1. introduction to os & unix

8/16/2019 1. Introduction to OS & Unix

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1. Introduction to OS andUnix

With introduction to the

module

1


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Module Overview Programmes: Diploma in elecommunications and

!lectronics !ngineering Module itle: U"I# and $ Programming Module $ode: $I%U$P%&%1 'ear: & $redit: 1( )ecturer ) *amwendo+ (,,-/,(

l0amwendopol2.ac.mw )ectures 34rs5W06: &

utorials: 1 Prere7uisites: $I%I$%1%1 Module 8im

he module provides the student with the necessar2 s0ills towrite structured programs using the $ programming languageand understand U"I# Operating s2stem &


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Intended )earningOutcomes

On completion o9 this module+ the student should eale to:

a. 4ave a asic understanding o9 U"I# operating s2stem;

. Use a wor0station 9or writing and deugging programsin $;

c. Solving engineering prolems using $.

/


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Indicative $ontenta.Algorithm & Flow

Charts

b.Introduction to OS &Unix

c.Basic commands of

Unix

d.Editing; undr Unix.!ariabls & "ata

#$%s

f. O%rators &

Ex%rssions.Control Flow

h.Arra$s

i. ointr

'. Function(.String O%rations

l. Fils

m.Shll rogramming

n.S$stms Calls

-


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8ssessment and )earning

Methods 8ssessment

!xamination


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Prescried text >oo0s 4orvath 4.*. 31,,-6. $ Program Design 9or

!ngineers. &nd edition. 8ddison Wesle2; IS>"%1/: ,?(&(1. W. and Aitchie D. M. 31,??6. he $

Programming )anguage. Prentice 4all; IS>"%1/:

,?(1/11(/@& Bott9ried >. Programming in $+ Schaum series.

Second !dition. McBraw%4ill; IS>"%1/: ,?%(((&-(/


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OS 8n OS is a program which acts as an

interface etween computer s2stem usersand the computer hardware.

It provides a user%9riendl2 environment in

which a user ma2 easil2 develop andexecute programs.

Otherwise+ hardware 0nowledge would e

mandator2 9or computer programming. So+ it can e said that an OS hides the

complexit2 o9 hardware 9rom uninterested

users.


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9unctions controls the ac0ing store and peripherals such

as scanners and printers deals with the trans9er o9 programs in and out

o9 memor2 organises the use o9 memor2 etween

programs organises processing time etween programs

and users

maintains securit2 and access rights o9 users deals with errors and user instructions allows the user to save les to a ac0ing store provides the inter9ace etween the user and the

computer issues simple error messages?


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computer s2stem resources

In general+ a computer s2stem hassome resources which ma2 e

utiliCed to solve a prolem. he2 are Memor2 Processor3s6

I5O File S2stem etc.


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computer s2stem resources

Mainboard


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Motheroard


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Motheroard

mainboard


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processor


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A8M


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OS services

he OS manages these resources andallocates them to specic programs and users.

With the management o9 the OS+ aprogrammer is rid o9 diGcult hardwareconsiderations.

8n OS provides services 9or Processor Management Memor2 Management File Management Device Management $oncurrenc2 $ontrol


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1@

8 0ernel connects the applicationso9tware to the hardware o9 a

computer


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predened lirar2

8nother aspect 9orthe usage o9 OS is

that; it is used as a predened library 9orhardware%so9twareinteraction.

his is wh2+ s2stemprograms appl2 tothe installed OS

since the2 cannot

Application Programs

System Programs

Operating System

Machine Language

HARDWARE


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hides the complexit2

Since we have an alread2 writtenlirar2+ namel2 the OS+ to add two

numers we simpl2 write the9ollowing line to our program:

c H a ;


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in a s2stem where there is no OS installed+ weshould consider some hardware wor0 as:

38ssuming an M$ @?(( computer hardware6

)D88 J?( )oading the numer at memor2 location ?(

)D8> J?1 )oading the numer at memor2 location ?1

8DD> 8dding these two numers

S88 J


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Portailit2

In an OS installed machine+ since wehave an intermediate la2er+ ourprograms otain some advantage of

mobility 2 not dealing withhardware.

For example+ the aove program

segment would not wor0 9or an ?(?@machine+ where as the

Kc H a ;L

s2ntax will e suitale 9or oth.


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A simple program

segment with no

hardware

consideration

A more

sophisticated

program segment

with hardware

consideration

Hardware

responseOS Machine

)anguag

e


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virtual 3extended6 machine

With the advantage o9 easier programmingprovided 2 the OS+ the hardware+ its machinelanguage and the OS constitutes a newcomination called as a )irtual *xtndd+machin.

Machine

Language

Hardware

Machine

Language

Hardware

Operating

System

Machine

Virtual

(Extended

Machine


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0ernel mode vs user mode

In a more simplistic approach+ in 9act+ OS itsel9is a program.

>ut it has a priorit2 which application programsdont have.

OS uses the (rnl mod o9 themicroprocessor+ whereas other programs usethe usr mod.

he diNerence etween two is that; all hardwareinstructions are valid in 0ernel mode+ where

some o9 them cannot e used in the user mode.


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4istor2 o9 Operating S2stems

It all started with computer hardware inaout 1,-(s.

E!"A# $%&'


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!"I8$ 3!lectronic "umerical Integratorand $omputer6+ at the U.S. 8rm2s

8erdeen Proving Bround in Mar2land. uilt in the 1,-(s+ weighed /( tons+

was eight 9eet high+ three 9eet deep+ and1(( 9eet long

contained over 1?+((( vacuum tues thatwere cooled 2 ?( air lowers.


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$omputers were using vacuum tuetechnolog2.

E!"A#s )acuum tubes


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4istor2 o9 OperatingS2stems

E!"A#s bac*side


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1.& 4istor2 o9 Operating S2stems

Programs were loaded into memory manually using switches+ punched

cards+ or paper tapes,

E!"A# - coding by cable connections


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punch card


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s or2 o pera ng


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s or2 o pera ngS2stems

Paper tape

s or2 o pera ng


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s or2 o pera ngS2stems


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1.& 4istor2 o9 Operating S2stems

Babbage’s analytical engine

(designed in 1840’s by !arles Babbage" b#t c$#ld n$t be c$nstr#cted by !im%

An earlier and simpler &ersi$n is c$nstr#cted in '00'" in $nd$n )

http-..www,computerhistory,org.babbage.

http://www.computerhistory.org/babbage/http://www.computerhistory.org/babbage/


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8da )ovalence 3at time o9 $harles>aage6 wrote code 9or anal2ticalengine to compute >ernulli "umers

4i 9 O i


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8s time went on+ card readers+ printers+and magnetic tape units were developed

as additional hardware elements. 8ssemlers+ loaders and simple utilit2

liraries were developed as so9tware

tools. )ater+ oN%line spooling and channel

program methods were developed

se7uentiall2.


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#ommodore PE/+

$%00


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Finall2+ the idea o9 multi%rogramming came.

Multiprogramming means sharing o9resources etween more than oneprocesses.

>2 multiprogramming the $PU+ time isnot wasted+ ecause+ while one processmoves on some I5O wor0+ the OS pic0s

another process to execute till the current


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With the development o9 interactivecomputation in 1,(s+ tim,sharing

s$stms emerged. In these s2stems+ multiple users have

terminals 3not computers6 connected to a

main computer and execute her tas0 inthe main computer.


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/erminals are connected to

the main computer and used

1or input and output, !oprocessing is made, /hey do

not ha)e #P2s,

Main computer3 ha)ing a

#P2 executing processes by

utili4ation o1 the OS+ (e,g,

2!"5,


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8nother computer s2stem is themulti%rocssor s$stm having

multiple processors sharing memor2 andperipheral devices.

With this conguration+ the2 have

greater computing power and higherreliailit2.


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Multiprocessor s2stems are classied intotwo as tightl2%coupled and loosel2%

coupled 3distriuted6. In the tightl2%coupled one+ each

processor is assigned a specic dut2 ut

processors wor0 in close association+possil2 sharing the same memor2.

In the loosel2 coupled one+ each

processor has its own memor2 and cop2


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Use o9 the networ0s re7uired OSs appropriate 9orthem.

In ntwor( s$stms+ each process runs in itsown machine ut the OS have access to othermachines.

>2 this wa2+ le sharing+ messaging+ etc. ecame

possile. In networ0s+ users are aware o9 the 9act that s5he

is wor0ing in a networ0 and when in9ormation isexchanged. he user explicitl2 handles the

trans9er o9 in9ormation.


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Each is a computer ha)ing its own#P2+ 6AM+ etc, An OS supporting

networ*s is installed on them,

i 9 i


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"istributd s$stms are similar to networ0s.4owever in such s2stems+ there is no need toexchange in9ormation explicitl2+ it is handled2 the OS itsel9 whenever necessar2.

With continuing innovations+ new architecturesand compatile OSs are developed. >ut theirdetails are not in the scope o9 this course sincethe oective here is to give onl2 a generalview aout developments in OS concept.

ommon s


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ommon s Windows

Windows is an operating s2stem owned and operated 2

Microso9t. It diNers 9rom open source s2stems in that onl2 Microso9t has

the ailit2 to ma0e changes to the code. 4owever+ it also diNers 9rom Mac OS # in that it can e installed

on a variet2 o9 diNerent computers 9rom a host o9 competing

manu9acturers+ oNering the user more 9reedom o9 choice whenit comes to hardware.

8ccording to "et Mar0et Share+ Windows is the most widel2used operating s2stem

Mac OS # While a version o9 Mac OS # comes pre%installed on all 8pple

Macintosh computers+ users must pa2 i9 the2 wish to use newerversions when the2 ecome availale.

he s2stem is not open source+ so onl2 8pple developers havethe ailit2 to legitimatel2 ma0e alterations or improvements toits code. -<


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$ommon OSs

8ndroid 8ndroid is a QmoileQ operating s2stem maintained

2 the Open 4andset 8lliance+ a group o9companies and organiCations that contriute to thes2stems development under the management o9Boogle Inc

he s2stem is an Qopen standard+Q meaning that an

entire communit2 o9 developers can alter theso9tware+ not ust Boogle. 8ndroid comes pre%installed on smartphones and talet P$s 9or which itwas designed.

-@

$ommon OSs


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$ommon OSs )inux

)inux is a 9amil2 o9 open%source operating

s2stems+ which means the2 can e modied anddistriuted 2 an2one around the world.

his is diNerent 9rom proprietar2 so9tware li0eWindows+ which can onl2 e modied 2 the

compan2 that owns it 3Microso9t6. he advantages o9 )inux are that it is 9ree+ and

there are man2 diNerent distriutionsRor versionsR2ou can choose 9rom.

!ach distriution has a diNerent loo0 and 9eel+ andthe most popular ones include Ubuntu- int- andFdora.

)inux is named a9ter )inus orvalds+ who created

the )inux 0ernel in 1,,1. -


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-?


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Mar0et share

-,

&(1/ worldwide device shipments 2 operatings2stemWhitne2+ )ance 3 anuar2 &(1-6. Q8ndroid device shipments to top 1

illion this 2ear %% BartnerQ.

What is Unix T


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What is Unix T he U"I# operating s2stem is a set o9 programs

that act as a lin0 etween the computer andthe user.

he computer programs that allocate thes2stem resources and coordinate all the details

o9 the computers internals is called theoperating s2stem or 0ernel.

Users communicate with the 0ernel through a

program 0nown as the shll. he shll is acommand line interpreter; it translatescommands entered 2 the user and convertsthem into a language that is understood 2 the

0ernel.


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8out Unix Unix was originall2 developed in 1,@, 2 a

group o9 8 emplo2ees at >ell )as+including *en hompson+ Dennis Aitchie+Douglas McIlro2+ and oe Ossanna.

here are various Unix variants availale inthe mar0et. Solaris Unix+ 8I#+ 4P Unix and>SD are 9ew examples. /inux is also a Vavoro9 Unix which is 9reel2 availale.

Several people can use a U"I# computer atthe same time; hence U"I# is called amultiuser s2stem.

8 user can also run multiple programs at thesame time; hence U"I# is called multitas0ing.


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Unix 8rchitecture 4ere is a asic loc0 diagram o9 a U"I#

s2stem


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Main Parts o9 Unix he main concept that unites all versions o9 U"I# is

the 9ollowing 9our asics 0rnl1 he 0ernel is the heart o9 the operating

s2stem. It interacts with hardware and most o9 thetas0s li0e memor2 management+ tas0 schedulingand le management.

Shll1 he shell is the utilit2 that processes 2our

re7uests. When 2ou t2pe in a command at 2ourterminal+ the shell interprets the command andcalls the program that 2ou want. he shell usesstandard s2ntax 9or all commands. $ Shell+ >ourne

Shell and *orn Shell are most 9amous shells which


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Main Parts o9 Unix

Commands and Utilitis1 here are variouscommand and utilities which 2ou would use in2our da2 to da2 activities. cp+ mv+ cat and grepetc. are 9ew examples o9 commands and utilities.

here are over &


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0ernel is the !ngine o9 an2 Operating S2stem+ so allthe vital 9unctions should e controlled and

managed 2 0ernel itsel9. here are various tas0sand 9unctions o9 a 0ernel ut some o9 the importantare given elow:

2. 3sourc allocation, he 0ernels primar2 9unction is

to manage the computers resources and allow otherprograms to run and use these resources. heseresources are% $PU+ Memor2 and I5O devices.

4. rocss anagmnt, 8 process deneswhich memor2 portions the application canaccess. he main tas0 o9 a 0ernel is to allow theexecution o9 applications and support them with9eatures such as hardware astraction.

o run an application+ a 0ernel rst set up an address space 9or the

application+ then loads the le containing the applications code


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*!A"!)5. mor$ anagmnt, he 0ernel has 9ull access to

the s2stems memor2. It allows processes to sa9el2

access this memor2 as the2 re7uire it.6. I7O ")ic anagmnt, o per9orm use9ul

9unctions+ processes need access to the peripheralsconnected to the computer+ which are controlled 2

the 0ernel through Device Drivers. 8 d)ic dri)r isa computer program that enales the operatings2stem to interact with a hardware device. It providesthe operating s2stem with in9ormation o9 how tocontrol and communicate with a certain piece o9

hardware.A (rnl maintains a list of a)ailabl d)ics. 8 devicemanager rst per9orms a scan on diNerent hardware uses+such as Peripheral $omponent Interconnect 3P$I6 or UniversalSerial >us 3US>6+ to detect installed devices+ then searches 9orthe appropriate drivers. he 0ernel provides the I5O to allow


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*!A"!)8. Intr, rocss Communication, *ernel

provides methods 9or S2nchroniCation and$ommunication etween processes+ called Inter%Process $ommunication 3IP$6. here are variousapproaches o9 IP$ sa2+ semaphore+ sharedmemor2+ message 7ueue+ pipe 3or named 9o6+

etc.

9. Schduling, In a Multitas0ing s2stem+ the 0ernelwill give ever2 program a slice o9 time and switch9rom process to process so 7uic0l2 that it willappear to the user as i9 these processes wereeing executed simultaneousl2. he 0ernel usesScheduling 8lgorithms to determine whichprocess is running next and how much time it wille given. he algorithm sets priorit2 among the


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:. S$stm Calls and Intrru%t andling, 8s2stem call is a mechanism that is used 2 the

application program to re7uest a service 9rom theoperating s2stem. S2stem calls include close+open+ read+ wait and write. o access the servicesprovided 2 the 0ernel we need to invo0e the

related 0ernel 9unctions. Most 0ernels provide a $)irar2 or an 8PI+ which in turn invo0es the related0ernel 9unctions.


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he U"I# Files2stem he tas0 o9 the les2stem is to provide a wa2 to

store data+ in an organised structure+ and

retrieve it when re7uested On one s2stem+ there ma2 e a large

accounting application+ which will store details

o9 nancial transactions. 8t the other end o9 the scale+ an individual ma2

use a s2stem to store private letters+ or collegenotes.

Someone else ma2 store an address oo0+phone numers+ and their diar2 on the s2stem.O9 course+ one s2stem could e used 9or an2 orall o9 these applications+ and endless others. he all have one thin in common: the need to


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the le concept he asic unit o9 the les2stem is+ as 2ou ma2

guess+ the le. o understand the concept o9 a le+ thin0 o9 a lan0

piece o9 paper. 8t rst+ it contains nothing. 4owever+ 2ou can write on it+

and 2ou can write an2thing. Similarl2+ a le ma2 e

empt2+ or it ma2 contain an2 amount o9 data. he data itcontains can e an2thing+ 9or example a list o9 phonenumers+ a letter to a customer+ or 2our compan2saccounts. In eNect+ a le is ust li0e a piece o9 paper % themain diNerence is that it ma2 store an2 amount o9 data.

he onl2 other thing to note aout les is that eachone has a name

!ver2thing in Unix is considered to e a le+

including ph2sical devices such as DXD%AOMs+ US>@(


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the le concept

8 le is a named collection o9 relatedin9ormation+ usuall2 as a se7uence o9

2tes+ with two views: )ogical 3programmers 6 view+ as the

users see it.

Ph2sical 3operating s2stem6 view+ as itactuall2 resides on secondar2 storage.

@1!xplain the le concept o9 Unix.

File attriutes


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File attriutes !ach le is associated with a collection

o9 in9ormation+ 0nown as attriutes: "8M!+ owner+ creator t2pe 3e.g.+ source+ data+ inar26 location 3e.g.+ I%node or dis0 address6 organiCation 3e.g.+ se7uential+ indexed+

random6 access permissions

time and date 3creation+ modication+ andlastcaccessed6

siCe variet2 o9 other 3e.g.+ maintenance6

in9ormation @&

File operations


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File operations here are six asic operations 9or le

manipulation: create+ write+ read+ delete+ reposition r5w

pointer 3a.0.a. see06+ and truncate 3not ver2common.6

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File t2pes


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2p 8 common implementation techni7ue 3as

organiCational help with consistent usage6 is to

include the t2pe as an extension to the lename:

Music+ video le t2pes Files are structured internall2 to meet the

expectations o9 the program3s6 that manipulate@-


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File access methods

he in9ormation stored in a le can e accessedin a variet2 o9 methods: Se7uential: in order+ one record a9ter another. Direct 3random6: in an2 order+ s0ipping the

previous records. *e2ed: in an2 order+ ut with particular

value3s6; e.g.+ hash tale or dictionar2. )>

loo0up is one example o9 a 0e2ed search. Other access methods+ such as indexed+ can e

uilt on top o9 the aove asic techni7ues.I>Ms indexed se7uential access method 3IS8M6

is uilt on random and se7uential access.@<

!ver2thing is a le


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!ver2thing is a le !ver2thing is a leQ descries one o9 the dening

9eatures o9 Unix+ and its derivatives R that a widerange o9 input5output resources such asdocuments+ directories+ hard%drives+ modems+0e2oards+ printers and even some inter%process

and networ0 communications are simple streams o92tes exposed through the les2stem name space Unix does not distinguish etween diNerent t2pes

o9 le.

he advantage o9 this approach is that the sameset o9 tools+ utilities and 8PIs can e used on a widerange o9 resources.

@@

Understand that Unix does notdistinguish etween diNerent t2pes o9

le.

Directories


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ec o es 8 director2 is a s2mol tale+ which can e

searched 9or in9ormation aout the les. 8lso+

it is the 9undamental wa2 o9 organiCing les. Usuall2+ a director2 is itsel9 a le. 8 t2pical director2 entr2 contains in9ormation

3attriutes6 aout a le. Director2 entries areadded as les are created+ and are removedwhen les are deleted.

$ommon director2 structures are: Single%level 3Vat6: shared 2 all users. wo%level: one level 9or each user. ree: aritrar2 3su6%tree 9or each user.

@

U"I# director2 structure


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U"I# uses an advanced 9orm o9 tree structure+0nown as directed ac2clic%graph 3D8B6 director2

@?

he Files2stem 3eg6


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he Files2stem 3eg6

/

bin etc home/ tmp usr

hollid2 scully bin etc

netprog unix X ls who


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File sharing 8llowing users to share les raises a maor issue:

%rotction. 8 general approach is to provide controlled access to

les through a set o9 operations such as rad- writ-dlt- list+ and a%%nd. hen permit users toper9orm one or more operations.

One popular protection mechanism is a condensed

version o9 access list+ where the s2stem recogniCesthr classi=cations of usrs with each le anddirector2: user group

(

File s2stem services


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2 8 le s2stem provides a mapping etween the

logical and ph2sical views o9 a le+ through a

set o9 services and an inter9ace. Simpl2 put+ thele s2stem hids all th d)ic,s%ci=cas%cts o9 le manipulation 9rom users.

he asic services o9 a le s2stem include: 0eeping trac0 o9 les 30nowing location6+ I5O support+ especiall2 the transmission

mechanism to and 9rom main memor2+ management o9 secondar2 storage+ sharing o9 I5O devices+ providing protection mechanisms 9or

in9ormation held on the s2stem. 1

File s2stem astraction


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File s2stem astraction

1. introduction to os & unix

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