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Unix

Unix is almost 40 year old Os

In 1964 OS called MULTICS (Multiplexed Information and

Computing System) was developed by Bell Labs, MIT &

General Electric.

Ken Thompson (System programmer of Bell Labs) wrote OS

on PDP - 7 Computer (Program Data Processor Model - 7),

assembler and few utilities, this is know as Unix (1969).

But this version of Unix was not portable. Then Unix was

rewrote in C. Because Unix written in 'C', it is portable. It

means Unix can run on verity of Hardware platform (1970-71).

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Unix

Unix is a layered operating system. The innermost layer isthe hardware that provides the services for the OS.

The operating system, referred to in Unix as the kernel,interacts directly with the hardware and provides the

services to the user programs.

These user programs dont need to know anything aboutthe hardware. They just need to know how to interact with

the kernel and its up to the kernel to provide the desiredservice.

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Most well written user programs are independent of theunderlying hardware, making them readily portable tonew systems.

User programs interact with the kernel through a set ofstandard system calls.

These system calls request services to be provided by thekernel.

Unix

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Such services would include

accessing a file: open close, read, write, link, or execute a file;

starting or updating accounting records;

changing ownership of a file or directory; changing to a newdirectory;

creating, suspending, or killing a process;

Enabling access to hardware devices;

And setting limits on system resources.

Unix

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Unix

Multi-user.

Multitasking .

Internet-aware Network OS.

Unix is . .

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Unix

Unix, Linux runs on different hardware platform :

Intel x86 processor (Celeron/PII/PIII/PIV/Old-

Pentiums/80386/80486)

Macintosh PC's

Cyrix processor

AMD processor

Sun Microsystems Sparc processor

Alpha Processor (Compaq)

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Unix

Minimum hardware required :

Intel x86 processor (Celeron/PII/PIII/PIV/Old-

Pentiums/80386/80486)

4 MB RAM

80 MB hard disk )

! Unix cannot run on 8086 Microprocessor . Because it can support

only 1 MB of Ram .

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Unix Architecture

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Shell

Computers dont have the inherent capability of

translating commands into action.

They require an interpreter that job is done by theouter part of the operating system the shell .

Its the interface between the User & the Kernel .

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Shell

When you enter a command through the keyboard , the

shell thoroughly examines the keyboard input forspecial characters.

It rebuilds a simplified command line and finally

communicates with the kernel to see that the commandis executed.

Ex.

$ echo Red Hat LinuxRed Hat Linux

While processing , the shell compress all multiplecontiguous spaces in the above command to the singleone.

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Locating Commands

All commands in Unix are essentially a files

( executable files )

These files are Stored in directories

ex ls is a command found in /bin directory

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Locating Commands

typecommand

Locating the executable program

$ type ls

ls is /bin/ls

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Locating Commands

PATH variable

Locating the executable program

$ echo $PATH

the sequence of directories the shell searches tolook for a command is specified in its own PATH

variable

/bin: /usr/bin :/usr/local/bin :/usr/java/bin:.

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Internal & External Commands

ls is a program having an independent existence (

/bin/ls ) hence it is branded as external commands

commands which are not found anywhere and

which are not executed even if they are in one of the

directories specified by PATH are called as internal

commands.

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to execute echo shell wont look in its PATHvariable (even if it is there in /bin). Rather it will

execute it from its own set of commands

even though the echo is found in /bin/echo the shell

always executes the internal echo command

$ type echo

echo is a shell built in

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List of Internal Commands

cd

pwd

umask

exit

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List of External Commands

ftp

telnet

ls

cp

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Command Structure

$ command [options ] [arguments]

Examples

$ lsl -a

$ lsla

$ ls$ lsl

$ lsla tmp$ lsla tmp tmp1 tmp2

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Combining Commands

wc note ; lsl note

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Command on different lines

echo This is

> a three-line

> Text message

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Man : The online help

Unix offers the online help manual with the man

command

$ man cp

man page for cp is displayed on the screen. It presents

the first page and pauses . It does this by sending its

output to the pager program which displays thecontents one page at a time

Different pagers are more or less

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Man : The online help

To advance to the next screen press for spacebar

To move back press b

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Man & its options

man -k

man withk option searches the summary database

and prints the online description of the command

$ mank awk

Alternatively you can use$ apropos awk

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Man & its options

man -f

It emulates the whatiscommand behavior

$ manf ftp

$ whatis ftp

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When things go wrong

List of Some Trap Signals

Ctrl-h Erases TextCtrl-c Interrupts a command

Ctrl-d Terminates a login session or a

program that expects input from thekeyboard

Ctrl-s Stops Scrolling of screen and locks

KeyboardCtrl-q Resumes Scrolling of screen and

unlocks Keyboard

Ctrl-z Suspends process and returns a shell

prompt

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When things go wrong

When you misspells a password and if

backspace doesnt work simply press ctrl - h

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General Purpose Utilities

To view the calendar of any specific month or a

complete year use the cal commandSyntax :

cal [ [ month ] year ]

Example :

$ cal

$ cal 03 2003$ cal 2003 | less

( Single argument to the cal command is interpreted as a

year )

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datecommand is used to display current date

and time

You can also have the formatted output$ date +%m

$ date +%h

$ date +%h %m

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printf an alternative to echo

example

Displaying Message

printf message using printf\nprintf my current shell is %s\n $SHELL

%s String

%30s print string in a space 30 character wide

%d Decimal Integer

%o Octal Integer

%x hexadecimal integer

%f floating point number

Following are the valid options :

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bc: The Calculator


bc is one of the powerful system tools

$ bc12 +517Ctrl + d to quit

Ex

You can enter multiple commands in the same line

12 +5 ; 2 ^ 1017

1024( Output is shown in different lines) (next ..)

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bc: The Calculator


To enable floating point computation set scale to the

number of digits of precision

scale = 2Ex

17 / 2

(next ..)

2.42

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bc: The Calculator


For converting numbers from one base to another

ibase = 2Ex

11001010

(next ..)

202

obase = 2

141110

Ex

Ex obase = 16

( Output in decimal )

( Binary of 14 )

14E

( Hexadecimal value of 14 )

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script: Recording your session


This command lets you record your login session in a

file

$ script

To stop recording type exit

The prompt returns all the keystroke to henceforth to

the file typescript

$ script -a$ script logfile

( Appends activity to existing file )

( logs activity to file logfile )

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who

Unix maintains an account of all users who are logged

on to the system

$ who

root Console Aug 1 07:51 (:0)

parag Pts/9 Aug 1 07:55 (192.168.1.2)

pratham Pts/10 Aug 1 07:56 (192.168.1.3)

Name Device name Time Machine name

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uname: Machines Characteristics

uname command is used to display certain features of

Operating System

$ unameSunOS Linux showsLinux

Release Name of UNIX

$ uname -r5.8 This is SunOS 5.8

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uname: Machines Characteristics

Implementation Name of Unix

$ uname -sSunOS

Machine Name

$ uname -ncipher

Documents

Unix Level -0 1