Rochkind - Advanced UNIX Programming

Second Edition

Marc J. Rochkind

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ISBN 0-13-141154-3

Text printed in the United States on recycled paper at RR Donnelley Crawfordsville in Crawfordsville, Indiana.

6th Printing September 2008

For Claire and Gillian

Brian W. Kernighan, Consulting Editor

Matthew H. Austern, Generic Programming and the STL: Using and Extending the C++ Standard Template Library

David R. Butenhof, Programming with POSIX Threads

Brent Callaghan, NFS Illustrated

Tom Cargill, C++ Programming Style

William R. Cheswick/Steven M. Bellovin/Aviel D. Rubin, Firewalls and Internet Security, Second Edition: Repelling the Wily Hacker

David A. Curry, UNIX System Security: A Guide for Users and System Administrators

Stephen C. Dewhurst, C++ Gotchas: Avoiding Common Problems in Coding and Design

Dan Farmer/Wietse Venema, Forensic Discovery

Erich Gamma/Richard Helm/Ralph Johnson/John Vlissides, Design Patterns: Elements of Reusable Object-Oriented Software

Erich Gamma/Richard Helm/Ralph Johnson/John Vlissides, Design Patterns CD: Elements of Reusable Object-Oriented Software

Peter Haggar, Practical Java Programming Language Guide

David R. Hanson, C Interfaces and Implementations: Techniques for Creating Reusable Software

Mark Harrison/Michael McLennan, Effective Tcl/Tk Programming: Writing Better Programs with Tcl and Tk

Michi Henning/Steve Vinoski, Advanced CORBA Programming with C++

Brian W. Kernighan/Rob Pike, The Practice of Programming

S. Keshav, An Engineering Approach to Computer Networking: ATM Networks, the Internet, and the Telephone Network

John Lakos, Large-Scale C++ Software Design

Scott Meyers, Effective C++ CD: 85 Specific Ways to Improve Your Programs and Designs

Scott Meyers, Effective C++, Third Edition: 55 Specific Ways to Improve Your Programs and Designs

Scott Meyers, More Effective C++: 35 New Ways to Improve Your Programs and Designs

Scott Meyers, Effective STL: 50 Specific Ways to Improve Your Use of the Standard Template Library

Robert B. Murray, C++ Strategies and Tactics

David R. Musser/Gillmer J. Derge/Atul Saini, STL Tutorial and Reference Guide, Second Edition: C++ Programming with the Standard Template Library

John K. Ousterhout, Tcl and the Tk Toolkit

Craig Partridge, Gigabit Networking

Radia Perlman, Interconnections, Second Edition: Bridges, Routers, Switches, and Internetworking Protocols

Stephen A. Rago, UNIX System V Network Programming

Eric S. Raymond, The Art of UNIX Programming

Marc J. Rochkind, Advanced UNIX Programming, Second Edition

Curt Schimmel, UNIX Systems for Modern Architectures: Symmetric Multiprocessing and Caching for Kernel Programmers

W. Richard Stevens, TCP/IP Illustrated, Volume 1: The Protocols

W. Richard Stevens, TCP/IP Illustrated, Volume 3: TCP for Transactions, HTTP, NNTP, and the UNIX Domain Protocols

W. Richard Stevens/Bill Fenner/Andrew M. Rudoff, UNIX Network Programming Volume 1, Third Edition: The Sockets Networking API

W. Richard Stevens/Stephen A. Rago, Advanced Programming in the UNIX Environment, Second Edition

W. Richard Stevens/Gary R. Wright, TCP/IP Illustrated Volumes 1-3 Boxed Set

John Viega/Gary McGraw, Building Secure Software: How to Avoid Security Problems the Right Way

Gary R. Wright/W. Richard Stevens, TCP/IP Illustrated, Volume 2: The Implementation

Ruixi Yuan/W. Timothy Strayer, Virtual Private Networks: Technologies and Solutions

Visit www.awprofessional.com/series/professionalcomputing for more information about these titles.

This book updates the 1985 edition of Advanced UNIX Programming to cover a few changes that have occurred in the last eighteen years. Well, maybe few isnt the right word! And updates isnt right either. Indeed, aside from a sentence here and there, this book is all new. The first edition included about 70 system calls; this one includes about 300. And none of the UNIX standards and implementations discussed in this bookPOSIX, Solaris, Linux, FreeBSD, and Darwin (Mac OS X)were even around in 1985. A few sentences from the 1985 Preface, however, are among those that I can leave almost unchanged:

The subject of this book is UNIX system callsthe interface between the UNIX kernel and the user programs that run on top of it. Those who interact only with commands, like the shell, text editors, and other application programs, may have little need to know much about system calls, but a thorough knowledge of them is essential for UNIX programmers. System calls are the only way to access kernel facilities such as the file system, the multitasking mechanisms, and the interprocess communication primitives.

System calls define what UNIX is. Everything elsesubroutines and commandsis built on this foundation. While the novelty of many of these higher-level programs has been responsible for much of UNIXs renown, they could as well have been programmed on any modern operating system. When one describes UNIX as elegant, simple, efficient, reliable, and portable, one is referring not to the commands (some of which are none of these things), but to the kernel.

Thats all still true, except that, regrettably, the programming interface to the kernel is no longer elegant or simple. In fact, because UNIX development has splintered into many directions over the last couple of decades, and because the principal standards organization, The Open Group, sweeps up almost everything thats out there (1108 functions altogether), the interface is clumsy, inconsistent, redundant, error-prone, and confusing. But its still efficient, reliably implemented, and portable, and thats why UNIX and UNIX-like systems are so successful. Indeed, the UNIX system-call interface is the only widely implemented portable one we have and are likely to have in our lifetime.