The Unix File System

Introduction

These notes describe the basic Unix file system and the kernel structures that support it. For further information the readers should consult The Design of Unix Operating System by M.J.Bach (Prentice-Hall 1986 ISBN 0-13-201757-1) and The Magic Garden Explained by B.Goodheart and J.Cox (Prentice-Hall 1994 0-13-098138-9). The Bach book is probably easier to read but the Goodheart and Cox book is more up-to-date.

Modern Unix systems use a Virtual File System (VFS), this allows the system to use many different actual file systems in a seamless fashion. At a low level, driver software is required for each actual file system. This allows Network File Systems (NFS), High-Sierra File Systems (HSFS - found on CDROMs), MSDOS File Systems (PCFS) amongst others to be included in the Unix view of an integrated hierarchy of files and directories. Included among the various supported file systems are the Unix File System (UFS) and the older System V File System (S5FS). These constitute the traditional Unix file system and will be described in detail in these notes.

• i-nodes
• directory structures
• Kernel buffer structures