Red Hat Enterprise Linux 8 Administration, RHCSA certification exam (2021)

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Red HatEnterprise Linux 8AdministrationMaster Linux administration skills and prepare forthe RHCSA certification examMiguel Pérez ColinoPablo Iranzo GómezScott McCartyBIRMINGHAM—MUMBAI

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Red Hat Enterprise Linux 8 AdministrationCopyright © 2021 Packt PublishingAll rights reserved. No part of this book may be reproduced, stored in a retrieval system,or transmitted in any form or by any means, without the prior written permission of thepublisher, except in the case of brief quotations embedded in critical articles or reviews.Every effort has been made in the preparation of this book to ensure the accuracy of theinformation presented. However, the information contained in this book is sold withoutwarranty, either express or implied. Neither the authors, nor Packt Publishing or its dealersand distributors, will be held liable for any damages caused or alleged to have been causeddirectly or indirectly by this book.Packt Publishing has endeavored to provide trademark information about all of the companiesand products mentioned in this book by the appropriate use of capitals. However, PacktPublishing cannot guarantee the accuracy of this information.The content reflects the views of the authors and does not reflect the views of the authors'employer (Red Hat, Inc.). This work has no connection to Red Hat, Inc. and is notendorsed or supported by Red Hat, Inc.Group Product Manager: Vijin BorichaPublishing Product Manager: Shrilekha InaniSenior Editor: Shazeen IqbalContent Development Editor: Romy DiasTechnical Editor: Arjun VarmaCopy Editor: Safis EditingProject Coordinator: Shagun SainiProofreader: Safis EditingIndexer: Subalakshmi GovindhanProduction Designer: Shankar KalbhorFirst published: September 2021Production reference: 1160921Published by Packt Publishing Ltd.Livery Place35 Livery StreetBirminghamB3 2PB, UK.ISBN 978-1-80056-982-9www.packt.com

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To all the people contributing to and being part of the open sourcecommunity, building it one piece at a time, pushing its boundariesto make huge things.

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ContributorsAbout the authorsMiguel Pérez Colinois an experienced IT enthusiast with a clear orientation towardsopen source software and open standards. He has an extensive background in IT, fromoperations to the architecture of large deployments and from identifying and prototypingsolutions to defining IT strategies. He has delivered large projects, including NATOinteroperable command and control systems in defense, extensive large deployments inretail (>15,000 devices), and digital transformation in the finance sector.Now, as part of the Cloud Platforms Business Unit of Red Hat, he works as a seniorprincipal product manager building tools and defining methodologies to easemodernization and migration for customers, enabling the use of open source.I want to thank my family, Sonia, Miguel, and Matilde, for the supportand patience they have had with me during the months that I have beenwriting this book. Also, to Pablo Iranzo for being part of this adventure, andwithout whom we would not have been able to finish it. The whole Packtediting team has helped this first-time book authors immensely, as well asScott and Gunnar, and I'd like to thank all of them for their contributions.

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Pablo Iranzo Gómezis a software engineer whose Linux exposure began while studyingphysics, a period during which he was also involved in LUGs and some projects related toHPC clusters and system administration and consultancy.Currently, he is a senior software engineer in Red Hat's SolEng department, focusingon OpenShift, with experience in consulting, cloud technical account management,OpenStack software maintenance in industries such as hospitality, retail, airlines,government, telco, 5G, partners, IT covering system administration and automation,virtualization, PaaS, support, the cloud, and so on, having a broad understanding ofdifferent views, needs, and risks across the industry.Pablo was born in and lives in Valencia, Spain with his family.I want to thank my wife, Eva, for all the support she offered me enrolling inthis endeavor; to my kid, Pau, for all the happy moments that empoweredme to drive forward; to Javier, for the countless hours of unconditionalunderstanding; and I want also to say thanks to Miguel for offering me tohelp him with this; and, of course, the whole Packt team, who have helped,guided, and advised me during the whole process.At Red Hat,Scott McCartyis a principal product manager for the container subsystemteam, which enables key product capabilities in OpenShift Container Platform and RedHat Enterprise Linux. His focus areas include container runtimes, tools, and images.Scott is a social media start-up veteran, an e-commerce old-timer, and a weatheredgovernment research technologist, with experience across a variety of companies andorganizations, from seven-person start-ups to 15,000-employee technology companies.This has culminated in a unique perspective on open source software development,delivery, and maintenance.First, I would like to thank all of the people in the open source communitythat have contributed to creating code and documentation that helpsus all achieve more. I would like to thank all of the people that build,distribute, document, and release Red Hat Enterprise Linux and bring itinto environments that I never thought Linux could reach. Finally, I'd alsolike to thank all of the sysadmins out there that run all of this software toprevent downtime and move projects forward.

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About the reviewerMatthew Bachis a senior specialist solutions architect at Red Hat, focused on theemerging technologies portfolio, such as OpenShift, middleware, and Ansible for DoDcustomers. He has been in the IT industry for over 17 years and is a 13-year US Navyinformation systems technician veteran. Matthew currently holds several Red Hat andother security-related certifications. When Matthew is not working with his customerson exciting technologies, he likes to spend time with his family, or on a mountain bikeexploring the many trails Virginia has to offer.To my wife, Ashley, with love: Thank you for your love, support, andpatience through all of my endeavors in the endless pursuit of this career.I can think of no one I'd rather be with for the rest of my days than you andour five awesome kids.To Maurice Carroll, thank you for the countless hours you spent cultivatingan interest in computers with a teenage grandson, and my very first box ofRed Hat Linux. You lit a spark in me that remains today.

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Table of ContentsPrefaceSection 1: Systems Administration –Software, User, Network, and ServicesManagement1Installing RHEL8Technical requirements4Obtaining RHEL software and asubscription4Installing RHEL88Preparation for a physical serverinstallation8Preparation for a virtual serverinstallation11Running an RHEL installation16Summary382RHEL8 Advanced Installation OptionsTechnical requirements40Automating RHEL deploymentswith Anaconda40Deploying RHEL on the cloud46Installation best practices53Summary56

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viii Table of Contents3Basic Commands and Simple Shell ScriptsLogging in as a user andmanaging multi-userenvironments58Using the root account59Using and understanding thecommand prompt60Changing users with the sucommand60Understanding users, groups,and basic permissions62Users63Groups65File permissions66Using the command line,environment variables,and navigating through thefilesystem68Command line and environmentvariables68Navigating the filesystem70Bash autocomplete71Filesystem hierarchy73Understanding I/O redirectionin the command line75Filtering output with grep andsed78Listing, creating, copying, andmoving files and directories,links, and hard links82Directories82Copying and moving83Symbolic and hard links86Using tar and gzip88Creating basic shell scripts90for loops92if conditionals94Exit codes96Using system documentationresources96Man pages96Info pages99Other documentation resources100Summary1014Tools for Regular OperationsTechnical requirements104Managing system services withsystemd104Systemd unit file structure107Managing services to be started andstopped at boot109Managing boot targets110Scheduling tasks with cron andsystemd113System-wide crontab114User crontab115Systemd timers116

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Table of Contents ixLearning about timesynchronization with chronyand NTP117NTP client118NTP server121Checking for free resources –memory and disk (free and df)122Memory123Disk space124CPU125Load average126Other monitoring tools127Finding logs, using journald,and reading log files, includinglog preservation and rotation132Log rotation134Summary1375Securing Systems with Users, Groups, and PermissionsCreating, modifying, anddeleting local user accountsand groups140Managing groups and reviewingassignments144Adjusting password policies145Configuring sudo access foradministrative tasks150Understanding sudo configuration151Using sudo to run admin commands152Configuring sudoers154Checking, reviewing, andmodifying file permissions155Using special permissions162Understanding and applying Set-UID162Understanding and applying Set-GID163Using the sticky bit164Summary1666Enabling Network ConnectivityTechnical requirements168Exploring networkconfiguration in RHEL168Getting to know theconfiguration files andNetworkManager170Configuring network interfaceswith IPv4and IPv6173IPv4 and IPv6... what does that mean?173Configuring interfaces with nmtui174Configuring interfaces with nm-connection-editor177Configuring interfaces with nmcli180Configuring interfaces with text files183Configuring hostname andhostname resolutions (DNS)186

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x Table of ContentsOverview of firewallconfiguration190Configuring the firewall192Testing network connectivity194Summary1967Adding, Patching, and Managing SoftwareRHEL subscription registrationand management198Managing repositories andsignatures with YUM/DNF205Doing software installations,updates, and rollbacks withYUM/DNF215Creating and syncingrepositories with createrepoand reposync226Understanding RPM internals232Summary233Section 2: Security with SSH, SELinux,a Firewall, and System Permissions8Administering Systems RemotelyTechnical requirements238SSH and OpenSSH overviewand base configuration238OpenSSH server239OpenSSH client241Accessing remote systemswith SSH242Key-based authenticationwith SSH244SSH agent248SCP/rsync – remote filemanagement251Transferring files with an OpenSSHsecure file copy252Transferring files with sftp254Transferring files with rsync256Advanced remotemanagement – SSH tunnelsand SSH redirections261Remote terminals with tmux263Summary266

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Table of Contents xi9Securing Network Connectivity with firewalldIntroduction to the RHELfirewall – firewalld268Enabling firewalld in thesystem and reviewing thedefault zones269Reviewing the different configurationitems under firewalld272Enabling and managingservices and ports276Creating and using servicedefinitions for firewalld282Configuring firewalld withthe web interface284Summary28910Keeping Your System Hardened with SELinuxTechnical requirements292SELinux usage in enforcing andpermissive modes292Reviewing the SELinux contextfor files and processes296Tweaking the policy withsemanage300Restoring changed filecontexts to the default policy303Using SELinux Booleansettings to enable services305SELinux troubleshootingand common fixes307Summary31111System Security Profiles with OpenSCAPGetting started with OpenSCAPand discovering systemvulnerabilities314Using OpenSCAP with securityprofiles for OSPP and PCI DSS321Scanning for OSPP compliance324Scanning for PCI DSS compliance327Summary329

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xii Table of ContentsSection 3: Resource Administration– Storage, Boot Process, Tuning, andContainers12Managing Local Storage and FilesystemsTechnical requirements334Let's start with a definition334A bit of history334Partitioning disks (MBR andGPT disks)336Formatting and mountingfilesystems343Setting default mountsand options in fstab346Using network filesystemswith NFS349Summary35013Flexible Storage Management with LVMTechnical requirements352Understanding LVM356Creating, moving, and removingphysical volumes357Combining physical volumesinto volume groups363Creating and extending logicalvolumes365Adding new disks to a volumegroup and extending a logicalvolume368Removing logical volumes,volume groups,and physical volumes374Reviewing LVM commands379Summary38114Advanced Storage Management with Stratis and VDOTechnical requirements384Understanding Stratis384Installing and enabling Stratis385Managing storage pools andfilesystems with Stratis387Preparing systems to use VDO391Creating a VDO volume392Assigning a VDO volume to anLVM volume395

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Table of Contents xiiiTesting a VDO volume andreviewing the stats396Summary39915Understanding the Boot ProcessUnderstanding the bootprocess – BIOS and UEFIbooting402Working with GRUB, thebootloader, and initrd systemimages404Managing the boot sequencewith systemd410Intervening in the boot processto gain access to a system413Summary41616Kernel Tuning and Managing Performance Profiles withtunedTechnical requirements418Identifying processes, checkingmemory usage, and killingprocesses418Adjusting kernel schedulingparameters to better manageprocesses424Installing tuned andmanaging tuning profiles427Creating a custom tunedprofile431Summary43417Managing Containers with Podman, Buildah, and SkopeoTechnical requirements436Introduction to containers436Installing container tools438Running a container usingPodman and UBI439Basic container management – pull,run, stop, and remove440Attaching persistent storage toa container443Deploying a container on a productionsystem with systemd444Building a container image usinga Dockerfile or Containerfile445Configuring Podman to search registryservers446Summary of Podman options448

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xiv Table of ContentsWhen to use Buildah andSkopeo448Building container imageswith Buildah449Inspecting a remote containerwith Skopeo451Summary451Section 4: Practical Exercises18Practice Exercises – 1Technical requirements455Tips for the exercise456Practice exercise 1457Exercise 1 resolution45919Practice Exercise – 2Technical requirements477Tips for the exercise478Practice exercise – 2478Answers to practice exercise 2480Other Books You May EnjoyIndex

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