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BEGINNINGLINUXPROGRAMMING1.Introduction

2.ArchitectureofLinux

3.DevelopmentandHardwaresupport

4.UsesofLinux

5.Linuxfiletree

6.Commandlinearguments

7.Controloperators

8.Filesub-system

9.Bash,Commandshell,PipingandRe-direction

10.WorkingwithLinuxfilesanddirectories

11.ShellscriptinginLinux

12.ListofOS

13.MoreeBooksandApps

14.OureBooksonITandComputerScience

DisclaimerThiseBookcontentsisforinformationalandstudypurposesonly.TheKnowledgeflowmakesnoclaims,promises,orguaranteesabouttheaccuracy,completeness,oradequacyofthecontentsofthiseBookandnolegalliabilityorotherresponsibilityisacceptedbyKnowledgeflowforanyerrors,omissions,orstatementsonthiseBook.

IntroductionLinuxisaUnix-likecomputeroperatingsystemassembledinsupervisionforbeingthemodeloffreeandopen-sourcesoftwaredevelopmentaswellasdistribution.ThereforethemostdefiningcomponentistheLinuxkernelthatisanoperatingsystemkernelthatwasfirstreleasedbyLinusTorvaldsonthedate5Octoberofyear1991.TheOpensourceaswellasfreeSoftwareFoundationusesthenameLinuxtodescribetheoperatingsystemthatwasabigcontroversy.LinuxwasdevelopedtobeafreeoperatingsystemforIntelx86whichwasbasedonpersonalcomputerbutithasalsobeenportedtomostofthecomputerhardwareplatformsthananyotheroperatingsystem.Atpresentithasbeentheleadingoperatingsystemonserversaswellasonotherbigironsystemssuchasmainframecomputersandalsointhesupercomputers,stillitisusedonlyaround1.5%ofdesktopcomputersatpresentcomputingscenario.Linuxcanrunonembeddedsystemswhodevicesareoperatingsystemwhichistypicallymadeintothefirmwareandisalsohighlytailoredtotheparticularsystemthisparticularsystemalsoincludesmobilephones,computers,tablets,networkrouters,televisionsandevenvariousvideogameconsoles.AndroidOSisalsobasedontheLinuxkernel.

Tuxthepenguin,MascotofLinux

CreationofLinux

TorvaldsstarteddevelopmentoftheLinuxkernelandalsomadetheapplicationswrittenforMINIXtobeusedonLinux.AftersometimelatertheLinuxmaturedandalsotheLinuxkerneldevelopmentalongwiththereplacementofGNUwiththeMINIXcomponentsalsotookplacesinceitwasanadvantagetousefreeofcostavailablecodefromtheparticularGNUProjectwiththefledglingOS.TorvaldsalsoswitchedfromtheoriginallicenseofhisownwhichprohibitedcommercialredistributionoftheGNUGPL.AlsothevariousdevelopersworkedtointegrateGNUcomponentsalongwiththeLinuxkerneltomakeitafreeoperatingsystem.

Recentdevelopment

Torvaldscontinuesthefurtherdevelopmentofthekernel.Finallywiththehelpofindividualsandcorporationsdevelopthirdpartyfornon-GNUcomponents.Thethirdpartycomponentscompriseofavastbodyoftheworkandmayalsoincludeboththekernelmodulesalongwiththeusersapplications.

ReasonforusingLinux

Givesfreedomtoruntheprogramirrespectiveofthepurpose.Givesfreedomtostudyhowtheprogramworksandalsoallowstomakechangesyouwishtomake.Toredistributethecopiessothatyoucanhelpyourneighbortoo.Alsoallowsdistributioncopiesfreelyofyourmodifiedversions.

DesignofLinuxLinux-basedsystemisamoduleoftheUnix-likeoperatingsystem.MuchofthebasicdesignsarederivedfromprinciplesestablishedinUNIXintheperiodofyear1970sand1980s.ThiskindofsystemusesamonolithickernelandtheLinuxkernelalongwithfilesystemaccess.Inthisthedevicedriversareeitherintegrateddirectlywiththekernelorareaddedasamoduleloadedwhilethesystemisinarunningstate.Separateprojectsthatareinterfacedwiththekernelprovidethesystemsmostofthehigher-levelfunctionality.GNUisanimportantpartofmostLinux-basedsystemssinceitisresponsibleforprovidingthemostcommonimplementationoftheClibraryandmanycommonUNIXtoolswhichcarriesoutbasicoperatingsystemtasks.ThisgraphicaluserinterfaceisusedbymostoftheLinuxsystemsbuiltonthetopofanimplementationoftheWindowSystem.

ArchitectureofLINUXkernel

ComponentsofLinux

VariouscomponentsinstalledofaLinuxsystemareasfollows-

Bootloader.ExampleGNUGRUB,SYSLINUX,Gummibootetc.LoadsLinuxkerneltocomputersmainmemorywhichisbeingexecutedby

computerwhenturnedonandafterinitializationofframeworkisperformed.ProgramslikethetraditionalsysvinitandUpstart.FirstprocesslaunchedbytheLinuxkernelwhichisalsoattherootoftheprocesstreesthatmeansallprocessesareusuallylaunchedbyinit.Itstartsprocessessuchasasystemservicesandloginprompts.Softwarelibrariescontaincodethatcanbeeasilyusedbyrunningprocesses.InLinuxsystemsusingELF-formatexecutablefileisadynamiclinkerthatcanmanagesuserofdynamiclibrariesthatiscalledld-linux.so.Theheaderfilesarealsoincludedfordescribingtheinterfaceofaninstalledlibrary.WidgettoolkitsareusedtobuildvariouscharacterizedGUIforthesoftwareapplications.LibrariesareprimarilydevelopedbytheEnlightenmentteam.Userinterfaceprogramsusedaresuchasthecommandshellsorthewindowingenvironments.

Theuserinterfaceknownastheshellwhichisacommand-lineinterface(CLI),agraphicaluserinterfaces(GUI)whichiscommonforanyembeddedsystems.

UserInterface

CLIshellsarethetext-baseduserinterfacesthatusetextforbothinputandoutput.ThesearedominantshellwhichisusedinLinuxwhichistheGNUBourne-AgainShellalsoknownasBASHthatisoriginallydevelopedfortheGNUproject.Mostlow-levelLinuxcomponents.TheCLIissuitedforautomationofrepetitiveaswellasdelayedtasks.AwindowmanagerprovidesamethodortoolbywhichtocontroltheplacementandtheappearanceoftheindividualapplicationwindowsanditcaninteractswiththeXWindowSystemalso.Thedesktopenvironmentsjustincludewindowmanagersaspartoftheirstandardinstallationsalthoughtheusermightprefertouseadifferentwindowmanageralsoifneeded.Waylandcompositorhasaroleofthedisplayserver,windowmanageraswellascompositingmanager.

DevelopmentinLinuxThemostimportantdifferencebetweenLinuxandmostoftheotherpopularcontemporaryoperatingsystemsarethatthekernelusedinLinuxthatistheLinuxkernelaswellasvariousothercomponentsarefreeofcostandalsoopensourcesoftware.Thereexistsomefreeaswellasopensourcesoftwarewhoselicensesarebasedonthevariousprinciplesofcopyleftandakindofreciprocity.Anyworkthatisderivedfromacopyleftpieceofthesoftwaremustalsobeacopyleftit.ThemostcommonfreelicensingistheGNUGeneralPublicLicense(GPL)thatisalsoaformofcopyleftandisusedfortheLinuxkernel.WhereasmanyofthecomponentsareusedfromtheGNUProject.Freesoftwareprojectsthataredevelopedthroughcollaborationareoftenproducedindependentlyforeachother.

SimplifiedUNIXlikearchitecture

HardwaresupportinLinuxLinuxkernelisanoperatingsystemkernelcanrunonaveryhighanddiverserangeofcomputerarchitecturesthatalsoincludethehandheldandARMbasediPAQeitherwiththeIBMmainframessystemz9orwithSystemz10thatwouldhelpincoveringthedevicesthatwouldrangefrommobilephonestothesupercomputers.Specializeddistributionsofkernelforksexistforlessmainstreamarchitectures.SuchastheELKSkernelforkcanrunonIntel8086aswellasIntel8028616-bitmicroprocessorswhereastheClinuxkernelforkmayrunonsystemswithoutamemorymanagementunit.Thekernelrunsonarchitecturesthatwereintendedtouseamanufacturer-createdoperatingsystemliketheMacintoshcomputers,variousvideogameconsolesanddifferenttypesofmobilephones.

Linuxinvarioustypesofhardware

Itisalsousedinvariousportablemusicplayers.Variousindustryassociationsaswellashardwareconferencesaredevoted

tomaintainandalsoimprovesupportforvariousdiversehardwareunderLinux,forane.g.FreedomHEC.WithtimethesupportsystemfordifferenthardwarehasimprovedinLinux.Asaresultinmanyofftheshelfpurchasesarehavingabetterofbeingcompatible.Itprovidesapoolofopenandprioritysoftwarewhichhelpstheusertocustomizeanduseinaccordancetohisneedsandpriority.ShellnamedbashwaswidelyusedbyLinux.BashwasaproductwhichwasdevelopedbyGNU.

BashdevelopedbyGNU

UsesofLinuxTheLinuxdistributionsbesidewasdesignedmostlyforthegeneralpurposesthatarebeperformedonthedesktopsaswellasservers.Thereforefurtherthedistributionshavetobespecializedforvariousotherpurposesthatincluded-computerarchitecturesupport,security,embeddedsystems,andlocalizationtoaspecificregion,stabilityandsupportforreal-timeapplications.Therearesomemoredistributionswhichdeliberatelyincludeonlyaccountingthefreesoftware.

Desktop

ThepopularityofLinuxnowadayonthestandarddesktopcomputersaswellasthelaptopshasbeenincreased.CurrentlymostdistributionsthataredoneincludeagraphicaluserenvironmentwiththetwoofthemostpopularenvironmentsthatareGNOMEandKDEPlasmaDesktop.TherenoexistenceofasingleLinuxdesktop-RatherdesktopenvironmentsaswellasLinuxdistributionsselectcomponentsfromthepooloffreeopen-sourcesoftwarewhichtheyusetoconstructaGUIimplementingsomemoreorlessstrictdesigningguidance.GNOMEcanbestatedasoneoftheexamplesforthehumaninterfaceguidelineswhichgivesthehumanmachineinterfacenotjustaplatformtoperformthegraphicaldesignbutalsoconsiderspeoplewithdisabilitiesandstillevenwhenfocusingonsecurity.NatureofcollaborationoffreesoftwaredevelopmentallowsperforminglanguagelocalizationforsomeoftheLinuxdistributionsfortheuseinlocaleswherethelocalizingproprietarysystemswouldnotbeeffectiveincostwise.

SoftwarecomponentsofLinuxkernel

Servers,mainframesandsupercomputersIthavelongbeenusedasserveroperatingsystemsthathaverisentoprominenceinthatareaofNetcraftreportedthateightofthetenarethemostreliableinternethostingcompaniesrunningLinuxdistributionsonvariouswebservers.Ithavebeenthecornerstoneandstillcontinuestobe,fortheLAMPserverandsoftwarecombinationwhichachievedfameamongvariousdevelopersandalsoisoneofthemostcommonplatformsusedforhostingwebsite.Itdistributionshavebecomeincreasinglypopularonmainframesinthelastdecadepartlyduetopricingandtheopen-sourcemodel.Linuxdistributionsarealsocommonlyusedasoperatingsystemsforsupercomputers.AndinthedecadetilltheEarthSimulatorsupercomputerallthefastestsupercomputershaveworkedwithLinux.

Lampsoftware

Embeddeddevices

Sinceitslowcostandeasytocustomizeitiswidelyusedasthefavoriteinembeddedsystems.Non-mobiletelecommunicationsequipmentmajorityofcustomerpremisesequipmenthardwarearerunningonvariousLinux-basedOS.OpenWrtiscommunitydrivenelementonwhichmanyOEMfirmwaresaredependent.

Specializeduses

Duetotheflexibility,freeandalsobeingaopensourcebynatureithasbecomepossibletohighlytunedLinuxforaspecifiedpurposes.

TherearetwomainmethodsforcreatingaspecializedLinux-

fromscratchfromageneralpurposedistribution

Avoidingresourceoverheadhascausedbythecomponentsareconsideredtoberedundantinthedistribution.

LinuxfiletreeContentsoftheLinuxfiletreesareasfollows.

/bin-Commonprograms,itissharedbythesystem,thesystemadministratoraswellaswiththeusers./boot-Inrecentdistributionshadalsogrubdatas.ThereforeGrubstandsfortheGrandUnifiedBootloaderthatisanattempttogetridofthemanyotheravailableboot-loaders./dev-ItconsistsaelementthatreferencestoalltheCPUperipheralhardwarethatarerepresentedasfileswithspecialproperties./etc-Consistofimportantsystemconfigurationfilesthatareavailablein/etcandthisdirectoryalsoconsistofdatasaresomewhatsimilartothecontrolpanelpresentinthewindowoperatingsystem./home-Itcontainssomeofthehomedirectoriesofthecommonusers./initrd-Itprovidesinformationforbooting./lib-ThisconsistsofLibraryfiles,includingthefilesforallkindsofprogramsneededbythesystemandalsobytheusers.

Linuxfiletree

/lost+found-Ineverypartitionhasalostandfoundinitsupperdirectoryand

thereforefilesthatweresavedwhenthefailureoccursarestoredhere./misc-Usedforvariousmiscellaneouspurposes./mnt-Thestandardmountpointfortheexternalfilesystems./net-Thestandardmountpointfortheentireremotefilesystemsisavailablehere./opt-Thiscontainsextraandthirdpartysoftware./root-Containingdataofthatoftheadministrativeusershomedirectoryandthereforeifmindthedifferencebetween/rootthehomedirectoryoftherootuser.

Linuxtrafficcontrol

IflowerPRIOclasscontainsnothingthenhighernumberedPRIOclassesareprocessed.Inorderofimportance3PRIOclassesareused.NoQdiscsarefilteredonlyplacetrafficintoclasses.TBFareratelimiting.HFBcanbeusedforratelimiting.

Representationtable

CommandlineConfiguringLinuxbyusingcommandlineutilizesthemostpopularandmostpreferredway.IfeverusedLinuxforpersonalorprofessionalworkwouldhavedefinitelyusedthecommandline.

Example

$ls-a

..dmrcgoogleMemory_layout.jpgPictures.pulse-cookie

.tmp_versions

..Documents.gstreamer-0.10modules.orderpractice

.recently-used.xbeltry.c

aDownloads.gtk-bookmarksModule.symversproc.c.recently-used.xbel.W69Q8VUnsavedDocument1

a1.dropbox.gvfs.mozillaprocEntry123~.SkypeVideos

.adobeDropbox.ICEauthority.mozilla-thunderbirdprocEntry12z~.ssh.vim

alpha.dropbox-dist.icons.mplayerproc.ko.sudo_as_admin_successful.viminfo

article_function_pointer.txt.esd_auth.javaMusic.proc.ko.cmd.teamviewervlc

.bash_history.fontconfig.kchmviewermydataproc.mod.ctemplate.htmlworm

.bash_logout.gconf.kdemy_lsproc.mod.oTemplates.xchat2

.cache.gconfd.lesshstmy_ls_alpha.c.proc.mod.o.cmdtestdisk.log.xchm

chmodOctal.txt.gegl-0.0libavmy_ls.cproc.otestfile.xsession-errors

.compiz.gimp-2.6.linuxmint.nautilus.proc.o.cmdtest.py

.xsession-errors.old

.config.gksu.lock.local.openoffice.org.profile.themes

.dbus.gnome2.macromediaoutput.logPublic.thumbnails

Desktop.gnome2_privateMakefilepics.pulse.thunderbird

Parsingcommandlineargument

Afterpassingthecommandlineargumentsthataremadeavailableinthecodethroughtheargcandargvargumentsofthismain()function.Thenextstepistoparsetheoptionsthenrunthecodeaccordingtoinputthatisprovidedbytheuserthroughtheprovidedflags.

Example

#include

#include

#include

#defineCMP_LENGTH3

enumop{

ADD,

SUB,

MUL,

DIV

};

intmain(intargc,char*argv[])

{

if(argc