TILDE Trees in the UNIX Environment

ABSrRACf TILDE is a multi-year research project exploring distributed computing in an environment where the primary computing engine consists of a cluster of UNIX·liket systems loosely coupled with high-speed local area networks. The goal of 'IU.DE is to extend UNIX to provide a transparent integration of local and remote facilities, allowing the user access to remote files and services without forcing the user to know about the location of data, processes, or other objects such as servers. One important aspect of TILDE is the Tilde naming scheme. The TILDE approach to naming objects in a distributed system provides a transparent, consistent mechanism-fol refer~!l.cing both local and remote objects.. The Tilde naming scheme substitutes a collection of directory hierarchies. known as Tilde trees. for the single UNIX directory hierarchy. A program executes in an environment composed of a forest of Tilde trees, which can be selected from the collection of Tilde trees known to the distributed computing system. In the prototype, each of the Tilde trees is mapped onto a UNIX subdirectory. As in UNIX, files are named either relative to the current working directory, or by a full pathp.ame. Full path names begin with tilde, and the first component identifies the appropriate Tilde tree, while the remainder of the t UNIX is a trademark of Bell Laboratories. ·2-pathname completely specifies the file within the Tilde tree. (The naming scheme c<:.n be viewed as an extension to C-sbeU naming mechanism.) A particular process executing within the TILDE system need not know the details of the storage organization or file location in the distributed '1O)'Stem; rather, there is a uniform mechanism for searching and accessing Tilde trees. This paper describes the naming scheme and a prototype implementation. It discusses alternative designs and compromises imposed by the limitations of a single-processor UNIX environment, as well as the impact of using the Tilde environment for tasks such as software development. We show how our Tilde naming software makes it possible to move large programs from one directory' to another or from one UNIX system to another without recompiling (even if path names have been bound into the code). Finally, future directions for this work, including extension to coUections of UNIX systems and modifications to include the Tilde tree naming system in the UNIX kernel, are also discussed.