ESPRIT LTR 21917 (Pegasus II) Deliverable 4.5.2: Unix functionality

Traditional operating systems present fixed, high-level abstractions to application developers and users. These are part of standard APIs, such as POSIX or X/OPEN, which are typically implemented as a thin library layer on top of monolithic kernels. Recent efforts in operating system research, however, have focussed on providing more flexibility and new functionality to applications by lowering the abstraction level to a minimal kernel interface. Higher-level abstractions are provided through user-level servers or, more recently, through shared libraries. These library based operating systems allow the design and implementation of arbitrary high-level abstractions as user-level shared libraries on top of a minimal kernel interface. Nemesis is a library based operating system which offers genuine support for multi-media data stream types by providing Quality of Service guarantees for all shared resources in the system. In Nemesis, the libraries implementing the high level abstractions are carefully designed to avoid interactions between different processes for shared state. Abstractions which rely on traditional stateful APIs are handled using library componets called personalities, described in (Neugebauer & Black 1998). This deliverable report describes the design and implementation of a personality offering Unix-like functionality for the Nemesis operating system. This effort was motivated on two grounds: first, to research the techniques and feasibility of providing such functionality in a single address space system such as Nemesis, and second, by the desire to take advantage of the vast amount of existing application code available for Unix systems.