Advanced Programming in the UNIX Environment / Edition 3

by W. Stevens, Stephen Rago

Overview

Practical, in-depth knowledge of the system programming interfaces that drive the UNIX and Linux kernels

Building on W. Rich Stevens’ pioneering work, this third edition of the classic was updated by Steve Rago, a colleague of Stevens, to reflect technical advances and best practices aligning with Version 4 of the Single UNIX Specification.

This edition covers more than seventy interfaces including:

• POSIX asynchronous I/O
• Spin locks
• Barriers
• POSIX semaphores

Steve carefully retains the spirit and approach that have made this book so valuable, starting with files, directories, and processes, carefully laying the groundwork for more advanced techniques, such as signal handling and terminal I/O. And he thoroughly covers threads and multithreaded programming, and socket-based IPC.

Filled with examples, case-studies, and access to thousands of lines of downloadable code, Advanced Programming in the UNIX® Environment has helped generations of programmers write code with exceptional power, performance, and reliability.

Product Details

ISBN-13:	9780321637734
Publisher:	Pearson Education
Publication date:	05/14/2013
Series:	Addison-Wesley Professional Computing Series
Pages:	1032
Sales rank:	272,684
Product dimensions:	7.30(w) x 9.10(h) x 2.10(d)

About the Author

The late W. Richard Stevens was the acclaimed author of UNIX® Network Programming, Volumes 1 and 2, widely recognized as the classic texts in UNIX networking; TCP/IP Illustrated, Volumes 1-3; and the first edition of this book.

Stephen A. Rago is the author of UNIX® System V Network Programming (Addison-Wesley, 1993). Rago was one of the Bell Laboratories developers who built UNIX System V Release 4. He served as a technical reviewer for the first edition of Advanced Programming in the UNIX® Environment. Rago currently works as a research staff member in the Storage Systems Group at NEC Laboratories America.

Read an Excerpt

Introduction

Rich Stevens and I first met through an e-mail exchange when I reported a typographical error in his first book, UNIX Network Programming. He used to kid me about being the person to send him his first errata notice for the book. Until his death in 1999, we exchanged e-mail irregularly, usually when one of us had a question we thought the other might be able to answer. We met for dinner at USENIX conferences and when Rich was teaching in the area.

Rich Stevens was a friend who always conducted himself as a gentleman. When I wrote UNIX System V Network Programming in 1993, I intended it to be a System V version of Rich's UNIX Network Programming. As was his nature, Rich gladly reviewed chapters for me, and treated me not as a competitor, but as a colleague. We often talked about collaborating on a STREAMS version of his TCP/IP Illustrated book. Had events been different, we might have actually done it, but since Rich is no longer with us, revising Advanced Programming in the UNIX Environment is the closest I'll ever get to writing a book with him.When the editors at Addison-Wesley told me that they wanted to update Rich's book, I thought that there wouldn't be too much to change. Even after 13 years, Rich's work still holds up well. But the UNIX industry is vastly different today from what it was when the book was first published.

• The System V variants are slowly being replaced by Linux. The major system vendors that ship their hardware with their own versions of the UNIX System have either made Linux ports available or announced support for Linux. Solaris is perhaps the last descendant of UNIX System V Release 4 with any appreciablemarket share.

• After 4.4BSD was released, the Computing Science Research Group (CSRG) from the University of California at Berkeley decided to put an end to its development of the UNIX operating system, but several different groups of volunteers still maintain publicly available versions.

• The introduction of Linux, supported by thousands of volunteers, has made it possible for anyone with a computer to run an operating system similar to the UNIX System, with freely available source code for the newest hardware devices. The success of Linux is something of a curiosity, given that several free BSD alternatives are readily available.

• Continuing its trend as an innovative company, Apple Computer abandoned its old Mac operating system and replaced it with one based on Mach and FreeBSD.

Thus, I've tried to update the information presented in this book to reflect these four platforms.

After Rich wrote Advanced Programming in the UNIX Environment in 1992, I got rid of most of my UNIX programmer 's manuals. To this day, the two books I keep closest to my desk are a dictionary and a copy of Advanced Programming in the UNIX Environment. I hope you find this revision equally useful.Changes from the First Edition

Rich's work holds up well. I've tried not to change his original vision for this book, but a lot has happened in 13 years. This is especially true with the standards that affect the UNIX programming interface.

Throughout the book, I've updated interfaces that have changed from the ongoing efforts in standards organizations. This is most noticeable in Chapter 2, since its primary topic is standards. The 2001 version of the POSIX.1 standard, which we use in this revision, is much more comprehensive than the 1990 version on which the first edition of this book was based. The 1990 ISO C standard was updated in 1999, and some changes affect the interfaces in the POSIX.1 standard.A lot more interfaces are now covered by the POSIX.1 specification. The base specifications of the Single UNIX Specification (published by The Open Group, formerly X/Open) have been merged with POSIX.1. POSIX.1 now includes several 1003.1 standards and draft standards that were formerly published separately. Accordingly, I've added chapters to cover some new topics. Threads and multithreaded programming are important concepts because they present a cleaner way for programmers to deal with concurrency and asynchrony.

The socket interface is now part of POSIX.1. It provides a single interface to interprocess communication (IPC), regardless of the location of the process, and is a natural extension of the IPC chapters.

I've omitted most of the real-time interfaces that appear in POSIX.1. These are best treated in a text devoted to real-time programming. One such book appears in the bibliography.

I've updated the case studies in the last chapters to cover more relevant real-world examples. For example, few systems these days are connected to a PostScript printer via a serial or parallel port. Most PostScript printers today are accessed via a network, so I've changed the case study that deals with PostScript printer communication to take this into account.

The chapter on modem communication is less relevant these days. So that the original material is not lost, however, it is available on the book's Web site in two formats: PostScript (http://www.apuebook.com/lostchapter/modem.ps) and PDF (http://www.apuebook.com/lostchapter/modem.pdf).

The source code for the examples shown in this book is also available at www.apuebook.com. Most of the examples have been run on four platforms:

1. FreeBSD 5.2.1, a derivative of the 4.4BSD release from the Computer Systems Research Group at the University of California at Berkeley, running on an Intel Pentium processor
2. Linux 2.4.22 (the Mandrake 9.2 distribution), a free UNIX-like operating system, running on Intel Pentium processors
3. Solaris 9, a derivative of System V Release 4 from Sun Microsystems, running on a64-bit UltraSPARC IIi processor
4. Darwin 7.4.0, an operating environment based on FreeBSD and Mach, supported by Apple Mac OS X, version 10.3, on a PowerPC processor

Stephen A. Rago

Warren, New Jersey

April 2005

[e-mail] to the First EditionIntroduction

This book describes the programming interface to the Unix system—the system call interface and many of the functions provided in the standard C library. It is intended for anyone writing programs that run under Unix.

Like most operating systems, Unix provides numerous services to the programs that are running—open a file, read a file, start a new program, allocate a region of memory, get the current time-of-day, and so on. This has been termed the system call interface. Additionally, the standard C library provides numerous functions that are used by almost every C program (format a variable's value for output, compare two strings, etc.).

The system call interface and the library routines have traditionally been described in Sections 2 and 3 of the Unix Programmer 's Manual. This book is not a duplication of these sections. Examples and rationale are missing from the Unix Programmer 's Manual, and that's what this book provides.Unix Standards

The proliferation of different versions of Unix during the 1980s has been tempered by the various international standards that were started during the late 1980s. These include the ANSI standard for the C programming language, the IEEE POSIX family (still being developed), and the X/Open portability guide. This book also describes these standards. But instead of just describing the standards by themselves, we describe them in relation to popular implementations of the standards—System V Release 4 and the forthcoming 4.4BSD. This provides a real-world description, which is often lacking from the standard itself and from books that describe only the standard.Organization of the Book

This book is divided into six parts:

An overview and introduction to basic Unix programming concepts and terminology (Chapter 1), with a discussion of the various Unix standardization efforts and different Unix implementations (Chapter 2).

1. I/O—unbuffered I/O (Chapter 3), properties of files and directories (Chapter 4), the standard I/O library (Chapter 5), and the standard system data files (Chapter 6).
2. Processes—the environment of a Unix process (Chapter 7), process control (Chapter 8), the relationships between different processes (Chapter 9), and signals (Chapter 10).
3. More I/O—terminal I/O (Chapter 11), advanced I/O (Chapter 12), and daemon processes (Chapter 13).
4. IPC—Interprocess communication (Chapters 14 and 15).
5. Examples—a database library (Chapter 16), communicating with a PostScript printer (Chapter 17), a modem dialing program (Chapter 18), and using pseudo terminals (Chapter 19).

A reading familiarity with C would be beneficial as would some experience using Unix. No prior programming experience with Unix is assumed. This text is intended for programmers familiar with Unix and programmers familiar with some other operating system who wish to learn the details of the services provided by most Unix systems.Examples in the Text

This book contains many examples—approximately 10,000 lines of source code. All the examples are in the C programming language. Furthermore, these examples are in ANSI C. You should have a copy of the Unix Programmer's Manual for your system handy while reading this book, since reference is made to it for some of the more esoteric and implementation-dependent features.

Almost every function and system call is demonstrated with a small, complete program. This lets us see the arguments and return values and is often easier to comprehend than the use of the function in a much larger program. But since some of the small programs are contrived examples, a few bigger examples are also included (Chapters 16, 17, 18, and 19). These larger examples demonstrate the programming techniques in larger, real-world examples.Systems Used to Test the Examples

Unfortunately all operating systems are moving targets. Unix is no exception. The following diagram shows the recent evolution of the various versions of System V and 4.xBSD.

4.xBSD are the various systems from the Computer Systems Research Group at the University of California at Berkeley. This group also distributes the BSD Net 1 and BSD Net 2 releases—publicly available source code from the 4.xBSD systems. SVRx refers to System V Release x from AT&T. XPG3 is the X/Open Portability Guide, Issue 3, and ANSI C is the ANSI standard for the C programming language. POSIX.1 is the IEEE and ISO standard for the interface to a Unix-like system. We'll have more to say about these different standards and the various versions of Unix in Sections 2.2 and 2.3.

In this text we use the term 4.3+BSDto refer to the Unix system from Berkeley that is somewhere between the BSD Net 2 release and 4.4BSD. At the time of this writing, 4.4BSD was not released, so the system could not be called 4.4BSD. Nevertheless a simple name was needed to refer to this system and 4.3+BSD is used throughout the text.

Most of the examples in this text have been run on four different versions of Unix:

1. Unix System V/386 Release 4.0 Version 2.0 (''vanilla SVR4'') from U.H. Corp. (UHC), on an Intel 80386 processor.
2. 4.3+BSD at the Computer Systems Research Group, Computer Science Division, University of California at Berkeley, on a Hewlett Packard workstation.
3. BSD/386 (a derivative of the BSD Net 2 release) from Berkeley Software Design, Inc., on an Intel 80386 processor. This system is almost identical to what we call 4.3+BSD.
4. SunOS 4.1.1 and 4.1.2 (systems with a strong Berkeley heritage but many System V features) from Sun Microsystems, on a SPARCstation SLC.

Numerous timing tests are provided in the text and the systems used for the test are identified.

W. Richard Stevens

Tucson, Arizona

April 1992

Table of Contents

Foreword to the Second Edition xix

Preface xxi

Preface to the Second Edition xxv

Preface to the First Edition xxix

Chapter 1: UNIX System Overview 1

1.1 Introduction 1

1.2 UNIX Architecture 1

1.3 Logging In 2

1.4 Files and Directories 4

1.5 Input and Output 8

1.6 Programs and Processes 10

1.7 Error Handling 14

1.8 User Identification 16

1.9 Signals 18

1.10 Time Values 20

1.11 System Calls and Librar y Functions 21

1.12 Summary 23

Chapter 2: UNIX Standardization and Implementations 25

2.1 Introduction 25

2.2 UNIX Standardization 25

2.3 UNIX System Implementations 33

2.4 Relationship of Standards and Implementations 36

2.5 Limits 36

2.6 Options 53

2.7 Feature Test Macros 57

2.8 Primitive System Data Types 58

2.9 Differences Between Standards 58

2.10 Summary 60

Chapter 3: File I/O 61

3.1 Introduction 61

3.2 File Descr iptors 61

3.3 open and openat Functions 62

3.4 creat Function 66

3.5 close Function 66

3.6 lseek Function 66

3.7 read Function 71

3.8 write Function 72

3.9 I/O Efficiency 72

3.10 File Shar ing 74

3.11 Atomic Operations 77

3.12 dup and dup2 Functions 79

3.13 sync, fsync, and fdatasync Functions 81

3.14 fcntl Function 82

3.15 ioctl Function 87

3.16 /dev/fd 88

3.17 Summary 90

Chapter 4: Files and Directories 93

4.1 Introduction 93

4.2 stat, fstat, fstatat, and lstat Functions 93

4.3 File Types 95

4.4 Set-User-ID and Set-Group-ID 98

4.5 File Access Per missions 99

4.6 Ownership of New Files and Directories 101

4.7 access and faccessat Functions 102

4.8 umask Function 104

4.9 chmod, fchmod, and fchmodat Functions 106

4.10 Sticky Bit 108

4.11 chown, fchown, fchownat, and lchown Functions 109

4.12 File Size 111

4.13 File Tr uncation 112

4.14 File Systems 113

4.15 link, linkat, unlink, unlinkat, and remove Functions 116

4.16 rename and renameat Functions 119

4.17 Symbolic Links 120

4.18 Creating and Reading Symbolic Links 123

4.19 File Times 124

4.20 futimens, utimensat, and utimes Functions 126

4.21 mkdir, mkdirat, and rmdir Functions 129

4.22 Reading Director ies 130

4.23 chdir, fchdir, and getcwd Functions 135

4.24 Device Special Files 137

4.25 Summary of File Access Per mission Bits 140

4.26 Summary 140

Chapter 5: Standard I/O Library 143

5.1 Introduction 143

5.2 Streams and FILE Objects 143

5.3 Standard Input, Standard Output, and Standard Error 145

5.4 Buffer ing 145

5.5 Opening a Stream 148

5.6 Reading and Writing a Stream 150

5.7 Line-at-a-Time I/O 152

5.8 Standard I/O Efficiency 153

5.9 Binary I/O 156

5.10 Positioning a Stream 157

5.11 For matted I/O 159

5.12 Implementation Details 164

5.13 Temporar y Files 167

5.14 Memory Streams 171

5.15 Alternatives to Standard I/O 174

5.16 Summary 175

Chapter 6: System Data Files and Information 177

6.1 Introduction 177

6.2 Password File 177

6.3 Shadow Passwords 181

6.4 Group File 182

6.5 Supplementary Group IDs 183

6.6 Implementation Differences 184

6.7 Other Data Files 185

6.8 Login Accounting 186

6.9 System Identification 187

6.10 Time and Date Routines 189

6.11 Summary 196

Chapter 7: Process Environment 197

7.1 Introduction 197

7.2 main Function 197

7.3 Process Termination 198

7.4 Command-Line Arguments 203

7.5 Environment List 203

7.6 Memory Lay out of a C Program 204

7.7 Shared Librar ies 206

7.8 Memory Allocation 207

7.9 Environment Var iables 210

7.10 setjmp and longjmp Functions 213

7.11 getrlimit and setrlimit Functions 220

7.12 Summary 225

Chapter 8: Process Control 227

8.1 Introduction 227

8.2 Process Identifiers 227

8.3 fork Function 229

8.4 vfork Function 234

8.5 exit Functions 236

8.6 wait and waitpid Functions 238

8.7 waitid Function 244

8.8 wait3 and wait4 Functions 245

8.9 Race Conditions 245

8.10 exec Functions 249

8.11 Changing User IDs and Group IDs 255

8.12 Interpreter Files 260

8.13 system Function 264

8.14 Process Accounting 269

8.15 User Identification 275

8.16 Process Scheduling 276

8.17 Process Times 280

8.18 Summary 282

Chapter 9: Process Relationships 285

9.1 Introduction 285

9.2 Ter minal Logins 285

9.3 Networ k Logins 290

9.4 Process Groups 293

9.5 Sessions 295

9.6 Controlling Terminal 296

9.7 tcgetpgrp, tcsetpgrp, and tcgetsid Functions 298

9.8 Job Control 299

9.9 Shell Execution of Programs 303

9.10 Orphaned Process Groups 307

9.11 FreeBSD Implementation 310

9.12 Summary 312

Chapter 10: Signals 313

10.1 Introduction 313

10.2 Signal Concepts 313

10.3 signal Function 323

10.4 Unreliable Signals 326

10.5 Interrupted System Calls 327

10.6 Reentrant Functions 330

10.7 SIGCLD Semantics 332

10.8 Reliable-Signal Ter minology and Semantics 335

10.9 kill and raise Functions 336

10.10 alarm and pause Functions 338

10.11 Signal Sets 344

10.12 sigprocmask Function 346

10.13 sigpending Function 347

10.14 sigaction Function 349

10.15 sigsetjmp and siglongjmp Functions 355

10.16 sigsuspend Function 359

10.17 abort Function 365

10.18 system Function 367

10.19 sleep, nanosleep, and clock_nanosleep Functions 373

10.20 sigqueue Function 376

10.21 Job-Control Signals 377

10.22 Signal Names and Numbers 379

10.23 Summary 381

Chapter 11: Threads 383

11.1 Introduction 383

11.2 Thread Concepts 383

11.3 Thread Identification 384

11.4 Thread Creation 385

11.5 Thread Termination 388

11.6 Thread Synchronization 397

11.7 Summary 422

Chapter 12: Thread Control 425

12.1 Introduction 425

12.2 Thread Limits 425

12.3 Thread Attr ibutes 426

12.4 Synchronization Attr ibutes 430

12.5 Reentrancy 442

12.6 Thread-Specific Data 446

12.7 Cancel Options 451

12.8 Threads and Signals 453

12.9 Threads and fork 457

12.10 Threads and I/O 461

12.11 Summary 462

Chapter 13: Daemon Processes 463

13.1 Introduction 463

13.2 Daemon Character istics 463

13.3 Coding Rules 466

13.4 Error Logging 469

13.5 Single-Instance Daemons 473

13.6 Daemon Conventions 474

13.7 Client–Server Model 479

13.8 Summary 480

Chapter 14: Advanced I/O 481

14.1 Introduction 481

14.2 Nonblocking I/O 481

14.3 Record Locking 485

14.4 I/O Multiplexing 500

14.5 Asynchronous I/O 509

14.6 readv and writev Functions 521

14.7 readn and writen Functions 523

14.8 Memory-Mapped I/O 525

14.9 Summary 531

Chapter 15: Interprocess Communication 533

15.1 Introduction 533

15.2 Pipes 534

15.3 popen and pclose Functions 541

15.4 Coprocesses 548

15.5 FIFOs 552

15.6 XSI IPC 556

15.7 Message Queues 561

15.8 Semaphores 565

15.9 Shared Memor y 571

15.10 POSIX Semaphores 579

15.11 Client–Server Proper ties 585

15.12 Summary 587

Chapter 16: Network IPC: Sockets 589

16.1 Introduction 589

16.2 Socket Descr iptors 590

16.3 Addressing 593

16.4 Connection Establishment 605

16.5 Data Tr ansfer 610

16.6 Socket Options 623

16.7 Out-of-Band Data 626

16.8 Nonblocking and Asynchronous I/O 627

16.9 Summary 628

Chapter 17: Advanced IPC 629

17.1 Introduction 629

17.2 UNIX Domain Sockets 629

17.3 Unique Connections 635

17.4 Passing File Descriptors 642

17.5 An Open Server, Version 1 653

17.6 An Open Server, Version 2 659

17.7 Summary 669

Chapter 18: Terminal I/O 671

18.1 Introduction 671

18.2 Over view 671

18.3 Special Input Characters 678

18.4 Getting and Setting Ter minal Attr ibutes 683

18.5 Ter minal Option Flags 683

18.6 stty Command 691

18.7 Baud Rate Functions 692

18.8 Line Control Functions 693

18.9 Ter minal Identification 694

18.10 Canonical Mode 700

18.11 Noncanonical Mode 703

18.12 Ter minal Window Size 710

18.13 termcap, terminfo, and curses 712

18.14 Summary 713

Chapter 19: Pseudo Terminals 715

19.1 Introduction 715

19.2 Over view 715

19.3 Opening Pseudo-Ter minal Devices 722

19.4 pty_fork Function 726

19.5 pty Program 729

19.6 Using the pty Program 733

19.7 Advanced Features 740

19.8 Summary 741

Chapter 20: A Database Library 743

20.1 Introduction 743

20.2 History 743

20.3 The Librar y 744

20.4 Implementation Over view 746

20.5 Centralized or Decentralized? 750

20.6 Concurrency 752

20.7 Building the Librar y 753

20.8 Source Code 753

20.9 Perfor mance 781

20.10 Summary 786

Chapter 21: Communicating with a Network Printer 789

21.1 Introduction 789

21.2 The Inter net Pr inting Protocol 789

21.3 The Hyper text Transfer Protocol 792

21.4 Printer Spooling 793

21.5 Source Code 795

21.6 Summary 843

Appendix A: Function Prototypes 845

Appendix B: Miscellaneous Source Code 895

B.1 Our Header File 895

B.2 Standard Error Routines 898

Appendix C: Solutions to Selected Exercises 905

Bibliography 947

Index 955

Preface

Introduction

Rich Stevens and I first met through an e-mail exchange when I reported a typographical error in his first book, UNIX Network Programming. He used to kid me about being the person to send him his first errata notice for the book. Until his death in 1999, we exchanged e-mail irregularly, usually when one of us had a question we thought the other might be able to answer. We met for dinner at USENIX conferences and when Rich was teaching in the area.

Rich Stevens was a friend who always conducted himself as a gentleman. When I wrote UNIX System V Network Programming in 1993, I intended it to be a System V version of Rich's UNIX Network Programming. As was his nature, Rich gladly reviewed chapters for me, and treated me not as a competitor, but as a colleague. We often talked about collaborating on a STREAMS version of his TCP/IP Illustrated book. Had events been different, we might have actually done it, but since Rich is no longer with us, revising Advanced Programming in the UNIX Environment is the closest I'll ever get to writing a book with him.When the editors at Addison-Wesley told me that they wanted to update Rich's book, I thought that there wouldn't be too much to change. Even after 13 years, Rich's work still holds up well. But the UNIX industry is vastly different today from what it was when the book was first published.

• The System V variants are slowly being replaced by Linux. The major system vendors that ship their hardware with their own versions of the UNIX System have either made Linux ports available or announced support for Linux. Solaris is perhaps the last descendant of UNIX System V Release 4 with any appreciablemarket share.

• After 4.4BSD was released, the Computing Science Research Group (CSRG) from the University of California at Berkeley decided to put an end to its development of the UNIX operating system, but several different groups of volunteers still maintain publicly available versions.

• The introduction of Linux, supported by thousands of volunteers, has made it possible for anyone with a computer to run an operating system similar to the UNIX System, with freely available source code for the newest hardware devices. The success of Linux is something of a curiosity, given that several free BSD alternatives are readily available.

• Continuing its trend as an innovative company, Apple Computer abandoned its old Mac operating system and replaced it with one based on Mach and FreeBSD.

Thus, I've tried to update the information presented in this book to reflect these four platforms.

After Rich wrote Advanced Programming in the UNIX Environment in 1992, I got rid of most of my UNIX programmer 's manuals. To this day, the two books I keep closest to my desk are a dictionary and a copy of Advanced Programming in the UNIX Environment. I hope you find this revision equally useful.

Changes from the First Edition

Rich's work holds up well. I've tried not to change his original vision for this book, but a lot has happened in 13 years. This is especially true with the standards that affect the UNIX programming interface.

Throughout the book, I've updated interfaces that have changed from the ongoing efforts in standards organizations. This is most noticeable in Chapter 2, since its primary topic is standards. The 2001 version of the POSIX.1 standard, which we use in this revision, is much more comprehensive than the 1990 version on which the first edition of this book was based. The 1990 ISO C standard was updated in 1999, and some changes affect the interfaces in the POSIX.1 standard.A lot more interfaces are now covered by the POSIX.1 specification. The base specifications of the Single UNIX Specification (published by The Open Group, formerly X/Open) have been merged with POSIX.1. POSIX.1 now includes several 1003.1 standards and draft standards that were formerly published separately. Accordingly, I've added chapters to cover some new topics. Threads and multithreaded programming are important concepts because they present a cleaner way for programmers to deal with concurrency and asynchrony.

The socket interface is now part of POSIX.1. It provides a single interface to interprocess communication (IPC), regardless of the location of the process, and is a natural extension of the IPC chapters.

I've omitted most of the real-time interfaces that appear in POSIX.1. These are best treated in a text devoted to real-time programming. One such book appears in the bibliography.

I've updated the case studies in the last chapters to cover more relevant real-world examples. For example, few systems these days are connected to a PostScript printer via a serial or parallel port. Most PostScript printers today are accessed via a network, so I've changed the case study that deals with PostScript printer communication to take this into account.

The chapter on modem communication is less relevant these days. So that the original material is not lost, however, it is available on the book's Web site in two formats: PostScript (

http://www.apuebook.com/lostchapter/modem.ps) and PDF (

http://www.apuebook.com/lostchapter/modem.pdf).

The source code for the examples shown in this book is also available at

www.apuebook.com. Most of the examples have been run on four platforms:

1. FreeBSD 5.2.1, a derivative of the 4.4BSD release from the Computer Systems Research Group at the University of California at Berkeley, running on an Intel Pentium processor
2. Linux 2.4.22 (the Mandrake 9.2 distribution), a free UNIX-like operating system, running on Intel Pentium processors
3. Solaris 9, a derivative of System V Release 4 from Sun Microsystems, running on a64-bit UltraSPARC IIi processor
4. Darwin 7.4.0, an operating environment based on FreeBSD and Mach, supported by Apple Mac OS X, version 10.3, on a PowerPC processor

Stephen A. Rago

Warren, New Jersey

April 2005

[e-mail]

Preface to the First EditionIntroduction

This book describes the programming interface to the Unix system—the system call interface and many of the functions provided in the standard C library. It is intended for anyone writing programs that run under Unix.

Like most operating systems, Unix provides numerous services to the programs that are running—open a file, read a file, start a new program, allocate a region of memory, get the current time-of-day, and so on. This has been termed the system call interface. Additionally, the standard C library provides numerous functions that are used by almost every C program (format a variable's value for output, compare two strings, etc.).

The system call interface and the library routines have traditionally been described in Sections 2 and 3 of the Unix Programmer 's Manual. This book is not a duplication of these sections. Examples and rationale are missing from the Unix Programmer 's Manual, and that's what this book provides.

Unix Standards

The proliferation of different versions of Unix during the 1980s has been tempered by the various international standards that were started during the late 1980s. These include the ANSI standard for the C programming language, the IEEE POSIX family (still being developed), and the X/Open portability guide. This book also describes these standards. But instead of just describing the standards by themselves, we describe them in relation to popular implementations of the standards—System V Release 4 and the forthcoming 4.4BSD. This provides a real-world description, which is often lacking from the standard itself and from books that describe only the standard.

Organization of the Book

This book is divided into six parts:

An overview and introduction to basic Unix programming concepts and terminology (Chapter 1), with a discussion of the various Unix standardization efforts and different Unix implementations (Chapter 2).

1. I/O—unbuffered I/O (Chapter 3), properties of files and directories (Chapter 4), the standard I/O library (Chapter 5), and the standard system data files (Chapter 6).
2. Processes—the environment of a Unix process (Chapter 7), process control (Chapter 8), the relationships between different processes (Chapter 9), and signals (Chapter 10).
3. More I/O—terminal I/O (Chapter 11), advanced I/O (Chapter 12), and daemon processes (Chapter 13).
4. IPC—Interprocess communication (Chapters 14 and 15).
5. Examples—a database library (Chapter 16), communicating with a PostScript printer (Chapter 17), a modem dialing program (Chapter 18), and using pseudo terminals (Chapter 19).

A reading familiarity with C would be beneficial as would some experience using Unix. No prior programming experience with Unix is assumed. This text is intended for programmers familiar with Unix and programmers familiar with some other operating system who wish to learn the details of the services provided by most Unix systems.

Examples in the Text

This book contains many examples—approximately 10,000 lines of source code. All the examples are in the C programming language. Furthermore, these examples are in ANSI C. You should have a copy of the Unix Programmer's Manual for your system handy while reading this book, since reference is made to it for some of the more esoteric and implementation-dependent features.

Almost every function and system call is demonstrated with a small, complete program. This lets us see the arguments and return values and is often easier to comprehend than the use of the function in a much larger program. But since some of the small programs are contrived examples, a few bigger examples are also included (Chapters 16, 17, 18, and 19). These larger examples demonstrate the programming techniques in larger, real-world examples.

Systems Used to Test the Examples

Unfortunately all operating systems are moving targets. Unix is no exception. The following diagram shows the recent evolution of the various versions of System V and 4.xBSD.

4.xBSD are the various systems from the Computer Systems Research Group at the University of California at Berkeley. This group also distributes the BSD Net 1 and BSD Net 2 releases—publicly available source code from the 4.xBSD systems. SVRx refers to System V Release x from AT&T. XPG3 is the X/Open Portability Guide, Issue 3, and ANSI C is the ANSI standard for the C programming language. POSIX.1 is the IEEE and ISO standard for the interface to a Unix-like system. We'll have more to say about these different standards and the various versions of Unix in Sections 2.2 and 2.3.

In this text we use the term 4.3+BSDto refer to the Unix system from Berkeley that is somewhere between the BSD Net 2 release and 4.4BSD. At the time of this writing, 4.4BSD was not released, so the system could not be called 4.4BSD. Nevertheless a simple name was needed to refer to this system and 4.3+BSD is used throughout the text.

Most of the examples in this text have been run on four different versions of Unix:

1. Unix System V/386 Release 4.0 Version 2.0 (''vanilla SVR4'') from U.H. Corp. (UHC), on an Intel 80386 processor.
2. 4.3+BSD at the Computer Systems Research Group, Computer Science Division, University of California at Berkeley, on a Hewlett Packard workstation.
3. BSD/386 (a derivative of the BSD Net 2 release) from Berkeley Software Design, Inc., on an Intel 80386 processor. This system is almost identical to what we call 4.3+BSD.
4. SunOS 4.1.1 and 4.1.2 (systems with a strong Berkeley heritage but many System V features) from Sun Microsystems, on a SPARCstation SLC.

Numerous timing tests are provided in the text and the systems used for the test are identified.

W. Richard Stevens

Tucson, Arizona

April 1992