Linux Basics - 4techbees.files.wordpress.com · 6/2/2018 · Ø Major Distributors for Unix...
14
Linux Basics Basics: Ø Unix is a proprietary commercial opera4ng system developed by Ken Thompson. Ø Linux is a free, open source opera4ng system developed by Linus Torvalds Ø Linux/Unix is 4mesharing, scalable, portable and mul4-tasking opera4ng system. Ø Major Distributors for Unix opera4ng system are AIX,SOLARIS and HP-UX. Ø There are many flavors of Linux opera4ng system in the market but for server versions organiza4ons typically use REDHAT and pay them for the support. Kernel: Ø In Linux/Unix kernel is the heart of opera4ng system which performs task scheduling, file management and handles communica4ons in response to system calls. Shell: Ø Shell is an interface between the user and kernel. Ø To Know the current shell we can use below commands. echo $SHELL echo $0
Transcript of Linux Basics - 4techbees.files.wordpress.com · 6/2/2018 · Ø Major Distributors for Unix...
LinuxBasicsBasics:Ø Unixisaproprietarycommercialopera4ngsystemdevelopedbyKenThompson.Ø Linuxisafree,opensourceopera4ngsystemdevelopedbyLinusTorvaldsØ Linux/Unixis4mesharing,scalable,portableandmul4-taskingopera4ngsystem.Ø MajorDistributorsforUnixopera4ngsystemareAIX,SOLARISandHP-UX.Ø TherearemanyflavorsofLinuxopera4ngsysteminthemarketbutforserver
versionsorganiza4onstypicallyuseREDHATandpaythemforthesupport.Kernel:Ø InLinux/Unixkernelistheheartofopera4ngsystemwhichperformstask
scheduling,filemanagementandhandlescommunica4onsinresponsetosystemcalls.
Shell:Ø Shellisaninterfacebetweentheuserandkernel.Ø ToKnowthecurrentshellwecanusebelowcommands.
echo$SHELLecho$0
LinuxBasicsØ /etc/shellswilllistalltheshellswhichareavailableonthemachineØ Belowarethedifferentshellsavailableinlinux/unix:
§ BourneShell:Oldestshellandthereisnoop4ontoeditpreviouscommandsortocontrolbackgroundjobs.
§ KornShell:ThisisbasedonBourneshellwithenhancementtoeditpreviouscommands.Wecanrunkshellusingkshorpdshfromthecurrentshell.TonavigatethroughthecommandweusehtomoveleWandltomoveright
§ CShell:TheCshellsyntaxistakenfromClanguageanditissuchausefultoolwhoarefamiliarwithC.Wecanruncshellusingcshfromthecurrentshell.
§ BashShell:BourneAgainstshellisacombina4onoffeaturesfromBourneshellandCshell.Ithasacommand-lineeditorthatallowstheuseofthecursorkeysinamore"userfriendly"mannerthantheKornshell.ItalsohasausefulhelpfacilityallowingyoutogetalistofcommandsbytypingthefirstfewleZersfollowedbythe"TAB"key.ItisthedefaultshellonmostLinuxdistribu4onsandunlessotherwisespecifiedistheshellusedforthefutureexamples.
Ø Alltheshellshave$promptexceptcshellwith%prompt.
LinuxBasicsFileSystem:Ø Filesystemisthemethodsanddatastructuresthatanopera4ngsystemusesto
keeptrackoffilesonadiskorpar44onsothatdataretrievalisfast,easyandsecure.
Ø Disk/Par44oninlinuxcontainssuperblock,inode,datablock,directoryblockandindirectblock.§ Superblock:Itcontainsinforma4onaboutfilesystemasawhole.§ inode:Itcontainsinforma4onaboutafileexceptitsname.§ Directory:containsfilenameandinodenumber.§ Indirectblock:Usedaspointerstotheaddi4onalblocksallocatedwhenfilegrowsin
size.Ø InordertocreatethefilessystemfirstdiskneedtobeformaZedbyalloca4ng
cylindersandpar44oningitthenweini4atethedisk/par44onwiththefilesystem.Ø Toiden4fythefilesystemofapar44on:
$df–TinLinuxMountinunix.
LinuxBasicsØ Linuxsupportsseveraltypesoffilesystems.Belowarethemostimportantones:
• Minix:Oldest,Presumedtobethemostreliable,butwithlimitedfeaturesandcapabili4es.Maximumfilesizewas64MBandmaximumfilenamelengthwas14characters.
• Xia:Amodifiedversionofminixfilesystemwhichsupportsbiggerfilesystem.Maximumfilesizeas2GBandmaximumlengthforfilenameis248characters.
• UFS:IsalsocalledastheBerkeleyFastFileSystem,FFS.Maximumfilesizeis8ZBaswellasthemaximumvolumewithafilelengthof255characters.Fordirectorysearching,theinforma4onisstoredinatable.NewerUFSsupportsDirhash.Dirhashmakesahashofthedirectoriestoperformfastersearchesthanthenormallinearsearchdonewithatable.DirhashisstoredinRAMwhichisfasterthanaccessingthehashfromdisk.
• Ext:Na4vefilesystemwhichisrarelyusedinnewinstalla4ons.ItwaswriZenbyremycardtoaddress2limita4onsofMinix.Extsupportedfilesofsize2GB,filenamesupto255charactersandfilesystemofsize2GB.Exthadonlyone4mestampanduseoflinkedlistsforfreespacewhichledtofragmenta4onandpoorperformance.
• Ext2:isthedefaultfilesystemforlinuxun4lext3camealong.Ext2s4llisafavouredfilesystemforflashandUSBdrivesduetolackofjournaling.Itsupportsfilesizesupto2TBandfilesystemupto32TBdependingontheblocksize.Thedirectoryandfilestructureisnotindexed,sosearchinginadirectorywithlargenumberoffilescanbe4meconsuming.Filesanddirectoriesarestoredwithininodes.
LinuxBasics• Ext3:Ext3filesystemwhichhasheabilityforanin-placeupgradefromext2and
supportsthesizelimita4onasext2.ext3supportsjournalingwhichallowsafilesystemtorecoverunwriZendatafromimpropershutdown.Onlineresizingcanbeperformedforspaceaddi4ons.
• ext4:ext4uses48-bitaddressingsystemwhichallowsamaximumfilesizeof16TBandfilesystemsizeof1Exabyte.FilesstoredonanEXT4filesystemarestoredinExtents.Extentsreducesfragmenta4onandimprovesperformance.Bitmapsareusedtotrackusedandunusedblocks.ext4supportsmul4-blockalloca4on,delayedalloca4on,onlinefragmenta4onandpersistentprealloca4on.
• ISO9660:isthestandardfilesystemforCD-ROMs.OnfreeBSDitiscalledascd9660andhsfs(HighSierraFileSystem)insolaris.
• SwapFileSystem:Swapfilesystemistheloca4on/sonadiskthatareusedforvirtualmemorybyUNIX.
Ø CreaIngaFilesystem:FirstdiskneedstoformaZedusingfdisk(withop4onsn,p,star4ng#ofcylindertoending#ofcylinderanwtosavethepar44on).Secondweusemke2fstocreatefilesystem(mke2fs/dev/sda1forext2,mke2fs–j/dev/sa1forext3andmke2fs–text4/dev/sda1).
Ø TomountaparIIons/CDweuse:TomountaCDwemusemount-oloop-t1so9660/dev/sr0/media/
LinuxBasicsØ Files:Ingeneral,everythinginUNIXandLinuxisafile,althoughsomeofthesefiles
areabitspecial.Mostfiles,orregularfilesastheyarecalled,justcontainnormaldataliketext,programsorimages.Specialfilesinclude• Directories:filethatcontainlistsofotherfiles.• IOfiles:areusedforinputandoutputdevicesandareheldinthe/devdirectory• Links:arepointerfilesusedtomakeagivenfileordirectoryvisibleinadifferentpartof
thefiletree.• Domainsockets:communica4onsocketsthatprovideinter-processnetworking• Namedpipes:abitlikesocketsbuttheyprovideaneasierwayforinterprocesses
communica4on.• Filenamescanbeupto256characterslong,butarebestkeptreasonablyshorttomake
themmanageable.Ifyouusestandardextensionslike.exeor.txt,theneveryonewillknowwhatafiledoes
Ø Directories:Filesareorganizedintodirectoriestomakeiteasiertofindthings,andtokeepcommonfilesinacentralloca4on.Thelowestleveldirectoryistherootdirectory,denotedbya/(forwardslash).Anumberofsub-directorieswillexistbelowtheroot,Commonorstandardsubdirectoriesareshownasbelow:
LinuxBasics
LinuxBasicsØ Tologintomachine:
• InrealworldalltheserversarelocatedindatacentersandweneedtologintotheremoteserverusingSSH.
• PuZyismostcommonSSHu4lityusedtoconnecttoremoteserver.• Wehavetoprovidetheport#andservernametoconnecttotheserver.Wecanalso
savethesessioninforma4onforfuturelogins.
LinuxBasics• Oncethesessionopensitpromptsorusernameandpassword
• FromtheabovescreenshotyoucanobserveusingpuZywegetacommandline
interface.InordertogetagraphicaluserinterfaceortorunaGUItoolfrompuZywehavetoenablex11underSSHonleWcategorypane.
LinuxBasics• Oncethesessionopenswehavetoexportthedisplaytowindows(local)machineip-
addressandopentheu4litytoprojectasaGUI.Rememberwehavetoinstallx-windowssoWware'slikeexceed,x-MingorVNC-clientonthelocalwindowsmachine.
LinuxBasicsWhyLinux/Unixoverwindowsforservers:1.Stability
– Linuxsystemsarewellknownfortheirabilitytorunforyearswithoutfailure;infact,manyLinuxusershaveneverseenacrash.That'sgreatforusersofeverykind,butit'spar4cularlyvaluableforsmallandmedium-sizedbusinesses,forwhichdown4mecanhavedisastrousconsequences.
– LinuxalsohandlesalargenumberofprocessesrunningatoncemuchbeZerthanWindowsdoes--that'ssomething,infact,thattendstodegradeWindows'stabilityquickly.
– Thenthere'stheneedforreboo4ng.WhereasinWindowsconfigura4onchangestypicallyrequireareboot--causinginevitabledown4me--there'sgenerallynoneedtorestartLinux.AlmostallLinuxconfigura4onchangescanbedonewhilethesystemisrunningandwithoutaffec4ngunrelatedservices.
– Similarly,whereasWindowsserversmustoWenbedefragmentedfrequently,that'sallbuteliminatedonLinux.Letyourcompe4torsenduretheplen4fuldown4methatinevitablygoeshand-in-handwithWindows;trustyLinuxwillkeepyouupandrunningandservingyourcustomersaroundtheclock.
LinuxBasics2.Security
– Linuxisalsoinnatelymoresecurethanwindowis,whetherontheserver,thedesktoporinanembeddedenvironmentThat'sduelargelytothefactthatLinux,whichisbasedonUnix,wasdesignedfromthestarttobeamul4useropera4ngsystem.Onlytheadministrator,orrootuser,hasadministra4veprivileges,andfewerusersandapplica4onshavepermissiontoaccessthekerneloreachother.Thatkeepseverythingmodularandprotected.
– Ofcourse,LinuxalsogetsaZackedlessfrequentlybyvirusesandmalware,andvulnerabili4estendbefoundandfixedmorequicklybyitslegionsofdevelopersandusers.Eventhesix-year-oldkernelbugthatwasrecentlyfixed,forinstance--anextremelyrareinstanceintheLinuxworld--hadneverbeenexploited.
– Internally,meanwhile,usersofaWindowssystemcansome4meshidefilesfromthesystemadministrator.OnLinux,however,thesysadminalwayshasaclearviewofthefilesystemandisalwaysincontrol.
3.HardwareWhereasWindowstypicallyrequiresfrequenthardwareupgradestoaccommodateitsever-increasingresourcedemands,Linuxisslim,trim,flexibleandscalable,anditperformsadmirablyonjustaboutanycomputer,regardlessofprocessorormachinearchitecture.Linuxcanalsobeeasilyreconfiguredtoincludeonlytheservicesneededforyourbusiness'spurposes,thusfurtherreducingmemoryrequirements,improvingperformanceandkeepingthingsevensimpler.
LinuxBasics4.TCO
– There'snobea4ngLinux'stotalcostofownership,sincethesoWwareisgenerallyfree.EvenanenterpriseversionpurchasedwithcorporatesupportwillbecheaperoverallthanWindowsorotherproprietarysoWware,whichgenerallyinvolveuser-basedlicensingandahostofexpensiveadd-ons,especiallyforsecurity.
– Samegoesformostofthetoolsandapplica4onsthatmightbeusedonlinuxserver.TheoverallTCOsimplycan'tbebeat.
5.Freedom– WithLinux,thereisnocommercialvendortryingtolockyouintocertainproductsor
protocols.Instead,you'refreetomixandmatchandchoosewhatworksbestforyourbusiness.
– Inshort,withallthemanyadvantagesLinuxprovidesintheserverrealm,it'snowondergovernments,organiza4onsandmajorcompaniesaroundtheworld--includingAmazonandGoogle--relyontheopensourceopera4ngsystemintheirownproduc4onsystems.
LinuxBasics
