How Linux Works: What Every Superuser Should Know

About the Author
About the Technical Reviewers
Acknowledgments
Preface
	Who Should Read This Book?
		Prerequisites
		How to Read This Book
		A Hands-on Approach
		How This Book Is Organized
		What’s New in the Third Edition?
		A Note on Terminology
Chapter 1: The Big Picture
		1.1	Levels and Layers of Abstraction in a Linux System
			1.2	Hardware: Understanding Main Memory
			1.3	The Kernel
			1.3.1	Process Management
			1.3.2	Memory Management
			1.3.3	Device Drivers and Management
			1.3.4	System Calls and Support
			1.4	User Space
			1.5	Users
			1.6	Looking Forward
Chapter 2: Basic Commands and Directory Hierarchy
		2.1	The Bourne Shell: /bin/sh
			2.2	Using the Shell
			2.2.1	The Shell Window
			2.2.2	cat
			2.2.3	Standard Input and Standard Output
			2.3	Basic Commands
			2.3.1	ls
			2.3.2	cp
			2.3.3	mv
			2.3.4	touch
			2.3.5	rm
			2.3.6	echo
			2.4	Navigating Directories
			2.4.1	cd
			2.4.2	mkdir
			2.4.3	rmdir
			2.4.4	Shell Globbing (“Wildcards”)
			2.5	Intermediate Commands
			2.5.1	grep
			2.5.2	less
			2.5.3	pwd
			2.5.4	diff
			2.5.5	file
			2.5.6	find and locate
			2.5.7	head and tail
			2.5.8	sort
			2.6	Changing Your Password and Shell
			2.7	Dot Files
			2.8	Environment and Shell Variables
			2.9	The Command Path
			2.10	Special Characters
			2.11	Command-Line Editing
			2.12	Text Editors
			2.13	Getting Online Help
			2.14	Shell Input and Output
			2.14.1	Standard Error
			2.14.2	Standard Input Redirection
			2.15	Understanding Error Messages
			2.15.1	Anatomy of a Unix Error Message
			2.15.2	Common Errors
			2.16	Listing and Manipulating Processes
			2.16.1	ps Command Options
			2.16.2	Process Termination
			2.16.3	Job Control
			2.16.4	Background Processes
			2.17	File Modes and Permissions
			2.17.1	Modifying Permissions
			2.17.2	Working with Symbolic Links
			2.18	Archiving and Compressing Files
			2.18.1	gzip
			2.18.2	tar
			2.18.3	Compressed Archives (.tar.gz)
			2.18.4	zcat
			2.18.5	Other Compression Utilities
			2.19	Linux Directory Hierarchy Essentials
			2.19.1	Other Root Subdirectories
			2.19.2	The /usr Directory
			2.19.3	Kernel Location
			2.20	Running Commands as the Superuser
			2.20.1	sudo
			2.20.2	/etc/sudoers
			2.20.3	sudo Logs
			2.21	Looking Forward
Chapter 3: Devices
		3.1	Device Files
			3.2	The sysfs Device Path
			3.3	dd and Devices
			3.4	Device Name Summary
			3.4.1	Hard Disks: /dev/sd*
			3.4.2	Virtual Disks: /dev/xvd*, /dev/vd*
			3.4.3	Non-Volatile Memory Devices: /dev/nvme*
			3.4.4	Device Mapper: /dev/dm-*, /dev/mapper/*
			3.4.5	CD and DVD Drives: /dev/sr*
			3.4.6	PATA Hard Disks: /dev/hd*
			3.4.7	Terminals: /dev/tty*, /dev/pts/*, and /dev/tty
			3.4.8	Serial Ports: /dev/ttyS*, /dev/ttyUSB*, /dev/ttyACM*
			3.4.9	Parallel Ports: /dev/lp0 and /dev/lp1
			3.4.10	Audio Devices: /dev/snd/*, /dev/dsp, /dev/audio, and More
			3.4.11	Device File Creation
			3.5	udev
			3.5.1	devtmpfs
			3.5.2	udevd Operation and Configuration
			3.5.3	udevadm
			3.5.4	Device Monitoring
			3.6	In-Depth: SCSI and the Linux Kernel
			3.6.1	USB Storage and SCSI
			3.6.2	SCSI and ATA
			3.6.3	Generic SCSI Devices
			3.6.4	Multiple Access Methods for a Single Device
Chapter 4: Disks and Filesystems
		4.1	Partitioning Disk Devices
		4.1.1	Viewing a Partition Table
			4.1.2	Modifying Partition Tables
			4.1.3	Creating a Partition Table
			4.1.4	Navigating Disk and Partition Geometry
			4.1.5	Reading from Solid-State Disks
			4.2	Filesystems
			4.2.1	Filesystem Types
			4.2.2	Creating a Filesystem
			4.2.3	Mounting a Filesystem
			4.2.4	Filesystem UUID
			4.2.5	Disk Buffering, Caching, and Filesystems
			4.2.6	Filesystem Mount Options
			4.2.7	Remounting a Filesystem
			4.2.8	The /etc/fstab Filesystem Table
			4.2.9	Alternatives to /etc/fstab
			4.2.10	Filesystem Capacity
			4.2.11	Checking and Repairing Filesystems
			4.2.12	Special-Purpose Filesystems
			4.3	Swap Space
			4.3.1	Using a Disk Partition as Swap Space
			4.3.2	Using a File as Swap Space
			4.3.3	Determining How Much Swap You Need
			4.4	The Logical Volume Manager
			4.4.2	Working with LVM
			4.4.3	The LVM Implementation
			4.5	Looking Forward: Disks and User Space
			4.6	Inside a Traditional Filesystem
			4.6.1	Inode Details and the Link Count
			4.6.2	Block Allocation
			4.6.3	Working with Filesystems in User Space
Chapter 5: How the Linux Kernel Boots
		5.1	Startup Messages
			5.2	Kernel Initialization and Boot Options
			5.3	Kernel Parameters
			5.4	Boot Loaders
			5.4.1	Boot Loader Tasks
			5.4.2	Boot Loader Overview
			5.5	GRUB Introduction
			5.5.1	Exploring Devices and Partitions with the GRUB Command Line
			5.5.2	GRUB Configuration
			5.5.3	GRUB Installation
			5.6	UEFI Secure Boot Problems
			5.7	Chainloading Other Operating Systems
			5.8	Boot Loader Details
			5.8.1	MBR Boot
			5.8.2	UEFI Boot
			5.8.3	How GRUB Works
Chapter 6: How User Space Starts
		6.1	Introduction to init
			6.2	Identifying Your init
			6.3	systemd
			6.3.1	Units and Unit Types
			6.3.2	Booting and Unit Dependency Graphs
			6.3.3	systemd Configuration
			6.3.4	systemd Operation
			6.3.5	systemd Process Tracking and Synchronization
			6.3.6	systemd Dependencies
			6.3.7	systemd On-Demand and Resource-Parallelized Startup
			6.3.8	systemd Auxiliary Components
			6.4	System V Runlevels
			6.5	System V init
			6.5.1	System V init: Startup Command Sequence
			6.5.2	The System V init Link Farm
			6.5.3	run-parts
			6.5.4	System V init Control
			6.5.5	systemd System V Compatibility
			6.6	Shutting Down Your System
			6.7	The Initial RAM Filesystem
			6.8	Emergency Booting and Single-User Mode
			6.9	Looking Forward
Chapter 7: System Configuration: Logging, System Time, Batch Jobs, and Users
		7.1	System Logging
		7.1.1	Checking Your Log Setup
			7.1.2	Searching and Monitoring Logs
			7.1.3	Logfile Rotation
			7.1.4	Journal Maintenance
			7.1.5	A Closer Look at System Logging
			7.2	The Structure of /etc
			7.3	User Management Files
			7.3.1	The /etc/passwd File
			7.3.2	Special Users
			7.3.3	The /etc/shadow File
			7.3.4	Manipulating Users and Passwords
			7.3.5	Working with Groups
			7.4	getty and login
			7.5	Setting the Time
			7.5.1	Kernel Time Representation and Time Zones
			7.5.2	Network Time
			7.6	Scheduling Recurring Tasks with cron and Timer Units
			7.6.1	Installing Crontab Files
			7.6.2	System Crontab Files
			7.6.3	Timer Units
			7.6.4	cron vs. Timer Units
			7.7	Scheduling One-Time Tasks with at
			7.7.1	Timer Unit Equivalents
			7.8	Timer Units Running as Regular Users
			7.9	User Access Topics
			7.9.1	User IDs and User Switching
			7.9.2	Process Ownership, Effective UID, Real UID, and Saved UID
			7.9.3	User Identification, Authentication, and Authorization
			7.9.4	Using Libraries for User Information
			7.10	Pluggable Authentication Modules
			7.10.1	PAM Configuration
			7.10.2	Tips on PAM Configuration Syntax
			7.10.3	PAM and Passwords
			7.11	Looking Forward
Chapter 8: A Closer Look at Processes and Resource Utilization
		8.1	Tracking Processes
			8.2	Finding Open Files with lsof
			8.2.1	Reading the lsof Output
			8.2.2	Using lsof
			8.3	Tracing Program Execution and System Calls
			8.3.1	strace
			8.3.2	ltrace
			8.4	Threads
			8.4.1	Single-Threaded and Multithreaded Processes
			8.4.2	Viewing Threads
			8.5	Introduction to Resource Monitoring
			8.5.1	Measuring CPU Time
			8.5.2	Adjusting Process Priorities
			8.5.3	Measuring CPU Performance with Load Averages
			8.5.4	Monitoring Memory Status
			8.5.5	Monitoring CPU and Memory Performance with vmstat
			8.5.6	I/O Monitoring
			8.5.7	Per-Process Monitoring with pidstat
			8.6	Control Groups (cgroups)
			8.6.1	Differentiating Between cgroup Versions
			8.6.2	Viewing cgroups
			8.6.3	Manipulating and Creating cgroups
			8.6.4	Viewing Resource Utilization
			8.7	Further Topics
Chapter 9: Understanding Your Network and Its Configuration
		9.1	Network Basics
			9.2	Packets
			9.3	Network Layers
			9.4	The Internet Layer
			9.4.1	Viewing IP Addresses
			9.4.2	Subnets
			9.4.3	Common Subnet Masks and CIDR Notation
			9.5	Routes and the Kernel Routing Table
			9.6	The Default Gateway
			9.7	IPv6 Addresses and Networks
			9.7.1	Viewing IPv6 Configuration on Your System
			9.7.2	Configuring Dual-Stack Networks
			9.8	Basic ICMP and DNS Tools
			9.8.1	ping
			9.8.2	DNS and host
			9.9	The Physical Layer and Ethernet
			9.10	Understanding Kernel Network Interfaces
			9.11	Introduction to Network Interface Configuration
			9.11.1	Manually Configuring Interfaces
			9.11.2	Manually Adding and Deleting Routes
			9.12	Boot-Activated Network Configuration
			9.13	Problems with Manual and Boot-Activated Network Configuration
			9.14	Network Configuration Managers
			9.14.1	NetworkManager Operation
			9.14.2	NetworkManager Interaction
			9.14.3	NetworkManager Configuration
			9.15	Resolving Hostnames
			9.15.1	/etc/hosts
			9.15.2	resolv.conf
			9.15.3	Caching and Zero-Configuration DNS
			9.15.4	/etc/nsswitch.conf
			9.16	Localhost
			9.17	The Transport Layer: TCP, UDP, and Services
			9.17.1	TCP Ports and Connections
			9.17.2	UDP
			9.18	Revisiting a Simple Local Network
			9.19	Understanding DHCP
			9.19.1	Linux DHCP Clients
			9.19.2	Linux DHCP Servers
			9.20	Automatic IPv6 Network Configuration
			9.21	Configuring Linux as a Router
			9.22	Private Networks (IPv4)
			9.23	Network Address Translation (IP Masquerading)
			9.24	Routers and Linux
			9.25	Firewalls
			9.25.1	Linux Firewall Basics
			9.25.2	Setting Firewall Rules
			9.25.3	Firewall Strategies
			9.26	Ethernet, IP, ARP, and NDP
			9.27	Wireless Ethernet
			9.27.1	iw
			9.27.2	Wireless Security
			9.28	Summary
Chapter 10: Network Applications and Services
		10.1	The Basics of Services
			10.2	A Closer Look
			10.3	Network Servers
			10.3.1	 Secure Shell
			10.3.2	 The sshd Server
			10.3.3	 fail2ban
			10.3.4	 The SSH Client
			10.4	Pre-systemd Network Connection Servers: inetd/xinetd
			10.5	Diagnostic Tools
			10.5.1	 lsof
			10.5.2	 tcpdump
			10.5.3	 netcat
			10.5.4	 Port Scanning
			10.6	Remote Procedure Calls
			10.7	Network Security
			10.7.1	 Typical Vulnerabilities
			10.7.2	 Security Resources
			10.8	Looking Forward
			10.9	Network Sockets
			10.10	Unix Domain Sockets
Chapter 11: Introduction to Shell Scripts
		11.1	Shell Script Basics
		11.1.1	Limitations of Shell Scripts
			11.2	Quoting and Literals
			11.2.1	Literals
			11.2.2	Single Quotes
			11.2.3	Double Quotes
			11.2.4	Literal Single Quotes
			11.3	Special Variables
			11.3.1	Individual Arguments: $1, $2, and So On
			11.3.2	Number of Arguments: $#
			11.3.3	All Arguments: $@
			11.3.4	Script Name: $0
			11.3.5	Process ID: $$
			11.3.6	Exit Code: $?
			11.4	Exit Codes
			11.5	Conditionals
			11.5.1	A Workaround for Empty Parameter Lists
			11.5.2	Other Commands for Tests
			11.5.3	elif
			11.5.4	Logical Constructs
			11.5.5	Testing Conditions
			11.5.6	case
			11.6	Loops
			11.6.1	for Loops
			11.6.2	while Loops
			11.7	Command Substitution
			11.8	Temporary File Management
			11.9	Here Documents
			11.10	Important Shell Script Utilities
			11.10.1	 basename
			11.10.2	 awk
			11.10.3	 sed
			11.10.4	 xargs
			11.10.5	 expr
			11.10.6	 exec
			11.11	Subshells
			11.12	Including Other Files in Scripts
			11.13	Reading User Input
			11.14	When (Not) to Use Shell Scripts
Chapter 12: Network File Transfer and Sharing
		12.1	Quick Copy
			12.2	rsync
			12.2.1	 Getting Started with rsync
			12.2.2	 Making Exact Copies of a Directory Structure
			12.2.3	 Using the Trailing Slash
			12.2.4	 Excluding Files and Directories
			12.2.5	 Checking Transfers, Adding Safeguards, and Using Verbose Mode
			12.2.6	 Compressing Data
			12.2.7	 Limiting Bandwidth
			12.2.8	 Transferring Files to Your Computer
			12.2.9	 Further rsync Topics
			12.3	Introduction to File Sharing
			12.3.1	 File Sharing Usage and Performance
			12.3.2	 File Sharing Security
			12.4	Sharing Files with Samba
			12.4.1	 Server Configuration
			12.4.2	 Server Access Control
			12.4.3	 Passwords
			12.4.4	 Manual Server Startup
			12.4.5	 Diagnostics and Logfiles
			12.4.6	 File Share Configuration
			12.4.7	 Home Directories
			12.4.8	 Printer Sharing
			12.4.9	 The Samba Client
			12.5	SSHFS
			12.6	NFS
			12.7	Cloud Storage
			12.8	The State of Network File Sharing
Chapter 13: User Environments
		13.1	Guidelines for Creating Startup Files
			13.2	When to Alter Startup Files
			13.3	Shell Startup File Elements
			13.3.1	 The Command Path
			13.3.2	 The Manual Page Path
			13.3.3	 The Prompt
			13.3.4	 Aliases
			13.3.5	 The Permissions Mask
			13.4	Startup File Order and Examples
			13.4.1	 The bash Shell
			13.4.2	 The tcsh Shell
			13.5	Default User Settings
			13.5.1	 Shell Defaults
			13.5.2	 Editor
			13.5.3	 Pager
			13.6	Startup File Pitfalls
			13.7	Further Startup Topics
Chapter 14: A Brief Survey of the Linux Desktop and Printing
		14.1	Desktop Components
		14.1.1	 Framebuffers
			14.1.2	 The X Window System
			14.1.3	 Wayland
			14.1.4	 Window Managers
			14.1.5	 Toolkits
			14.1.6	 Desktop Environments
			14.1.7	 Applications
			14.2	Are You Running Wayland or X?
			14.3	A Closer Look at Wayland
			14.3.1	 The Compositing Window Manager
			14.3.2	 libinput
			14.3.3	 X Compatibility in Wayland
			14.4	A Closer Look at the X Window System
			14.4.1	 Display Managers
			14.4.2	 Network Transparency
			14.4.3	Ways of Exploring X Clients
			14.4.4	 X Events
			14.4.5	 X Input and Preference Settings
			14.5	D-Bus
			14.5.1	 System and Session Instances
			14.5.2	 D-Bus Message Monitoring
			14.6	Printing
			14.6.1	 CUPS
			14.6.2	 Format Conversion and Print Filters
			14.7	Other Desktop Topics
Chapter 15: Development Tools
		15.1	The C Compiler
		15.1.1	 Compiling Multiple Source Files
			15.1.2	 Linking with Libraries
			15.1.3	Working with Shared Libraries
			15.1.4	 Working with Header (Include) Files and Directories
			15.2	make
			15.2.1	 A Sample Makefile
			15.2.2	 Built-in Rules
			15.2.3	 Final Program Build
			15.2.4	 Dependency Updates
			15.2.5	 Command-Line Arguments and Options
			15.2.6	 Standard Macros and Variables
			15.2.7	 Conventional Targets
			15.2.8	 Makefile Organization
			15.3	Lex and Yacc
			15.4	Scripting Languages
			15.4.1	 Python
			15.4.2	 Perl
			15.4.3	 Other Scripting Languages
			15.5	Java
			15.6	Looking Forward: Compiling Packages
Chapter 16: Introduction to Compiling Software from C Source Code
		16.1	Software Build Systems
			16.2	Unpacking C Source Packages
			16.3	GNU Autoconf
			16.3.1	 An Autoconf Example
			16.3.2	 Installation Using a Packaging Tool
			16.3.3	 configure Script Options
			16.3.4	 Environment Variables
			16.3.5	 Autoconf Targets
			16.3.6	 Autoconf Logfiles
			16.3.7	 pkg-config
			16.4	Installation Practice
			16.4.1	 Where to Install
			16.5	Applying a Patch
			16.6	Troubleshooting Compiles and Installations
			16.6.1	 Specific Errors
			16.7	Looking Forward
Chapter 17: Virtualization
		17.1	Virtual Machines
		17.1.1	 Hypervisors
			17.1.2	 Hardware in a Virtual Machine
			17.1.3	 Common Uses of Virtual Machines
			17.1.4	 Drawbacks of Virtual Machines
			17.2	Containers
			17.2.1	 Docker, Podman, and Privileges
			17.2.2	 A Docker Example
			17.2.3	 LXC
			17.2.4	 Kubernetes
			17.2.5	 Pitfalls of Containers
			17.3	Runtime-Based Virtualization
Bibliography
Index