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CentOS7LinuxServerCookbookSecondEdition
TableofContents
CentOS7LinuxServerCookbookSecondEdition
Credits
AbouttheAuthors
AbouttheReviewer
www.PacktPub.com
Supportfiles,eBooks,discountoffers,andmore
WhySubscribe?
FreeAccessforPacktaccountholders
Preface
Whatthisbookcovers
Whatyouneedforthisbook
Whothisbookisfor
Sections
Gettingready
Howtodoit…
Howitworks…
There’smore…
Conventions
Readerfeedback
Customersupport
Errata
Piracy
Questions
1.InstallingCentOS
Introduction
DownloadingCentOSandconfirmingthechecksumonWindowsorOSX
Gettingready
Howtodoit…
Howitworks…
CreatingUSBinstallationmediaonWindowsorOSX
Gettingready
Howtodoit…
Howitworks…
PerforminganinstallationofCentOSusingthegraphicalinstaller
Gettingready
Howtodoit…
Howitworks…
RunninganetinstalloverHTTP
Gettingready
Howtodoit…
Howitworks…
InstallingCentOS7usingakickstartfile
Gettingready
Howtodoit…
Howitworks…
Gettingstartedandcustomisingthebootloader
Gettingready
Howtodoit…
Howitworks…
Troubleshootingthesysteminrescuemode
Gettingready
Howtodoit…
Reachingrescuemode
Accessingthefilesystem
Accessingthefilesystem
Re-installtheCentOSbootloader
Howitworks…
Updatingtheinstallationandenhancingtheminimalinstallwithadditionaladministrationanddevelopmenttools
Gettingready
Howtodoit…
Howitworks…
2.ConfiguringtheSystem
Introduction
Navigatingtextfileswithless
Gettingready
Howtodoit…
Howitworks…
IntroductiontoVim
Gettingready
Howtodoit…
Howitworks…
Speakingtherightlanguage
Gettingready
Howtodoit…
Howitworks…
There’smore…
SynchronizingthesystemclockwithNTPandthechronysuite
Gettingready
Howtodoit…
Howitworks…
There’smore…
Settingyourhostnameandresolvingthenetwork
Gettingready
Howtodoit…
Howitworks…
There’smore…
Buildingastaticnetworkconnection
Gettingready
Howtodoit…
Howitworks…
Becomingasuperuser
Gettingready
Howtodoit…
Howitworks…
Customizingyoursystembannersandmessages
Gettingready
Howtodoit…
Howitworks…
There’smore…
Primingthekernel
Gettingready
Howtodoit…
Howitworks…
There’smore…
3.ManagingtheSystem
Introduction
Knowingandmanagingyourbackgroundservices
Gettingready
Howtodoit…
Howitworks…
There’smore…
Troubleshootingbackgroundservices
Gettingready
Howtodoit…
Howitworks…
Trackingsystemresourceswithjournald
Gettingready
Howtodoit…
Howitworks…
Configuringjournaldtomakeitpersistent
Gettingready
Howtodoit…
Howitworks…
Managingusersandtheirgroups
Gettingready
Howtodoit…
Howitworks…
Schedulingtaskswithcron
Gettingready
Howtodoit…
Howitworks…
There’smore…
Synchronizingfilesanddoingmorewithrsync
Gettingready
Howtodoit…
Howitworks…
Maintainingbackupsandtakingsnapshots
Gettingready
Howtodoit…
Howitworks…
Monitoringimportantserverinfrastructure
Gettingready
Howtodoit…
Howitworks…
TakingcontrolwithGITandSubversion
Gettingready
Howtodoit…
Howitworks
There’smore…
4.ManagingPackageswithYUM
Introduction
UsingYUMtoupdatethesystem
Gettingready
Howtodoit…
Howitworks…
There’smore…
UsingYUMtosearchforpackages
Gettingready
Howtodoit…
Howitworks…
There’smore…
UsingYUMtoinstallpackages
Gettingready
Howtodoit…
Howitworks…
There’smore…
UsingYUMtoremovepackages
Gettingready
Howtodoit…
Howitworks…
KeepingYUMcleanandtidy
Gettingready
Howtodoit…
Howitworks…
There’smore…
Knowingyourpriorities
Gettingready
Howtodoit…
Howitworks…
Usingathird-partyrepository
Gettingready
Howtodoit…
Howitworks…
There’smore…
CreatingaYUMrepository
Gettingready
Howtodoit…
Howitworks…
There’smore…
WorkingwiththeRPMpackagemanager
Gettingready
Howtodoit…
Howitworks…
There’smore…
5.AdministeringtheFilesystem
Introduction
Creatingavirtualblockdevice
Gettingready
Howtodoit…
Howitworks…
There’smore…
Formattingandmountingafilesystem
Gettingready
Howtodoit…
Howitworks…
There’smore…
Usingdiskquotas
Gettingready
Howtodoit…
Enablinguserandgroupquotas
Enablingproject(directory)quotas
Howitworks…
There’smore…
Maintainingafilesystem
Gettingready
Howtodoit…
Howitworks…
There’smore…
Extendingthecapacityofthefilesystem
Gettingready
Howtodoit…
Howitworks…
6.ProvidingSecurity
Introduction
LockingdownremoteaccessandhardeningSSH
Gettingready
Howtodoit…
Howitworks…
There’smore…
ChangingtheSSHportnumberofyourserver
LimitingSSHaccessbyuserorgroup
Installingandconfiguringfail2ban
Gettingready
Howtodoit…
Howitworks…
Workingwithafirewall
Gettingready
Howtodoit…
Howitworks…
There’smore…
Forgingthefirewallrulesbyexample
Gettingready
Howtodoit…
Tochangeanexistingfirewalldservice(ssh)
Tocreateyourownnewservice
Howitworks…
There’smore…
Generatingself-signedcertificates
Gettingready
Howtodoit…
Howitworks…
There’smore…
UsingsecurealternativestoFTP
Gettingready
Howtodoit…
SecuringyourvsftpdserverwithSSL–FTPS
SecuringyourvsftpdserverusingSSH–SFTP
Howitworks…
There’smore…
7.BuildingaNetwork
Introduction
PrintingwithCUPS
Gettingready
Howtodoit…
Howitworks…
There’smore…
HowtoaddanetworkprintertotheCUPSserver
HowtosharealocalprintertotheCUPSserver
RunningaDHCPserver
Gettingready
Howtodoit…
Howitworks…
There’smore…
UsingWebDAVforfilesharing
Gettingready
Howtodoit…
Howitworks…
InstallingandconfiguringNFS
Gettingready
Howtodoit…
InstallingandconfiguringtheNFSserver
Creatinganexportshare
Howitworks…
WorkingwithNFS
Gettingready
Howtodoit…
Howitworks…
SecurelysharingresourceswithSamba
Gettingready
Howtodoit…
Howitworks…
There’smore…
8.WorkingwithFTP
Introduction
InstallingandconfiguringtheFTPservice
Gettingready
Howtodoit…
Howitworks…
There’smore…
WorkingwithvirtualFTPusers
Gettingready
Howtodoit…
Howitworks…
CustomizingtheFTPservice
Gettingready
Howtodoit…
Howitworks…
Troubleshootingusersandfiletransfers
Gettingready
Howtodoit…
Howitworks…
9.WorkingwithDomains
Introduction
Installingandconfiguringacaching-onlynameserver
Gettingready
Howtodoit…
Configuringacaching-onlyUnboundDNSserver
ConfiguringaforwardingonlyDNSserver
Howitworks…
There’smore…
Settingupanauthoritative-onlyDNSserver
Gettingready
Howtodoit…
Howitworks…
There’smore…
Creatinganintegratednameserversolution
Gettingready
Howtodoit…
Howitworks
There’smore…
Populatingthedomain
Gettingready
Howtodoit…
Howitworks…
Buildingasecondary(slave)DNSserver
Gettingready
Howtodoit…
ChangestotheprimaryDNSserver
ChangestothesecondaryDNSserver(s)
Howitworks…
10.WorkingwithDatabases
Introduction
InstallingaMariaDBdatabaseserver
Gettingready
Howtodoit…
Howitworks…
ManagingaMariaDBdatabase
Gettingready
Howtodoit…
Howitworks…
There’smore…
Reviewingandrevokingpermissionsordroppingauser
AllowingremoteaccesstoaMariaDBserver
Gettingready
Howtodoit…
Howitworks…
InstallingaPostgreSQLserverandmanagingadatabase
Gettingready
Howtodoit…
Howitworks…
There’smore…
ConfiguringremoteaccesstoPostgreSQL
Gettingready
Howtodoit…
Howitworks…
InstallingphpMyAdminandphpPgAdmin
Gettingready
Howtodoit…
InstallingandconfiguringphpMyAdmin
InstallingandconfiguringphpPgAdmin
Howitworks…
11.ProvidingMailServices
Introduction
Configuringadomain-widemailservicewithPostfix
Gettingready
Howtodoit…
Howitworks…
There’smore…
Changingane-mail’sappearingdomainname
UsingTLS-(SSL)encryptionforSMTPcommunication
ConfigureBINDtouseyournewmailserver
WorkingwithPostfix
Howtodoit…
ConnectingmailxtoaremoteMTA
Readingyourlocalmailsfromthemailbox
Howitworks…
DeliveringthemailwithDovecot
Gettingready
Howtodoit…
Howitworks…
There’smore…
Settingupe-mailsoftware
UsingFetchmail
Gettingready
Howtodoit…
Howitworks…
There’smore…
ConfiguringFetchmailwithgmail.comandoutlook.come-mailaccounts
AutomatingFetchmail
12.ProvidingWebServices
Introduction
InstallingApacheandservingwebpages
Gettingready
Howtodoit…
Howitworks…
Enablingsystemusersandbuildingpublishingdirectories
Gettingready
Howtodoit…
Howitworks…
Implementingname-basedhosting
Gettingready
Howtodoit…
Howitworks…
ImplementingCGIwithPerlandRuby
Gettingready
Howtodoit…
CreatingyourfirstPerlCGIscript
CreatingyourfirstRubyCGIscript
Howitworks…
There’smore…
Installing,configuring,andtestingPHP
Gettingready
Howtodoit…
Howtodoit…
SecuringApache
Gettingready
Howtodoit…
Configuringhttpd.conftoprovidebettersecurity
Removingunneededhttpdmodules
ProtectingyourApachefiles
Howitworks…
SettingupHTTPSwithSecureSocketsLayer(SSL)
Gettingready
Howtodoit…
Howitworks…
There’smore…
13.OperatingSystem-LevelVirtualization
Introduction
InstallingandconfiguringDocker
Gettingready
Howtodoit…
Howitworks…
Downloadinganimageandrunningacontainer
Gettingready
Howtodoit…
Howitworks…
There’smore…
Stoppingandstartingacontainer
Attachingandinteractingwithyourcontainer
CreatingyourownimagesfromDockerfilesanduploadingtoDockerHub
Gettingready
Howtodoit…
UploadingyourimagetotheDockerHub
Howitworks…
SettingupandworkingwithaprivateDockerregistry
Gettingready
Howtodoit…
StepstobedoneonourDockerregistryserver(192.168.1.100)
Stepstobedoneoneveryclientneedingaccesstoourregistry
Howitworks…
14.WorkingwithSELinux
Introduction
InstallingandconfiguringimportantSELinuxtools
Gettingready
Howtodoit…
Howitworks…
There’smore…
WorkingwithSELinuxsecuritycontexts
Gettingready
Howtodoit…
Howitworks…
Workingwithpolicies
Gettingready
Howtodoit…
Howitworks…
There’smore…
TroubleshootingSELinux
Gettingready
Howtodoit…
Howitworks…
15.MonitoringITInfrastructure
Introduction
InstallingandconfiguringNagiosCore
Gettingready
Howtodoit…
Howitworks…
SettingupNRPEonremoteclienthosts
Gettingready
Howtodoit…
Howitworks…
Monitoringimportantremotesystemmetrics
Gettingready
Howtodoit…
Howitworks…
Index
CentOS7LinuxServerCookbookSecondEdition
CentOS7LinuxServerCookbookSecondEditionCopyright©2016PacktPublishing
Allrightsreserved.Nopartofthisbookmaybereproduced,storedinaretrievalsystem,ortransmittedinanyformorbyanymeans,withoutthepriorwrittenpermissionofthepublisher,exceptinthecaseofbriefquotationsembeddedincriticalarticlesorreviews.
Everyefforthasbeenmadeinthepreparationofthisbooktoensuretheaccuracyoftheinformationpresented.However,theinformationcontainedinthisbookissoldwithoutwarranty,eitherexpressorimplied.NeithertheauthornorPacktPublishing,anditsdealersanddistributorswillbeheldliableforanydamagescausedorallegedtobecauseddirectlyorindirectlybythisbook.
PacktPublishinghasendeavoredtoprovidetrademarkinformationaboutallofthecompaniesandproductsmentionedinthisbookbytheappropriateuseofcapitals.However,PacktPublishingcannotguaranteetheaccuracyofthisinformation.
Firstpublished:April2013
Secondedition:January2016
Productionreference:1250116
PublishedbyPacktPublishingLtd.
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BirminghamB32PB,UK.
ISBN978-1-78588-728-4
www.packtpub.com
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CreditsAuthors
OliverPelz
JonathanHobson
Reviewer
MitjaResman
CommissioningEditor
PriyaSingh
AcquisitionEditor
KevinColaco
ContentDevelopmentEditor
PoojaMhapsekar
TechnicalEditor
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Proofreader
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AbouttheAuthorsOliverPelzhasmorethan10yearsofexperienceasasoftwaredeveloperandsystemadministrator.HegraduatedwithadiplomadegreeinbioinformaticsandiscurrentlyworkingattheGermanCancerResearchcenterinHeidelbergwherehehasauthoredandco-authoredseveralscientificpublicationsinthefieldofBioinformatics.Aswellasdevelopingwebapplicationsandbiologicaldatabasesforhisdepartmentandscientistsallovertheworld,headministersadivision-wideLinux-baseddatacenterandhassetuptwohigh-performanceCentOSclustersfortheanalysisofhigh-throughputmicroscopeandgenomesequencingdata.Heloveswritingcode,ridinghismountainbikeintheBlackForestofGermanyandhasbeenanabsoluteLinuxandopensourceenthusiastformanyyears.Hehascontributedtoseveralopen-sourceprojectsinthepastandalsoworkedasarevieweronthebookCentOSHighPerformance,PacktPublishing.HemaintainsanITtechblogatwww.oliverpelz.de.
IwouldliketothankmyfamilyandespeciallymywonderfulwifeBeatriceandlittlesonJonahfortheirpatienceandunderstandingduringallthelongworkinghourswhilewritingthisbook.AlsoIwouldliketothankthefolksatPacktPublishingforalltheirsupportandtheopportunitytotowritethisbook,itwasagreatpleasureforme.LastbutnotleastIwouldliketothankJonathanHobsonforwritingthefirsteditionofthisbook:withouthimnosecondeditionofthisbookwouldhavebeenpossible.
IwouldalsoliketothankallofthementorsthatI’vehadovertheyears,especiallyProf.Dr.TobiasDykerhoff,whointroducedmetothewholeworldofLinuxalongtimeagoandinfectedmewithhisenthusiasmaboutopensourceandthefreesoftwaremovement.
JonathanHobsonisawebdeveloper,systemsengineer,andapplicationsprogrammer.Formorethan20years,hehasbeenworkingbehindthescenestosupportcompanies,organizations,andindividualsaroundtheworldtorealizetheirdigitalambitions.Withanhonorsdegreeinbothenglishandhistoryandasarespectedpractitionerofmanycomputerlanguages,Jonathanenjoyswritingcode,publishingarticles,buildingcomputers,playingthevideogames,andgetting‘outandabout’inthebigoutdoors.HehasbeenusingCentOSsinceitsinception,andovertheyears,ithasnotonlyearnedhistrust,butithasalsobecomehisfirstchoiceforaserversolution.CentOSisafirstclasscommunity-basedenterpriseclassoperatingsystem.Itisapleasuretoworkwithandbecauseofthis,Jonathanhaswrittenthisbooksothathisknowledgeandexperiencecanbepassedontoothers.
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AbouttheReviewerMitjaResmancomesfromasmall,beautifulcountrycalledSlovenia,locatedinsouthernCentralEurope.MitjaisafanofLinuxandanopensourceenthusiast,andalsoaRedHatCertifiedEngineerandLinuxProfessionalInstituteprofessional.Workingasasystemadministrator,MitjagotyearsofprofessionalexperiencewithopensourcesoftwareandLinuxsystemadministrationonlocalandinternationalprojectsworldwide.SwissArmyknifesyndromemakesMitjaanexpertinthefieldsofVMwarevirtualization,Microsoftsystemadministration,andalsoAndroidsystemadministration.
Mitjahasastrongdesiretolearn,develop,andshareknowledgewithothers.ThisisthereasonhestartedablogcalledGeekPeek.Net.ThiswebsiteprovidesCentOSLinuxguidesand“howto”articlescoveringallsortsoftopicsappropriateforbeginnersandadvancedusers.MitjawroteabookcalledCentOSHighAvailability,PacktPublishing,coveringhowtoinstall,configure,andmanageclusteronCentOSLinux.
Mitjaisalsoadevotedfatherandhusband.Histwodaughtersandwifetakehismindoffthegeekstuffandmakehimappreciatelife,lookingforwardtothingstocome.
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ThisworkisdedicatedtomysonMarlinPelzwhowastragicallystillbornon2.10.15,twoweeksbeforehisexpecteddateofdeliverywhileIwaswritingthelastfewchaptersofthisbook.Marlin,wordscannotexpresshowmuchImissyou!
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PrefaceThisisthesecondeditionofthehighlyratedCentOSLinuxServerCookbook.WiththeadventofCentOS7inmid2014,therehasbeenalonglistofsignificantchangesandnewfeaturestothisfamousoperatingsystem.Tonameafew,thereisanewinstaller,suiteofsystemmanagementservices,firewalldaemon,enhancedLinuxcontainersupport,andanewstandardfilesystem.Withallthesenewadvancesintheoperatingsystem,amajorpartoftherecipesfromtheCentOS6LinuxServerCookbookbecameobsoleteorevennon-functional,makinganupdateofthebook’soriginalcontentessential.Butthisbookisnotjustarefresherofthetopicscoveredinthefirstedition:twobrandnewchaptershavebeenincludedaswelltokeepuptodatewiththelatestopensourcetechnologiesaswellasprovidingbettersecurity:operatingsystem-levelvirtualizationandSELinux.Finally,tomakethebookamorecomprehensiveserver-administrationbook,anotherchapteraboutservermonitoringhasbeenincludedaswell.
Buildingaservercanpresentachallenge.Itisoftendifficultatthebestoftimesandfrustratingattheworstoftimes.Theycanrepresentthebiggestofproblemsorgiveyouagreatsenseofprideandachievement.Wheretheword“server”candescribemanythings,itistheintentionofthisbooktoliftthelidandexposetheinnerworkingsofthisenterprise-classcomputingsystemwiththeintentionofenablingyoutobuildyourprofessionalserversolutionofchoice.CentOSisacommunity-basedenterpriseclassoperatingsystem.Itisavailablefreeofcharge,andasafullycompatiblederivativeofRedHatEnterpriseLinux(RHEL),itrepresentsthefirstchoiceoperatingsystemfororganizations,companies,professionals,andhomeusersallovertheworldwhointendtorunaserver.It’swidelyrespectedasaverypowerfulandflexibleLinuxdistributionandregardlessofwhetheryouintendtorunawebserver,fileserver,FTPserver,domainserver,oramulti-rolesolution,itisthepurposeofthisbooktodeliveraseriesofturnkeysolutionsthatwillshowyouhowquicklyyoucanbuildafullycapableandcomprehensiveserversystemusingtheCentOSoperatingsystem.Sowiththisinmind,youcouldsaythatthisbookrepresentsmorethanjustanotherintroductiontoyetanotherserver-basedoperatingsystem.Thisisacookbookaboutanenterprise-classoperatingsystemthatprovidesastep-by-stepapproachtomakingitwork.So,regardlessofwhetheryouareaneworanexperienceduser,thereissomethinginsidethesepagesforeveryone,asthisbookwillbecomeyourpracticalguidetogettingthingsdoneandastartingpointtoallthingsCentOS.
WhatthisbookcoversChapter1,InstallingCentOS,isaseriesofrecipesthatintroducesyoutothetaskofinstallingyourserver,updating,andenhancingtheminimalinstallwithadditionaltools.Itisdesignedtogetyoustartedandtoprovideareferencethatshowsyouanumberofwaystoachievethedesiredinstallation.
Chapter2,ConfiguringtheSystem,isdesignedtofollowonfromasuccessfulinstallationtoofferahelpinghandandprovideyouwithanumberofrecipesthatwillenableyoutoachievethedesiredstartingserverconfiguration.Beginningwithshowingyouhowtoworkwithtextfiles,thenchanginglanguageandtimeanddatesettings,youwillnotonlylearnhowconfigureyournetworksettingsbutalsohowtoresolveafullyqualifieddomainnameandworkwithkernelmodules.
Chapter3,ManagingtheSystem,providesthebuildingblocksthatwillenableyoutochampionyourserverandtakecontrolofyourenvironment.Itisherewhereyouwillkickstartyourroleasaserveradministratorbydisseminatingawealthofinformationthatwillwalkyouthroughavarietyofstepsthatarerequiredtodevelopafullyconsideredandprofessionalserversolution.
Chapter4,ManagingPackageswithYUM,servestointroduceyoutoworkingwithsoftwarepackagesonCentOS7.Fromupgradingthesystemtofinding,installing,removing,andenhancingyoursystemwithadditionalrepositories,itisthepurposeofthischaptertoexplaintheopensourcecommand-linepackagemanagementutilityknownastheYellowdogUpdaterModified(YUM)aswellastheRPMpackagemanager.
Chapter5,AdministeringtheFilesystem,focusesonworkingwithyourserver’sfilesystem.Fromcreatingmockingdiskdevicestotest-driveconceptsexpertlevelformattingandpartitioningcommands,youwilllearnhowtoworkwiththeLogicalVolumeManager,maintainyourfilesystemandworkwithdiskquotas.
Chapter6,ProvidingSecurity,discussestheneedtoimplementaseriesofsolutionsthatwilldeliverthelevelofprotectionyouneedtorunasuccessfulserversolution.FromprotectingyoursshandFTPservices,tounderstandingthenewfirewalldmanagerandcreatingcertificates,youwillseehoweasyitistobuildaserverthatnotonlyconsiderstheneedtoreduceriskfromexternalattackbutonethatwillprovideadditionalprotectionforyourusers.
Chapter7,BuildingaNetwork,explainsthestepsrequiredtoimplementvariousformsofresourcesharingwithinyournetwork’scomputers.FromIPaddressesandprintingdevicestovariousformsoffilesharingprotocols,thischapterplaysanessentialroleofanyserverwhetheryouareintendingtosupportahomenetworkorafullcorporateenvironment.
Chapter8,WorkingwithFTP,concentratesontheroleofVSFTPwithaseriesofrecipesthatwillprovidetheguidanceyouneedtoinstall,configureandmanagetheFileTransferProtocol(FTP)youwanttoprovideonaCentOS7server.
Chapter9,WorkingwithDomains,considersthestepsrequiredtoimplementdomain
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names,domainresolution,andDNSqueriesonaCentOS7server.Thedomainnamesystemisanessentialroleofanyserverandwhetheryouareintendingtosupportahomenetworkorafullcorporateenvironment,itisthepurposeofthischaptertoprovideaseriesofsolutionsthatwilldeliverthebeginningofafuture-proofsolution.
Chapter10,WorkingwithDatabases,providesaseriesofrecipesthatdeliverinstantaccesstoMySQLandPostgreSQLwiththeintentionofexplainingthenecessarystepsrequiredtodeploythemonaCentOS7server.
Chapter11,ProvidingMailServices,introducesyoutotheprocessofenablingadomain-wideMailTransportAgenttoyourCentOS7server.FrombuildingalocalPOP3/SMTPservertoconfiguringFetchmail,thepurposeofthischapteristoprovidethegroundworkforallyourfuturee-mail-basedneeds.
Chapter12,ProvidingWebServices,investigatestheroleofthewell-knownApacheservertechnologytofulleffect,andwhetheryouareintendingtorunadevelopmentserveroraliveproductionserver,thischapterprovidesyouwiththenecessarystepstodeliverthefeaturesyouneedtobecomethemasterofyourwebbasedpublishingsolution.
Chapter13,OperatingSystem-LevelVirtualization,introducesyoutothewordofLinuxcontainersusingthestate-of-the-artopensourceplatformDocker,andguidesyouthroughbuilding,running,andsharingyourfirstDockerimage.
Chapter14,WorkingwithSELinux,helpstounderstandanddemystifySecurityEnhancedLinux,whichisoneofthemostlittle-knowntopicsofCentOS7.
Chapter15,MonitoringITInfrastructure,introducesandshowshowtosetupNagiosCore,thede-factoindustrystandardformonitoringyourcompleteITinfrastructure.
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WhatyouneedforthisbookTherequirementsofthisbookarerelativelysimpleandbeginwiththeneedtodownloadtheCentOSoperatingsystem.Thesoftwareisfree,butyouwillneedacomputerthatiscapableoffulfillingtheroleofaserver,somefreeinstallationmedia(blankCD-R/DVD-RorUSBdevice),anInternetconnection,somesparetime,andadesiretohavefun.
Insayingthat,manyreaderswillbeawarethatyoudonotneedasparecomputertotakeadvantageofthisbookastheoptionofinstallingCentOSonvirtualizationsoftwareisalwaysavailable.Thisapproachisquitecommonandwheretherecipescontainedwithinthesepagesremainapplicable,youshouldbeawarethattheuseofvirtualizationsoftwareisnotconsideredbythisbook.Forthisreason,anyrequestsforsupportregardingtheuseofthissoftwareshouldbedirectedtowardstheappropriatesupplier.
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WhothisbookisforThisisapracticalguideforbuildingaserversolution,andratherthanbeingaboutCentOSitself,thisisabookthatwillshowyouhowtogetCentOSupandrunning.Itisabookthathasbeenwrittenwiththenovice-to-intermediateLinuxuserinmindwhoisintendingtouseCentOSasthebasisoftheirnextserver.However,ifyouarenewtooperatingsystemsasawhole,thendon’tworry;thisbookwillalsoservetoprovideyouwiththestep-by-stepapproachyouneedtobuildacompleteserversolutionwithplentyoftricksofthetradethrowninforgoodmeasure.
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SectionsInthisbook,youwillfindseveralheadingsthatappearfrequently(Gettingready,Howtodoit,HowitworksandThere’smore).
Togiveclearinstructionsonhowtocompletearecipe,weusethesesectionsasfollows:
GettingreadyThissectiontellsyouwhattoexpectintherecipe,anddescribeshowtosetupanysoftwareoranypreliminarysettingsrequiredfortherecipe.
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Howtodoit…Thissectioncontainsthestepsrequiredtofollowtherecipe.
Howitworks…Thissectionusuallyconsistsofadetailedexplanationofwhathappenedintheprevioussection.
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There’smore…Thissectionconsistsofadditionalinformationabouttherecipeinordertomakethereadermoreknowledgeableabouttherecipe.
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ConventionsInthisbook,youwillfindanumberoftextstylesthatdistinguishbetweendifferentkindsofinformation.Herearesomeexamplesofthesestylesandanexplanationoftheirmeaning.
Codewordsintext,databasetablenames,foldernames,filenames,fileextensions,pathnames,dummyURLs,userinput,andTwitterhandlesareshownasfollows:“Forthepurposeofthisrecipe,itisassumedthatallthedownloadswillbestoredonWindowsinyourpersonalC:\Users\\Downloadsfolder,orifusinganOSXsystem,inthe/Users//Downloadsfolder.”
Ablockofcodeissetasfollows:
enableFTPSports
Anycommand-lineinputoroutputiswrittenasfollows:
sudodiskutilunmountDisk/dev/disk3sudoddif=./CentOS-7-x86_64-Minimal-XXXX.isoof=/dev/disk3bs=1M
Newtermsandimportantwordsareshowninbold.Wordsthatyouseeonthescreen,forexample,inmenusordialogboxes,appearinthetextlikethis:“ClickingtheNextbuttonmovesyoutothenextscreen.”
NoteWarningsorimportantnotesappearinaboxlikethis.
TipTipsandtricksappearlikethis.
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Chapter1.InstallingCentOSInthischapter,wewillcover:
DownloadingCentOSandconfirmingthechecksumonWindowsorOSXCreatingUSBinstallationmediaonWindowsorOSXPerforminganinstallationofCentOSusingthegraphicalinstallerRunninganetinstalloverHTTPInstallingCentOSusingakickstartfileRe-installingthebootloaderTroubleshootingthesysteminrescuemodeGettingstartedandcustomizingthebootloaderUpdatingtheinstallationandenhancingtheminimalinstallwithadditionaladministrationanddevelopmenttools
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IntroductionThischapterisacollectionofrecipesthatcoversthebasicpracticeofinstallingtheCentOS7operatingsystem.ThepurposeofthischapteristoshowyouhowquicklyyoucangetCentOSupandrunningwhilstenablingyoutocustomizeyourinstallationwithafew‘tricksofthetrade’throwninforgoodmeasure.
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DownloadingCentOSandconfirmingthechecksumonWindowsorOSXInthisrecipe,wewilllearnhowtodownloadandconfirmthechecksumofoneormoreCentOS7diskimagesusingatypicalWindowsorOSXdesktopcomputer.CentOSismadeavailableinvariousformatsbyHTTP,FTP,orthersyncprotocolfromaseriesofmirrorsiteslocatedacrosstheworldorviatheBitTorrentnetwork.FordownloadingveryimportantfilesfromtheInternet,suchasoperatingsystemimages,itisconsideredbestpracticestovalidatethosefiles’checksum,inordertoensurethatanyresultingmediawouldfunctionandperformasexpectedwheninstalling.Thisalsomakescertainthatthefilesaregenuineandcomefromtheoriginalsource.
GettingreadyTocompletethisrecipe,itisassumedthatyouareusingatypicalWindows-based(Windows7,WindowsVista,orsimilar)orOSXcomputerwithfulladministrationrights.YouwillneedanInternetconnectiontodownloadtherequiredinstallationfilesandalsoneedaccesstoastandardDVD/CDdiskburnerwiththeappropriatesoftware,inordertocreatetherelevantinstallationdisksfromtheimagefiles.Forthepurposeofthisrecipe,itisassumedthatallthedownloadswillbestoredonWindowsinyourpersonalC:\Users\\Downloadsfolder,orifusinganOSXsystem,inthe/Users//Downloadsfolder.
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Howtodoit…Regardlessofthetypeofinstallationfilesyoudownload,thefollowingtechniquescanbeappliedtoalltheimagefilessuppliedbytheCentOSproject:
1. Let’sbeginbyvisitinghttp://www.centos.orginawebbrowserandnavigatetothebuttonlinkGetCentOSNow.Thenclickthelinklistofthecurrentmirrorsinthetext.
2. Themirrorsitesarecategorized,sofromtheresultinglistoflinks,chooseamirrorthatisgeographicallynearyourcurrentlocation.Forexample,ifyouareinLondon(UK),youcanchooseamirrorfromEUandUnitedKingdom.NowchooseamirrorsitebyselectingeithertheHTTPortheFTPlink.
3. Havingmadeyourselection,youwillnowseealistofdirectoriesofalltheavailableCentOSversions.Toproceed,simplyclicktheappropriatefolderthatreads7.Next,youwillseeanadditionallistofdirectories,suchasatomic,centosplus,cloud,andsoon.Weproceedbychoosingtheisosdirectory.
4. CentOS7currentlyonlysupportsthe64-bitarchitecture,sobrowsetotheonlydirectoryavailablelabeledx86_64,whichisacontainerforthe64-bitversion.
5. Youwillnowbepresentedwithaseriesoffilesavailablefordownload.Beginbydownloadingacopyofthevalidchecksumresultidentifiedasmd5sum.txt.
6. IfyouarenewtoCentOSorareintendingtofollowtherecipesfoundthroughoutthisbook,thentheminimalinstallationisideal.Thiscontainstheleastamountofpackagestohaveafunctionalsystem,sochoosethefollowing(XXXXisthemonthstampofthisrelease):
CentOS-7-x86_64-Minimal-XXXX.iso
7. OnaWindows-basedsystemonly(onMac,thistoolisalreadyavailableinthesystem),visithttp://mirror.centos.org/centos/dostools/inyourbrowseranddownloadtheprogrammd5sum.exe.
8. NowonWindows,openthecommandprompt(typicallyfoundatStart|AllPrograms|Accessories|CommandPrompt)andtypethefollowingcommandsintothewindowthatwillopen(presstheEnterkeyattheendofallthelines):
cddownloadsdir
9. OnOSX,opentheprogramFinder|Applications|Utilities|Terminal,thentypethefollowingcommands(presstheEnterkeyattheendofallthelines):
cd~/Downloadsls
10. Youshouldnowseeallthefilesinyourdownloadfolder(includingallthedownloadedCentOSinstallationimagefiles,themd5sum.txtfileandonWindows,themd5sum.exeprogram).
11. Basedonthefilenamesshown,modifythefollowingcommandinordertocheckthechecksumofyourdownloadedISOimagefile.OnWindows,typethefollowing
http://www.centos.orghttp://mirror.centos.org/centos/dostools/
command(changetheXXXXmonthstampaccordingly):
md5sum.exeCentOS-7-x86_64-Minimal-XXXX.iso
12. OnOSX,useinstead:
md5CentOS-7-x86_64-Minimal-XXXX.iso
13. PresstheReturnkeytoproceedandthenwaitforthecommandprompttorespond.TheresponseisknownastheMD5sumandtheresultcouldlooklikethefollowing:
d07ab3e615c66a8b2e9a50f4852e6a77CentOS-7-x86_64-Minimal-1503-01.iso
14. Nowlookatthethesumandcompareagainsttherelevantlistingforyourparticularimagefileinmd5sum.txt(openinatexteditor).Ifboththenumbersmatch,thenyoucanbeconfidentthatyouhaveindeeddownloadedavalidCentOSimagefile.Ifnot,yourdownloadedfileisprobablycorrupted,sopleaserestartthisprocedurebydownloadingtheimagefileagain.
15. Whenyouhavefinished,simplyburnyourimagefile(s)toablankCD-ROMorDVD-ROMusingyourpreferreddesktopsoftware,orcreateaUSBinstallationmediafromit,aswewillshowyouinthenextrecipeinthischapter.
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Howitworks…Sowhathavewelearnedfromthisexperience?
TheactofdownloadingaCentOSinstallationimageisjustthefirststeptowardsbuildingtheperfectserver.Althoughthisprocessisverysimple,manydoforgettheneedtoconfirmthechecksum.Inthisbook,wewillworkwiththeminimalinstallationimage,butyoushouldbeawarethatthereareotherinstallationoptionsavailabletoyou,suchasNetInstall,DVD,Everything,andvariousLiveCDs.
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CreatingUSBinstallationmediaonWindowsorOSXInthisrecipe,wewilllearnhowtocreateaUSBinstallationmediaonWindowsorOSX.Nowadays,moreandmoreserversystems,desktopPCs,andlaptopsgetshippedwithoutanyopticaldrive.Installinganewoperatingsystem,suchasCentOSLinuxusingUSBdevicesgetsessentialforthemasnootherinstallationoptionisavailable,asthereisnootherwaytoboottheinstallationmedia.Also,installingCentOSusingUSBmediacanbeconsiderablyfasterthanusingtheCD/DVDapproach.
GettingreadyBeforewebegin,itisassumedthatyouhavefollowedthepreviousrecipeinwhichyouwereshownhowtodownloadaminimalCentOSimageandconfirmthechecksumoftherelevantimagefiles.Itisalsoassumedthatallthedownloads(includingthedownloadedISOfile)arestoredonWindowsinyourC:\Users\\DownloadsfolderorifusingaOSXsystem,inthe/Users//Downloadsfolder.Next,youwillneedafreeUSBdevicewhichcanbediscoveredbyyouroperatingsystem,withenoughtotalspace,andwhichisemptyorwithdataonitthatcanbediscarded.ThetotalspaceoftheUSBdeviceneededforpreparingasaninstallationmediaforCentOS7fortheminimalversionmustberoughly700megabyte.IfyouareworkingonaWindowscomputer,youwillneedaworkingInternetconnectiontodownloadadditionalsoftware.OnOSX,youneedanadministratoruseraccount.
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Howtodoit…Tobeginthisrecipe,startupyourWindowsorOSXoperatingsystem,thenconnectafreeUSBdevicewithenoughcapacity,andwaituntilitgetsdiscoveredbyFileManagerunderWindowsorFinderunderOSX.
1. OnaWindowsbasedsystem,weneedtodownloadanadditionalsoftwarecalleddd.Visithttp://www.chrysocome.net/ddinyourfavoritebrowser.Nowdownloadthelatestdd-XX.zipfileyoucanfindthere,withXXbeingthelateststableversionnumber.Forexample,dd-0.5.zip.
2. OnWindows,navigatetoyourDownloadsfolderusingFileManager.Hereyouwillfindthedd-05.zipfile.Right-clickonitandclickonExtractAll,andextractthedd.exefilewithoutcreatinganysubdirectory.
3. OnWindows,openthecommandprompt(typicallyfoundatStart|AllPrograms|Accessories|CommandPrompt)andtypethefollowingcommands:
cddownloadsdd.exe--list
4. OnOSX,opentheprogramFinder|Applications|Utilities|Terminal,andthentypethefollowingcommands:
cd~/Downloadsdiskutillist
5. OnWindows,tospotthenameoftherightUSBdeviceyouwanttouseasinstallationmedia,lookintotheoutputofthecommandundertheremovablemediasection.Belowthat,youshouldfindalinestartingwithMountingonandthenadriveletter,forexample,\.\e:.Thiscrypticwrittendriveletteristhemostimportantpartweneedinthenextstep,sopleasewriteitdown.
6. OnOSX,thedevicepathcanbefoundintheoutputoftheformercommandandhastheformatof/dev/disk,wherenumberisauniqueidentifierofthedisk.Thedisksarenumbered,startingwithzero(0).Disk0islikelytobetheOSXrecoverydisk,anddisk1islikelytobeyourmainOSXinstallation.ToidentifyyourUSBdevice,trytocomparetheNAME,TYPE,andSIZEcolumnstothespecificationsofyourUSBstick.Ifyouhaveidentifiedthedevicename,writeitdown,forexample,/dev/disk3.
7. OnWindows,typethefollowingcommand,assumingyourUSBdeviceselectedasainstallationmediahastheWindowsdevicename\\.\e:(changethisasrequiredandbecarefulwhatyoutype–thiscancreatetremendousdataloss).Also,substituteXXXXwiththecorrectisofileversionnumberinthenextcommand:
dd.exeif=CentOS-7-x86_64-Minimal-XXXX.isoof=\\.\e:bs=1M
8. OnOSX,youneedtwocommandswhichwillaskfortheadministratorpassword(replaceXXXXanddisk3withthecorrectversionnumberandthecorrectUSBdevicepath):
sudodiskutilunmountDisk/dev/disk3
http://www.chrysocome.net/dd
sudoddif=./CentOS-7-x86_64-Minimal-XXXX.isoof=/dev/disk3bs=1m
9. Aftertheddprogramfinishes,therewillbesomeoutputstatisticsonhowlongittookandhowmuchdatahasbeentransferredduringthecopyprocess.OnOSX,ignoreanywarningmessagesaboutthedisknotbeingreadable.
10. Congratulations!YounowhavecreatedyourfirstCentOS7USBinstallationmedia.YounowcansafelyremovetheUSBdriveinWindowsorOSX,andphysicallyunplugthedeviceanduseitasabootdeviceforinstallingCentOS7onyourtargetmachine.
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Howitworks…Sowhathavewelearnedfromthisexperience?
ThepurposeofthisrecipewastointroduceyoutotheconceptofcreatinganexactcopyofaCentOSinstallationISOfileonaUSBdevice,usingtheddcommand-lineprogram.TheddprogramisaUnixbasedtoolwhichcanbeusedtocopybitsfromasourcetoadestinationfile.Thismeansthatthesourcegetsreadbitbybitandwrittentoadestinationwithoutconsideringthecontentorfileallocation;itjustinvolvesreadingandwritingpurerawdata.Itexpectstwofilenamebasedarguments:inputfile(if)andoutputfile(of).WewillusetheCentOSimagefileasourinputfilenametocloneitexactly1:1totheUSBdevice,whichisaccessiblethroughitsdevicefileasouroutputfileparameter.Thebsparameterdefinestheblocksize,whichistheamountofdatatobecopiedatonce.Becareful,itisanabsoluteexperttoolandoverwritesanyexistingdataonyourtargetwhilecopyingdataonitwithoutfurtherconfirmationoranysafetychecks.Soatleastdouble-checkthedevicedrivelettersofyourtargetUSBdeviceandneverconfusethem!Forexample,ifyouhaveasecondharddiskinstalledatD:andyourUSBdeviceatE:(onOSX,at/dev/disk2and/dev/disk3respectively)andyouconfusethedriveletterE:withD:(or/dev/disk3with/dev/disk2),yoursecondharddiskwouldbeerasedwithlittletonochancesofrecoveringanylostdata.Sohandlewithcare!Ifyou’reindoubtofthecorrectoutputfiledevice,neverstarttheddprogram!
Inconclusion,itisfairtosaythatthereareotherfarmoreconvenientsolutionsavailableforcreatingaUSBinstallationmediaforCentOS7thantheddcommand,suchastheFedoraLiveUSBCreator.Butthepurposeofthisrecipewasnotonlytocreateaready-to-useCentOSUSBinstallerbutalsotogetyouusedtotheddcommand.It’sacommonLinuxcommandthateveryCentOSsystemadministratorshouldknowhowtouse.Itcanbeusedforabroadvarietyofdailytasks.Forexample,forsecurelyerasingharddisks,benchmarkingnetworkspeed,orcreatingrandombinaryfiles.
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PerforminganinstallationofCentOSusingthegraphicalinstallerInthisrecipe,wewilllearnhowtoperformatypicalinstallationofCentOSusinganewgraphicalinstallerinterfaceintroducedinCentOS7.Inmanyrespects,thisisconsideredtobetherecommendedapproachtoinstallingyoursystem,asitnotonlyprovidesyouwiththeabilitytocreatethedesiredharddiskpartitionsbutalsotocustomizeyourinstallationinlotsofways(forexample,keyboardlayout,packageselection,installationtype,andsoon).Yourinstallationwillthenformthebasisofaserveronwhichyoucanbuild,develop,andrunanytypeofserviceyoumaywanttoprovideinthefuture.
GettingreadyBeforewebegin,itisassumedthatyouhavefollowedthepreviousrecipeinwhichyouwereshownhowtodownloadaCentOSimage,confirmthechecksumoftherelevantimagefiles,andcreatetherelevantinstallationopticaldisksorUSBmedia.Yoursystemmustbea64bit(x64_86)architecture,musthaveatleast406MBRAMtoloadthegraphicalinstaller1GBormoreisrecommendedifinstallingagraphicalwindowmanagersuchasGnome),andhaveatleast10GBfreeharddiskspace.
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Howtodoit…Tobeginthisrecipe,insertyourinstallationmedia(CD/DVDorUSBdevice),restartthecomputer,andpressthecorrectkeyforselectingthebootdeviceduringstartup.Thenchoosetheinserteddevicefromthelist(formanycomputers,thiscanbereachedusingF11orF12butcanbedifferentonyoursystem.Pleaserefertoyourmotherboard’smanual).
1. Onthewelcomesplashscreen,theoptionTestthismedia&installCentOS7ispreselectedandwewillusethisoption.Whenyouareready,presstheReturnkeytoproceed.
2. Afterloadingsomeinitialfiles,theinstallerthenstartstotesttheinstallationmedia.Asingletestshouldtakebetween30secondstofiveminutesandwillreportifthereareanyerrorsonyourinstallationmedia.Whenthisprocessiscomplete,thesystemwillfinallyloadthegraphicalinstaller.
3. TheCentOSinstallerwillnowpresentthegraphicalinstallationwelcomescreen.Fromthispointonwards,youcanuseyourkeyboardandmouse(thelatterishighlyrecommended),butremembertoenablethenumberlockonyourkeyboardifyouintendtousethekeypad.
4. Ontheleftsideyouseethemainlanguagecategoryandontherightside,thesub-languagesfortheinstaller.Youcanalsosearchforalanguageusingthetextboxontheleftbottom.Allchangestoyourlanguagesettingswilltakeeffectimmediately,sowhenyouareready,choosetheContinuebuttontoproceed.
5. Nowwereachthemaininstallationmenu,whichiscalledInstallationsummary.6. Mostoptionsshownherealreadyhavesomepredefinedvaluesandcanbeused
withoutchanging,otherswhichdonothaveanydefaultvalueandwhichneedyourattentionarelabeledwitharedexclamationmarkliketheInstallationDestinationunderSystemcategory.Solet’sclickonitusingthemouse.
7. AfterclickingtheInstallationDestinationbutton,youwillseeagraphicallistofalltheharddiskdevicescurrentlyconnectedtoyourcomputer,whichyoucanuseforinstallingtheoperatingsystemon.Youcanselectyourtargetharddiskbyclickingonthecorrectharddisksymbol.Itwillthenputacheckmarkonit.Ifyouareunsureabouttherightharddisk,trytoidentifyitbycomparingitsbrandandtotalsizeshowninthemenu.Beforetheinstallationcanproceed,youmustselectaharddisk.Becarefulandchooseyourtargetharddiskwiselyasitwilleraseanyexistingdataonitduringtheinstallation.Whenyouareready,clicktheDonebutton.
8. Ifyourselectedharddiskalreadycontaineddata,thenwhenclickingonDone,youmayseewhatcouldbedescribedasawarning/errormessage.Themessagemayread:Youdon’thaveenoughspaceavailabletoinstallCentOS.Don’tworry!Thisistobeexpectedandthemessageissimplyaskingyoutore-initializeyourharddiskbecauseCentOScanonlybeinstalledonanemptydisk.Inmostcases,especiallyifyouhavemorethanonepartitionontheharddisk,simplyclickonReclaimspacewhichwillshowanewwindowwithadetailedlistofallthepartitionsonthisdrive.HerejustclickonDeleteAllandthenagainonReclaimspacetodiscardanydataonthisdisk,whichwillcompletethetaskofdiskinitializationandenableyouto
proceedtothenextstep.Whenfinished,clicktheDonebutton.9. BackattheInstallationSummaryscreen,theexclamationmarkontheInstallation
Destinationitemshouldbegonenow.10. Optionally,wecanclickonNetwork&HostnameunderSystemcategory.Onthe
followingpage,ontheleftside,youcanchoosetheprimarynetworkadapteryouwouldliketoconnecttotheInternetandselectitbyclickingonit.Fortheselecteddevice,clickontheswitchontherightsidetoenableandconnectitautomaticallyusingtheOnpositionoftheswitch.Finally,beforeclosingthissubmenu,changethehostnameinitstextfieldtosomethingappropriate.ClickDone.
11. NowbackattheInstallationSummaryscreen,alltheimportantsettingshavebeenmadeorhavegotpredefinedvalues,andalltheexclamationmarksaregone.Ifyouarehappywiththesesettings,clickontheStartinstallationbuttonorchangethesettingsappropriately.
12. Onthenextscreen,youwillberequiredtocreateandconfirmarootpasswordfortherootuserwhilethenewsystemgetsinstalledinthebackground.Chooseasecurepasswordwithnotlessthansixcharacters.
13. Hereonthisscreenyoucanalsocreateastandarduseraccountwhichishighlyrecommended.IfyoucreateanewuserdonotcheckMakethisuseradministrator.Whenyouareready,clickDone(ifyouenteredaweakpassword,youhavetoconfirmthisbyclickingtwice)
14. CentOSwillnowpartitionateandformatyourharddiskinthebackgroundandresolveanydependencies,andtheinstallerwillbeginwritingtotheharddisk.Thismaytakesometime,butaprogressbarwillindicatethestatusofyourinstallation.Whenfinished,theinstallerwillinformyouthattheentireprocessiscompleteandthattheinstallationwassuccessful.Sowhenyouareready,clickontheRebootbutton.Nowreleaseyourinstallationmediafromthedrive.
15. Congratulations!YouhavenowinstalledCentOS7onyourcomputer.
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Howitworks…Inthisrecipe,youhavediscoveredhowtoinstalltheCentOS7operatingsystem.Havingcoveredthetypicalapproachtothegraphicalinstallationprocess,youarenowinapositiontodeveloptheserverwithadditionalconfigurationchangesandpackagesthatwillsuittheroleyouintendtheservertofulfill.Thisgraphicalinstallerhasbeenbuiltwiththeaimtobeveryintuitiveandflexible,andmakesinstallationveryeasyasitwillguidetheuserthroughsomemandatorytasksthathehastofulfillbeforetheinstallationofthemainsystemcanbestarted.
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RunninganetinstalloverHTTPInthisrecipe,wewilllearnhowtoinitiatetheprocessofrunninganetinstalloverHTTP(usingtheURLmethod)inordertoinstallCentOS7.Itisaprocessinwhichasmallimagefileisusedtobootthecomputerandlettheuserselectandinstallonlythesoftwarepackagesandserviceshewantsandnothingmoreoveranetworkconnectionthusprovidinggreatflexibility.
GettingreadyBeforewebegin,itisassumedthatyoualreadyknowhowtodownloadandchecksumaCentOS7installationimageandhowtocreatetherelevantinstallationmediafromit.Forthisrecipehere,wewillneedtodownloadandcreateinstallationmediaforthenetinstallimage(downloadthelatestCentOS-7-x86_64-NetInstall-XXXX.isofile)insteadoftheminimalISOshowninanotherrecipeinthischapter.Also,itisassumedthatyouhaveatleastgonethroughthegraphicalinstallationprocedureoncetoexactlyknowhowtobootfromyourinstallationmediaandworkwiththeinstallerprogram.
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Howtodoit…Tobeginthisrecipe,insertyourpreparednetinstallmedia,bootyourcomputerfromit,andwaitforthewelcomescreentoappear:
1. Onthewelcomesplashscreen,theoptionTestthismedia&installCentOS7ispreselectedandwewillusethisoption.Whenyouareready,presstheReturnkeytoproceed.
2. Afterthetestsfinish,thegraphicalinstallerwillloadandpresentthetypicalgraphicalinstallationsummaryscreen.
NoteHeretheinstallershouldbeconfiguredexactlyasinthenormalgraphicalinstallationrecipe,besidesthefollowingmandatorychangestotheNetwork&HostnameandInstallationsourcemenuitems(whichisshownbytheredexclamationmarks).
3. BeforewecaninstallCentOSoverthenetwork,wehavetomakesurethatwehaveaworkingnetworkconnection.Therefore,youshouldfirstclickontheNetwork&Hostnamemenuentryandactivateoneofyournetworkadapterstotheconnectedstate.Refertothenormalinstallationrecipeformoredetails.
4. Next,clickonInstallationsourcetoenterthesettings.AswewillbeinstallingoverHTTP(alsoreferredtoastheURLmethod),youshouldleavethedefaultOnthenetworkselectedintheWhichinstallationsourcewouldyouliketouse?section.
5. NowtypeinthefollowingURLinthestandardhttp://textfield,whichwewillusetodownloadalltherequiredinstallationpackagesathttp://mirror.centos.org/centos/7/os/x86_64/.
6. Alternatively,youcanalsouseapersonalrepositorywhichyouwouldhavetocreateinadvance(seeChapter4,ManagingPackageswithYUM)
7. Whenyouareready,clickonDonetostarttheinitializationprocess.8. Onsuccess,theinstallerwillbegintoretrievetheappropriateinstall.imgfile.This
maytakeseveralminutestocomplete,butonceresolved,aprogressbarwillindicateallthedownloadactivity.Whenthisprocessfinishessuccessfully,theexclamationmarkattheinstallationsourcewillgoawaybutanotheronewillpopupwhichwilltelltheuserthatitismissingthesoftwareselection.Clickonitandchoosewhateverfitsyourneed.Asforthepurposeofthisrecipe,justselectMinimalinstallunderBaseenvironmentandthenclickonDone.
9. IftheWhichinstallationsourcewouldyouliketousestaysgreyedoutandcannotbechanged,thenthereareconnectionproblemswithyournetworkadapter.Ifthisisthecase,gobacktoconfigureNetwork&Hostnameandchangethenetworksettingsuntiltheconnectedstatecanbereached.
10. CentOS7willnowinstalltheoperatingsystemtheusualwayandwillcongratulateyouwhenthisprocessfinishes.ItmaybeslowerthaninstallingfromaphysicalinstallationmediasinceallthepackageshavetoberetrievedfromtheInternet.
http://%20http://mirror.centos.org/centos/7/os/x86_64/
Howitworks…ThepurposeofthisrecipewastointroduceyoutotheconceptoftheCentOSnetworkinstallationprocess,inordertoshowyoujusthowsimplethisapproachcanbe.Bycompletingthisrecipeyouhavenotonlysavedtimebylimitingyourinitialdownloadtothosefilesthatarerequiredbytheinstallationprocess,butyouhavealsobeenabletotakeadvantageofthefullgraphicalinstallationmethodwithouttheneedforacompleteDVDsuite.
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InstallingCentOS7usingakickstartfileWhileinstallingCentOS7manuallyusingthegraphicalinstallerutilityisfineonasingleserver,doingsoonamultiplenumberofsystemscanbetedious.Kickstartfilescanautomatetheinstallationprocessofaserversystemandherewewillshowhowthiscanbedone.Theyaresimpletextbasedconfigurationfileswhichprovidedetailedandexactinstructionsonhowthetargetsystemshouldbesetupandinstalled(forexample,whichkeyboardlayoutoradditionalsoftwarepackagestoinstall).
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GettingreadyTosuccessfullycompletethisrecipe,youwillneedaccesstoanalreadyinstalledCentOS7systemtoretrievethekickstartconfigurationfilewewanttoworkwithanduseforautomatedinstallation.Onthispre-installedCentOSserver,youalsoneedaworkingInternetconnectiontodownloadadditionalsoftware.
Next,wewillneedtodownloadandcreateinstallationmediafortheDVDortheEverythingimage(downloadthelatestCentOS-7-x86_64-DVD-XXXX.isoorCentOS-7-x86_64-Everything-XXXX.isofile),insteadoftheminimalisofileshowninanotherrecipeinthischapter.ThenyouneedanotherUSBdevicewhichmustbereadandwritableonLinuxsystems(formattedasFAT16,FAT32,EXT2,EXT3,EXT4,orXFSfilesystem).
Howtodoit…Forthisrecipetowork,wefirstneedphysicalaccesstoanexistingkickstartfilefromanotherfinishedCentOS7installation,whichwewilluseasatemplateforanewCentOS7installation.
1. LoginasrootontheexistingCentOS7systemandmakesurethekickstartconfigurationfileexistsbytypingthefollowingcommandandpressingtheReturnkeytoexecute(thiswillshowyouthedetailsofthefile):
ls-l/root/anaconda-ks.cfg
2. Next,physicallypluginaUSBdeviceandthentypethefollowingcommand,whichwillgiveyoualistofalltheharddiskdevicescurrentlyconnectedtothecomputer:
fdisk-l
3. Trytoidentifythedevicenamebycomparingitssize,partitions,andidentifiedfilesystemswiththespecificationsofyourUSBdevice.Thedevicenamewillbeofkind/dev/sdX,whereXisanalphabeticalcharacter,suchasb,c,d,e,…andsoon.IfyoucannotfindtherightdevicenameforyourUSBmediausingthefdiskcommand,trythefollowingtrick:runfdisk-ltwice-firstwithplugged-outandthenwithplugged-inUSBdeviceandcomparehowthesecondoutputchanged-ithasonedevicenamemorethanthefirstoutput:yourdevicenameofinterest!
4. Ifyouhavefoundtherightdevicenameinthelist,createadirectorytomountittothecurrentfilesystem:
mkdir/mnt/kickstart-usb
5. Next,actuallymountthesticktothisfolder,assumingthatyourUSBpartitionofchoiceisat/dev/sdc1(changethisasrequired):
mount/dev/sdc1/mnt/kickstart-usb
6. NowwewillcreateourworkingcopyofthekickstartfileontheUSBdeviceforcustomizing:
cp/root/anaconda-ks.cfg/mnt/kickstart-usb
7. Next,openthecopiedkickstartfileontheUSBdevicewithyourfavoritetexteditor(herewewillusetheeditornano,ifyouhavenotinstalledityettypeyuminstallnano):
nano/mnt/kickstart-usb/anaconda-ks.cfg
8. WewillnowmodifythefileforinstallingCentOSonanewtargetsystem.Innano,usetheupanddownarrowkeystogotothelinewhichstartswith(willbethenameofthehostnameyougaveduringinstallatione.g.minimal.home):
network--hostname=
9. Noweditthestringtogiveitanewuniquehostname.Forexample,adda-2totheendofanyexistingname,asshownnext:
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network--hostname=minimal-2.home
10. Next,movethecursordownusingtheupanddownarrowkeysuntilitstopsatthelinewhichsays%packages.Appendthefollowinglinesrightbelowit(youcanfurthercustomizethisandprovideadditionalpackagesthatyouwanttoinstallautomatically):
mariadb-serverhttpdrsyncnet-tools
11. Nowsaveandclosethefile,todothisinthenanoeditorusethekeycombinationCtrl+o(whichmeans,holddowntheCtrlkeyonthekeyboardandthentheokeywithoutreleasingtheCtrlkey)towritethechanges.ThenpressReturntoconfirmthefilenameandCtrl+xtoexittheeditor.
12. Next,installthefollowingCentOSpackage:
yuminstallsystem-config-kickstart
13. Nowwevalidatethesyntaxofourkickstartfileusingtheksvalidatorprogram,whichisincludedinthepackagewejustinstalled:
ksvalidator/mnt/kickstart-usb/anaconda-ks.cfg
14. Iftheconfigfileiserror-free,unmounttheUSBsticknowbyusingthefollowingcommands:
cdumount/mnt/kickstart-usb
15. Whenyougetanewcommandpromptagain,unplugtheUSBdevicewiththekickstartfileforusingonthetargetmachinephysicallyfromthesystem.
16. NowyouneedphysicalaccesstothetargetmachineyouwanttoinstallCentOSon,usingthekickstartfilejustcreated.Disconnectanyotherexternalfilestorage(s)thatyoudonotneedduringtheinstallation.
17. PoweronthecomputerandputinyourpreparedCentOSinstallationmedia(mustbeaCentOSDVDorEverythinginstallationdiskimagepreparedonaCD/DVDdiscoraUSBdeviceinstaller).AlsoconnecttothecomputertheUSBstickcontainingthekickstartfileyoujustcreatedintheearliersteps(ifyouusingaUSBdriveforinstallingCentOSthenyouwillneedtwofreeUSBportsintotaltocompletethisrecipe).
18. Next,starttheserverandpressthecorrectkeyduringtheinitialbootupscreen,associatedwithbootingtheCentOSinstallationmediayoujustconnected.
19. AftertheCentOSinstallerstartsloading,thecommonstandardCentOS7installationwelcomescreenwillshowupandtheoptionTestthismedia&installCentOS7willbepre-selectedbythecursor.
20. Next,presstheEsckeyonyourkeyboardoncetoswitchtotheboot:prompt.21. Nowwearereadytostartthekickstartinstallation.Todothis,youneedtoknowthe
exactpartitionnameontheUSBdevicewherethekickstartfileislocated.Typethe
followingcommand,assumingthatyourpartitionisat/dev/sdc1(changethisasrequired),andpresstheReturnkeytostartthekickstartinstallationprocess:
linuxks=hd:sdc1:/anaconda-ks.cfg
NoteIfyoucannotfindouttherightdeviceandpartitionnameoftheUSBstick,youhavetostartthetargetsysteminrescuemode(refertotheTroubleshootingthesysteminrescuemoderecipe)toidentifytherightdevicenameandpartitionnumberbycomparingitssize,partitions,andidentifiedfilesystemswiththespecificationsofyourstick.
22. Thenewsystemnowgetsinstalledautomaticallyusingtheinstructionsfromtheprovidedkickstartfile.Youcanwatchtheinstallationoutputmessagesasitisshowingtheuserdetailedinstallationprogress.
23. Ifthesystemhasfinishedinstalling,rebootthesystemandlogintoyournewmachinetoverifythatthenewsystemhasbeensetupthewaywedescribedusingthekickstartfile.
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Howitworks…Inthisrecipe,youhaveseenthateveryserverrunningaCentOS7installationkeepsthekickstartfileinitsrootdirectory,whichcontainsdetailedinformationonhowthesystemhadbeensetupduringtheinstallation.Thekickstartfilescanbeusedtoautomatetheinstallationsofmultiplesystemswiththesameconfiguration.Thiscansavealotoftimedoingrepetitiveworkasnouserinteractionduringinstallationisneeded.Also,wecanusethismethodifthetargetmachinesdon’tmeettheminimumrequirementinRAMforgraphicalbasedinstallationsbutwhenneededotherfeaturesthetextmodeinstallerdoesnotprovidesuchascustompartitioningofthesystem.Kickstartconfigurationfilesaresimpleplaintextfileswhichcanbecreatedmanuallyfromscratch.Becausetherearequiteanumberofdifferentcommandsavailabletoconstructyoursystemusingthekickstartsyntax,weusedanexistingfileasatemplateandcustomizedittofitourneeds,insteadofstartingoutcompletelynew.WedidnotusetheminimalinstallationimagetodriveourkickstartinstallationbecauseweinstalledsomeextrapackagesnotincludedontheminimalISOfile,suchastheApachewebserver.
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GettingstartedandcustomisingthebootloaderWhenyouturnonyourcomputer,thebootloaderisthefirstprogramthatstartsupandisresponsibleforloadingandtransferringcontroltoanunderlyingoperatingsystem.Nowadays,almostanymodernLinuxdistributionusestheGRandUnifiedBootloaderversion2(GRUB2)forstartingthesystem.Ithasalotofflexibilityinconfigurationandsupportsalotofdifferentoperatingsystems.Inthisrecipe,wewillshowhowtocustomizetheGRUB2bootloaderbydisablingthewaitingtimeofthemenudisplayandthereforeimprovingthetimeittakesforbootingthesystem.
GettingreadyTocompletethisrecipe,youwillrequireaccesstoanalreadyinstalledCentOS7operatingsystem(minimaloranyotherCentOS7installationtypewillwork)withrootprivileges.Also,youneedtohavesomebasicexperienceswithatextbasededitor,suchasnano,forchangingtheconfigurationfiles.
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Howtodoit…WebeginthisrecipebyopeningthemainGRUB2configurationfilewithourtexteditorofchoiceandmodifyingit.
1. FirstloginasrootintoyoursystemandcreateacopyoftheGRUB2configurationfileforbackupandrollback,ifneeded.PresstheReturnkeytofinish:
cp/etc/default/grub/etc/default/grub.BAK
2. OpenthemainGRUB2configurationfilethatwewanttoeditwiththefollowingcommandandpresstheReturnkey(herewewillusetheeditornano,ifyouhavenotinstalledityettypeyuminstallnano):
nano/etc/default/grub
3. PresstheReturnkeyinthefirstlinewherethecursorisattoinsertanewlineatthetop,andtheninsertthefollowingline:
GRUB_HIDDEN_TIMEOUT=0
4. Adda#signtothebeginningofthefollowingline,asshown:
GRUB_TIMEOUT=0
5. NowsavethefileinthenanousingCtrl+o(andReturntoconfirmthefilenametosave).UseCtrl+xtoexittheeditorandthenrunthefollowingcommand:
dmesg|grep-Fq"EFIv"
6. Iftheprecedingcommanddoesnotproduceanyoutput,runthefollowingcommand:
grub2-mkconfig-o/boot/grub2/grub.cfg
7. Otherwise,ifthereisanoutput,run:
grub2-mkconfig-o/boot/efi/EFI/centos/grub.cfg
8. Ifgrub2-mkconfigissuccessful,itwillprintDone.Nowrebootyoursystemusingthefollowingcommand:
reboot
9. Duringtherebootingprocess,youwillnoticethattheGRUB2bootmenuwillnotappearanymoreandthesystemwillbootupfaster.
Howitworks…Havingcompletedthisrecipe,wenowknowhowtocustomizetheGRUB2bootloader.Inthisveryeasyrecipe,weonlyshowedyouverybasicmodificationstothebootloaderbutitcandomuchmore!Itsupportsabroadvarietyoffilesystemsandcanbootalmostanycompatibleoperatingsystem.Thisisalsoparticularlyusefulifyouplantorunmultipleoperatingsystemsonthesamemachine.TolearnmoreaboutGRUB2’sconfigurationfilesyntaxtypetheinfogrub2|lesscommandandgotothesection6.1Simpleconfigurationhandling(readtherecipeNavigatingtextfileswithlessinChapter2,ConfiguringtheSystemtolearnhowtobrowsethisdocument).
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TroubleshootingthesysteminrescuemodeWeallmakemistakesandthisisespeciallytruefornoviceLinuxsystemadministrators.LinuxcanhaveasteeplearningcurveandsoonerorlatertherewillbeapointinyourcareerwhereyourCentOSinstallationdoesnotstartupduetobroadnumberofreasons,includinghardwareproblemsorhumanmistakessuchasconfigurationerrors.IfthishashappenedtoyouthenyoucanusetheCentOSrescuemodeinordertobootanotherwiseunbootablesystemandtrytoundoyourmistakesorfindouttherootoftheproblems.Inthisrecipe,wewillshowyouthreecommonusecaseswhentousethisoption:
AccessingthefilesystemforrecoveringimportantdataorundoingchangestoconfigurationfilesifCentOSisnotbootingupChangingtherootpasswordifyouforgotitRe-installingthebootloaderwhichcanbedamagedwheninstallinganotheroperatingsystemonthesameharddiskwhereCentOSisinstalled
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GettingreadyTocompletethisrecipe,youwillrequireastandardinstallationmedia(CD/DVDorUSBdevice)oftheCentOS7operatingsystem.Forrecoveringthedatafromthesystem,youwillneedtoconnectsomesortofexternalstoragedevicetothesystem,suchasanexternalharddiskoraworkingnetworkconnectiontoanothercomputertocopyallyourpreciousdatatoadifferentlocation.
Howtodoit…Tobeginthisrecipe,youshouldbootyourserverfromtheCentOSinstallationCD/DVDortheUSBdeviceandwaituntilthefirstwelcomesplashscreenappearswiththecursorwaitingattheTestthismedia&installCentOS7menuoption.
Reachingrescuemode1. Fromthemainmenu,usethedownarrowkeytoselectTroubleshootingandthen
presstheReturnkeytoproceed.2. OntheTroubleshootingscreen,usethedownarrowkeytohighlightRescuea
CentOSsystem.Whenyouareready,presstheReturnkeytoproceed.3. Aftersomeloadingtime,weentertherescuescreen,whichincludesvarious
confirmationsub-screens.Tobeginthissection,usetheleftandrightarrowkeystochooseContinueandpresstheReturnkeytoproceed.
4. Onthefirstsub-screen,chooseOKandpresstheReturnkeytoproceed.5. Again,inthefollowingsub-screen,chooseOKandpresstheReturnkeytoproceed.6. Onthenextscreen,choosetheStartshellandbyusingtheTabkey,highlightOK
andpresstheReturnkeytoproceed.7. Bycompletingtheprecedingsteps,youwilllaunchashellsession.Youwillnotice
thisatthebottomofyourdisplay.Thecurrentstatusoftheshellsessionwillreadasfollows:
bash-4.2#_
8. Attheprompt,typethefollowinginstructiontochangetherootfilesystem,beforepressingtheReturnkeytocompleteyourrequest:
chroot/mnt/sysimage
9. Congratulations!Youjustreachedtherescuemode.Toexititatanytime,simplytypethefollowingcommandandthenpresstheReturnkeytocompleteyourrequest(don’tdothisrightnowasthiswillrestartthesystem):
reboot
10. Afterthebasicrescuemodeisreached,wehavethefollowingoptions,dependingonthetypeofproblem.
AccessingthefilesystemIfyouarenowintherescuemodeandneedtobackupimportantfilesfromthefilesystem,youneedadestinationlocationforthedatatransfer.FortransferringthedatawewanttorecoverfromtheservertoanothercomputerpleasephysicallyconnectanexternalUSBdevicetoit.Youcanalsousenetworkstoragesfortherecovery.Forexample,youcouldimportanNFSservershareandcopydatatoit.RefertotheWorkingwithNFSrecipeinChapter7,BuildingaNetwork.
1. Ontherescuemodecommandline,typeinthefollowingcommand,whichwillshow
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youallthecurrentpartitionsconnectedtothesystem,andthenpresstheReturnkeytocompleteyourrequest:
fdisk-l
2. Younowneedtofindouttherightdevicenamewiththepartitionnumberofyourconnecteddevice;comparingthetotalsizeorthefilesystemoutputofthevariousdeviceswiththespecificationsfromyourstickcanhelpyouinthisprocess.Youcanalsotrythefollowingtrick:runthefdisk-lcommandtwice,firstwiththeplugged-inUSBdeviceandthenagainwiththeUSBdeviceunplugged,andcomparetheoutputofboththecommands.Itshouldbedifferentbyonedevicenamewhichyouaresearchingfor!
3. Ifyouhavefoundtherightdevicenameinthelist,createadirectorytomountthesticktothefilesystem:
mkdir/mnt/hdd-recovery
4. Next,mountthediskpartitiontothisfolder.HereweassumethattheUSBdeviceofinteresthasthedevicenamesdd1(pleasechangeifdifferentonyoursystem):
mount/dev/sdd1/mnt/hdd-recovery
5. Theoriginalsystem’sharddisk’srootpartitionhasbeenmountedunderaspecificfolderbytherescuesystemautomatically(under/mnt/sysimage),ifyouneedtoaccessitforexampletochangeconfigurationfileswhichcausedstartupproblemsormakeafullorpartialbackup.Forexample,ifyouneedtobackupyourApachewebserverconfigurationfiles,use:
cp-r/mnt/sysimage/etc/http/mnt/hdd-recovery
6. Ifyouneedtoaccessthedatathatlivesonpartitionsotherthanthecurrentlymountedrootpartition,usefdisk-ltoidentifythepartitionofinterest.ThencreateadirectoryandmountthepartitiontoitandchangetothatdirectorytoaccessyourdatasimilaryoudidwhenmountingtheUSBdevice.
7. Tofinishbackingupthefiles,type:
reboot
Accessingthefilesystem1. Ifyouareintherescuemodeforchangingtherootpassword,justusethefollowing
commandandprovideanewpassword:
passwd
2. Tocompletechangingthepassword,type:
reboot
Re-installtheCentOSbootloader
1. Wewillnowusethefdiskcommandtofindthenameofallthecurrentpartitions.Todothis,typethefollowinginstructionandthenpresstheReturnkeytocompleteyourrequest:
fdisk–l
2. Nowrunthefollowingcommand:
dmesg|grep-Fq"EFIv"
3. Iftheprecedingcommanddoesnotproduceanyoutputlookforthe*symbolinthefdisklistinginthebootcolumntofindthecorrectstartpartition,andassumingthatyourbootdiskison/dev/sda1(changethisasrequired),typethefollowing:
grub2-install/dev/sda
4. Otherwise,ifthereisanoutput,runinstead:
yumreinstallgrub2-efishim
5. Ifnoerrorisreported,theconsoleshouldrespondasfollows:
#thisdevicemapwasgeneratedbyanaconda(hd0)/dev/sda
6. TheconsoleoutputfromthelaststephasconfirmedthatGRUBhasnowbeensuccessfullyrestored.
7. Torebootthecomputer,type:
reboot
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Howitworks…Thereareabroadvarietyofproblemswhichcanberesolvedbythetoolsprovidedthroughtherescuemodeenvironment.Oftentheseproblemsrefertobootingproblemsbutcanalsobefromdifferenttypes,suchasforgettingtherootpassword.Rescuemodecanbealife-saverandanunderstandingofitisaveryimportantskilltolearn.Itwasfeltthatsucharecipeshouldthusremaincloseathand.
TipRemembertoalwaysbecarefulwhenworkingwithbootloadercommandsasimproperusecanmakeyouroperatingsystemunbootable.
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UpdatingtheinstallationandenhancingtheminimalinstallwithadditionaladministrationanddevelopmenttoolsInthisrecipe,wewilllearnhowtoenhancetheminimalinstallwithadditionaltoolsthatwillgiveyouavarietyofadministrativeanddevelopmentoptions,whichinturnwillprovevitalduringthelifetimeofyourserverandwhichareessentialforsomerecipesinthisbook.Theminimalinstallisprobablythemostefficientwayyoucaninstallaserver,buthavingsaidthat,aminimalinstalldoesrequiresomeadditionalfeaturesinordertomakeitamorecompellingmodel.
GettingreadyTocompletethisrecipe,youwillrequireaminimalinstallationoftheCentOS7operatingsystemwithrootprivilegesandaconnectiontotheInternetinordertofacilitatethedownloadofadditionalpackages.
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Howtodoit…Wewillbeginthisrecipebyupdatingthesystem.
1. Toupdatethesystem,loginasrootandtype:
yum-yupdate
2. CentOSwillnowsearchfortherelevantupdatesand,ifavailable,theywillbeinstalled.Oncompletionanddependingonwhatwasupdated(thatis,kernelandnewsecurityfeaturestonamebutafew),youcandecidetorebootyourcomputer.Todothis,type:
reboot
3. Yourserverwillnowrebootandreturntotheloginscreen.Wewillnowcompletethisrecipeandenhanceourcurrentinstallationwithaseriesofpackagegroupsthatwillprovetobeveryusefulinthefuture.Todothis,loginasrootandtype:
yum-ygroupinstall"Base""DevelopmentLibraries""DevelopmentTools"yum-yinstallpolicycoreutils-python
Howitworks…ThepurposeofthisrecipeistoenhancetheminimalinstallationoftheCentOS7operatingsystemandbydoingthisyouhavenotonlyintroducedyourselftotheYellowdogUpdaterModified(YUM)packagemanager(somethingtowhichwewillreturntolateroninthisbook),butyounowhaveasystemthatiscapableofrunningavastamountofapplicationsrightout-of-the-box.
Sowhathavewelearnedfromthisexperience?
Westartedtherecipebyupdatingthesysteminordertoensurethatitisuptodate.Atthisstage,itisoftenagoodideatorebootthesystem.Itisnotexpectedthatwewilldothisveryoftenbutitisexpectedwhenupdatingforthefirsttimeaftertheinstallationoftheoperatingsystem,asitismostlikelythattherearemajorchangesavailable.Thereasonbehindthisistypicallybasedonthedesiretotakeadvantageofanewkernelorrevisedsecurityupdates.Inthenextphase,therecipeshowedyouhowtoaddaseriesofpackagegroupsthatmayprovetobemorethanusefulinthefuture.Tosavetime,wewrappedtheinstructiontoinstallthethreemainpackagegroups:Base,DevelopmentLibraries,andDevelopmentTools.Theprecedingactionaloneinstallsover200individualpackages,therebygivingyourservertheabilitytocompilethecodeandrunavastarrayofapplicationsout-of-the-box,thatyoumayneedoverthelifetimeofyourserver.Toseealistofallthepackageswithinagroup,forexample,fromBase,runtheyumgroupinfoBasecommand.Anotherpackageweinstalledwaspolicycoreutils-pythonwhichprovidestoolsandprogramstomanagethesecurityenhancedaccesscontroltoLinux,whichwewillusequiteoftenthroughoutthechaptersofthisbook.
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Chapter2.ConfiguringtheSystemInthischapter,wewillcoverthefollowingtopics:
NavigatingtextfileswithlessIntroductiontoVimSpeakingtherightlanguageSynchronizingthesystemclockwithNTPandthechronysuiteSettingyourhostnameandresolvingthenetworkBecomingasuperuserBuildingastaticnetworkconnectionCustomizingyoursystembannersandmessagesPrimingthekernel
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IntroductionThischapterisacollectionofrecipesthatcoversthebasicpracticeofestablishingthebasicneedsofaserver.Formany,buildingaservercanoftenseemtobeadauntingtask,andsothepurposeofthischapteristoprovideyouwithaninstantmethodtoachievethedesiredgoals.
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NavigatingtextfileswithlessThroughoutthisbook,youwilloftenuseprogramsandtoolsthatusetheprogramlessoraless-likenavigationtoviewandreadfilecontentordisplayoutput.Atfirst,thecontrolcanseemabitunintuitive.Here,inthisrecipe,wewillshowyouthebasicsofhowtonavigatethroughafileusinglesscontrols.
GettingreadyTocompletethisrecipe,youwillrequireaworkinginstallationoftheCentOS7operatingsystemwithrootprivileges.
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Howtodoit…1. Tobegin,loginasrootandtypethefollowingcommandtoopenaprogramthatuses
lessfornavigation:
manman
2. Tonavigate,presstheupanddownkeytoscrollupanddownonelineatatime,thespacebartoscrolldownapage,andthebkeytoscrollupapage.Youcansearchwithinthetextusingtheforwardslashkey,/,followedbythesearchterm,thenpressReturntosearch.Pressntojumptothenextsearchresult.Presstheqkeytoexit.
Howitworks…Here,inthisshortrecipe,wehaveshownyoutheverybasicsoflessnavigation,whichisessentialforreadingmanpagesandisusedbyalotofotherprogramsthroughoutthisbooktodisplaytext.Weonlyshowedyouthebasiccommandsandthereismuchmoretolearn.Pleasereadthelessmanualtofindoutmoreonmanlesscommand.
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IntroductiontoVimInthisrecipe,wewillgiveyouaverybriefintroductiontothetexteditor,Vim,whichisusedasthestandardtexteditorthroughoutthisbook.Youcanalsouseanyothertexteditoryouprefer,suchasnanooremacs,instead.
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GettingreadyTocompletethisrecipe,youwillrequireaworkinginstallationoftheCentOS7operatingsystemwithrootprivileges.
Howtodoit…Wewillstartthisrecipebyinstallingthevim-enhancedpackage,asitcontainsatutorialyoucanusetolearnworkingwithVim:
1. Tobegin,loginasrootandinstallthefollowingpackage:
yuminstallvim-enhanced
2. Afterwards,typethefollowingcommandtostarttheVimtutorial:
vimtutor
3. ThiswillopentheVimtutorialintheVimeditor.Tonavigate,presstheupanddownkeytoscrollupanddownsingle-linewise.Toexitthetutorial,presstheEsckey,thentype:q!,followedbytheReturnkeytoexit.
4. YoushouldnowreadthroughthefileandgothroughthelessonstogetabasicunderstandingofVim,tolearnhowtoedityourtextdocuments.
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Howitworks…ThetutorialshowninthisrecipeshouldbeseenasastartingpointfromwhichtolearnthebasicsforworkingwithoneofthemostpowerfulandeffectivetexteditorsavailableforLinux.Vimhasaverysteeplearningcurve,butafterdedicatingabouthalfanhourtothevimtutorguideyoushouldbeabletodoallthecommontexteditingtaskswithoutanyproblem,suchasopening,editing,andsavingtextfiles.
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SpeakingtherightlanguageInthisrecipe,wewillshowyouhowtochangethelanguagesettingsofyourCentOS7installationforthewholesystemandforsingleusers.Theneedtochangethisisrarebutcanbeimportant,forexampleifweaccidentallychosethewronglanguageduringinstallation.
GettingreadyTocompletethisrecipe,youwillrequireaworkinginstallationoftheCentOS7operatingsystemwithrootprivileges,andaconsole-basedtexteditorofyourchoice.YoushouldhavereadtheNavigatingtextfileswithlessrecipe,becausesomecommandsinthisrecipewilluselessforprintingoutput.
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Howtodoit…Therearetwocategoriesofsettingsthatyouhavetoadjustifyouwanttochangethesystem-widelanguagesettingsofyourCentOS7system.Webeginbychangingthesystemlocaleinformationandthenthekeyboardsettings:
1. Tobegin,loginasrootandtypethefollowingcommandtoshowthecurrentlocalesettingsfortheconsole,graphicalwindowmanagers(X11layout),andalsothecurrentkeyboardlayout:
localectlstatus
2. Next,tochangethesesettings,wefirstneedtoknowalltheavailablelocaleandkeyboardsettingsonthissystem(bothcommandsuselessnavigation):
localectllist-localeslocalectllist-keymaps
3. Ifyouhavepickedtherightlocalefromtheoutputaboveinourexample,de_DE.utf8andkeymapde-mac(changetoyourownappropriateneeds),youcanchangeyourlocaleandkeyboardsettingsusing:
localectlset-localeLANG=de_DE.utf8localectlset-keymapde-mac
4. Now,verifythepersistenceofyourchangesusingthesamecommandagain:
localectlstatus
Howitworks…Aswehaveseen,thelocalectlcommandisaveryconvenienttoolthatcantakecareofmanagingallimportantlanguagesettingsinaCentOS7system.
Sowhathavewelearnedfromthisexperience?
Westartedbyloggingintoourcommandlinewiththerootuser.Then,weranthelocalectlcommandwiththeparameterstatus,whichgaveusanoverviewofthecurrentlanguagesettingsinthesystem.TheoutputofthiscommandshowedusthatlanguagepropertiesinaCentOS7systemcanbeseparatedintolocale(systemlocale)andkeymap(VCkeymapandallX11layoutproperties)settings.
LocalesonLinuxareusedtosetthesystem’slanguageaswellasotherlanguage-specificproperties.Thiscanincludetextsfromerrormessages,logoutput,userinterfaces,and,ifyouareusingawindowmanagersuchasGnome,evenGraphicalUserInterfaces(GUI).Localesettingscanalsodefineregion-specificformattingsuchaspapersizes,numbersandtheirnaturalsorting,currencyinformation,andsoon.Theyalsodefinecharacterencoding,whichcanbeimportantifyouchosealanguagethathascharactersthatcannotbefoundinthestandardASCIIencoding.
Keymapsettingsontheotherhanddefinetheexactlayoutofeachkeyonyourkeyboard.
Next,tochangethesesettings,wefirstissuedthelocalectlcommandwiththelist-localesparametertoretrieveafulllistofalllocalesonthesystem,andlist-keymapstoshowalistofallkeyboardsettingsavailableinthesystem.Localesasoutputtedfromthelist-localesparameteruseaverycompactannotationfordefiningalanguage:
Language[_Region][.Encoding][@Modificator]
OnlytheLanguagepartismandatory,alltherestisoptional.Examplesforlanguageandregionare:en_USforEnglishandregionUnitedStatesorAmericanEnglish,es_CUwouldbelanguageSpanishandRegionCubaorCubanSpanish.
EncodingsareimportantforspecialcharacterssuchasGermanumlautoraccentsintheFrenchlanguage.Thememoryrepresentationofthesespecialcharacterscanbeinterpreteddifferentlydependingontheusedencodingtype.IngeneralUTF-8shouldbeusedasitiscapableofencodingalmostanycharacterineverylanguage.
Modificatorsareusedtochangesettingsdefinedbythelocale.Forexample,sr_RS.utf8@latinisusedifyouwanttohaveLatinsettingsforserbianSerbia,whichnormallyusesCyrillicdefinitions.Thiswillchangetowesternsettingssuchassorting,currencyinformation,andsoon.
Tochangetheactuallocale,weusedtheset-localeLANG=de_DE.utf8parameter.Here,theencodingwasselectedtodisplayproperGermanumlauts.PleasenotethatweusedtheLANGoptiontosetthesamelocalevalue(forexample,de_DE.utf8)forallavailablelocaleoptions.Ifyoudon’twanttohavethesamelocalevalueforallavailableoptions,youcanuseamorefine-grainedcontroloversinglelocaleoptions.Pleaserefertothelocaledescriptionusingthemanpage,man7locale(onminimalinstallation;youneedto
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installallLinuxdocumentationmanpagesbeforeusingtheyuminstallman-pagescommand).Youcansettheseadditionaloptionsusingasimilarsyntax,forexample,tosetthetimelocaleuse:
localectlset-localeLC_TIME="de_DE.utf8"
Next,weshowedallavailablekeymapcodesusingthelist-keymapsparameter.Aswehaveseenfromrunninglocalectlstatus,thekeymapscanbeseparatedinnon-graphical(VCkeymap)andgraphical(X11layout)settings,whichallowstheflexibleconfigurationofdifferentkeyboardlayoutswhenusingawindowmanagersuchasGnomeandfortheconsole.Runninglocalectlwiththeparameter,set-keymapde-mac,setsthecurrentkeymaptoaGermanAppleMacintoshkeyboardmodel.ThiscommandappliesthegivenkeyboardtypetoboththenormalVCandtheX11keyboardmappings.IfyouwantdifferentmappingsforX11thanfortheconsole,uselocalectl--no-convertset-x11-keymapcz-querty,whereweusecz-quertyforthekeymapcodetoaCzechquertykeyboardmodel(changethisaccordingly).
There’smore…Sometimes,singlesystemusersneeddifferentlanguagesettingsthanthesystem’slocale(whichcanonlybesetbytherootuser),accordingtotheirregionalkeyboarddifferencesandforinteractingwiththesystemintheirpreferredhumanlanguage.System-widelocalesgetinheritedbyeveryuseraslongastheyarenotoverwrittenbylocalenvironmentvariables.
NoteChangingsystem-widelocalesdoesnotnecessarilyhaveaneffectonyouruser’slocalesiftheyhavealreadydefinedsomethingelseforthemselves.
Toprintallthecurrentlocaleenvironmentvariablesforanysystemuser,wecanusethecommand,locale.Tosetsingleenvironmentvariableswiththeappropriatevariablename;forexample,tosetthetimelocaletoUStimewewouldusethefollowingline:
exportLC_TIME="en_US.UTF-8"
But,mostlikelywewouldwanttochangeallthelocalestothesamevalue;thiscanbedonebysettingLANG.Forexample,tosetallthelocalestoAmericanEnglish,usethefollowingline:
exportLANG="en_US.UTF-8"
Totesttheeffectoflocalechanges,wecannowproduceanerrormessagethatwillbeshowninthelanguagesetbythelocalecommand.HereisthedifferentlanguageoutputforchanginglocalefromEnglishtoGerman:
exportLANG="en_US.UTF-8"ls!
Thefollowingoutputwillbeprinted:
ls:cannotaccess!:Nosuchfileordirectory
Now,changetoGermanlocalesettings:
exportLANG="de_DE.UTF-8"ls!
Thefollowingoutputwillbeprinted:
ls:Zugriffauf!nichtmöglich:DateioderVerzeichnisnichtgefunden
Settingalocaleinanactiveconsoleusingtheexportcommandwillnotsurviveclosingthewindoworopeninganewterminalsession.Ifyouwanttomakethosechangespermanent,youcansetanylocaleenvironmentvariables,suchastheLANGvariable,inafilecalled.bashrcinyourhomedirectory,whichwillbereadeverytimeashellisopened.Tochangethelocalesettingspermanentlytode_DE.UTF-8inourexample(changethistoyourownneeds)usethefollowingline:
echo"exportLANG='de_DE.UTF-8'">>~/.bashrc
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SynchronizingthesystemclockwithNTPandthechronysuiteInthisrecipe,wewilllearnhowtosynchronizethesystemclockwithanexternaltimeserverusingtheNetworkTimeProtocol(NTP)andthechronysuite.Fromtheneedtotime-stampdocuments,e-mails,andlogfiles,tosecuring,running,anddebugginganetwork,ortosimplyinteractwithshareddevicesandservices,everythingonyourserverisdependentonmaintaininganaccuratesystemclock,anditisthepurposeofthisrecipetoshowyouhowthiscanbeachieved.
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GettingreadyTocompletethisrecipe,youwillrequireaworkinginstallationoftheCentOS7operatingsystemwithrootprivileges,aconsole-basedtexteditorofyourchoice,andaconnectiontotheInternettofacilitatedownloadingadditionalpackages.
Howtodoit…Inthisrecipe,wewillusethechronyservicetomanageourtimesynchronization.AschronyisnotinstalledbydefaultonCentOSminimal,wewillstartthisrecipebyinstallingit:
1. Tobegin,loginasrootandinstallthechronyservice,thenstartitandverifythatitisrunning:
yuminstall-ychronysystemctlstartchronydsystemctlstatuschronyd
2. Also,ifwewanttousechronypermanently,wewillhavetoenableitonserverstartup:
systemctlenablechronyd
3. Next,weneedtocheckwhetherthesystemalreadyusesNTPtosynchronizeoursystemclockoverthenetwork:
timedatectl|grep"NTPsynchronized"
4. IftheoutputfromthelaststepshowedNoforNTPsynchronized,weneedtoenableitusing:
timedatectlset-ntpyes
5. Ifyourunthecommand(fromstep3)again,youshouldseethatitisnowsynchronizingNTP.
6. Thedefaultinstallationofchronywilluseapublicserverthathasaccesstotheatomicclock,butinordertooptimizetheservicewewillneedtomakeafewsimplechangestostreamlineandoptimizeatwhattimeserversareused.Todothis,openthemainchronyconfigurationfilewithyourfavoritetexteditor,asshownhere:
vi/etc/chrony.conf
7. Inthefile,scrolldownandlookforthelinescontainingthefollowing:
server0.centos.pool.ntp.orgiburstserver1.centos.pool.ntp.orgiburstserver2.centos.pool.ntp.orgiburstserver3.centos.pool.ntp.orgiburst
8. Replacethevaluesshownwithalistofpreferredlocaltimeservers:
server0.uk.pool.ntp.orgiburstserver1.uk.pool.ntp.orgiburstserver2.uk.pool.ntp.orgiburstserver3.uk.pool.ntp.orgiburst
NoteVisithttp://www.pool.ntp.org/toobtainalistoflocalserversgeographicallynearyourcurrentlocation.Remember,theuseofthreeormoreserverswillhavea
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tendencytoincreasetheaccuracyoftheNTPservice.
9. Whencomplete,saveandclosethefilebeforesynchronizingyourserverusingthesytstemctlcommand:
systemctlrestartchronyd
10. Tocheckwhetherthemodificationsintheconfigfileweresuccessful,youcanusethefollowingcommand:
systemctlstatuschronyd
11. Tocheckwhetherchronyistakingcareofyoursystemtimesynchronization,usethefollowing:
chronyctracking
12. Tocheckthenetworksourceschronyusesforsynchronization,usethefollowing:
chronycsources
Howitworks…OurCentOS7operatingsystem’stimeissetoneverybootbasedonthehardwareclock,whichisasmall-batterydrivenclocklocatedonthemotherboardofyourcomputer.Often,thisclockistooinaccurateorhasnotbeensetright,thereforeit’sbettertogetyoursystemtimefromareliablesourceovertheInternet(thatusesrealatomictime).Thechronydaemon,chronyd,setsandmaintainssystemtimethroughaprocessofsynchronizationwitharemoteserverusingtheNTPprotocolforcommunication.
So,whathavewelearnedfromthisexperience?
Asafirststep,weinstalledthechronyservice,sinceitisnotavailablebydefaultonaCentOS7minimalinstallation.Afterwards,weenabledthesynchronizationofoursystemtimewithNTPusingthetimedatectlset-ntpyescommand.
Afterthat,weopenedthemainchronyconfigurationfile,/etc/chrony.conf,andshowedhowtochangetheexternaltimeserversused.ThisisparticularlyusefulifyourserverisbehindacorporatefirewallandhaveyourownNTPserverinfrastructure.
Havingrestartedtheservice,wethenlearnedhowtocheckandmonitorournewconfigurationusingthechronyccommand.Thisisausefulcommandlinetool(cstandsforclient)forinteractingandcontrollingachronydaemon(locallyorremotely).Weusedthetrackingparameterwithchronyc,whichshowedusdetailedinformationofthecurrentNTPsynchronizationprocesswithaspecificserver.Pleaserefertothemanpagesofthechronyccommandifyouneedfurtherhelpaboutthepropertiesshownintheoutput(manchronyc).
Wealsousedthesourcesparameterwiththechronycprogram,whichshowedusanoverviewoftheusedNTPtimeservers.
Youcanalsousetheolderdatecommandtovalidatecorrecttimesynchronization.Itisimportanttorealizethattheprocessofsynchronizingyourservermaynotbeinstantaneous,anditcantakeawhilefortheprocesstocomplete.However,youcannowrelaxinthefullknowledgethatyounowknowhowtoinstall,manageandsynchronizeyourtimeusingtheNTPprotocol.
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There’smore…Inthisrecipe,wesetoursystem’stimeusingthechronyserviceandtheNTPprotocol.Usually,systemtimeissetasCoordinatedUniversalTime(UTC)orworldtime,whichmeansitisonestandardtimeusedacrossthewholeworld.Fromit,weneedtocalculateourlocaltimeusingtimezones.Tofindtherighttimezone,usethefollowingcommand(readtheNavigatingtextfileswithlessrecipetoworkwiththeoutput):
timedatectllist-timezones
Ifyouhavefoundtherighttimezone,writeitdownanduseitinthenextcommand;forexample,ifyouarelocatedinGermanyandarenearthecityofBerlin,usethefollowingcommand:
timedatectlset-timezoneEurope/Berlin
Usetimedatectlagaintocheckifyourlocaltimeiscorrectnow:
timedatectl|grep"Localtime"
Finally,ifitiscorrect,youcansynchronizeyourhardwareclockwithyoursystemtimetomakeitmoreprecise:
hwclock--systohc
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SettingyourhostnameandresolvingthenetworkTheprocessofsettingthehostnameistypicallyassociatedwiththeinstallationprocess.Ifyoueverneedtochangeitoryourserver’sDomainNameSystem(DNS)resolver,thisrecipewillshowyouhow.
GettingreadyTocompletethisrecipe,youwillrequireaworkinginstallationoftheCentOS7operatingsystemwithrootprivileges,andaconsole-basedtexteditorofyourchoice.
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Howtodoit…Tobeginthisrecipe,weshallstartbyaccessingthesystemasrootandopeningthefollowingfileinordertonameorrenameyourcurrentserver’shostname:
1. Loginasrootandtypeinthefollowingcommandtoseethecurrenthostname:
hostnamectlstatus
2. Now,changethehostnamevaluetoyourpreferredname.Forexample,ifyouwanttocallyourserverjimi,youwouldtype(changeappropriately):
hostnamectlset-hostnamejimi
NoteStatichostnamesarecase-sensitiveandres
