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LEARNINGSTARTSWITHVIEWINGTHEWORLDDIFFERENTLY.
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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
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DisclaimerThiseBookcontentsisforinformationalandstudypurposesonly.TheKnowledgeflowmakesnoclaims,promises,orguaranteesabouttheaccuracy,completeness,oradequacyofthecontentsofthiseBookandnolegalliabilityorotherresponsibilityisacceptedbyKnowledgeflowforanyerrors,omissions,orstatementsonthiseBook.
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IntroductionLinuxisaUnix-likecomputeroperatingsystemassembledinsupervisionforbeingthemodeloffreeandopen-sourcesoftwaredevelopmentaswellasdistribution.ThereforethemostdefiningcomponentistheLinuxkernelthatisanoperatingsystemkernelthatwasfirstreleasedbyLinusTorvaldsonthedate5Octoberofyear1991.TheOpensourceaswellasfreeSoftwareFoundationusesthenameLinuxtodescribetheoperatingsystemthatwasabigcontroversy.LinuxwasdevelopedtobeafreeoperatingsystemforIntelx86whichwasbasedonpersonalcomputerbutithasalsobeenportedtomostofthecomputerhardwareplatformsthananyotheroperatingsystem.Atpresentithasbeentheleadingoperatingsystemonserversaswellasonotherbigironsystemssuchasmainframecomputersandalsointhesupercomputers,stillitisusedonlyaround1.5%ofdesktopcomputersatpresentcomputingscenario.Linuxcanrunonembeddedsystemswhodevicesareoperatingsystemwhichistypicallymadeintothefirmwareandisalsohighlytailoredtotheparticularsystemthisparticularsystemalsoincludesmobilephones,computers,tablets,networkrouters,televisionsandevenvariousvideogameconsoles.AndroidOSisalsobasedontheLinuxkernel.
Tuxthepenguin,MascotofLinux
CreationofLinux
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TorvaldsstarteddevelopmentoftheLinuxkernelandalsomadetheapplicationswrittenforMINIXtobeusedonLinux.AftersometimelatertheLinuxmaturedandalsotheLinuxkerneldevelopmentalongwiththereplacementofGNUwiththeMINIXcomponentsalsotookplacesinceitwasanadvantagetousefreeofcostavailablecodefromtheparticularGNUProjectwiththefledglingOS.TorvaldsalsoswitchedfromtheoriginallicenseofhisownwhichprohibitedcommercialredistributionoftheGNUGPL.AlsothevariousdevelopersworkedtointegrateGNUcomponentsalongwiththeLinuxkerneltomakeitafreeoperatingsystem.
Recentdevelopment
Torvaldscontinuesthefurtherdevelopmentofthekernel.Finallywiththehelpofindividualsandcorporationsdevelopthirdpartyfornon-GNUcomponents.Thethirdpartycomponentscompriseofavastbodyoftheworkandmayalsoincludeboththekernelmodulesalongwiththeusersapplications.
ReasonforusingLinux
Givesfreedomtoruntheprogramirrespectiveofthepurpose.Givesfreedomtostudyhowtheprogramworksandalsoallowstomakechangesyouwishtomake.Toredistributethecopiessothatyoucanhelpyourneighbortoo.Alsoallowsdistributioncopiesfreelyofyourmodifiedversions.
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DesignofLinuxLinux-basedsystemisamoduleoftheUnix-likeoperatingsystem.MuchofthebasicdesignsarederivedfromprinciplesestablishedinUNIXintheperiodofyear1970sand1980s.ThiskindofsystemusesamonolithickernelandtheLinuxkernelalongwithfilesystemaccess.Inthisthedevicedriversareeitherintegrateddirectlywiththekernelorareaddedasamoduleloadedwhilethesystemisinarunningstate.Separateprojectsthatareinterfacedwiththekernelprovidethesystemsmostofthehigher-levelfunctionality.GNUisanimportantpartofmostLinux-basedsystemssinceitisresponsibleforprovidingthemostcommonimplementationoftheClibraryandmanycommonUNIXtoolswhichcarriesoutbasicoperatingsystemtasks.ThisgraphicaluserinterfaceisusedbymostoftheLinuxsystemsbuiltonthetopofanimplementationoftheWindowSystem.
ArchitectureofLINUXkernel
ComponentsofLinux
VariouscomponentsinstalledofaLinuxsystemareasfollows-
Bootloader.ExampleGNUGRUB,SYSLINUX,Gummibootetc.LoadsLinuxkerneltocomputersmainmemorywhichisbeingexecutedby
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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.
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DevelopmentinLinuxThemostimportantdifferencebetweenLinuxandmostoftheotherpopularcontemporaryoperatingsystemsarethatthekernelusedinLinuxthatistheLinuxkernelaswellasvariousothercomponentsarefreeofcostandalsoopensourcesoftware.Thereexistsomefreeaswellasopensourcesoftwarewhoselicensesarebasedonthevariousprinciplesofcopyleftandakindofreciprocity.Anyworkthatisderivedfromacopyleftpieceofthesoftwaremustalsobeacopyleftit.ThemostcommonfreelicensingistheGNUGeneralPublicLicense(GPL)thatisalsoaformofcopyleftandisusedfortheLinuxkernel.WhereasmanyofthecomponentsareusedfromtheGNUProject.Freesoftwareprojectsthataredevelopedthroughcollaborationareoftenproducedindependentlyforeachother.
SimplifiedUNIXlikearchitecture
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HardwaresupportinLinuxLinuxkernelisanoperatingsystemkernelcanrunonaveryhighanddiverserangeofcomputerarchitecturesthatalsoincludethehandheldandARMbasediPAQeitherwiththeIBMmainframessystemz9orwithSystemz10thatwouldhelpincoveringthedevicesthatwouldrangefrommobilephonestothesupercomputers.Specializeddistributionsofkernelforksexistforlessmainstreamarchitectures.SuchastheELKSkernelforkcanrunonIntel8086aswellasIntel8028616-bitmicroprocessorswhereastheClinuxkernelforkmayrunonsystemswithoutamemorymanagementunit.Thekernelrunsonarchitecturesthatwereintendedtouseamanufacturer-createdoperatingsystemliketheMacintoshcomputers,variousvideogameconsolesanddifferenttypesofmobilephones.
Linuxinvarioustypesofhardware
Itisalsousedinvariousportablemusicplayers.Variousindustryassociationsaswellashardwareconferencesaredevoted
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tomaintainandalsoimprovesupportforvariousdiversehardwareunderLinux,forane.g.FreedomHEC.WithtimethesupportsystemfordifferenthardwarehasimprovedinLinux.Asaresultinmanyofftheshelfpurchasesarehavingabetterofbeingcompatible.Itprovidesapoolofopenandprioritysoftwarewhichhelpstheusertocustomizeanduseinaccordancetohisneedsandpriority.ShellnamedbashwaswidelyusedbyLinux.BashwasaproductwhichwasdevelopedbyGNU.
BashdevelopedbyGNU
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UsesofLinuxTheLinuxdistributionsbesidewasdesignedmostlyforthegeneralpurposesthatarebeperformedonthedesktopsaswellasservers.Thereforefurtherthedistributionshavetobespecializedforvariousotherpurposesthatincluded-computerarchitecturesupport,security,embeddedsystems,andlocalizationtoaspecificregion,stabilityandsupportforreal-timeapplications.Therearesomemoredistributionswhichdeliberatelyincludeonlyaccountingthefreesoftware.
Desktop
ThepopularityofLinuxnowadayonthestandarddesktopcomputersaswellasthelaptopshasbeenincreased.CurrentlymostdistributionsthataredoneincludeagraphicaluserenvironmentwiththetwoofthemostpopularenvironmentsthatareGNOMEandKDEPlasmaDesktop.TherenoexistenceofasingleLinuxdesktop-RatherdesktopenvironmentsaswellasLinuxdistributionsselectcomponentsfromthepooloffreeopen-sourcesoftwarewhichtheyusetoconstructaGUIimplementingsomemoreorlessstrictdesigningguidance.GNOMEcanbestatedasoneoftheexamplesforthehumaninterfaceguidelineswhichgivesthehumanmachineinterfacenotjustaplatformtoperformthegraphicaldesignbutalsoconsiderspeoplewithdisabilitiesandstillevenwhenfocusingonsecurity.NatureofcollaborationoffreesoftwaredevelopmentallowsperforminglanguagelocalizationforsomeoftheLinuxdistributionsfortheuseinlocaleswherethelocalizingproprietarysystemswouldnotbeeffectiveincostwise.
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SoftwarecomponentsofLinuxkernel
Servers,mainframesandsupercomputersIthavelongbeenusedasserveroperatingsystemsthathaverisentoprominenceinthatareaofNetcraftreportedthateightofthetenarethemostreliableinternethostingcompaniesrunningLinuxdistributionsonvariouswebservers.Ithavebeenthecornerstoneandstillcontinuestobe,fortheLAMPserverandsoftwarecombinationwhichachievedfameamongvariousdevelopersandalsoisoneofthemostcommonplatformsusedforhostingwebsite.Itdistributionshavebecomeincreasinglypopularonmainframesinthelastdecadepartlyduetopricingandtheopen-sourcemodel.Linuxdistributionsarealsocommonlyusedasoperatingsystemsforsupercomputers.AndinthedecadetilltheEarthSimulatorsupercomputerallthefastestsupercomputershaveworkedwithLinux.
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Lampsoftware
Embeddeddevices
Sinceitslowcostandeasytocustomizeitiswidelyusedasthefavoriteinembeddedsystems.Non-mobiletelecommunicationsequipmentmajorityofcustomerpremisesequipmenthardwarearerunningonvariousLinux-basedOS.OpenWrtiscommunitydrivenelementonwhichmanyOEMfirmwaresaredependent.
Specializeduses
Duetotheflexibility,freeandalsobeingaopensourcebynatureithasbecomepossibletohighlytunedLinuxforaspecifiedpurposes.
TherearetwomainmethodsforcreatingaspecializedLinux-
fromscratchfromageneralpurposedistribution
Avoidingresourceoverheadhascausedbythecomponentsareconsideredtoberedundantinthedistribution.
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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
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thereforefilesthatweresavedwhenthefailureoccursarestoredhere./misc-Usedforvariousmiscellaneouspurposes./mnt-Thestandardmountpointfortheexternalfilesystems./net-Thestandardmountpointfortheentireremotefilesystemsisavailablehere./opt-Thiscontainsextraandthirdpartysoftware./root-Containingdataofthatoftheadministrativeusershomedirectoryandthereforeifmindthedifferencebetween/rootthehomedirectoryoftherootuser.
Linuxtrafficcontrol
IflowerPRIOclasscontainsnothingthenhighernumberedPRIOclassesareprocessed.Inorderofimportance3PRIOclassesareused.NoQdiscsarefilteredonlyplacetrafficintoclasses.TBFareratelimiting.HFBcanbeusedforratelimiting.
Representationtable
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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
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.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
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