This book is all about DTrace, with the emphasis on using DTrace to understand, observe, and diagnose systems and applications. A deep understanding of the details of how DTrace works is not necessary to using DTrace to diagnose and solve problems; thus, the book covers using DTrace on systems and applications, with command-line examples and a great many D scripts. Depending on your level of experience, we intend the book’s organization to facilitate its use as a reference guide, allowing you to refer to specific chapters when diagnosing a particular area of the system or application.