

Press .

The cursor moves to the first occurrence of that text.

To repeat the search in a forward direction, type

n

To repeat the search in a backward direction, type

N

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To save the edits you have made, but leave vim

running and your file open:

Press .

Type :w

Press .

To quit vim, and discard any changes your have made

since last saving:

Press .

Type :q!

Press .

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