CentOS 7 Linux Server Cookbook - Second Edition

CentOS7LinuxServerCookbookSecondEdition

TableofContents


Credits

AbouttheAuthors

AbouttheReviewer

www.PacktPub.com

Supportfiles,eBooks,discountoffers,andmore

WhySubscribe?

FreeAccessforPacktaccountholders

Preface

Whatthisbookcovers

Whatyouneedforthisbook

Whothisbookisfor

Sections

Gettingready

Howtodoit

Howitworks

Theresmore

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

Theresmore

SynchronizingthesystemclockwithNTPandthechronysuite

Gettingready

Howtodoit

Howitworks

Theresmore

Settingyourhostnameandresolvingthenetwork

Gettingready

Howtodoit

Howitworks

Theresmore

Buildingastaticnetworkconnection

Gettingready

Howtodoit

Howitworks

Becomingasuperuser

Gettingready

Howtodoit

Howitworks

Customizingyoursystembannersandmessages

Gettingready

Howtodoit

Howitworks

Theresmore

Primingthekernel

Gettingready

Howtodoit

Howitworks

Theresmore

3.ManagingtheSystem

Introduction

Knowingandmanagingyourbackgroundservices

Gettingready

Howtodoit

Howitworks

Theresmore

Troubleshootingbackgroundservices

Gettingready

Howtodoit

Howitworks

Trackingsystemresourceswithjournald

Gettingready

Howtodoit

Howitworks

Configuringjournaldtomakeitpersistent

Gettingready

Howtodoit

Howitworks

Managingusersandtheirgroups

Gettingready

Howtodoit

Howitworks

Schedulingtaskswithcron

Gettingready

Howtodoit

Howitworks

Theresmore

Synchronizingfilesanddoingmorewithrsync

Gettingready

Howtodoit

Howitworks

Maintainingbackupsandtakingsnapshots

Gettingready

Howtodoit

Howitworks

Monitoringimportantserverinfrastructure

Gettingready

Howtodoit

Howitworks

TakingcontrolwithGITandSubversion

Gettingready

Howtodoit

Howitworks

Theresmore

4.ManagingPackageswithYUM

Introduction

UsingYUMtoupdatethesystem

Gettingready

Howtodoit

Howitworks

Theresmore

UsingYUMtosearchforpackages

Gettingready

Howtodoit

Howitworks

Theresmore

UsingYUMtoinstallpackages

Gettingready

Howtodoit

Howitworks

Theresmore

UsingYUMtoremovepackages

Gettingready

Howtodoit

Howitworks

KeepingYUMcleanandtidy

Gettingready

Howtodoit

Howitworks

Theresmore

Knowingyourpriorities

Gettingready

Howtodoit

Howitworks

Usingathird-partyrepository

Gettingready

Howtodoit

Howitworks

Theresmore

CreatingaYUMrepository

Gettingready

Howtodoit

Howitworks

Theresmore

WorkingwiththeRPMpackagemanager

Gettingready

Howtodoit

Howitworks

Theresmore

5.AdministeringtheFilesystem

Introduction

Creatingavirtualblockdevice

Gettingready

Howtodoit

Howitworks

Theresmore

Formattingandmountingafilesystem

Gettingready

Howtodoit

Howitworks

Theresmore

Usingdiskquotas

Gettingready

Howtodoit

Enablinguserandgroupquotas

Enablingproject(directory)quotas

Howitworks

Theresmore

Maintainingafilesystem

Gettingready

Howtodoit

Howitworks

Theresmore

Extendingthecapacityofthefilesystem

Gettingready

Howtodoit

Howitworks

6.ProvidingSecurity

Introduction

LockingdownremoteaccessandhardeningSSH

Gettingready

Howtodoit

Howitworks

Theresmore

ChangingtheSSHportnumberofyourserver

LimitingSSHaccessbyuserorgroup

Installingandconfiguringfail2ban

Gettingready

Howtodoit

Howitworks

Workingwithafirewall

Gettingready

Howtodoit

Howitworks

Theresmore

Forgingthefirewallrulesbyexample

Gettingready

Howtodoit

Tochangeanexistingfirewalldservice(ssh)

Tocreateyourownnewservice

Howitworks

Theresmore

Generatingself-signedcertificates

Gettingready

Howtodoit

Howitworks

Theresmore

UsingsecurealternativestoFTP

Gettingready

Howtodoit

SecuringyourvsftpdserverwithSSLFTPS

SecuringyourvsftpdserverusingSSHSFTP

Howitworks

Theresmore

7.BuildingaNetwork

Introduction

PrintingwithCUPS

Gettingready

Howtodoit

Howitworks

Theresmore

HowtoaddanetworkprintertotheCUPSserver

HowtosharealocalprintertotheCUPSserver

RunningaDHCPserver

Gettingready

Howtodoit

Howitworks

Theresmore

UsingWebDAVforfilesharing

Gettingready

Howtodoit

Howitworks

InstallingandconfiguringNFS

Gettingready

Howtodoit

InstallingandconfiguringtheNFSserver

Creatinganexportshare

Howitworks

WorkingwithNFS

Gettingready

Howtodoit

Howitworks

SecurelysharingresourceswithSamba

Gettingready

Howtodoit

Howitworks

Theresmore

8.WorkingwithFTP

Introduction

InstallingandconfiguringtheFTPservice

Gettingready

Howtodoit

Howitworks

Theresmore

WorkingwithvirtualFTPusers

Gettingready

Howtodoit

Howitworks

CustomizingtheFTPservice

Gettingready

Howtodoit

Howitworks

Troubleshootingusersandfiletransfers

Gettingready

Howtodoit

Howitworks

9.WorkingwithDomains

Introduction

Installingandconfiguringacaching-onlynameserver

Gettingready

Howtodoit

Configuringacaching-onlyUnboundDNSserver

ConfiguringaforwardingonlyDNSserver

Howitworks

Theresmore

Settingupanauthoritative-onlyDNSserver

Gettingready

Howtodoit

Howitworks

Theresmore

Creatinganintegratednameserversolution

Gettingready

Howtodoit

Howitworks

Theresmore

Populatingthedomain

Gettingready

Howtodoit

Howitworks

Buildingasecondary(slave)DNSserver

Gettingready

Howtodoit

ChangestotheprimaryDNSserver

ChangestothesecondaryDNSserver(s)

Howitworks

10.WorkingwithDatabases

Introduction

InstallingaMariaDBdatabaseserver

Gettingready

Howtodoit

Howitworks

ManagingaMariaDBdatabase

Gettingready

Howtodoit

Howitworks

Theresmore

Reviewingandrevokingpermissionsordroppingauser

AllowingremoteaccesstoaMariaDBserver

Gettingready

Howtodoit

Howitworks

InstallingaPostgreSQLserverandmanagingadatabase

Gettingready

Howtodoit

Howitworks

Theresmore

ConfiguringremoteaccesstoPostgreSQL

Gettingready

Howtodoit

Howitworks

InstallingphpMyAdminandphpPgAdmin

Gettingready

Howtodoit

InstallingandconfiguringphpMyAdmin

InstallingandconfiguringphpPgAdmin

Howitworks

11.ProvidingMailServices

Introduction

Configuringadomain-widemailservicewithPostfix

Gettingready

Howtodoit

Howitworks

Theresmore

Changingane-mailsappearingdomainname

UsingTLS-(SSL)encryptionforSMTPcommunication

ConfigureBINDtouseyournewmailserver

WorkingwithPostfix

Howtodoit

ConnectingmailxtoaremoteMTA

Readingyourlocalmailsfromthemailbox

Howitworks

DeliveringthemailwithDovecot

Gettingready

Howtodoit

Howitworks

Theresmore

Settingupe-mailsoftware

UsingFetchmail

Gettingready

Howtodoit

Howitworks

Theresmore

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

Theresmore

Installing,configuring,andtestingPHP

Gettingready

Howtodoit

Howtodoit

SecuringApache

Gettingready

Howtodoit

Configuringhttpd.conftoprovidebettersecurity

Removingunneededhttpdmodules

ProtectingyourApachefiles

Howitworks

SettingupHTTPSwithSecureSocketsLayer(SSL)

Gettingready

Howtodoit

Howitworks

Theresmore

13.OperatingSystem-LevelVirtualization

Introduction

InstallingandconfiguringDocker

Gettingready

Howtodoit

Howitworks

Downloadinganimageandrunningacontainer

Gettingready

Howtodoit

Howitworks

Theresmore

Stoppingandstartingacontainer

Attachingandinteractingwithyourcontainer

CreatingyourownimagesfromDockerfilesanduploadingtoDockerHub

Gettingready

Howtodoit

UploadingyourimagetotheDockerHub

Howitworks

SettingupandworkingwithaprivateDockerregistry

Gettingready

Howtodoit

StepstobedoneonourDockerregistryserver(192.168.1.100)

Stepstobedoneoneveryclientneedingaccesstoourregistry

Howitworks

14.WorkingwithSELinux

Introduction

InstallingandconfiguringimportantSELinuxtools

Gettingready

Howtodoit

Howitworks

Theresmore

WorkingwithSELinuxsecuritycontexts

Gettingready

Howtodoit

Howitworks

Workingwithpolicies

Gettingready

Howtodoit

Howitworks

Theresmore

TroubleshootingSELinux

Gettingready

Howtodoit

Howitworks

15.MonitoringITInfrastructure

Introduction

InstallingandconfiguringNagiosCore

Gettingready

Howtodoit

Howitworks

SettingupNRPEonremoteclienthosts

Gettingready

Howtodoit

Howitworks

Monitoringimportantremotesystemmetrics

Gettingready

Howtodoit

Howitworks

CentOS7LinuxServerCookbookSecondEditionCopyright2016PacktPublishing

Allrightsreserved.Nopartofthisbookmaybereproduced,storedinaretrievalsystem,ortransmittedinanyformorbyanymeans,withoutthepriorwrittenpermissionofthepublisher,exceptinthecaseofbriefquotationsembeddedincriticalarticlesorreviews.

Everyefforthasbeenmadeinthepreparationofthisbooktoensuretheaccuracyoftheinformationpresented.However,theinformationcontainedinthisbookissoldwithoutwarranty,eitherexpressorimplied.NeithertheauthornorPacktPublishing,anditsdealersanddistributorswillbeheldliableforanydamagescausedorallegedtobecauseddirectlyorindirectlybythisbook.

PacktPublishinghasendeavoredtoprovidetrademarkinformationaboutallofthecompaniesandproductsmentionedinthisbookbytheappropriateuseofcapitals.However,PacktPublishingcannotguaranteetheaccuracyofthisinformation.

Firstpublished:April2013

Secondedition:January2016

Productionreference:1250116

PublishedbyPacktPublishingLtd.

LiveryPlace

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BirminghamB32PB,UK.

ISBN978-1-78588-728-4

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CreditsAuthors

OliverPelz

JonathanHobson

Reviewer

MitjaResman

CommissioningEditor

PriyaSingh

AcquisitionEditor

KevinColaco

ContentDevelopmentEditor

PoojaMhapsekar

TechnicalEditor

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CopyEditor

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Proofreader

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Indexer

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CoverWork

ManuJoseph

AbouttheAuthorsOliverPelzhasmorethan10yearsofexperienceasasoftwaredeveloperandsystemadministrator.HegraduatedwithadiplomadegreeinbioinformaticsandiscurrentlyworkingattheGermanCancerResearchcenterinHeidelbergwherehehasauthoredandco-authoredseveralscientificpublicationsinthefieldofBioinformatics.Aswellasdevelopingwebapplicationsandbiologicaldatabasesforhisdepartmentandscientistsallovertheworld,headministersadivision-wideLinux-baseddatacenterandhassetuptwohigh-performanceCentOSclustersfortheanalysisofhigh-throughputmicroscopeandgenomesequencingdata.Heloveswritingcode,ridinghismountainbikeintheBlackForestofGermanyandhasbeenanabsoluteLinuxandopensourceenthusiastformanyyears.Hehascontributedtoseveralopen-sourceprojectsinthepastandalsoworkedasarevieweronthebookCentOSHighPerformance,PacktPublishing.HemaintainsanITtechblogatwww.oliverpelz.de.

IwouldliketothankmyfamilyandespeciallymywonderfulwifeBeatriceandlittlesonJonahfortheirpatienceandunderstandingduringallthelongworkinghourswhilewritingthisbook.AlsoIwouldliketothankthefolksatPacktPublishingforalltheirsupportandtheopportunitytotowritethisbook,itwasagreatpleasureforme.LastbutnotleastIwouldliketothankJonathanHobsonforwritingthefirsteditionofthisbook:withouthimnosecondeditionofthisbookwouldhavebeenpossible.

IwouldalsoliketothankallofthementorsthatIvehadovertheyears,especiallyProf.Dr.TobiasDykerhoff,whointroducedmetothewholeworldofLinuxalongtimeagoandinfectedmewithhisenthusiasmaboutopensourceandthefreesoftwaremovement.

JonathanHobsonisawebdeveloper,systemsengineer,andapplicationsprogrammer.Formorethan20years,hehasbeenworkingbehindthescenestosupportcompanies,organizations,andindividualsaroundtheworldtorealizetheirdigitalambitions.Withanhonorsdegreeinbothenglishandhistoryandasarespectedpractitionerofmanycomputerlanguages,Jonathanenjoyswritingcode,publishingarticles,buildingcomputers,playingthevideogames,andgettingoutandaboutinthebigoutdoors.HehasbeenusingCentOSsinceitsinception,andovertheyears,ithasnotonlyearnedhistrust,butithasalsobecomehisfirstchoiceforaserversolution.CentOSisafirstclasscommunity-basedenterpriseclassoperatingsystem.Itisapleasuretoworkwithandbecauseofthis,Jonathanhaswrittenthisbooksothathisknowledgeandexperiencecanbepassedontoothers.

http://www.oliverpelz.de

AbouttheReviewerMitjaResmancomesfromasmall,beautifulcountrycalledSlovenia,locatedinsouthernCentralEurope.MitjaisafanofLinuxandanopensourceenthusiast,andalsoaRedHatCertifiedEngineerandLinuxProfessionalInstituteprofessional.Workingasasystemadministrator,MitjagotyearsofprofessionalexperiencewithopensourcesoftwareandLinuxsystemadministrationonlocalandinternationalprojectsworldwide.SwissArmyknifesyndromemakesMitjaanexpertinthefieldsofVMwarevirtualization,Microsoftsystemadministration,andalsoAndroidsystemadministration.

Mitjahasastrongdesiretolearn,develop,andshareknowledgewithothers.ThisisthereasonhestartedablogcalledGeekPeek.Net.ThiswebsiteprovidesCentOSLinuxguidesandhowtoarticlescoveringallsortsoftopicsappropriateforbeginnersandadvancedusers.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,makinganupdateofthebooksoriginalcontentessential.Butthisbookisnotjustarefresherofthetopicscoveredinthefirstedition:twobrandnewchaptershavebeenincludedaswelltokeepuptodatewiththelatestopensourcetechnologiesaswellasprovidingbettersecurity:operatingsystem-levelvirtualizationandSELinux.Finally,tomakethebookamorecomprehensiveserver-administrationbook,anotherchapteraboutservermonitoringhasbeenincludedaswell.

Buildingaservercanpresentachallenge.Itisoftendifficultatthebestoftimesandfrustratingattheworstoftimes.Theycanrepresentthebiggestofproblemsorgiveyouagreatsenseofprideandachievement.Wherethewordservercandescribemanythings,itistheintentionofthisbooktoliftthelidandexposetheinnerworkingsofthisenterprise-classcomputingsystemwiththeintentionofenablingyoutobuildyourprofessionalserversolutionofchoice.CentOSisacommunity-basedenterpriseclassoperatingsystem.Itisavailablefreeofcharge,andasafullycompatiblederivativeofRedHatEnterpriseLinux(RHEL),itrepresentsthefirstchoiceoperatingsystemfororganizations,companies,professionals,andhomeusersallovertheworldwhointendtorunaserver.ItswidelyrespectedasaverypowerfulandflexibleLinuxdistributionandregardlessofwhetheryouintendtorunawebserver,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,focusesonworkingwithyourserversfilesystem.Fromcreatingmockingdiskdevicestotest-driveconceptsexpertlevelformattingandpartitioningcommands,youwilllearnhowtoworkwiththeLogicalVolumeManager,maintainyourfilesystemandworkwithdiskquotas.

Chapter6,ProvidingSecurity,discussestheneedtoimplementaseriesofsolutionsthatwilldeliverthelevelofprotectionyouneedtorunasuccessfulserversolution.FromprotectingyoursshandFTPservices,tounderstandingthenewfirewalldmanagerandcreatingcertificates,youwillseehoweasyitistobuildaserverthatnotonlyconsiderstheneedtoreduceriskfromexternalattackbutonethatwillprovideadditionalprotectionforyourusers.

Chapter7,BuildingaNetwork,explainsthestepsrequiredtoimplementvariousformsofresourcesharingwithinyournetworkscomputers.FromIPaddressesandprintingdevicestovariousformsoffilesharingprotocols,thischapterplaysanessentialroleofanyserverwhetheryouareintendingtosupportahomenetworkorafullcorporateenvironment.

Chapter8,WorkingwithFTP,concentratesontheroleofVSFTPwithaseriesofrecipesthatwillprovidetheguidanceyouneedtoinstall,configureandmanagetheFileTransferProtocol(FTP)youwanttoprovideonaCentOS7server.

Chapter9,WorkingwithDomains,considersthestepsrequiredtoimplementdomain

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.

WhatyouneedforthisbookTherequirementsofthisbookarerelativelysimpleandbeginwiththeneedtodownloadtheCentOSoperatingsystem.Thesoftwareisfree,butyouwillneedacomputerthatiscapableoffulfillingtheroleofaserver,somefreeinstallationmedia(blankCD-R/DVD-RorUSBdevice),anInternetconnection,somesparetime,andadesiretohavefun.

Insayingthat,manyreaderswillbeawarethatyoudonotneedasparecomputertotakeadvantageofthisbookastheoptionofinstallingCentOSonvirtualizationsoftwareisalwaysavailable.Thisapproachisquitecommonandwheretherecipescontainedwithinthesepagesremainapplicable,youshouldbeawarethattheuseofvirtualizationsoftwareisnotconsideredbythisbook.Forthisreason,anyrequestsforsupportregardingtheuseofthissoftwareshouldbedirectedtowardstheappropriatesupplier.

WhothisbookisforThisisapracticalguideforbuildingaserversolution,andratherthanbeingaboutCentOSitself,thisisabookthatwillshowyouhowtogetCentOSupandrunning.Itisabookthathasbeenwrittenwiththenovice-to-intermediateLinuxuserinmindwhoisintendingtouseCentOSasthebasisoftheirnextserver.However,ifyouarenewtooperatingsystemsasawhole,thendontworry;thisbookwillalsoservetoprovideyouwiththestep-by-stepapproachyouneedtobuildacompleteserversolutionwithplentyoftricksofthetradethrowninforgoodmeasure.

SectionsInthisbook,youwillfindseveralheadingsthatappearfrequently(Gettingready,Howtodoit,HowitworksandTheresmore).

Togiveclearinstructionsonhowtocompletearecipe,weusethesesectionsasfollows:

GettingreadyThissectiontellsyouwhattoexpectintherecipe,anddescribeshowtosetupanysoftwareoranypreliminarysettingsrequiredfortherecipe.

HowtodoitThissectioncontainsthestepsrequiredtofollowtherecipe.

HowitworksThissectionusuallyconsistsofadetailedexplanationofwhathappenedintheprevioussection.

TheresmoreThissectionconsistsofadditionalinformationabouttherecipeinordertomakethereadermoreknowledgeableabouttherecipe.

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

IntroductionThischapterisacollectionofrecipesthatcoversthebasicpracticeofinstallingtheCentOS7operatingsystem.ThepurposeofthischapteristoshowyouhowquicklyyoucangetCentOSupandrunningwhilstenablingyoutocustomizeyourinstallationwithafewtricksofthetradethrowninforgoodmeasure.

DownloadingCentOSandconfirmingthechecksumonWindowsorOSXInthisrecipe,wewilllearnhowtodownloadandconfirmthechecksumofoneormoreCentOS7diskimagesusingatypicalWindowsorOSXdesktopcomputer.CentOSismadeavailableinvariousformatsbyHTTP,FTP,orthersyncprotocolfromaseriesofmirrorsiteslocatedacrosstheworldorviatheBitTorrentnetwork.FordownloadingveryimportantfilesfromtheInternet,suchasoperatingsystemimages,itisconsideredbestpracticestovalidatethosefileschecksum,inordertoensurethatanyresultingmediawouldfunctionandperformasexpectedwheninstalling.Thisalsomakescertainthatthefilesaregenuineandcomefromtheoriginalsource.

GettingreadyTocompletethisrecipe,itisassumedthatyouareusingatypicalWindows-based(Windows7,WindowsVista,orsimilar)orOSXcomputerwithfulladministrationrights.YouwillneedanInternetconnectiontodownloadtherequiredinstallationfilesandalsoneedaccesstoastandardDVD/CDdiskburnerwiththeappropriatesoftware,inordertocreatetherelevantinstallationdisksfromtheimagefiles.Forthepurposeofthisrecipe,itisassumedthatallthedownloadswillbestoredonWindowsinyourpersonalC:\Users\\Downloadsfolder,orifusinganOSXsystem,inthe/Users//Downloadsfolder.

HowtodoitRegardlessofthetypeofinstallationfilesyoudownload,thefollowingtechniquescanbeappliedtoalltheimagefilessuppliedbytheCentOSproject:

1. Letsbeginbyvisitinghttp://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.

HowitworksSowhathavewelearnedfromthisexperience?

TheactofdownloadingaCentOSinstallationimageisjustthefirststeptowardsbuildingtheperfectserver.Althoughthisprocessisverysimple,manydoforgettheneedtoconfirmthechecksum.Inthisbook,wewillworkwiththeminimalinstallationimage,butyoushouldbeawarethatthereareotherinstallationoptionsavailabletoyou,suchasNetInstall,DVD,Everything,andvariousLiveCDs.

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.

HowtodoitTobeginthisrecipe,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:(changethisasrequiredandbecarefulwhatyoutypethiscancreatetremendousdataloss).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.

HowitworksSowhathavewelearnedfromthisexperience?

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!Ifyoureindoubtofthecorrectoutputfiledevice,neverstarttheddprogram!

Inconclusion,itisfairtosaythatthereareotherfarmoreconvenientsolutionsavailableforcreatingaUSBinstallationmediaforCentOS7thantheddcommand,suchastheFedoraLiveUSBCreator.Butthepurposeofthisrecipewasnotonlytocreateaready-to-useCentOSUSBinstallerbutalsotogetyouusedtotheddcommand.ItsacommonLinuxcommandthateveryCentOSsystemadministratorshouldknowhowtouse.Itcanbeusedforabroadvarietyofdailytasks.Forexample,forsecurelyerasingharddisks,benchmarkingnetworkspeed,orcreatingrandombinaryfiles.

PerforminganinstallationofCentOSusingthegraphicalinstallerInthisrecipe,wewilllearnhowtoperformatypicalinstallationofCentOSusinganewgraphicalinstallerinterfaceintroducedinCentOS7.Inmanyrespects,thisisconsideredtobetherecommendedapproachtoinstallingyoursystem,asitnotonlyprovidesyouwiththeabilitytocreatethedesiredharddiskpartitionsbutalsotocustomizeyourinstallationinlotsofways(forexample,keyboardlayout,packageselection,installationtype,andsoon).Yourinstallationwillthenformthebasisofaserveronwhichyoucanbuild,develop,andrunanytypeofserviceyoumaywanttoprovideinthefuture.

GettingreadyBeforewebegin,itisassumedthatyouhavefollowedthepreviousrecipeinwhichyouwereshownhowtodownloadaCentOSimage,confirmthechecksumoftherelevantimagefiles,andcreatetherelevantinstallationopticaldisksorUSBmedia.Yoursystemmustbea64bit(x64_86)architecture,musthaveatleast406MBRAMtoloadthegraphicalinstaller1GBormoreisrecommendedifinstallingagraphicalwindowmanagersuchasGnome),andhaveatleast10GBfreeharddiskspace.

HowtodoitTobeginthisrecipe,insertyourinstallationmedia(CD/DVDorUSBdevice),restartthecomputer,andpressthecorrectkeyforselectingthebootdeviceduringstartup.Thenchoosetheinserteddevicefromthelist(formanycomputers,thiscanbereachedusingF11orF12butcanbedifferentonyoursystem.Pleaserefertoyourmotherboardsmanual).

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.Soletsclickonitusingthemouse.

7. AfterclickingtheInstallationDestinationbutton,youwillseeagraphicallistofalltheharddiskdevicescurrentlyconnectedtoyourcomputer,whichyoucanuseforinstallingtheoperatingsystemon.Youcanselectyourtargetharddiskbyclickingonthecorrectharddisksymbol.Itwillthenputacheckmarkonit.Ifyouareunsureabouttherightharddisk,trytoidentifyitbycomparingitsbrandandtotalsizeshowninthemenu.Beforetheinstallationcanproceed,youmustselectaharddisk.Becarefulandchooseyourtargetharddiskwiselyasitwilleraseanyexistingdataonitduringtheinstallation.Whenyouareready,clicktheDonebutton.

8. Ifyourselectedharddiskalreadycontaineddata,thenwhenclickingonDone,youmayseewhatcouldbedescribedasawarning/errormessage.Themessagemayread:YoudonthaveenoughspaceavailabletoinstallCentOS.Dontworry!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.

HowitworksInthisrecipe,youhavediscoveredhowtoinstalltheCentOS7operatingsystem.Havingcoveredthetypicalapproachtothegraphicalinstallationprocess,youarenowinapositiontodeveloptheserverwithadditionalconfigurationchangesandpackagesthatwillsuittheroleyouintendtheservertofulfill.Thisgraphicalinstallerhasbeenbuiltwiththeaimtobeveryintuitiveandflexible,andmakesinstallationveryeasyasitwillguidetheuserthroughsomemandatorytasksthathehastofulfillbeforetheinstallationofthemainsystemcanbestarted.

RunninganetinstalloverHTTPInthisrecipe,wewilllearnhowtoinitiatetheprocessofrunninganetinstalloverHTTP(usingtheURLmethod)inordertoinstallCentOS7.Itisaprocessinwhichasmallimagefileisusedtobootthecomputerandlettheuserselectandinstallonlythesoftwarepackagesandserviceshewantsandnothingmoreoveranetworkconnectionthusprovidinggreatflexibility.

GettingreadyBeforewebegin,itisassumedthatyoualreadyknowhowtodownloadandchecksumaCentOS7installationimageandhowtocreatetherelevantinstallationmediafromit.Forthisrecipehere,wewillneedtodownloadandcreateinstallationmediaforthenetinstallimage(downloadthelatestCentOS-7-x86_64-NetInstall-XXXX.isofile)insteadoftheminimalISOshowninanotherrecipeinthischapter.Also,itisassumedthatyouhaveatleastgonethroughthegraphicalinstallationprocedureoncetoexactlyknowhowtobootfromyourinstallationmediaandworkwiththeinstallerprogram.

HowtodoitTobeginthisrecipe,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/

HowitworksThepurposeofthisrecipewastointroduceyoutotheconceptoftheCentOSnetworkinstallationprocess,inordertoshowyoujusthowsimplethisapproachcanbe.Bycompletingthisrecipeyouhavenotonlysavedtimebylimitingyourinitialdownloadtothosefilesthatarerequiredbytheinstallationprocess,butyouhavealsobeenabletotakeadvantageofthefullgraphicalinstallationmethodwithouttheneedforacompleteDVDsuite.

InstallingCentOS7usingakickstartfileWhileinstallingCentOS7manuallyusingthegraphicalinstallerutilityisfineonasingleserver,doingsoonamultiplenumberofsystemscanbetedious.Kickstartfilescanautomatetheinstallationprocessofaserversystemandherewewillshowhowthiscanbedone.Theyaresimpletextbasedconfigurationfileswhichprovidedetailedandexactinstructionsonhowthetargetsystemshouldbesetupandinstalled(forexample,whichkeyboardlayoutoradditionalsoftwarepackagestoinstall).

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).

HowtodoitForthisrecipetowork,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:

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.

HowitworksInthisrecipe,youhaveseenthateveryserverrunningaCentOS7installationkeepsthekickstartfileinitsrootdirectory,whichcontainsdetailedinformationonhowthesystemhadbeensetupduringtheinstallation.Thekickstartfilescanbeusedtoautomatetheinstallationsofmultiplesystemswiththesameconfiguration.Thiscansavealotoftimedoingrepetitiveworkasnouserinteractionduringinstallationisneeded.Also,wecanusethismethodifthetargetmachinesdontmeettheminimumrequirementinRAMforgraphicalbasedinstallationsbutwhenneededotherfeaturesthetextmodeinstallerdoesnotprovidesuchascustompartitioningofthesystem.Kickstartconfigurationfilesaresimpleplaintextfileswhichcanbecreatedmanuallyfromscratch.Becausetherearequiteanumberofdifferentcommandsavailabletoconstructyoursystemusingthekickstartsyntax,weusedanexistingfileasatemplateandcustomizedittofitourneeds,insteadofstartingoutcompletelynew.WedidnotusetheminimalinstallationimagetodriveourkickstartinstallationbecauseweinstalledsomeextrapackagesnotincludedontheminimalISOfile,suchastheApachewebserver.

GettingstartedandcustomisingthebootloaderWhenyouturnonyourcomputer,thebootloaderisthefirstprogramthatstartsupandisresponsibleforloadingandtransferringcontroltoanunderlyingoperatingsystem.Nowadays,almostanymodernLinuxdistributionusestheGRandUnifiedBootloaderversion2(GRUB2)forstartingthesystem.Ithasalotofflexibilityinconfigurationandsupportsalotofdifferentoperatingsystems.Inthisrecipe,wewillshowhowtocustomizetheGRUB2bootloaderbydisablingthewaitingtimeofthemenudisplayandthereforeimprovingthetimeittakesforbootingthesystem.

GettingreadyTocompletethisrecipe,youwillrequireaccesstoanalreadyinstalledCentOS7operatingsystem(minimaloranyotherCentOS7installationtypewillwork)withrootprivileges.Also,youneedtohavesomebasicexperienceswithatextbasededitor,suchasnano,forchangingtheconfigurationfiles.

HowtodoitWebeginthisrecipebyopeningthemainGRUB2configurationfilewithourtexteditorofchoiceandmodifyingit.

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.

HowitworksHavingcompletedthisrecipe,wenowknowhowtocustomizetheGRUB2bootloader.Inthisveryeasyrecipe,weonlyshowedyouverybasicmodificationstothebootloaderbutitcandomuchmore!Itsupportsabroadvarietyoffilesystemsandcanbootalmostanycompatibleoperatingsystem.Thisisalsoparticularlyusefulifyouplantorunmultipleoperatingsystemsonthesamemachine.TolearnmoreaboutGRUB2sconfigurationfilesyntaxtypetheinfogrub2|lesscommandandgotothesection6.1Simpleconfigurationhandling(readtherecipeNavigatingtextfileswithlessinChapter2,ConfiguringtheSystemtolearnhowtobrowsethisdocument).

TroubleshootingthesysteminrescuemodeWeallmakemistakesandthisisespeciallytruefornoviceLinuxsystemadministrators.LinuxcanhaveasteeplearningcurveandsoonerorlatertherewillbeapointinyourcareerwhereyourCentOSinstallationdoesnotstartupduetobroadnumberofreasons,includinghardwareproblemsorhumanmistakessuchasconfigurationerrors.IfthishashappenedtoyouthenyoucanusetheCentOSrescuemodeinordertobootanotherwiseunbootablesystemandtrytoundoyourmistakesorfindouttherootoftheproblems.Inthisrecipe,wewillshowyouthreecommonusecaseswhentousethisoption:

AccessingthefilesystemforrecoveringimportantdataorundoingchangestoconfigurationfilesifCentOSisnotbootingupChangingtherootpasswordifyouforgotitRe-installingthebootloaderwhichcanbedamagedwheninstallinganotheroperatingsystemonthesameharddiskwhereCentOSisinstalled

GettingreadyTocompletethisrecipe,youwillrequireastandardinstallationmedia(CD/DVDorUSBdevice)oftheCentOS7operatingsystem.Forrecoveringthedatafromthesystem,youwillneedtoconnectsomesortofexternalstoragedevicetothesystem,suchasanexternalharddiskoraworkingnetworkconnectiontoanothercomputertocopyallyourpreciousdatatoadifferentlocation.

HowtodoitTobeginthisrecipe,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(dontdothisrightnowasthiswillrestartthesystem):

reboot

10. Afterthebasicrescuemodeisreached,wehavethefollowingoptions,dependingonthetypeofproblem.

AccessingthefilesystemIfyouarenowintherescuemodeandneedtobackupimportantfilesfromthefilesystem,youneedadestinationlocationforthedatatransfer.FortransferringthedatawewanttorecoverfromtheservertoanothercomputerpleasephysicallyconnectanexternalUSBdevicetoit.Youcanalsousenetworkstoragesfortherecovery.Forexample,youcouldimportanNFSservershareandcopydatatoit.RefertotheWorkingwithNFSrecipeinChapter7,BuildingaNetwork.

1. Ontherescuemodecommandline,typeinthefollowingcommand,whichwillshow

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. Theoriginalsystemsharddisksrootpartitionhasbeenmountedunderaspecificfolderbytherescuesystemautomatically(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:

fdiskl

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

HowitworksThereareabroadvarietyofproblemswhichcanberesolvedbythetoolsprovidedthroughtherescuemodeenvironment.Oftentheseproblemsrefertobootingproblemsbutcanalsobefromdifferenttypes,suchasforgettingtherootpassword.Rescuemodecanbealife-saverandanunderstandingofitisaveryimportantskilltolearn.Itwasfeltthatsucharecipeshouldthusremaincloseathand.

TipRemembertoalwaysbecarefulwhenworkingwithbootloadercommandsasimproperusecanmakeyouroperatingsystemunbootable.

UpdatingtheinstallationandenhancingtheminimalinstallwithadditionaladministrationanddevelopmenttoolsInthisrecipe,wewilllearnhowtoenhancetheminimalinstallwithadditionaltoolsthatwillgiveyouavarietyofadministrativeanddevelopmentoptions,whichinturnwillprovevitalduringthelifetimeofyourserverandwhichareessentialforsomerecipesinthisbook.Theminimalinstallisprobablythemostefficientwayyoucaninstallaserver,buthavingsaidthat,aminimalinstalldoesrequiresomeadditionalfeaturesinordertomakeitamorecompellingmodel.

GettingreadyTocompletethisrecipe,youwillrequireaminimalinstallationoftheCentOS7operatingsystemwithrootprivilegesandaconnectiontotheInternetinordertofacilitatethedownloadofadditionalpackages.

HowtodoitWewillbeginthisrecipebyupdatingthesystem.

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

HowitworksThepurposeofthisrecipeistoenhancetheminimalinstallationoftheCentOS7operatingsystemandbydoingthisyouhavenotonlyintroducedyourselftotheYellowdogUpdaterModified(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.

Chapter2.ConfiguringtheSystemInthischapter,wewillcoverthefollowingtopics:

NavigatingtextfileswithlessIntroductiontoVimSpeakingtherightlanguageSynchronizingthesystemclockwithNTPandthechronysuiteSettingyourhostnameandresolvingthenetworkBecomingasuperuserBuildingastaticnetworkconnectionCustomizingyoursystembannersandmessagesPrimingthekernel

IntroductionThischapterisacollectionofrecipesthatcoversthebasicpracticeofestablishingthebasicneedsofaserver.Formany,buildingaservercanoftenseemtobeadauntingtask,andsothepurposeofthischapteristoprovideyouwithaninstantmethodtoachievethedesiredgoals.

NavigatingtextfileswithlessThroughoutthisbook,youwilloftenuseprogramsandtoolsthatusetheprogramlessoraless-likenavigationtoviewandreadfilecontentordisplayoutput.Atfirst,thecontrolcanseemabitunintuitive.Here,inthisrecipe,wewillshowyouthebasicsofhowtonavigatethroughafileusinglesscontrols.

GettingreadyTocompletethisrecipe,youwillrequireaworkinginstallationoftheCentOS7operatingsystemwithrootprivileges.

Howtodoit1. Tobegin,loginasrootandtypethefollowingcommandtoopenaprogramthatuses

lessfornavigation:

manman

2. Tonavigate,presstheupanddownkeytoscrollupanddownonelineatatime,thespacebartoscrolldownapage,andthebkeytoscrollupapage.Youcansearchwithinthetextusingtheforwardslashkey,/,followedbythesearchterm,thenpressReturntosearch.Pressntojumptothenextsearchresult.Presstheqkeytoexit.

HowitworksHere,inthisshortrecipe,wehaveshownyoutheverybasicsoflessnavigation,whichisessentialforreadingmanpagesandisusedbyalotofotherprogramsthroughoutthisbooktodisplaytext.Weonlyshowedyouthebasiccommandsandthereismuchmoretolearn.Pleasereadthelessmanualtofindoutmoreonmanlesscommand.

IntroductiontoVimInthisrecipe,wewillgiveyouaverybriefintroductiontothetexteditor,Vim,whichisusedasthestandardtexteditorthroughoutthisbook.Youcanalsouseanyothertexteditoryouprefer,suchasnanooremacs,instead.

GettingreadyTocompletethisrecipe,youwillrequireaworkinginstallationoftheCentOS7operatingsystemwithrootprivileges.

HowtodoitWewillstartthisrecipebyinstallingthevim-enhancedpackage,asitcontainsatutorialyoucanusetolearnworkingwithVim:

1. Tobegin,loginasrootandinstallthefollowingpackage:

yuminstallvim-enhanced

2. Afterwards,typethefollowingcommandtostarttheVimtutorial:

vimtutor

3. ThiswillopentheVimtutorialintheVimeditor.Tonavigate,presstheupanddownkeytoscrollupanddownsingle-linewise.Toexitthetutorial,presstheEsckey,thentype:q!,followedbytheReturnkeytoexit.

4. YoushouldnowreadthroughthefileandgothroughthelessonstogetabasicunderstandingofVim,tolearnhowtoedityourtextdocuments.

HowitworksThetutorialshowninthisrecipeshouldbeseenasastartingpointfromwhichtolearnthebasicsforworkingwithoneofthemostpowerfulandeffectivetexteditorsavailableforLinux.Vimhasaverysteeplearningcurve,butafterdedicatingabouthalfanhourtothevimtutorguideyoushouldbeabletodoallthecommontexteditingtaskswithoutanyproblem,suchasopening,editing,andsavingtextfiles.

SpeakingtherightlanguageInthisrecipe,wewillshowyouhowtochangethelanguagesettingsofyourCentOS7installationforthewholesystemandforsingleusers.Theneedtochangethisisrarebutcanbeimportant,forexampleifweaccidentallychosethewronglanguageduringinstallation.

GettingreadyTocompletethisrecipe,youwillrequireaworkinginstallationoftheCentOS7operatingsystemwithrootprivileges,andaconsole-basedtexteditorofyourchoice.YoushouldhavereadtheNavigatingtextfileswithlessrecipe,becausesomecommandsinthisrecipewilluselessforprintingoutput.

HowtodoitTherearetwocategoriesofsettingsthatyouhavetoadjustifyouwanttochangethesystem-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

HowitworksAswehaveseen,thelocalectlcommandisaveryconvenienttoolthatcantakecareofmanagingallimportantlanguagesettingsinaCentOS7system.

Sowhathavewelearnedfromthisexperience?

Westartedbyloggingintoourcommandlinewiththerootuser.Then,weranthelocalectlcommandwiththeparameterstatus,whichgaveusanoverviewofthecurrentlanguagesettingsinthesystem.TheoutputofthiscommandshowedusthatlanguagepropertiesinaCentOS7systemcanbeseparatedintolocale(systemlocale)andkeymap(VCkeymapandallX11layoutproperties)settings.

LocalesonLinuxareusedtosetthesystemslanguageaswellasotherlanguage-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.Ifyoudontwanttohavethesamelocalevalueforallavailableoptions,youcanuseamorefine-grainedcontroloversinglelocaleoptions.Pleaserefertothelocaledescriptionusingthemanpage,man7locale(onminimalinstallation;youneedto

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).

TheresmoreSometimes,singlesystemusersneeddifferentlanguagesettingsthanthesystemslocale(whichcanonlybesetbytherootuser),accordingtotheirregionalkeyboarddifferencesandforinteractingwiththesystemintheirpreferredhumanlanguage.System-widelocalesgetinheritedbyeveryuseraslongastheyarenotoverwrittenbylocalenvironmentvariables.

NoteChangingsystem-widelocalesdoesnotnecessarilyhaveaneffectonyouruserslocalesiftheyhavealreadydefinedsomethingelseforthemselves.

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!nichtmglich:DateioderVerzeichnisnichtgefunden

Settingalocaleinanactiveconsoleusingtheexportcommandwillnotsurviveclosingthewindoworopeninganewterminalsession.Ifyouwanttomakethosechangespermanent,youcansetanylocaleenvironmentvariables,suchastheLANGvariable,inafilecalled.bashrcinyourhomedirectory,whichwillbereadeverytimeashellisopened.Tochangethelocalesettingspermanentlytode_DE.UTF-8inourexample(changethistoyourownneeds)usethefollowingline:

echo"exportLANG='de_DE.UTF-8'">>~/.bashrc

SynchronizingthesystemclockwithNTPandthechronysuiteInthisrecipe,wewilllearnhowtosynchronizethesystemclockwithanexternaltimeserverusingtheNetworkTimeProtocol(NTP)andthechronysuite.Fromtheneedtotime-stampdocuments,e-mails,andlogfiles,tosecuring,running,anddebugginganetwork,ortosimplyinteractwithshareddevicesandservices,everythingonyourserverisdependentonmaintaininganaccuratesystemclock,anditisthepurposeofthisrecipetoshowyouhowthiscanbeachieved.

GettingreadyTocompletethisrecipe,youwillrequireaworkinginstallationoftheCentOS7operatingsystemwithrootprivileges,aconsole-basedtexteditorofyourchoice,andaconnectiontotheInternettofacilitatedownloadingadditionalpackages.

HowtodoitInthisrecipe,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

http://www.pool.ntp.org/

tendencytoincreasetheaccuracyoftheNTPservice.

9. Whencomplete,saveandclosethefilebeforesynchronizingyourserverusingthesytstemctlcommand:

systemctlrestartchronyd

10. Tocheckwhetherthemodificationsintheconfigfileweresuccessful,youcanusethefollowingcommand:

systemctlstatuschronyd

11. Tocheckwhetherchronyistakingcareofyoursystemtimesynchronization,usethefollowing:

chronyctracking

12. Tocheckthenetworksourceschronyusesforsynchronization,usethefollowing:

chronycsources

HowitworksOurCentOS7operatingsystemstimeissetoneverybootbasedonthehardwareclock,whichisasmall-batterydrivenclocklocatedonthemotherboardofyourcomputer.Often,thisclockistooinaccurateorhasnotbeensetright,thereforeitsbettertogetyoursystemtimefromareliablesourceovertheInternet(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.

TheresmoreInthisrecipe,wesetoursystemstimeusingthechronyserviceandtheNTPprotocol.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

SettingyourhostnameandresolvingthenetworkTheprocessofsettingthehostnameistypicallyassociatedwiththeinstallationprocess.IfyoueverneedtochangeitoryourserversDomainNameSystem(DNS)resolver,thisrecipewillshowyouhow.

GettingreadyTocompletethisrecipe,youwillrequireaworkinginstallationoftheCentOS7operatingsystemwithrootprivileges,andaconsole-basedtexteditorofyourchoice.

HowtodoitTobeginthisrecipe,weshallstartbyaccessingthesystemasrootandopeningthefollowingfileinordertonameorrenameyourcurrentservershostname:

1. Loginasrootandtypeinthefollowingcommandtoseethecurrenthostname:

hostnamectlstatus

2. Now,changethehostnamevaluetoyourpreferredname.Forexample,ifyouwanttocallyourserverjimi,youwouldtype(changeappropriately):

hostnamectlset-hostnamejimi

NoteStatichostnamesarecase-sensitiveandrestrictedtousinganInternet-friendlyalphanumericstringoftext.Theoveralllengthshouldbenolongerthan63characters,buttrytokeepitmuchshorter.

3. Next,weneedtheIPaddressoftheserver.Typeinthefollowingcommandtofindit(youneedtoidentifythecorrectnetworkinterfaceintheoutput):

ipaddrlist

4. Afterwards,wewillsettheFullyQualifiedDomainName(FQDN),inordertodothis,wewillneedtoopenandeditthehostsfile:

vi/etc/hosts

5. Here,youshouldaddanewlineappropriatetoyourneeds.Forexample,ifyourservershostnamewascalledjimi,(withanIPaddressof192.168.1.100,andadomainnameofhenry.com)yourfinallinetoappendwilllooklikethis:

192.168.1.100jimi.henry.comjimi

NoteForaserverfoundonalocalnetworkonly,itisadvisabletouseanon-Internetbasedtop-leveladdress.Forexample,youcoulduse.localor.lan,oreven.home,andbyusingthesereferencesyouwillavoidanyconfusionwiththetypical.com,.co.uk,or.netdomainnames.

6. Next,wewillopentheresolv.conffile,whichisresponsibleforconfiguringstaticDNSserveraddressesthatthesystemwilluse:

vi/etc/resolv.conf

7. Replacethecontentofthefilewiththefollowing:

#usegooglefordnsnameserver8.8.8.8nameserver8.8.4.4

8. Whencomplete,saveandcloseyourfilebeforerebootingyourservertoallowthe

changestotakeimmediateeffect.Todothis,returntoyourconsoleandtype:

reboot

9. Onasuccessfulreboot,youcannowcheckyournewhostnameandFQDNbytypingthefollowingcommandsandwaitingfortheresponse:

hostname--fqdn

10. TotestifwecanresolvedomainnamestoIPaddressesusingourstaticDNSserveraddresses,usethefollowingcommand:

ping-c10google.com

HowitworksAhostnameisauniquelabelcreatedtoidentifyamachineonanetwork.Itisrestrictedtoalphanumeric-basedcharacters,andmakingachangetoyourservershostnamecanbeachievedbyusingthehostnamectlcommand.ADNSserverisusedtotranslatedomainnamestoIPaddresses.ThereareseveralpublicDNSserversavailable;inalaterrecipe,wewillbuildourownDNSservice.

So,whathavewelearnedfromthisexperience?

Inthefirststageoftherecipe,wechangedthecurrenthostnameusedbyourserverwiththehostnamectlcommand.Thiscommandcansetthreedifferenttypesofhostnames.Usingthecommandwiththeset-hostnameparameterwillsetthesamenameforallthreehostnames:thehigh-levelprettyhostname,whichmightincludeallkindsofspecialcharacters(forexample,Lennart'sLaptop),thestatichostnamewhichisusedtoinitializethekernelhostnameatboot(forexamplelennarts-laptop),andthetransienthostname,whichisadefaultreceivedfromnetworkconfigurations.

Followingthis,wesettheFQDNofourserver.AFQDNisthehostnamealongwithadomainnameafterit.AdomainnamegetsimportantwhenyouarerunningaprivateDNS,orallowingexternalaccesstoyourserver.BesidesusingaDNSserversettingtheFQDNcanbeachievedbyupdatingthehostsfilefoundat/etc/hosts.

ThisfileisusedbyCentOStomaphostnamestoanIPaddress,anditisoftenfoundtobeincorrectonanew,un-configured,orrecentlyinstalledserver.Forthisreason,wefirsthadtofindouttheIPaddressoftheserverusingipaddrlist.

AnFQDNshouldconsistofashorthostnameandthedomainname.Basedontheexampleshowninthisrecipe,wesettheFQDNforaservernamedhenry,whoseIPaddressis192.168.1.100anddomainnameishenry.com.

Savingthisfilewouldarguablycompletethisprocess.However,becausethekernelmakesarecordofthehostnameduringthebootprocess,thereisnochoicebuttorebootyourserverbeforeyoucanusethechangedsettings.

Next,weopenedthe

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