introduction to linux operating system basic information

Logging In and Logging Out, Anatomy of Linux OS, Directory
Structure, /usr Directory
File Types: User data files, System data files, Executable files. Naming
files and directories, Spawning Processes.
Shell: Creating User Account, Shell Program, bash shell, Changing shell
prompt.

1. B.Sc. Part II Semester IV
(Paper II)
LINUX OPERATING SYSTEM
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Dr. Dileep Sadhankar,
St. Francis De Sales College, Nagpur

2. UNIT -I :
LoggingInandLoggingOut,AnatomyofLinuxOS,Directory
Structure,/usrDirectory
FileTypes:Userdatafiles,Systemdatafiles,Executablefiles.Naming
filesanddirectories,SpawningProcesses.
Shell:CreatingUserAccount,ShellProgram,bashshell,Changingshell
prompt.
Commands:BasicSyntaxforacommand,ExploringtheHome
Directory,ls,mkdir,rmdir,stat,cat,rm,mv,cp
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Dr. Dileep Sadhankar, St. Francis De Sales
College, Nagpur

3. ExplaintheprocessoflogginginandloggingoutinLinuxoperatingsystem.
Whenwebootthesystem,loginpromptappearswherewehavetotypeauniquenamethat
identifiesasanauthorizeduseronthesystem.
DependingonthedistributioninstalledandhowtheXwindowsystemisset,thelogin
prompttakesvariousshapesandforms.
ifweinstalledLinuxMandrakeand
electednottostarttheXwindowsystem
whenthesystemboots,theloginprompt
andassociatedlateofinformationmight
lookasshownbelow:
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Dr. Dileep Sadhankar, St. Francis De Sales
College, Nagpur

4. INTRODUCTION
LinuxisaUnixclone.
Itcanrunon32/64bithardware.ItCanaddressupto64GBRAM.
Linuxistruemultitaskingenvironment.
LinuxwascreatedbyLinusTorvaldsin1991,andithasbeendeveloped
withthehelpofmanyprogrammersacrosstheInternet
ThesourcecodeforLinuxisfreelyavailabletoeveryone.
Ithasevolvedintoaveryfunctional,powerfulandusablecloneofUnix
whichhasatleast10millionusersworldwide.
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Dr. Dileep Sadhankar, St. Francis De Sales
College, Nagpur

5. 5
Dr. Dileep Sadhankar, St. Francis De Sales
College, Nagpur

6. Portable:LinuxoperatingsystemcanworkondifferenttypesofhardwareaswellasLinux
kernelsupportstheinstallationofanykindofhardwareplatform.
OpenSource:SourcecodeofLINUXoperatingsystemisfreelyavailable.
Multiuser:Linuxoperatingsystemisamultiusersystem,whichmeans,multipleuserscan
accessthesystemresourceslikeRAM,MemoryorApplicationprogramsatthesametime.
Multiprogramming:Linuxoperatingsystemisamultiprogrammingsystem,whichmeans
multipleapplicationscanrunatthesametime.
HierarchicalFileSystem:Linuxoperatingsystemaffordsastandardfilestructureinwhich
systemfilesoruserfilesarearranged.
Shell:Linuxoperatingsystemoffersaspecialinterpreterprogram,thatcanbeusedtoexecute
commandsoftheOS.Itcanbeusedtodoseveraltypesofoperationslikecallapplication
programs,andsoon.
Security:Linuxoperatingsystemoffersusersecuritysystemsusingauthenticationfeatureslike
encryptionofdataorpasswordprotectionorcontrolledaccesstoparticularfiles.
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Dr. Dileep Sadhankar, St. Francis De Sales
College, Nagpur

7. Why Linux?
1.ALinuxDistributionhasthousandsofdollarsworthofsoftwarefornocost.Fullsourcecode
isprovidedandfree.
2.Linuxisacompleteoperatingsystem:
1.stable-thecrashofanapplicationismuchlesslikelytobringdowntheOSunder
Linux.
2.Reliable-Linuxserversareoftenupforhundredsofdayscomparedwiththeregular
rebootsrequiredwithaWindowssystem.
3.extremelypowerful
3.Linuxprovidesacompletedevelopmentenvironment.
4.Excellentnetworkingfacilities
5.Idealenvironmenttorunserverssuchasawebserver,oranftpserver.
6.AwidevarietyofcommercialsoftwareisavailableifnotsatisfiedbythefreesoftwareEasily
upgradeable.
7.Supportsmultipleprocessors.
8.Truemulti-tasking,multi-userOS.
9.AnexcellentwindowsystemcalledX,theequivalentofWindowsbutmuchmoreflexible.
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Dr. Dileep Sadhankar, St. Francis De Sales
College, Nagpur

8. Loggingininvolvessupplyingausernameandapassword,whichLinuxverifiesto
determinewhethertheuserhastheauthoritytoaccessthecomputersystem.
Whentheloginscreenappears,firsttypetheusernameassignedandthenpress
enter.
Youwillbeaskedforthepassword.Noticethatyoudonotseethepasswordasyou
type.
Afteryouhavetypedpasswordpressenter.Nowyouarereadytostartexploring.
Theloginsessionforregularuseraccountisshownbelow:
localhost login: sfsuser1
Password :
[sfsuser1@localhost sfsuser1]$
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Dr. Dileep Sadhankar, St. Francis De Sales
College, Nagpur

9. Logginginasthesuperuser.
Thesuperuserhasunrestrictedaccesstotheentireoperatingsystem(hehasaccessto
everyfileandeverycommand).Onlythesuperusercanchangethesystemsetupand
configuration.
Therearetwowaystoworkasthesuperuser.
1)Logintotherootaccountdirectly.Thatistypetheusernamerootandthengivethe
passwordfortherootaccount
2)Temporarilyswitchtothesuperuseraccountwhileworkinginuseraccount.This
involvesexecutingSucommand
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Dr. Dileep Sadhankar, St. Francis De Sales
College, Nagpur

10. Exploring the Login process
Following are the steps to log in to the superuser account and your unprivileged user account.
1)Access the superuser account. At the login prompt type root and press enter. The password prompt
will appear.
2)Type the root password and press enter. The shell prompt for the root user account displays as
shown below:
[root @localhost root/ #
3)Change to a different console press Alt + F2.
4)To access your user account. At the login prompt, type the username for the unprivileged user
account and press Enter. You, will be asked for the account's password. Type the password and
press Enter
5)Temporarily change to the superuser account from the unprivileged user account. Type Su and
press Enter. You will be asked for the password for the root user account. Type the password and
press Enter. The shell prompt will look like:
[root@localhost root]#
6)Exit the superuser account: Type exit and press enter. You will be returned to your user account
and the shell prompt look like:
[sfsuser1@localhost sfsuser1]$ 10
Dr. Dileep Sadhankar, St. Francis De Sales
College, Nagpur

11. Shuttingdownthesystem
Shuttingdownthesystemisajobforthesystemadministratorbecausethe
shutdowncommandcanbeexecutedonlybythesuperuseraccountfollowingare
thestepstoturnoffthecomputer.
1)Logoutofuseraccount.TypelogoutandpressEnter.
2)ReturntotheconsolewheretherootuserisloggedinpressAlt+F1.
3)Terminatethesession:Typeshutdown-hnowandpressEnter.Thesystem
willgothroughtheshutdownprocessandwillturnoffservicesandunmount
devices.
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Dr. Dileep Sadhankar, St. Francis De Sales
College, Nagpur

12. ThecenteroftheLinux
operatingsystemisthekernel.
Thekernelisapieceofsoftware
thatprovidesaninterface
betweenuser,thecomputer
hardware,and attached
peripherals.Thekernelis
responsibleformaintainingthe
filesystem, executing
commands,startingprograms,
timingsystemactivitiesand
managingsystemmemoryand
otherresources.Thefollowing
Figureshowshowthedifferent
partsofthekernelworktogether
Figure. The kernel uses several tools to help it run the operating system.
AnatomyOfTheLinuxOperatingSystem
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Dr. Dileep Sadhankar, St. Francis De Sales
College, Nagpur

13. Thekernelgivesinstructionstothesystemusingsystemcalls.
Systemcallsarecommunicationsbetweenthekernelandthedevicesit
manages,whichdirecttheperformanceofactionsrequestedbycommands
itreceivesfrominternalsystemprocessesorrunningapplications,orare
passedfromtheshell.
Thesearethevehiclesusedbythekerneltoexecuteshellcommands.The
systemcallscoordinatetheactivitiesofthekerneltoproducetheoutputfor
acommandthathasbeenexecutedbythesystemuser.
Mostimportantjobthekernelmanagethecomputer'smemoryresources.
Thememoryresourcesarerequiredtostartprocessesthatactivatedevices
andservicesandcausethecomputersystemtoperformitsjob.Allthese
happeningsaremanagedthroughthefilesystem.
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Dr. Dileep Sadhankar, St. Francis De Sales
College, Nagpur

14. Linux Directory Structure
(File System Structure)
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Dr. Dileep Sadhankar, St. Francis De Sales
College, Nagpur

15. 1./(RootDirectory):EverythingonyourLinuxsystemislocatedunderthe/directory,
knownastherootdirectory..Onlyrootuserhaswriteprivilegeunderthisdirectory.
Pleasenotethat/rootisrootuser’shomedirectory,whichisnotsameas/.
2./bin(UserBinariesorprograms):Containsbinaryexecutables.CommonLinux
commandsyouneedtouseinsingle-usermodesarelocatedunderthisdirectory.
Commandsusedbyalltheusersofthesystemarelocatedhere.Forexample:ps,ls,
ping,grep,cp.
3./sbin(SystemBinaries):Justlike/bin,/sbinalsocontainsbinaryexecutables.But,the
linuxcommandslocatedunderthisdirectoryareusedtypicallybysystemaministrator,
forsystemmaintenancepurpose.Forexample:iptables,reboot,fdisk,ifconfig,swapon
4./etc(ConfigurationFiles):Containsconfigurationfilesrequiredbyallprograms.This
alsocontainsstartupandshutdownshellscriptsusedtostart/stopindividualprograms.
Forexample:/etc/resolv.conf,/etc/logrotate.conf
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Dr. Dileep Sadhankar, St. Francis De Sales
College, Nagpur

16. 5./dev(DeviceFiles):Linuxexposesdevicesasfiles,andthe/devdirectorycontainsa
numberofspecialfilesthatrepresentdevices.Theseincludeterminaldevices,usb,orany
deviceattachedtothesystem.Forexample:/dev/tty1,/dev/usbmon0
6./proc(ProcessInformation):Containsinformationaboutsystemprocess.Thisisa
pseudofilesystemcontainsinformationaboutrunningprocess.Forexample:/proc/{pid}
directorycontainsinformationabouttheprocesswiththatparticularpid.Thisisavirtual
filesystemwithtextinformationaboutsystemresources.Forexample:/proc/uptime
7./var(VariableFiles):varstandsforvariablefiles.Contentofthefilesthatareexpectedto
growcanbefoundunderthisdirectory.Thisincludes—systemlogfiles(/var/log);
packagesanddatabasefiles(/var/lib);emails(/var/mail);printqueues(/var/spool);lock
files(/var/lock);tempfilesneededacrossreboots(/var/tmp);
8./tmp(TemporaryFiles):Directorythatcontainstemporaryfilescreatedbysystemand
users.Filesunderthisdirectoryaredeletedwhensystemisrebooted.
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Dr. Dileep Sadhankar, St. Francis De Sales
College, Nagpur

17. 9./usr(UserPrograms):Containsbinaries,libraries,documentation,andsource-codefor
secondlevelprograms./usr/bincontainsbinaryfilesforuserprograms.Ifcan’tfinda
userbinaryunder/bin,lookunder/usr/bin.Forexample:at,awk,cc,less,scp./usr/sbin
containsbinaryfilesforsystemadministrators.Ifcan’tfindasystembinaryunder/sbin,
lookunder/usr/sbin.Forexample:atd,cron,sshd,useradd,userdel./usr/libcontains
librariesfor/usr/binand/usr/sbin./usr/localcontainsusersprogramsthatyouinstall
fromsource.Forexample,whenyouinstallapachefromsource,itgoesunder
/usr/local/apache2
10./home(HomeDirectories):Homedirectoriesforalluserstostoretheirpersonalfiles.
Forexample:/home/john,/home/nikita
11./boot(BootLoaderFiles):The/bootdirectorycontainsthefilesneededtobootthe
system.Kernelinitrd,vmlinux,grubfilesarelocatedunder/boot.Forexample:
initrd.img-2.6.32-24-generic,vmlinuz-2.6.32-24-generic
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Dr. Dileep Sadhankar, St. Francis De Sales
College, Nagpur

18. 12./lib(SystemLibraries):Containslibraryfilesthatsupportsthebinarieslocatedunder/bin
and/sbin.Libraryfilenamesareeitherld*orlib*.so.*Forexample:ld-2.11.1.so,
libncurses.so.5.7
13./opt(Optionaladd-onApplications):optstandsforoptional.Containsadd-on
applicationsfromindividualvendors.add-onapplicationsshouldbeinstalledundereither
/opt/or/opt/sub-directory.
14./mnt(MountDirectory):Temporarymountdirectorywheresysadminscanmount
filesystems.
15./media(RemovableMediaDevices):The/mediadirectorycontainssubdirectorieswhere
removablemediadevicesinsertedintothecomputeraremounted.Forexamples,
/media/cdromforCD-ROM;/media/floppyforfloppydrives;/media/cdrecorderforCD
writer
16./srv(ServiceData):srvstandsforservice.Containsserverspecificservicesrelateddata.
Forexample,/srv/cvscontainsCVSrelateddata.
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Dr. Dileep Sadhankar, St. Francis De Sales
College, Nagpur

19. Types of Files in Linux
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Dr. Dileep Sadhankar, St. Francis De Sales
College, Nagpur

20. Linuxcontainsmanyfiles,eachfilledwithdifferentinformation.
Mainlytherearethreetypesoffiles:
Userdatafiles
Systemdatafiles
Executablefiles
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Dr. Dileep Sadhankar, St. Francis De Sales
College, Nagpur

21. Userdatafiles:Thesefilesarecreatedbytheuserandusuallycontainsimple
datamadeupoftextandnumbers.Filessuchas.txtfilescanbereadwitha
texteditor.Butthemorecomplexfiles,suchasthefileswhichusercreatewith
graphicsorspreadsheetprogramsrequiresaviewerorinterpreterprogramto
displaythem.
Systemdatafiles:Thesefilesareusedbytheoperatingsystemtokeeptrackof
userpasswords,logins,filepermissions,andotherthingspertainingtokeeping
thesystemrunningsmoothly.
Executablefiles:Thesefilescontaintheinstructionsthattellthecomputer
whattodo.Thesefilesareusuallycalledprograms.Whentheusergivethe
commandtothecomputer,thismeansusertellingittofollowtheinstructions
inanexecutablefile.
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Dr. Dileep Sadhankar, St. Francis De Sales
College, Nagpur

22. RulesfornamingfilesanddirectoriesinLinuxoperatingsystem
•Anysystemconfigurationfilesthatusermayeditandanyapplicationprogramsthat
usermayinstallareassignednamesandaplacewheretheyliveinthesystem.
•Userworkwiththeseapplicationsandcanaddnewfilestothefilesystemforthe
letters,reports,spreadsheets,webpagesandpicturesthathecreate.
•Tosaveadocumentforthefirsttimeuserneedstoselectadirectoryinthefile
systeminwhichtostorethefileandgivethefileaname.
Followingarethedifferentrulestostorefilesanddirectoriesintherightplace
andnamingthem.
1)Afilenameshouldnotexceed256characters.Itisnotjustthenameofthe
individualfile,itincludesthedirectorypaththatleadstothefile.Forex:The
individualfilenamedpicture.jpgthatislocatedinthe/home/sfs/images
directory.Theactualfilenameis,/home/sfs/images/picture.jpgis28characters
long. 22
Dr. Dileep Sadhankar, St. Francis De Sales
College, Nagpur

23. 2)Uppercaseletters(AtoZ),lowercaseletters(atoz)oranynumber(0-9)
canbeusedwhencreatingafilename.Dash(-),underscore(_)anddot
(.)canalsobeusedinfilename.
3)Donotputaspaceinthefilename.Avoidthefollowingusecharactersthat
cancauseproblemsinfilenames.
<,>,',“,#,* , | ,:, ( , ) ,^,!,\, & , ? , ^ , ~
4)Tocreatehiddenfiles,beginthefilenamewithaperiod(.).Forex:
.diary.txt
5)Typecat>practiceandpressEntertocreateafilenamedpractice.The
cursorwillmovetothenextlineonthescreen.Typefewwordsandpress
Entertomovetothenextlinepressctrl+Dtosaveandclosethefile.
6)TypecatpracticeandpressEntertoreadthefileyoujustcreated.
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Dr. Dileep Sadhankar, St. Francis De Sales
College, Nagpur

24. SPAWNINGPROCESSES
Spawnincomputingreferstoafunctionthatloadsandexecutesanew
childprocess.Thecurrentprocessmaywaitforthechildtoterminateormay
continuetoexecuteconcurrentcomputing.Creatinganewsub-process
requiresenoughmemoryinwhichboththechildprocessandthecurrent
programcanexecute.
Linuxdefinesrunningprograms,applications,utilitiesanddaemons(servers)
asprocesses.Itmaintainsavirtualfilesysteminthe/procdirectory,where
thepointerstoalltheongoingprocessesinthesystemaremaintained.
Linuxisatruemultitaskingoperatingsystem(canperformmorethanone
thingatatime).Toaccomplishthis,theLinuxkerneljustcallsupafew
daemons,andthedaemonstakeoverandperformthejob.
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Dr. Dileep Sadhankar, St. Francis De Sales
College, Nagpur

25. SPAWNINGPROCESSES
Whileaprocessisrunning,itcanspawnotherprocesses.Spawningis
accomplishedthroughtheuseofasystemcall,fork.Systemcallsare
clearlydefined,directentrypointsintothekernelthroughwhichprocesses
requestservicesfromthekernel.
Thefirststepinspawninganewprocessisforanexistingprocesstocreate
anidenticalwayofitself.Thiscopyisthentransferredintothenew
process,anditinturn,cancreateadditionalprocesses,therebyresultingon
multiplegenerationsofprocesses.(i.e.parentprocessesspawnchildren
processeswhichthenspawnsgrandchildrenprocesses).
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Dr. Dileep Sadhankar, St. Francis De Sales
College, Nagpur

26. Whatisshellprogram?
AshellprogramistheuserinterfacetothecomputersystemfortheLinux
operatingsystem.Thisinterfaceacceptscommandsfromtheuserand
translatesitintoalanguagethattheoperatingsystemcanunderstand.
Theshellcanalsobeusedtowriteprograms,automatejobcontrol,and
provideascriptingmechanismtocustomizethewaythesystemworks.
ShellprogramisoneofthemostimportantprogramsinstalledontheLinux
system.
Thefollowingfigureillustrateshowtheprocessoperatesusingshell.
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Dr. Dileep Sadhankar, St. Francis De Sales
College, Nagpur

27. 27
Dr. Dileep Sadhankar, St. Francis De Sales
College, Nagpur

28. Whatisbashshell?Explain.
Theshellisaprogramthattakescommandsfromthekeyboardandgives
themtotheoperatingsystemtoperform.
Bash(BourneAgainShell)isthefreeversionoftheBourne
shelldistributedwithLinuxandGNUoperatingsystems.Thebashshellis
themostwidelyusedshellinLinux.
Createdtoimproveontheearliershshell,Bashincludesfeaturesfrom
theKornshellandtheCshell.
Itoffersfunctionalimprovementsovershforbothinteractiveand
programminguse.
ThebashshellworksliketheBourneshell(sh).Thereisasymboliclink,in
the/bindirectoryofshthatpointstothebashshell.
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Dr. Dileep Sadhankar, St. Francis De Sales
College, Nagpur

29. Explaintheprocessofrunningthebashshell.
Followingarethestepstostartorrunthebashshell.
1)Displaytheshellyouareusing.ThisinformationisfoundintheSHELL
environmentvariable.
Typeecho$SHELLandpressEnter
Ifyouareusingbashshellthesystemwilldisplaythefollowing.
[sfsuser1@localhost/sfsuser1]$echo$SHELL
/bin/bash
[sfsuser1@localhost/sfsuser1]$
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Dr. Dileep Sadhankar, St. Francis De Sales
College, Nagpur

30. 2)Ifyouarenotusingbash,changetothebashshell.TypebashandpressEnter.
3)Ifyouwantbashtobethedefaultshell,typechsh-5/bin/bashandpressEnter.
4)Displaythebashhelpfunction.Typehelpandpressenter.Thehelpcommand
listsallthecommandsthatarebuiltintotheshell.
[sfsuser1@localhost/sfsuser1]$helpandpressenter
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Dr. Dileep Sadhankar, St. Francis De Sales
College, Nagpur

31. Whatisshellprompt?Explain.
Theshellprompt(orcommandline)iswhereonetypescommands.When
accessingthesystemthroughatext-basedterminal,theshellisthemain
wayofaccessingprogramsanddoingworkonthesystem.Theshell
keepstrackoftheworkthatisperformedonthecomputer.
Theprompt,$,whichiscalledthecommandprompt,isissuedbythe
shell.Whilethepromptisdisplayed,youcantypeacommand.
ShellreadsyourinputafteryoupressEnter.
Thedefaultshellpromptisoftendifferentfordifferentdistributions.
Whenloggedinasroot(superuser)theshellpromptlookslike:
[root@localhostroot]#
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Dr. Dileep Sadhankar, St. Francis De Sales
College, Nagpur

32. $date ⏎
Thu Jun 25 08:30:19 MST 2009
You can customize your command prompt using the environment variable PS1
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Dr. Dileep Sadhankar, St. Francis De Sales
College, Nagpur

33. Explainthestepsofchangingtheshellprompt.
Theshellpromptcanbechangedtodisplayinformationsuchasthe
usernameforauser,thedirectoryinwhichtheuserisworking,the
currentdateandtime,oraspecialmessage.
Tochangetheshellpromptforcurrentloginsessionfollowthesteps
below:
1)Displaytheshellvariables:Attheshellprompt,typeprintenvand
pressEnter
2)Lookfortheps1variable:Theps1variableonaLinux-Mandrake
systemmightlookasfollows:
ps1=[\u@\h\w]\$
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Dr. Dileep Sadhankar, St. Francis De Sales
College, Nagpur

34. Thisvariabletellsthesystemtodisplaytheusernameforwheneverusing
thehostcomputerandthatuser'scurrentworkingdirectoryinside
bracketsfollowedbythe$prompt(or#promptforrootaccount).
3)Writedowntheinformationfromtheps1variable.
4)Changethepromptsothatitdisplaysthetime,thedate,thecurrent
workingdirectory,andthe$prompt.
Typeps1=“[\t\d\w]\$”andpressEnter.
Theshellpromptwillchangetodisplaythefollowing:
[09:55:33ThuFeb11sfsuser1]$
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Dr. Dileep Sadhankar, St. Francis De Sales
College, Nagpur

35. CharacterDescription
\! Displays the number used in the history list to access the command that will be
executed at the shell prompt.
\$ Displays a $ in the prompt for regular users and a # for the super user.
\\ Displays the backslash character
\d Display the current date.
\h Displays the hostname of the computer at which the user is working
\s Displays the name of the shell in which user
\t Display the current time
\u Displays the username of the user who is logged in to the system.
\w Displays the current working directory.
\xxx Displays any special comments (replace xxx with your text)
Following table shows the character codes that can be used to customize the shell prompt.
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Dr. Dileep Sadhankar, St. Francis De Sales
College, Nagpur

36. Whatiscommand?ExplainthebasicsyntaxforacommandLinux
operatingsystem.
ThecommandscanbeusedtomanagetheLinuxsystemandthesecommands
canbemodifiedtobehavetheway,theuserwant,alsocanbemodifiedto
performtasksinadditiontothedefaultactionsofthecommand.
Thesemodificationscantaketheformofacommandoption,aparameter,an
input/outputredirection,orapipe.
Afterdiscovering,howalltheseelementsworktogetheronthecommand
line,theusercanuseanyLinuxcommand
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Dr. Dileep Sadhankar, St. Francis De Sales
College, Nagpur

37. TheBasicsyntaxforacommand.
Followingisthebasicsyntaxforacommand.
Commandname-options[Parameter]
Commandistypedaftertheshellprompt.Toexecutethecommandpress
Enter.
Forex:ls-1/usr/doc
Thecommandusedinthisexampleisls,whichdisplaysafilelistforthe
contentsofthecurrentworkingdirectory.Thecommandoptionis-1,which
modifiestheinformationdisplayedabouteachfileinthelisting.The
parametertellsthecommandtolistthecontentsofthe/usr/docdirectory
insteadofcurrentworkingdirectory.
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Dr. Dileep Sadhankar, St. Francis De Sales
College, Nagpur

38. ExplainthestepsofcreatingtemporaryuseraccountinLinuxoperating
system.
WhentheLinuxisinstalled,asuperuser(orrootuser)accountandpossibly
oneunprivilegeduseraccountiscreated.
ButifduringtheinstallationofLinuxoperatingsystemanaccountfor
unprivilegeduseraccountisnotcreatedthenusethefollowingstepstocreateit.
1)Selecttheusername:Usernameshouldnotbemorethaneightcharacters.
Tomakethejobofthesystemadministratorsimpler,uselowercaseletters
forusername.Forex.:sfsuser1
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Dr. Dileep Sadhankar, St. Francis De Sales
College, Nagpur

39. 2)Choose password: A password should be at least eight characters long.
Use upper case letters, lowercase letters and numbers to create password.
3)Log in as superuser: Type username rootand press .Type password and
press Enter. The shell prompt for the superuser account appears shown
below..
[root@localhost/root]#
4)Create the user account: At the shell prompt, type adduser sfsuser1 and
press Enter. For ex:
[root@localhost/root]# adduser sfsuser1
[root@localhost/root]#
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Dr. Dileep Sadhankar, St. Francis De Sales
College, Nagpur

40. 5)Assign the password to the account: Type passwd sfsuser1 and press Enter.
[root@localhost/root]# passwd sfsuser1
Changing password for sfsuser1
Enter new password:
Type password and press Enter
The system displays the following message
Retype new password:
Passwd: all authentication tokens updated successfully
[root@localhost/root]#
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Dr. Dileep Sadhankar, St. Francis De Sales
College, Nagpur

41. 6)Switchtonewterminal:Insteadofloggingoutofthesuperuseraccountto
gettouseraccount,pressALT+F2todisplaynewterminalwindow.To
returntosuperuseraccountpressALT+F1.
7)Logintouseraccount:Attheloginprompttypeusernameandpress
Enter.TypethepasswordandpressEnter.Theshellpromptappearsas
shownbelow:
[sfsuser1@localhost/sfsuser1]$
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Dr. Dileep Sadhankar, St. Francis De Sales
College, Nagpur

42. Anatomy of Linux OS
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Dr. Dileep Sadhankar, St. Francis De Sales
College, Nagpur

43. Figure: Anatomy of Linux operating System
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Dr. Dileep Sadhankar, St. Francis De Sales
College, Nagpur

44. Linuxbasedsystemcomprisesofseveralparts.Theseare:
•TheKernel
•SystemLibraries
•CommandShellandcommandlineutilities
•GraphicalUserInterfaces
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Dr. Dileep Sadhankar, St. Francis De Sales
College, Nagpur

45. TheKernel:
Thekernelistheheartoftheoperatingsystem.
Linuxkerneliswhatiscalledasa“monolithickernel”,whichmeansthatallthe
corekernelfunctionsandanyhardwaredrivermodulesarebuildintoasingle
executablewhichisthenexecutedinwhatisknownas“kernelspace”,which
meansithasfullprivilegedaccesstotheunderlyinghardware.
TheLinuxkernelprovidesanabstractionofthehardware,alongwithasetof
operationsknownas“systemcalls”.
System Libraries:
•The“libraries”areacollectionofcomputercodethatprovideawayofdoing
commontasks,suchasreadingorwritingafromafile,oropeninganetwork
connection,andtheseareusedtomakeprogrammingsimplerandtoensurethatall
programswhichuseaparticularlibraryinterfacewiththekernelandother
programsthesameway.
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Dr. Dileep Sadhankar, St. Francis De Sales
College, Nagpur

46. CommandShellandcommandlineutilities
Theshellisaninterfacebetweentheuserandthekernel.Ittakescommandsfromthe
userandexecuteskernel’sfunctions.Thisincludesthingslikethingslikemountandun-
mountfilesystems,listandaccesscontentsofafilesystems,startandstopprocesses,
loadandunloadkerneldrivermodules,andmanyothertasks.
TheShellareclassifiedintotwotypes:commandlineshellsandgraphicalshells.The
commandlineshellsprovideacommandlineinterface,whilethegraphicallineshells
provideagraphicaluserinterface.Thoughbothshellsperformoperations,butthe
graphicaluserinterfaceshellsperformslowerthanthecommandlineinterfaceshells.
Typesofshellsareclassifiedintofour:
Kornshell
Bourneshell
Cshell
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Dr. Dileep Sadhankar, St. Francis De Sales
College, Nagpur

47. GraphicalUserInterfaces:
ThevariousgraphicaluserinterfacesthatarepossibleonasystemLinuxcomewitha
suiteofapplicationsandutilitiestomakethesystemlookmuchprettier,more
functional,orsimplyeasiertouse.
The“Xwindowssystem”isthemostcommonlyusedgraphicaluserinterfacesystem
providedbyvariousLinuxdistributions,anditismostcommonlyinstalledonLinux
baseddesktopsandlaptops.
47
Dr. Dileep Sadhankar, St. Francis De Sales
College, Nagpur

48. https://bellard.org/jslinux/vm.html?url=alpine-
x86.cfg&mem=192
48
Dr. Dileep Sadhankar, St. Francis De Sales
College, Nagpur