Apress automating UNIX and linux administration sep 2003 ISBN 1590592123

AutomatingUNIXandLinux
Administration
byKirkBauer
Apress©2003

ISBN:1590592123

Thisbookfocusesonautomatingthetedious
dailytasksofsystemadministration.It
providesreal-worldexamplesandexploresthe
toolsusefulformanaging2or5,000systems.
TableofContents
AutomatingUNIXandLinuxAdministration
Preface
Chapter1 - IntroducingtheBasicsofAutomation
UsingSSHtoSecurelyAutomateSystem
Chapter2 Administration
Chapter3 - CreatingLoginScriptsandShellScripts
Pre-Installation—NetworkPreparation
Chapter4 andManagement
Chapter5 - AutomatingandCustomizingInstallation
Chapter6 - AutomaticSystemConfiguration
Chapter7 - SharingDataBetweenSystems
Chapter8 - PackagesandPatches
Chapter9 - SystemMaintenanceandChanges
Chapter10 - SystemMonitoring
Chapter11 - ImprovingSystemSecurity
Chapter12 - BackingUpandRestoringData
Chapter13 - UserInterfaces
AppendixA - IntroductiontoBasicTools

AppendixB - CustomizingandAutomatingRedHat
LinuxInstallation
BuildingRedHatPackageManager(RPM)
AppendixC Packages
Index
ListofFigures
ListofTables
ListofSidebars


BackCover
Wouldn’tyouliketoautomatethetediousdailytasks
ofsystemadministration?AutomatingUNIXandLinux
Administrationwillshowyouhow,byexploringexisting
toolsandofferingreal-worldexamples.Partsofthe
bookareLinux-specific,butmostofitappliestoa
UNIXsystem,includingmultiplevariantsofUNIX.
AuthorKirkBauerbrieflyoverviewstoolsand
technologies—andassumespreliminaryknowledge
abouteditingaconfigurationfileormountingafile
system.
Thetechniques,methods,andtoolsinthisbookwill
helpyoumanageasinglesystem—butwillprove
especiallypowerfulacrossmultiplesystems.Nomatter
ifthesystemsaredesktops,servers,orBeowulf
clusters—allofthemwillbenefitfromthisautomation.
Andmanagingfivetofivethousandsystemswill
becomeasimplertask!
AbouttheAuthor

KirkBauerhasbeeninvolvedincomputer
programmingsince1985.Hehasbeenusingand
administeringUNIXsystemssince1994.Althoughhis
personalfavoriteUNIXvariantisLinux,hehas
administeredanddevelopedoneverythingfrom
FreeBSDtoSolaris,AIX,andIRIX.Heistheauthorof
variousopen-sourcesystemadministrationprograms
suchasAutoRPMandLogwatch.
Bauerhasbeeninvolvedwithsoftwaredevelopment
andsystem/networkadministrationsincehisfirstyear


atGeorgiaTech.HehasdoneworkfortheGeorgia
TechResidentialNetwork,theGeorgiaTechResearch
Institute,andtheFermiNationalAccelerator
Laboratory.Bauerwasoneofthefoundersandthe
CTOofTogetherWebin2000,whichwaspurchasedin
2003byProficientSystems.Heiscurrentlyasoftware
architectwithProficientSystems,andcontinuesto
supportanddevelopthecollaborativebrowsing
softwareandLinux-basednetworkappliancecreated
byTogetherWeb,includingC++serversoftwarethat
provideshighscalability,highefficiency,andhigh
reliability.
KirkgraduatedfromGeorgiaTechin2001witha
bachelor’sdegreeincomputerengineering.Shortly
thereafter,hebeganworkonhisfirstbook,
AutomatingUNIXandLinuxAdministration,whichwas
publishedbyApressinSeptember2003.

AutomatingUNIXandLinuxAdministration
KirkBauer
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Copyright©2003KirkBauer
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TechnicalReviewers:NateCampi,ErikMelander,AlfWachsmann
EditorialBoard:DanAppleman,CraigBerry,GaryCornell,TonyDavis,
StevenRycroft,JulianSkinner,MartinStreicher,JimSumser,Karen
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becauseddirectlyorindirectlybytheinformationcontainedinthiswork.
Thesourcecodeforthisbookisavailabletoreadersat
intheDownloadssection.
Tomyparents,especiallymyfather,whostartedandsupportedmy
interestincomputers,andmylovingwifeAmber,whohassupported
methroughoutthisprocess.
AbouttheAuthor
KirkBauerhasbeenusingcomputersandprogrammingsince1985.He
hasbeenusingandadministeringUNIXsystemssince1994.Although
hispersonalfavoriteUNIXvariantisLinux,hehasadministered
everythingfromFreeBSDtoSolaris,AIX,andIRIX.
Kirkhasbeeninvolvedwithsoftwaredevelopmentandsystem/network
administrationsincehisfirstyearatGeorgiaTech.Hehasdoneworkfor
theGeorgiaTechResidentialNetwork,theGeorgiaTechResearch
Institute,andtheFermiNationalAcceleratorLaboratory.Kirkwasoneof

thefoundersandtheCTOofTogetherWebin2000,whichwas
purchasedin2003byProficientSystems.Kirkiscurrentlyasoftware


architectwithProficientSystemsandcontinuestosupportanddevelop
thecollaborativebrowsingsoftwareandLinux-basednetworkappliance
createdbyTogetherWeb.
Kirk'slatestdevelopmentisafullyautomatedinstallation,configuration,
management,andmonitoringsystemthatisusedtodeployProficient's
softwareonRLXServerBlades.Savingtimethroughautomationhas
alwaysbeenhispassion,asevidencedbyhiscollectionofopen-source
software—themostpopularbeingAutoRPMandLogwatch.
ShortlyaftergraduatingfromGeorgiaTechin2002withabachelor'sof
scienceinComputerEngineering,KirkmarriedAmber,theloveofhislife.
TheycurrentlyliveinPeoria,AZwiththeirtwodogsandfourcats.When
notusingacomputer,Kirkcanbefoundinvolvedinoneofhismany
hobbies.Kirkenjoysreading,playingstrategygames,takingpictures,
andwatchingmovies.Helikestosnowski,waterski,andscubadive
whenhegetstheopportunity.Skydivingishisfavoritesport—Kirkhas
madeover1,400jumpstodate.
AbouttheTechnicalReviewers
NateCampiisaUNIXandnetworkadministratorinSiliconValley.Heis
currentlyemployedata(Linux-based)networkappliancevendor,running
allaspectsoftheirinternalIT,helpingguidedevelopmentofproducts,
anddesigningDNSarchitecturesforcustomers.
Pastjobsincludepostmaster,hostmaster,andwebmasterdutiesatTerra
Lycos,UNIXandnetworkadministratoratseveralSiliconValleyweb
hostingcompanies,andatourasahospitalcorpsmanintheUSNavy.
WhileintheNavy,Natedevelopedaloveofteachingasainstructorfor
basicandadvancedlifesupport,andalsopediatricadvancedlifesupport

fortheAmericanHeartAssociation.
Heismarried,hasasonandadaughter,livesintheSanFranciscoEast
Bay,anddreamsofonedayowningahomeinthearea.
ErikMelander,ManagingArchitectofCentralSystemsatWyndham
International,hasadecadeofexperiencewithUNIXsystems,including
timeworkingwiththeUniversityofMinnesotaandIBMGlobalServices.


Currently,heisevolvingWyndham'sITinfrastructuretorealizeashared
visionofautonomiccomputing.
AlfWachsmannholdsadoctorateofnaturalscienceinComputer
SciencefromtheUniversityofPaderborninGermany.Hewrotehis
thesisaboutparallelanddistributedcomputing.
HethenworkedatDESY,Germany'snationalhigh-energyphysicslab,
wherehelearnedsystemsoftwareprogrammingandsystem
administrationinaveryheterogeneousUNIXenvironment.Hisspecialty
becameautomation.
WachsmannthenmovedfromGermanytotheSanFranciscoBayarea,
wherehenowworksattheStanfordLinearAcceleratorCenter,asite
withfewerUNIXversionsbutwithalotmorecomputers.Hismainfocus
isagainautomatingsystemadministrationandsysteminfrastructure
tasks.
OtherprofessionalinterestsincludetheOpenAFSfilesystemand
Kerberos5authentication.
Acknowledgments
IhaveusedcomputerssinceIwasveryyoungandhavealwaysloved
them,thanksinlargeparttothesupportofmyparentsthroughoutmy
childhood.Theyhavealwayshelpedmelearnandhavesupportedmein
whateverIwantedtodo.Ihavetoparticularlythankmyfatherwho,much
tomyMom'schagrin,camehomeonedaywithmyveryfirstcomputer—

aCommodoreVic20.Mylifewasneverthesameafterthat.
Ialsothankmylovelywife,Amber,whohassharedmewiththisbookfor
many,manymonths.Shehasbeensupportiveandunderstanding,even
thoughIstartedwritingthebookjustafterourhoneymoonwasover.
Inaddition,myfriendandcolleagueMosheJacobsonhasbeenvery
helpfulinthisprocess.Hequicklyansweredmymanyquestionsand
evendidsomeofthetechnicalreview.Hehelpedmakewritingthisbook
thelearningexperiencethatitwas.


Finally,ImustthankeverybodyatApressforhelpingmethroughmyfirst
book—especiallymyeditor,JimSumser,whohasstuckbymethrough
thislongandarduousprocess.


Preface
Admitit.Youarereadingthisbookbecauseyouarelazy.Lazysystem
administratorsarewonderfulpeople—whoelseiswillingtospendso
muchtimenowinordertodonothinglater?Wealldreamofwakingupin
themorning,grabbingthelaptopfromthebedsidetable,checkingour
email,andthenheadingofftothelakefortheday.
Usingthetechniquesinthisbook,youcangetclosertotheidealworldof
fullyautomatedsystemadministration.Althoughunexpectedthings
alwaysgowrong,wecanatleastdelegateallofthemundaneand
repetitivetaskstothecomputer(whosepurpose,ofcourse,wastomake
ourliveseasier).Iwillleaveituptoyoutoconvinceyourbossthatyou
onlyneedtocomeintoworkonedayperweek.


BenefitsofAutomation

Inmostcases,themotivationbehindautomationissavingtime.Weare
busypeopleandourtimeisvaluable.Wewouldratherwriteascriptto
addauserthanaddonemanuallyafewtimesaday.Wecanthentake
thattimewesaveandspenditdoingthingsthataren'taseasyto
automate(orthingsthataremuchmoreentertaining).Thereareother
benefitsofautomation,however,thatarenotquiteasapparent.
Inmanycases,automationallowsotherstodothingsthattheydon'thave
enoughdirectknowledgetodothemselves.Theseotherpeoplerange
frominexperiencedsystemadministratorsworkingunderyoutosupport
staffmanningthecorporatehelpdesk.Yourautomationmakes
everybody'slivesmucheasier.Theydon'thavetobotheryousomuch,
andyoudon'thavetoanswerthesamequestionseveryday.
Equallyimportantistheunintentionaldocumentationthatcanresultfrom
automation.Forexample,toaddanewaccount,youhavetoaddittothe
passwd,shadow,andgroupfiles,aswellascreateahomedirectory
onthefileserverandsetuptheautomounttables.Althoughyounormally
thoroughlydocumentandfollowstep-by-stepproceduresformostofyour
administrationtasks,yousomehowmanagetoneglectthisparticular
task.
Thisiswhereautomationisveryhelpful.Ifyouwriteascripttodoallof
thetasksrequiredtocreateauser,youhaveeffectivelywrittenastep-bystepguideexplaininghowtocreateanewaccount.Ifyouputsomegood
commentsinthescript,youhavedocumentedtheprocessaswell.The
scriptcomesinhandywhenyouhaven'taddedanewaccountforthree
months.Evenifthescriptisdatedandfailstooperatecorrectly,youstill
knowwhatwassupposedtohappenandthatitwassupposedtowork.
Insteadofhavingtore-createtheprocessfromscratch,youcanjust
tweakthescriptsothatitwillworkthistimeandthenext.


UsesforAutomationTechniques

Automationcanbebeneficialevenwhenitislimitedtoonesystem.
Regardlessofhowsimplethesystemisorhowlittleitdoes,menialtasks
stillneedtobedone,logsneedtobemonitored,andsoon.Ofcourse,
thebenefitsofautomationreallystarttooutweighthecostswhenitis
deployedacrossseveralsystems.
Managinghundredsoreventhousandsofmachinescanbefun.Itcan
alsobeanightmareifthingsarenotdoneright.Toavoidthisandreduce
yourfutureworkload,makesuretodothingscorrectlyfromthestart.
However,therearealsomanythingsyoucandotomakelifeeasierwhen
youaremanagingexistingsetsofmachines.Soevenifyoucan'tstart
fromscratch,youmaystillfindthisbookveryhelpful.Forexample,aswe
willdiscusslater,youcanusemethodstoautomaticallystandardize
machinesinyourexistingnetwork.
Ifyouaremanagingmorethanonemachine,youprobablythinkthatit
wouldbeniceifallofthemachineshadthesamehardware,operating
system,andsoftware.Sometimesthisispossible(ifyouareusing
Beowulfclusters,forinstance);usuallyitisnot(especiallyinasoftware
engineeringcompanywith1,000programmers).Thisbookdealswith
bothuniformandmixedUNIXenvironments.AlthoughtheexamplesI
useonlydirectlyapplytoLinuxandUNIXenvironments,youcanapply
theseideastoanysituation.


WhoWillBenefit?
Ihavewrittenthisbookfortheexperiencedsystemadministrator.This
doesn'tmeanthatyouhavetobeanexpert,itjustmeansthatyouneed
tohavealittleexperiencebeforeyouwillfindthisbookvaluable.For
instance,ifyoucan'trememberhowtomountafilesystemwithout
lookingitupinareferencemanual,thenthisbookmaybetooadvanced
foryou.

Inadditiontoassumingthatyoucanperformbasicsystemadministration
tasks,IassumethatyouarefamiliarwithbothPerland/orbashscripting.
Inaddition,Iexpectyoutounderstandbasicregularexpressionsyntax.
IfyouareastudentandarerunningaLinuxserver,thenthisbookcould
beforyou.IfyouhaveafewUNIXboxesatwork,thenyouwillprobably
findthisbookuseful.IfyouadministerafewUNIXworkstations,asetof
UNIXservers,awebfarm,oraBeowulfcluster,thenthisbookcouldbea
lifesaver.


TechniquesCovered
Youcantakeoneofthreeapproacheswhenyougotosolvethe
automationproblemsIpresentinthisbook:
Open-sourcesoftware:Open-sourcesolutionsexistformanyofthe
problemsIpresentinthisbook,butIdonotattempttocoverevery
opensourcesolutiontoeveryproblem.Instead,Icoverthemost
popularandmaturesoftwareineachcategory.SomeprogramsI
coverincludeGNUcfengine,Logwatch,Swatch,AutoRPM,and
NetSaint(whichiscurrentlybeingdevelopedasNagios).Thisbook
isnotacompleteinstructionmanualforanyofthissoftware,butit
doesprovideenoughinformationforyoutoconsiderandbeginto
usetheseprograms.
Customscriptsandsoftware:Anotherfocusofthisbookinvolves
customsolutions.WhyamIadvocatingcustomsolutionswhen
open-sourcesolutionsalreadyexist?I'mnot.Idefinitelyrecommend
thatyouuseexistingsolutionswhenpossible.However,thereare
manycasesinwhichexistingsolutionsaretoocomplicated,arenot
powerfulenough,oraretoorestrictiveforyourparticularneeds.In
addition,therearealsoplentyofareaswithinautomationwhere
existingsolutionsarehardtocomeby.Thisisusuallybecausethe

situationissignificantlydifferentineachcaseorthesolutionistoo
simpletoreleaseasaproduct.
Commercialsoftware:Idonotcovercommercialsoftwareinthis
book—notbecausethereisanythingwrongwiththesoftware,itis
justtoocostlyformanysituations(especiallywhenyouconsiderthe
consultingcoststypicallyassociatedwiththistypeofsoftware).In
addition,notenoughinformationisavailableonthecommercial
solutionsformetofullydiscussthemwithinthisbook.However,for
somesituationscommercialsoftwaremaybethebestsolutionandI
suggestthatyouconsideritifitfitsyourneeds.


ChapterSummary
Thebookbeginswithintroductorychaptersthatyoushouldbevery
familiarwithbeforeyoumoveontothemeatofthetext.Itthenproceeds
withonechapteroneachcoreareaofautomation.Eachchapterfully
discussestheareainquestion,describesbothexistingandcustom
solutionstoeachproblem,andprovidesnumerousexamples.
Chapter1:IntroducingtheBasicsofAutomationcoversthe
methodologybehindsystemadministration.automation.
Chapter2:UsingSSHtoSecurelyAutomateSystem
Administration
coversthebasicsofusingSecureShell(SSH),discussesSSH
securityconcerns,describeshowtosetuppasswordlessSSH,and
delvesintovariousotherrelatedtopics.
Chapter3:CreatingLoginScriptsandShellScriptsdiscusses
somemoreadvancedfeaturesofbashandhowyoucanusethemto
customizeyourprompt,createcommandaliases,enhancetab
completion,andotherwiseenhanceyourshellexperience.This
chapteralsoprovidesscriptsthatallowcommandstorunacross

multiplesystems.
Chapter4:Pre-Installation:NetworkPreparationand
Management
discussesthetasksyouneedtocompletetoaddanewsystemto
yournetworkandprovidesacustom,modularshellscriptyoucan
usetoautomatethesetasks.
Chapter5:AutomatingandCustomizingInstallationdiscusses
theoptionsavailabletoyouwhenyouwanttoautomaticallyperform
operatingsysteminstallations.Thischapteralsodiscussesyour
optionsforcustomizingyouroperatingsystemsandprovidesscripts
thatallowanewsystem(evenwithoutacustomoperatingsystem)to
quicklyandeasilyjoinyourautomationsystem.


Chapter6:AutomaticSystemConfigurationcoverstheautomatic
configurationallofthesystemsonyournetwork,regardlessofthe
operatingsystemstheyrunorthetaskstheyperform.Thischapter
providesbothacustomsolutionandacomprehensivediscussionof
<application>GNUcfengine</application>.
Chapter7:SharingDataBetweenSystemsdiscussesmany
methodsyoucanusetosharedataamongyourvarioussystems
andtalksaboutnetworkfilesystemssuchastheNetworkFile
System(NFS),NetworkInformationServices(NIS/NIS+),GNU
cfengine,rsync,ConcurrentVersioningSystem(CVS),andthe
HypertextTransferProtocol(HTTP)andtheFileTransferProtocol
(FTP)protocols.
Chapter8:PackagesandPatchesdiscussestheissuesinvolvedin
updatingmanysystems.ThischapteralsotalksaboutbothSolaris
andcustompatches,theRedHatPackageManager(RPM)and
Debianpackageformats,andacustompackagesolution.In

addition,itcoversautomaticpackageinstallationwithAutoRPMand
introducestheOpenPKGsystem,whichprovidespackagesthatcan
beinstalledonmanydifferentoperatingsystems.
Chapter9:SystemMaintenanceandChangescoversthevarious
maintenancetasksinherentinmostmodernoperatingsystems.This
includestimesynchronization,accountmanagement,logfile
rotation,andgeneralsystemcleanup.
Chapter10:SystemMonitoringintroducestechniquesfor
monitoringyoursystems.ThischapterpresentsLogwatchand
swatchforlogmonitoringandNetSaintfornetworkmonitoring.
Chapter11:ImprovingSystemSecuritydiscussestoolsthatcan
enhanceyoursystem'ssecuritywithminimalmaintenanceonyour
part.ThischapteralsoshowsyouhowtouseandconfigureTripwire,
howtocreateautomaticfirewallconfigurations,andhowtouseGNU
cfenginetoincreaseyoursystemandnetworksecurity.
Chapter12:BackingUpandRestoringDatapresentssimpleand
inexpensivesolutionsforautomaticallybackingupyoursystems'


data.
Chapter13:UserInterfacesshowsyouhowtocreateboth
console-andweb-baseduserinterfacesforyourautomationsystem
usingbash,Perl,andMason.
AppendixA:IntroductiontoBasicToolsprovidesabasic
introductiontothetoolsusedthroughoutthebookandprovidesa
goodstartingpointforunderstandingandutilizingtheexamples
presentedinthistext.Thisappendixcoversthefollowingtools:bash,
Perl,grep,sed,andawk.
AppendixB:CustomizingandAutomatingRedHatLinux
Installation

showsyouhowtoautomatetheinstallationofRedHatLinux.Also
thisappendixshowsyouhowtocreateyourowncustomLinux
distributionderivedfromRedHatLinux.
AppendixC:BuildingRedHatPackageManager(RPM)
Packageshousescomprehensiveinstructionsonhowtobuildyour
ownRPMs.


AdditionalResources
Theprocessofautomatingsystemadministrationcoversawiderangeof
topics.Throughoutthebook,Iwillsuggestadditionalreadingmaterial.
Also,thereareseveraladditionalbooksthatyouwillmostlikelyfind
helpfulandIwouldliketomentionthemhere:
UNIXSystemAdministrationHandbook(3rdEdition),byEvi
Nemeth,GarthSnyder,ScottSeebass,TrentR.Hein(Prentice
Hall,2000).Thisbookcoversalmostanythingyoueverwantedto
knowaboutUNIXsystemadministration.
PrinciplesofNetworkandSystemAdministration,byMark
Burgess(JohnWiley&Sons,2000).Thisbookdiscussesthe
theoryandprinciplesbehindgoodnetworkandsystem
administration.
UnixStorageManagement,byRayA.KampaandLydiaV.Bell
(Apress,2002).Thisbookcoverseverythingyoueverwantedto
knowaboutstoringdataonUNIXsystems.
LearningthebashShell,byCameronNewhamandBill
Rosenblatt(O'ReillyandAssociates,1998).Thisbookcoversthe
bashcommandshellaswellasbashshellscripting.
LearningPerl,byRandalL.SchwartzandTomPhoenix(O'Reilly
andAssociates,2001).Thisisthefirstplacetostartifyouwantto
learnPerl,averypowerfulscriptinglanguagethatisused

extensivelythroughoutthisbook.
ProgrammingPerl,byLarryWalletal.(O'ReillyandAssociates,
2000).ThismoreadvancedguidetoPerlprovidesextensive
referencematerial.
PerlforSystemAdministration,byDavidN.Blank-Edelman
(O'ReillyandAssociates,2000).YoualreadyknowweusePerl
extensivelyinthisbook.Bylookingatthetitle,youalsoprobably
knowthatthisbookisaboutautomatingsystemadministration.
Anyquestions?


PracticalUNIX&InternetSecurity,bySimsonGarfinkel,Alan
Schwartz,andGeneSpafford(O'ReillyandAssociates,2003).
Thisbookdiscussessecurity,whichshouldalwaysbeonyour
mind,especiallywhenyouautomatingsystemadministration.


ConventionsUsedinThisBook
Ihaveusedseveralspecialfontandformattingconventionsinthisbook.
Thissectionreviewstheseconventionsandhowtheyareapplied.
Herearesomeofthemostcommonformattingconventionsyouwill
comeacross:
Note Notescallattentiontoimportantissuesorinterestingfacts
aboutthegivensubject.
Tip Tipsprovideadditionalinformationaboutthesubjectthatyou
mayfinduseful.
Caution Cautionsservetoalertyouaboutpotentiallydangerousside
effectsyouractionsorthepresentedscriptsmaycause.
Warning Warningsprovideimportantinformationthatyoumustbe
awareofbeforeproceeding,suchaspotentiallyserious

sideeffects.
Sidebars
Sidebarsareusedtoprovidelargeramountsofrelatedinformation
thatyoumayormaynotbeinterestedinreading.

Thisbookcontainsalargenumberofprogramlistings.Sometimesthey
areshownasablockofcode:
#!/bin/bash
echo"hello,howareyou?"
Othertimestheymaybebrokenintosections.Imayfirstdefinea
function:
say_hello(){
echo"Hello,howareyou?"


}
andthenprovidethecodethatcallsthefunction:
case$0in
hello)
say_hello
;;
esac
Totrytheseexamples,youcandownloadthecodesamplesfromthe
DownloadssectionoftheApresswebsite().
Alternatively,youcancreateyourownscriptfilebycombiningthe
separatepartsofthescriptintoonefile,withtheproperinterpreter
declarationatthetop(suchas#!/bin/bash).
Finally,somecodelistingswillhavetheirlinesnumberedandsomeofthe
numberedlineswillbebold.Theselineswillbediscussedinmoredetail
afterthecode.Hereisanexample:

1#!/bin/bash
2
3echo"Hello,howareyou?"
Line1:Runthisusingbashastheinterpreter.
Line3:Outputthestringtostdoutusingtheechocommand.
Throughoutthebook,youwilloftenseeexamplesofcommandsbeing
runasfollows:
%./hello
echo"Hello,howareyou?"
Notethataconstant-widthfontisused,justlikeonaterminal.Anything
thatyoushouldtypeispresentedinbold.
Herearesomeofthemostcommonfontconventionsyouwillcome


across:
Monospaced:Monospacedfontisusedforavarietyofpurposesin
thisbook.Iuseittoidentifyliteralstrings,suchasHello,how
areyou?.IalsouseitforURLs(suchas),
commands(likegrep),filenames(/etc/passwd),andwithin
programlistings.
Bold:Boldisusedtoindicatesomethingthereaderorusershould
type,usuallyatacommandprompt.
Italics:Italicsisusedtoemphasissomethingortoindicatethata
termisbeingdefined.


We'dLiketoHearfromYou
Wehavegonethroughseveralstagesofproofreadinganderrorchecking
duringtheproductionofthisbookinanefforttoreducethenumberof
errors.Wehavealsotriedtomaketheexamplesandtheexplanationsas

clearaspossible.
Theremay,however,stillbeerrorsandunclearareasinthisbook.Ifyou
havequestionsorfindanyoftheseerrors,pleasefeelfreetocontactme
atYoucanalsovisittheApresswebsiteat
todownloadcodefromthebookandseeany
availableerrata.


Chapter1:IntroducingtheBasicsofAutomation


Overview
WhenIwasinhighschool,Igotmyfirstpart-timejobkeepingsomeof
theschool'scomputersrunning.Itwasgreat.Idideverythingbyhand.
Andsincetherewereonlytwoorthreecomputers,doingeverythingby
handwasn'tabigissue.Buteventhen,asthenumberofsystemsgrew
tofive,six,andfinallymorethanten,Irealizedjusthowmuchtimeyou
canspenddoingthesamethingsoverandoveragain.Thisishowmy
loveofautomationwasborn.
Inthischapteryouwilllearnthebasicsofautomatingsystem
administrationsothatyoucanbegintomakeyourlifeeasier—aswellas
thelivesofeverybodywhousesordependsonyoursystems.Thetopics
coveredinthisbookareapplicabletoawidevarietyofsituations.
Whetheryouhavethousandsofisolatedsystems(soldtoyour
customers,forexample),alargenumberofdiversemachines(alarge
companyoruniversitycampus),orjustafewserversinyourhomeor
smallbusiness,most,ifnotall,ofthetechniquescoveredwillsaveyou
timeandmakeyouabetteradministrator.
Throughoutthisbook,Ihaveassumedthatthereaderhasabasicsetof
UNIXskillsandsomepriorexperienceasasystemsadministrator.Iused

numeroustoolsthroughoutthebooktoprovideexampleautomation
solutions.Thesetoolsincludethefollowing:
Thebashshell
Perl
Regularexpressions
Thegrepcommand
ThesedStreamEditor
awk
Ifyouarenotveryfamiliarwithoneormoreofthesetools,Iurgeyouto