This edition has been restructured in two parts - fundamental system services, and advanced and special features. It has also been updated throughout to reflect the following hierarchy of standards in the UNIX world - the IEEE POSIX standard, AT & T's SVID (System V Interface Definition) Issue 3, corresponding to UNIX System V.4, and X/Open. In an appendix new to this edition, the relationship between UNIX implementations and standards is explored. All examples conform to UNIX System V and the European Standard XOPEN.