This book describes the design and implementation of the BSD operating system-previously known as the Berkeley version of UNIX®. Today BSD is found in nearly every variant of UNIX, and is widely used for Internet services and firewalls, timesharing, and multiprocessing systems. The authors, key participants in the development of 4.4BSD, update the history and goals of the BSD system and provide a coherent overview of its design and implementation. While explaining key design decisions, they provide details to major changes in process and memory management, describe the new extensible and stackable filesystem interface, and update information on networking and interprocess communication.

This book is an extensive revision of the first authoritative and full-length description of the design and implementation of the research versions of the UNIX system developed at the University of California at Berkeley. Most detail is given about 4.4BSD, which incorporates the improvements of the previous Berkeley versions. Although 4.4BSD includes nearly 500 utility programs in addition to the kernel, this book concentrates almost exclusively on the kernel. The UNIX System The UNIX system runs on computers ranging from personal home systems to the largest supercomputers. It is the operating system of choice for most multiprocessor, graphics, and vector-processing systems, and is widely used for its original purpose of timesharing. It is the most common platform for providing network services (from FTP to WWW) on the Internet. It is the most portable operating system ever developed. This portability is due partly to its implementation language, C Kernighan & Ritchie, 1978 (which is itself one of the most widely ported languages), and partly to the elegant design of the system. Many of the system's features are imitated in other systems O'Dell, 1987. Since its inception in 1969 Ritchie & Thompson, 1978, the UNIX system has developed in a number of divergent and rejoining streams. The original developers continued to advance the state of the art with their Ninth and Tenth Edition UNIX inside AT&T Bell Laboratories, and then their Plan 9 successor to UNIX. Meanwhile, AT&T licensed UNIX System V as a product, before selling it to Novell. Novell passed the UNIX trademark to X/OPEN and sold the source code and distribution rights to Santa Cruz Operation (SCO). Both System V and Ninth Edition UNIX were strongly influenced by the Berkeley Software Distributions produced by the Computer Systems Research Group (CSRG) of the University of California at Berkeley. Berkeley Software Distributions These Berkeley systems have introduced several useful programs and facilities to the UNIX community: 2BSD (the Berkeley PDP-11 system): the text editor vi 3BSD (the first Berkeley VAX system): demand-paged virtual-memory support 4.0BSD: performance improvements 4.1BSD: job control, autoconfiguration, and long C identifiers 4.2BSD and 4.3BSD: reliable signals; a fast filesystem; improved networking, including a reference implementation of TCP/IP; sophisticated interprocess-communication (IPC) primitives; and more performance improvements 4.4BSD: a new virtual memory system; a stackable and extensible vnode interface; a network filesystem (NFS); a log-structured filesystem, numerous filesystem types, including loopback, union, and uid/gid mapping layers; an ISO9660 filesystem (e.g., CD-ROM); ISO networking protocols; support for 68K, SPARC, MIPS, and PC architectures; POSIX support, including termios, sessions, and most utilities; multiple IP addresses per interface; disk labels; and improved booting 4.2BSD, 4.3BSD, and 4.4BSD are the bases for the UNIX systems of many vendors, and are used internally by the development groups of many other vendors. Many of these developments have also been incorporated by System V, or hav e been added by vendors whose products are otherwise based on System V. The implementation of the TCP/IP networking protocol suite in 4.2BSD and 4.3BSD, and the availability of those systems, explain why the TCP/IP networking protocol suite is implemented so widely throughout the world. Numerous vendors have adapted the Berkeley networking implementations, whether their base system is 4.2BSD, 4.3BSD, 4.4BSD, System V, or even Digital Equipment Corporation's VMS or Microsoft's Winsock interface in Windows '95 and Windows/NT. 4BSD has also been a strong influence on the POSIX (IEEE Std 1003.1) operating-system interface standard, and on related standards. Several featu