Beginning Unix®
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Paul Love (Cincinnati, OH), CISSP, CISA, CISM, Security+, has been in the IT field for 15 years. Paul holds a Masters of Science degree in Network Security and a Bachelor’s in Information Systems. He has co-authored two Linux security books, contributed to multiple Linux/Unix books, and has been the technical editor for over 10 best selling Linux and Unix books. Paul also ran a successful Linux portal site during the dot com era and has been an avid Unix/Linux user and administrator both professionally and as a hobby for many years.
Joe Merlino (Boston, MA) is an experienced system administrator with Unix and Linux for more than a decade.
Craig Zimmerman (New York, NY) manages UNIX, Macintosh, and Windows systems for Spontaneous, a post-production company in New York City. He previously worked at Chiat/Day helping build the world’s most famous virtual advertising agency, managing and networking Unix and Macintosh systems in multiple offices.
Jeremy C. Reed (Marysville, WA) is a programmer, a member of NetBSD, and has actively taught FreeBSD, NetBSD, and OpenBSD administration classes for the past three years.
Paul Weinstein (Chicago, IL) has worked on various Unix-based computing platforms, from the mainframe (Harris HCX-9) to the desktop (Powerbook G4) and has developed applications on just about all of the current major branches of Unix in the course of the past 10 years. Recently he has been focusing a lot of his attention on developing and integrating Web-based systems using tools such as Linux, Apache, MySQL, and Perl, and in doing so has brought his unique understanding to a wide range of computing environments ranging from public elementary schools to pioneering open source companies. Currently, Paul works as President and Chief Consultant for the computer consulting firm Kepler Solutions, Inc.
David Mercer (Cape Town, South Africa) is a long-time Unix user and PHP programmer who contributed to Beginning PHP4 and Beginning PHP5. He has maintained a keen interest in all things open source ever since he managed to put together a working Beowulf cluster by nicking old computer parts from colleagues and assembling them under his desk.
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I would like to thank my family and those who mentored me throughout my career.
I would like to thank the staff at Wiley, particularly Debra Williams Cauley, who helped get this book started and whose participation during the writing of this book was instrumental in its completion. I would also like to thank Maryann and the technical editors whose tough first reviews and great insight helped develop the book into a far greater work. All others at the Wrox team who helped make this book a better product through their input or editing are greatly appreciated.
Finally, I would like to thank all the developers of the Unix systems and their derivatives. Their tireless pursuit of excellence has given us one of the most elegant and stable operating systems available today.
—Paul Love
The new millennium has seen many changes in many areas of computing, from new forms of storage with massive amounts of storage space, to systems that are far more powerful than the first computer users could have ever imagined. Designed and initially created more than 30 years ago, the Unix operating system has been part of the evolution of computers, so it’s no accident that Unix is still one of the most popular operating systems for mission-critical tasks.
Unix is the basis for some of the most-used operating systems today, from Apple’s Mac OS X to Linux to the more commonly known Unix versions, such as Sun’s Solaris Unix and IBM’s AIX. Today many of the versions of Unix are available free to users and corporations, allowing for a larger use base than many had imagined when Unix was first being developed. Unix is now seen as a user-friendly, very secure, and robust operating system rather than the cold, command line–only operating system once thought to be useful only to computer experts.
Beginning Unix covers all basic aspects of the Unix operating system. What is unique about this book is that it covers not only the standard Unix systems, such as Sun’s Solaris and IBM’s AIX, but also Unix derivatives, such as Apple’s Mac OS X and the various Linuxes. Additionally, this book includes a unique conversion section explaining how to convert Mac OS X–specific or Windows operating systems commands that you may already know into their Unix equivalents, making the transition from other operating systems much easier.
This book also includes a CD-ROM with the KNOPPIX operating system. This fully functional version of Linux enables you to restart your computer into a Linux environment. KNOPPIX requires no technical experience, and it will not damage or modify your current operating system. Using KNOPPIX is an easy way for you to follow along with the book, learning Unix without the consequences of having to lose any data or operating systems on your computer.
This book is for anyone who is interested in understanding the concepts and operation of the Unix operating system, including any of the Unix derivatives available today (Apple OS X, Linux, or BSD, for example). It is designed for absolute beginners to the Unix operating system, including those who have only worked with the many graphical user interfaces available for the different Unix systems (Apple’s Aqua interface, KDE, GNOME, and so forth). This book can also be useful for veteran Unix users, because no one knows everything about Unix, as a refresher on known concepts or as a tool to fill gaps in some knowledge areas.
No assumptions are made about the reader’s skill level or prior use of computers. If you have used computers and other operating systems such as Mac OS X or Microsoft Windows, you will understand some of the concepts faster, but all readers will gain some insight from this book, regardless of their present expertise.
This book covers all versions of Unix in their most basic form, as well as commands and concepts common to all versions of Unix and its derivatives, including:
Special emphasis is placed on Sun’s Solaris, Mac OS X, and Linux because they are the most popular available. The different versions of Unix utilize the same principles and commands with small differences, so any version of Unix can be used with this book.
This book also covers basic programming, including shell scripting and Perl programming, which enable you to automate your system as much as possible—one of the strengths of the Unix operating system. The coverage of these programming concepts creates a firm foundation for more advanced programming covered by other books.
This book presents basic concepts of the Unix operating system first, progressing to more advanced topics and programming later in the book. If you are familiar with the concepts or commands covered in one chapter, you can simply skip to one that has information you need to learn.
Chapters 1 through 4 provide the fundamental information you need to understand Unix methodology, how Unix is designed, and the basics of logging in to and out of a Unix system.
su command.Chapters 5–7 put you to work, from customizing your working environment to editing files on Unix. These chapters extend your repertoire of Unix commands.
With a good foundation in place, you’re ready to move on to more-advanced topics. Chapters 8–11 discuss how to use some powerful Unix tools, how to manage processes, and how to schedule programs to run at specific times. Chapter 12 takes on the important subject of security.
sed and awk are two very powerful tools that enable a user to manipulate files in an efficient manner. These commands are essential, and you will find yourself using them frequently. This chapter goes from the ground up in showing you how to use these commands.Chapters 13–17 delve into shell scripting and other methods of “automating” common tasks in Unix systems. Although these tasks often fall within the purview of system administrators, other users, including home users, may benefit.
Chapters 18 and 19 cover two important topics: backing up your data and installing Unix programs.
Chapters 20 and 21 provide maps to Unix operating systems for those who are more familiar with Microsoft Windows, Microsoft DOS, Mac OS 9, and Mac OS X. These chapters are great references for those who have used other operating systems and want to compare Unix to what they already know.
The book concludes with two appendixes. Appendix A, “Answers,” provides the solutions to the exercise(s) at the end of most chapters. These exercises will enable you to test your grasp of the concepts presented in the chapter. Appendix B, “Useful Unix Web Sites,” provides links to some of the best Unix-related Web sites on the Internet.
There are no requirements to use this book, but to make the learning process easier, the KNOPPIX distribution of Linux is provided on the CD-ROM accompanying this book. This enables you to use a Unix-based operating system any time, with no commitment of hard-drive resources or system alterations. The KNOPPIX distribution runs completely from CD-ROM and can be run at any time. If you have a Mac OS X system, you are already using a Unix operating system. The CD-ROM version of KNOPPIX runs only on Intel- or AMD-based systems; it will not work on Apple’s line of hardware.
This book uses the conventions discussed in this section to make the importance of specific information stand out.
Interesting tidbits or tips are formatted in italics, like this.
Code or commands are in this monotype format.
The text also uses specific styles to denote their significance:
Any actual Tab characters in code are represented by a right arrow: →.
The source code for all the code in this book is available online if you prefer to cut and paste rather than copy by hand from the book. It is available at www.wrox.com. At the Wrox Web site, you can find the book’s source code by searching for the book title (Beginning Unix) or ISBN (0-7645-7994-0).
This book has been checked for technical and grammatical errors, but as is human nature, errors can occur. The errata page for this book is available at www.wrox.com, in the book details section. If you find an error in the book that is not listed, the authors would greatly appreciate it if you go to www.wrox.com/contact/techsupport.shtml and complete the form to submit the error. By submitting any errors you discover, you help us to make this book even better.
The Unix operating system was created more than 30 years ago by a group of researchers at AT&T’s Bell Laboratories. During the three decades of constant development that have followed, Unix has found a home in many places, from the ubiquitous mainframe to home computers to the smallest of embedded devices. This chapter provides a brief overview of the history of Unix, discusses some of the differences among the many Unix systems in use today, and covers the fundamental concepts of the basic Unix operating system.
In terms of computers, Unix has a long history. Unix was developed at AT&T’s Bell Laboratories after Bell Labs withdrew from a long-term collaboration with General Electric (G.E.) and MIT to create an operating system called MULTICS (Multiplexed Operating and Computing System) for G.E.’s mainframe. In 1969, Bell Labs researchers created the first version of Unix (then called UNICS, or Uniplexed Operating and Computing System), which has evolved into the common Unix systems of today.
Unix was gradually ported to different machine architectures from the original PDP-7 minicomputer and was used by universities. The source code was made available at a small fee to encourage its further adoption. As Unix gained acceptance by universities, students who used it began graduating and moving into positions where they were responsible for purchasing systems and software. When those people began purchasing systems for their companies, they considered Unix because they were familiar with it, spreading adoption further. Since the first days of Unix, the operating system has grown significantly, so that it now forms the backbone of many major corporations’ computer systems.
Unix no longer is an acronym for anything, but it is derived from the UNICS acronym. Unix developers and users use a lot of acronyms to identify things in the system and for commands.
In the early days Unix was made available as source code rather than in the typical binary form. This made it easier for others to modify the code to meet their needs, and it resulted in forks in the code, meaning that there are now many disparate versions (also known as flavors).
Source code represents the internal workings of a program, specifying line by line how a program or application operates. Access to source code makes it easier to understand what is occurring in the program and allows for easier modification of the program. Most commercial programs are distributed in binary form, meaning they are ready to be run, but the internal lines of code are not readable by people.
There are primarily two base versions of Unix available: AT&T System V and Berkley Software Distribution (BSD). The vast majority of all Unix flavors are built on one of these two versions. The primary differences between the two are the utilities available and the implementations of the file structure. Most of the Unix flavors incorporate features from each base version; some include the System V version utilities in /usr/bin and the BSD version in /usr/ucb/bin, for example, so that you have the choice of using a utility with which you are comfortable. This arrangement is indicative of the Unix way of providing the flexibility to do things in different ways.
The various versions of Unix systems provide the user the power of choice: you can select the flavor that best matches your needs or system requirements. This ability to choose is considered by many as a strength, although some see it as a weakness in that these slightly differing versions and flavors create some incompatibilities (in the implementation, commands, communications, or methods, for example). There is no “true” version of Unix or one that is more official than others; there are just different implementations. Linux, for example, is a variant of Unix that was built from the ground up as a free Unix-like alternative to the expensive commercial Unix versions available when Linux was first created in 1991. Here are some of the more popular flavors of Unix available:
| Sun Microsystem’s Solaris Unix | Yellow Dog Linux (for Apple systems) |
| IBM AIX | Santa Cruz Operations SCO OpenServer |
| Hewlett Packard HP-UX | SGI IRIX |
| Red Hat Enterprise Linux | FreeBSD |
| Fedora Core | OpenBSD |
| SUSE Linux | NetBSD |
| Debian GNU/Linux | OS/390 Unix |
| Mac OS X | Plan 9 |
| KNOPPIX |
Each of these flavors implements its version of Unix in a slightly different way, but even though the implementation of a command may vary on some systems, the core command and its functionality follow the principles of one of the two major variations. Most versions of Unix utilize SVR4 (System V) and add the BSD components as an option to allow for maximum interoperability. This is especially true with commands; for example, there are two versions of the ps command (for showing processes) available on most systems. One version of ps might reside in /usr/bin/ps (the System V version) while the other might exist in /usr/ucb/bin (BSD version); the commands operate similarly, but provide output or accept optional components in a different manner.
Many vendors have attempted to standardize the Unix operating system. The most successful attempt, a product of the noncommercial Institute for Electrical and Electronics Engineers, is standard 1003 (IEEE 1003), also known as the POSIX (Portable Operating Systems Interface) standard. That standard is also registered with the International Organization for Standardization under ISO/IEC 9945-1, which you can find at http://iso.org/iso/en/CombinedQueryResult.CombinedQueryResult?queryString=9945. The POSIX standard merged with the Single Unix Specification (SUS) standard to become one integrated standard for all Unix flavors. It retained the name POSIX standard. Not all Unix versions follow the POSIX standard to the letter, but most do adhere to the major principles outlined in the standard.
Early Unix systems were mainly commercial commodities like most software for sale; to run the operating system, you generally had to pay for that right. In 1984 an engineer named Richard Stallman began work on the GNU Project, which was an effort to create an operating system that was like Unix and that could be distributed and used freely by anyone. He currently runs the Free Software Foundation (http://gnu.org/fsf/fsf.html), and many of the programs he and his supporters have created are used in both commercial and open-source versions of Unix.
GNU stands for GNU’s Not Unix, which is a recursive acronym. The GNU Project wanted to create a Unix-like operating system, not a Unix derivative (which would imply that it was a source-code copy of Unix).
In 1991 Linus Torvalds, a Finnish graduate student, began work on a Unix-like system called Linux. Linux is actually the kernel (kernels are discussed later in this chapter), while the parts with which most people are familiar—the tools, shell, and file system—are the creations of others (usually the GNU organization). As the Linux project gained momentum, it grew into a major contender in the Unix market. Many people are first introduced to Unix through Linux, which makes available to desktop machines the functionality of a Unix machine that used to costs thousands of dollars. The strength of Linux lies in its progressive licensing, which allows for the software to be freely distributable with no royalty requirements. The only requirement for the end user is that any changes made to the software be made available to others in the community, thus permitting the software to mature at an incredibly fast rate. The license under which Linux is distributed is called the GNU Public License (GPL), available at http://gnu.org/licenses/licenses.html.
Another free variant of Unix that has gained popularity is the BSD family of software, which uses the very lenient BSD License (http://opensource.org/licenses/bsd-license.php). This license allows for free modification without the requirement of providing the software source code to others. After a landmark 1994 lawsuit settlement, BSD Unix became freely distributable and has evolved into the NetBSD, FreeBSD, and OpenBSD projects, and it also forms the underlying technology for Darwin (upon which Mac OS X is based).
These freely available Unix derivatives have given new life to the Unix operating system, which had been experiencing a decline as the Microsoft Windows juggernaut advanced. Additionally, Apple has become the highest-volume supplier of Unix systems. Now Unix is moving forward in the corporate environment as well as in the end-user desktop market.
An operating system is the software interface between the user and the hardware of a system. Whether your operating system is Unix, DOS, Windows, or OS/2, everything you do as a user or programmer interacts with the hardware in some way. In the very early days of computers, text output or a series of lights indicated the results of a system request. Unix started as a command-line interface (CLI) system—there was no graphical user interface (GUI) to make the system easier to use or more aesthetically pleasing. Now Unix has some of the most customizable user interfaces available, in the forms of the Mac OS X Aqua and Linux’s KDE and GNOME interfaces among others, making the Unix system truly ready for the average user’s desktop.
Let’s take a brief look at the components that make up the Unix operating system: the kernel, the shell, the file system, and the utilities (applications).
The kernel is the lowest layer of the Unix system. It provides the core capabilities of the system and allows processes (programs) to access the hardware in an orderly manner. Basically, the kernel controls processes, input/output devices, file system operations, and any other critical functions required by the operating system. It also manages memory. These are all called autonomous functions, in that they are run without instructions by a user process. It is the kernel that allows the system to run in multiuser (more than one user accessing the system at the same time), multitasking (more than one program running at a time) mode.
A kernel is built for the specific hardware on which it is operating, so a kernel built for a Sun Sparc machine can’t be run on an Intel processor machine without modifications. Because the kernel deals with very low-level tasks, such as accessing the hard drive or managing multitasking, and is not user friendly, it is generally not accessed by the user.
One of the most important functions of the kernel is to facilitate the creation and management of processes. Processes are executed programs (called jobs or tasks in some operating systems) that have owners—human or systems—who initiate their calling or execution. The management of these can be very complicated because one process often calls another (referred to as forking in Unix). Frequently processes also need to communicate with one another, sending and receiving information that allows other actions to be performed. The kernel manages all of this outside of the user’s awareness.
The kernel also manages memory, a key element of any system. It must provide all processes with adequate amounts of memory, and some processes require a lot of it. Sometimes a process requires more memory than is available (too many other processes running, for example). This is where virtual memory comes in. When there isn’t enough physical memory, the system tries to accommodate the process by moving portions of it to the hard disk. When the portion of the process that was moved to hard disk is needed again, it is returned to physical memory. This procedure, called paging, allows the system to provide multitasking capabilities, even with limited physical memory.
Another aspect of virtual memory is called swap, whereby the kernel identifies the least-busy process or a process that does not require immediate execution. The kernel then moves the entire process out of RAM to the hard drive until it is needed again, at which point it can be run from the hard drive or from physical RAM. The difference between the two is that paging moves only part of the process to the hard drive, while swapping moves the entire process to hard drive space. The segment of the hard drive used for virtual memory is called the swap space in Unix, a term you will want to remember as you move through this book. Running out of swap space can cause significant problems, up to and including system failure, so always be sure you have sufficient swap space. Whenever swapping occurs, you pay a heavy price in significantly decreased performance, because disks are appreciably slower than physical RAM. You can avoid swapping by ensuring that you have an adequate amount of physical RAM for the system.
The shell is a command line interpreter that enables the user to interact with the operating system. A shell provides the next layer of functionality for the system; it is what you use directly to administer and run the system. The shell you use will greatly affect the way you work. The original Unix shells have been heavily modified into many different types of shells over the years, all with some unique feature that the creator(s) felt was lacking in other shells. There are three major shells available on most systems: the Bourne shell (also called sh), the C shell (csh), and the Korn shell (ksh). The shell is used almost exclusively via the command line, a text-based mechanism by which the user interacts with the system.
The Bourne shell (also simply called Shell) was the first shell for Unix. It is still the most widely available shell on Unix systems, providing a language with which to script programs and basic user functionality to call other programs. Shell is good for everyday use and is especially good for shell scripting because its scripts are very portable (they work in other Unix versions’ Bourne shells). The only problem with the Bourne shell is that it has fewer features for user interaction than some of the more modern shells.
The C shell is another popular shell commonly available on Unix systems. This shell, from the University of California at Berkeley, was created to address some of the shortcomings of the Bourne shell and to resemble the C language (which is what Unix is built on). Job control features and the capability to alias commands (discussed in Chapter 5) make this shell much easier for user interaction. The C shell had some early quirks when dealing with scripting and is often regarded as less robust than the Bourne shell for creating shell scripts. The quirks were eventually fixed, but the C shell still has slight variations, resulting from different implementations based on which entity (commercial provider or other resource) is providing the shell.
The Korn shell was created by David Korn to address the Bourne shell’s user-interaction issues and to deal with the shortcomings of the C shell’s scripting quirks. The Korn shell adds some functionality that neither the Bourne or C shell has while incorporating the strong points of each shell. The only drawback to the Korn shell is that it requires a license, so its adoption is not as widespread as that of the other two.
These are by no means the only shells available. Here’s a list of some of the many shells available for the different Unix systems:
As with everything Unix, there are many different implementations, and you are free to choose the shell that best suits your needs based on the features provided. Chapter 5 examines several shells in detail.
The other Unix components are the file system and the utilities. The file system enables the user to view, organize, secure, and interact with, in a consistent manner, files and directories located on storage devices. The file system is discussed in depth in Chapter 4.
Utilities are the applications that enable you to work on the system (not to be confused with the shell). These utilities include the Web browser for navigating the Internet, word processing utilities, e-mail programs, and other commands that will be discussed throughout this book.
The KNOPPIX distribution has been optimized to run within RAM from the CD-ROM. It does not need to modify the hard drive or install itself anywhere. It can be run without fear of damaging the current contents of your hard drive.
This chapter briefly discussed the history of Unix and introduced some of the versions of Unix. The Unix core components—the kernel, shells, file system, and utilities—were introduced.
In the past, Unix was considered a system geared to the most computer-savvy users and those who wanted a system for core functionality, with no regard to aesthetics or user friendliness. Unix has evolved to fit the needs of many different types of users, from the no-nonsense corporate environment to the novice computer user’s desktop. There are rich desktop environments available for many flavors of Unix, for example, and every currently selling Macintosh computer is running a version of Unix right out of the box.
In Chapter 2, you begin using a Unix system from initial login to logout.