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
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