Beginning the Linux Command Line

Transcription

1 Beginning the Linux Command Line Second Edition Sander van Vugt

2 Beginning the Linux Command Line, Second edition Copyright 2015 by Sander van Vugt This work is subject to copyright. All rights are reserved by the Publisher, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmission or information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed. Exempted from this legal reservation are brief excerpts in connection with reviews or scholarly analysis or material supplied specifically for the purpose of being entered and executed on a computer system, for exclusive use by the purchaser of the work. Duplication of this publication or parts thereof is permitted only under the provisions of the Copyright Law of the Publisher s location, in its current version, and permission for use must always be obtained from Springer. Permissions for use may be obtained through RightsLink at the Copyright Clearance Center. Violations are liable to prosecution under the respective Copyright Law. ISBN-13 (pbk): ISBN-13 (electronic): Trademarked names, logos, and images may appear in this book. Rather than use a trademark symbol with every occurrence of a trademarked name, logo, or image we use the names, logos, and images only in an editorial fashion and to the benefit of the trademark owner, with no intention of infringement of the trademark. The use in this publication of trade names, trademarks, service marks, and similar terms, even if they are not identified as such, is not to be taken as an expression of opinion as to whether or not they are subject to proprietary rights. While the advice and information in this book are believed to be true and accurate at the date of publication, neither the authors nor the editors nor the publisher can accept any legal responsibility for any errors or omissions that may be made. The publisher makes no warranty, express or implied, with respect to the material contained herein. Managing Director: Welmoed Spahr Lead Editor: Michelle Lowman Technical Reviewer: Stewart Watkiss Editorial Board: Steve Anglin, Louise Corrigan, Jim DeWolf, Jonathan Gennick, Robert Hutchinson, Michelle Lowman, James Markham, Susan McDermott, Matthew Moodie, Jeff Olson, Jeffrey Pepper, Douglas Pundick, Ben Renow-Clarke, Gwenan Spearing Coordinating Editor: Mark Powers Compositor: SPi Global Indexer: SPi Global Artist: SPi Global Distributed to the book trade worldwide by Springer Science+Business Media New York, 233 Spring Street, 6th Floor, New York, NY Phone SPRINGER, fax (201) , orders-ny@springer-sbm.com, or visit Apress Media, LLC is a California LLC and the sole member (owner) is Springer Science + Business Media Finance Inc (SSBM Finance Inc). SSBM Finance Inc is a Delaware corporation. For information on translations, please rights@apress.com, or visit Apress and friends of ED books may be purchased in bulk for academic, corporate, or promotional use. ebook versions and licenses are also available for most titles. For more information, reference our Special Bulk Sales ebook Licensing web page at Any source code or other supplementary material referenced by the author in this text is available to readers at For detailed information about how to locate your book s source code, go to Readers can also access source code at SpringerLink in the Supplementary Material section for each chapter.

3 This book is dedicated to Florence. Your love is making me invincible.

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5 Contents at a Glance About the Author...xix Introduction...xxi Chapter 1: Starting Linux Command-Line Administration... 1 Chapter 2: Performing Essential Command Line tasks Chapter 3: Administering the Linux File System Chapter 4: Working with Text Files Chapter 5: Managing Partitions and Logical Volumes Chapter 6: Managing Users and Groups Chapter 7: Managing Permissions Chapter 8: Managing Software Chapter 9: Process and System Management Chapter 10: System Logging Chapter 11: Configuring the Network Chapter 12: Configuring a File Server Chapter 13: Working with the Kernel Chapter 14: Introduction to Bash Shell Scripting Appendix A: Installing Linux Index v

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7 Contents About the Author...xix Introduction...xxi Chapter 1: Starting Linux Command-Line Administration... 1 Linux Distributions... 1 Linux History... 1 Open Source... 2 The First Distributions... 2 Linux Turning Mainstream... 2 Logging In and Out... 4 Different Login Interfaces... 4 Working with a User Account... 7 Command-Line Basics... 8 Bash: The Command Interpreter... 9 Commands, Options, and Arguments... 9 Piping and Redirection Piping Redirection Getting Help Using man to Get Help Using the --help Option Getting Information on Installed Packages vii

8 Contents Working with the Shell Using the Shell to Best Effect Managing Bash with Key Sequences Summary Chapter 2: Performing Essential Command Line tasks Changing Your Password Working with Virtual Consoles Becoming Another User Obtaining Information About Other Users Communicating with Other Users Real-Time Communication Sending Mail from the Command Line Finding Your Way in the File System Default Directories Working with the Linux File System Working with Directories Working with Files Cool Commands Displaying a Calendar with cal Clearing Your Screen with clear Displaying System Information with uname and hostname Counting Words, Lines, and Characters with wc Changing and Showing Date and Time with date Summary Chapter 3: Administering the Linux File System Mounting Disks Using the mount Command Unmounting Devices Automating Mounts with /etc/fstab viii

9 Contents Checking File System Integrity Creating Backups Making File Backups with tar Making Device Backups Using dd Working with Links Why Use Links? Working with Symbolic Links Working with Hard Links Links Recap Summary Chapter 4: Working with Text Files Working with Vi Vi Modes Saving and Quitting Cutting, Copying, and Pasting Deleting Text Moving Through Text Files Changing All Occurrences of a String in a Text File Vi Summarized Displaying Contents of Text Files Showing File Contents with cat and tac Showing a File s Last Lines with tail Displaying the First Lines in a File with head Browsing File Contents with less and more Cool Text File Manipulation Tools Changing Contents in a Batch with tr Sorting Text Files with sort Finding Differences Between Text Files with diff Checking Whether a Line Exists Twice with uniq Getting Specific Information with cut ix

10 Contents Advanced Text File Filtering and Processing Working with Basic Regular Expressions Working with Programmable Filters Printing Files Managing CUPS Print Queues Finding Files Summary Chapter 5: Managing Partitions and Logical Volumes Addressing Storage Devices File System Labels udev Device Names Working with UUID Creating Partitions Understanding Partitions Understanding MBR and GPT Disks Creating MBR Partitions Managing Partitions with fdisk Creating Partitions Creating GPT Partitions with gdisk Working with cfdisk Recovering Lost Partitions with gpart Creating Logical Volumes Understanding Logical Volumes Setting Up a Disk with Logical Volume Manager Creating Physical Volumes Creating Volume Groups Creating Logical Volumes Working with Snapshots Basic LVM Troubleshooting x

11 Contents Working with File Systems Understanding File Systems About Superblocks, Inode Bitmaps, and Block Bitmaps Journaling Indexing Btrfs Formatting File Systems Maintaining File Systems Analyzing and Repairing Ext Analyzing and Repairing XFS File Systems Resizing File Systems Resizing a File System in a Logical Volume Resizing Partitions with GParted Working with Windows File Systems Cloning Devices Summary Chapter 6: Managing Users and Groups Setting Up User Accounts Understanding Users and Their Properties Commands for User Management Working with Default Values for User Management Managing Passwords Performing Account Maintenance with passwd Managing Password Expiration Behind the Commands: Configuration Files Group Membership Creating Groups The Use of Group Passwords Managing the User s Shell Environment Creating Shell Login Scripts Showing Messages to Users Logging In xi

12 Contents Applying Quota to Allow a Maximum Amount of Files Installing the Quota Software Preparing the File System for Quota Initializing Quota Setting Quota for Users and Groups Techniques Behind Authentication Understanding Pluggable Authentication Modules Discovering PAM Modules The role of /etc/nsswitch.conf Configuring Administrator Tasks with sudo Summary Chapter 7: Managing Permissions Setting Ownership Displaying Ownership Changing User Ownership Changing Group Ownership Default Ownership Basic Permissions: Read, Write, and Execute Understanding Read, Write, and Execute Permissions Applying Read, Write, and Execute Permissions Advanced Permissions Understanding Advanced Permissions Applying Advanced Permissions Working with Access Control Lists Understanding ACLs Preparing Your File System for ACLs Changing and Viewing ACL Settings with setfacl and getfacl Setting Default Permissions with umask Working with Attributes Summary xii

13 Contents Chapter 8: Managing Software Understanding Software Management Managing RPM Packages Working with RPM Working with yum Working with zypper Managing DEB Packages Managing.deb Software Repositories Ubuntu Package Management Utilities Summary Chapter 9: Process and System Management Understanding Linux Processes Monitoring Processes Monitoring Processes with top Finding Processes with ps Finding PIDs with pgrep Showing Parent-Child Relations with pstree Managing Processes Adjusting Process Priority with nice Process Management from top Scheduling Processes Creating user crontabs Understanding cron.{hourly daily weekly monthly} Using /etc/cron.d Summary Chapter 10: System Logging Understanding Logging Monitoring Files in /var/log Configuring the syslog Service xiii

14 Contents Configuring syslog-ng Sending Logs Yourself with logger Rotating Old Log Files Understanding Journald Summary Chapter 11: Configuring the Network A Quick Introduction to Computer Networking Understanding Network Device Naming Setting the IP Address Using the ip Tool Using ifconfig Using Virtual Ip addresses with ifconfig Storing Address Configuration Storing IP Address Configuration on Ubuntu Storing IP Address Configuration on Red Hat Storing IP Address Configuration on SUSE Configuring Routing Managing the Default Route with route Managing the Default Route with the ip Tool Storing Routing Information Resolving DNS Names to IP Addresses The Role of the /etc/nsswitch.conf File Using the /etc/hosts File Tuning the Network Card with ethtool Analyzing Network Connections Testing Connectivity Testing Routing Testing Availability of Services xiv

15 Contents Connecting Remotely with Secure Shell Working with Public/Private Key Pairs Working with Secure Shell Configuring SSH Using SSH Key-Based Authentication Caching Keys with ssh- ssh-agent Tunneling Traffic with SSH Summary Chapter 12: Configuring a File Server Operating File Servers Securely Creating a Samba File Server Background of the Samba Project Configuring a Samba File Server Accessing a Samba File Server Basic Samba Troubleshooting Configuring an NFS Server NFS Backgrounds Understanding NFS Processes Configuring an NFS Server Configuring an NFS Client Summary Chapter 13: Working with the Kernel Understanding the Kernel Managing Kernel Modules Listing Modules with lsmod Loading and Unloading Modules with modprobe Displaying Module Properties with modinfo Changing Module Options Managing Module Dependencies Legacy Commands for Module Management xv

16 Contents Tuning Kernel Parameters Writing Changes to /proc Some Useful /proc Parameters Compiling Your Own Kernel and Kernel Modules Understanding Make Modifying and Compiling the Kernel Compiling Modules Managing the Grub2 Bootloader Summary Chapter 14: Introduction to Bash Shell Scripting Basic Shell Script Components Elements of a Good Shell Script Executing the Script Working with Variables and Input Understanding Variables Variables, Subshells, and Sourcing Working with Script Arguments Asking for Input Using Command Substitution Substitution Operators Changing Variable Content with Pattern Matching Performing Calculations Using Control Structures Using if... then... else Case Using while Using until Using for Summary xvi

17 Contents Appendix A: Installing Linux Installation Requirements Installing CentOS Installing Ubuntu Server Index xvii

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19 About the Author Sander van Vugt is a Linux expert working from the Netherlands as an author, technical trainer, and consultant for clients around the world. Sander has published several books about different Linux distributions and is a regular contributor to major international Linux-related web sites. As a consultant, he is specialized in Linux high availability and performance optimization. As a technical trainer, Sander is an authorized trainer for SUSE Linux Enterprise Server and Red Hat Enterprise Linux. More information about the author can be found at his web site at xix

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21 Introduction This book is for anyone who wants to master Linux from the command line. When writing it, I had in mind system administrators, software developers, and enthusiastic users who want to get things going from the Linux command line. For beginning users, this may be a daunting task, as Linux commands often have many options documented only in man pages that are not that easy to understand. This book is distribution agnostic. That is, while writing it, I ve checked all items against Ubuntu, Red Hat, and SUSE. Since most distributions are quite similar to one of these three, this book should help you with other distributions as well. There is only one item in the book that is not distribution agnostic: the Appendix, which explains how to install either CentOS or Ubuntu. The book begins with an introduction to exactly what I m talking about when discussing Linux and its different appearances: the distributions. In Chapter 1, you ll also find essential information on how to log on to the computer and how to find out more about the way a command should be used. Chapter 2 follows with some essential Linux commands. After reading this chapter, you ll already start to feel at ease on the Linux command line; among other things, it teaches you how to work with files and directories and how to communicate with other users. Chapter 3 moves the focus to one of the most important tasks you ll perform when working with Linux: working with files. In this chapter, you ll learn not only how to copy files and make directories, but also how to mount devices to your Linux system. Working with Linux from the command line means working with text files. In Chapter 4, you ll learn about the tools that are at your disposal to do this. You ll get familiar with some of the classic tools, such as find and grep, and also with some of the more advanced tools, such as awk and sed. Following that, in Chapter 5 you ll learn more about partitions, logical volumes, and other advanced file system management tasks. After reading this chapter, you ll start feeling at ease on the Linux command line. Chapters 6 and 7 move on to two other essential subjects: the management of users and permissions. Chapter 8 covers a topic that seems to be handled differently by all the Linux distributions: software management. This chapter teaches you about generic ways to install and manage software packages, such as rpm and dpkg, and also about some of the distribution- specific ways to deal with these tasks, such as aptget, rpm, and zypper. Chapters 9 and 10 cover tasks that are important for system administration. In these chapters, you ll learn how to manage processes and how to handle logging on your computer. By the time you reach Chapters 11 and 12, you re ready to explore network-related tasks. In these chapters, you ll learn how to configure a network interface and how to set up the Samba and NFS file services. Chapters 13 and 14 cover two advanced but useful topics: kernel management and shell scripting. After you finish the last chapter, you ll have all the knowledge you need to work with Linux from the command line. In Appendix B you'll find some additional exercises, which help making this book an excellent study guide that can be used in classroom environments. I hope you enjoy reading this book and that it prepares you for getting things done from the Linux command line! xxi