A superb book, a classic. Good explanations and lot's of ready to use code segments. Stevens was a Guru to most programmers and all appreciated his writings very much. I give only the table of contents, because that is something I like in reviews about such kinds of books:
1.) Introduction, 2.) Unix Standardization and Implementations, 3.) File I/O, 4.) Files and Directories, 5.) Standard I/O Library, 6.) System Data Files and Information, 7.) The Environment of a Unix Process, 8.) Process Control, 9.) Process Relationships, 10.) Signals, 11.) Terminal I/O, 12.) Advanced I/O, 13.) Daemon Processes, 14.) Interprocess Communication, 15.) Advanced Interprocess Communication, 16.) A Database Library, 17.) Communicating with a PostScript Printer, 18.) A Modem Dialer, 19.) Pseudo Terminals.
For many topics one needs his further books. Either the tripple set about TCP/IP or the double set about network programming. The last one is the newest book of him, just finished, before he died.