Editing Unix File System (section)

== Design ==

A UFS volume is composed of the following parts:

* A few blocks at the beginning of the partition reserved for [[Bootstrapping (computing)|boot blocks]] (which must be initialized separately from the filesystem)
* A superblock, containing a [[magic number (programming)|magic number]] identifying this as a UFS filesystem, and some other vital numbers describing this filesystem's geometry and statistics and behavioral tuning parameters
* A collection of cylinder groups. Each cylinder group has the following components:
** A backup copy of the superblock
** A cylinder group header, with statistics, free lists, etc., about this cylinder group, similar to those in the superblock
** A number of [[inode]]s, each containing file attributes
** A number of [[Block (data storage)|data blocks]]

Inodes are numbered sequentially, starting at 0. Inode 0 is reserved for unallocated directory entries, inode 1 was the inode of the bad block file in historical UNIX versions, followed by the inode for the [[root directory]], which is always inode 2 and the inode for the lost+found directory which is inode 3.

Directory files contain only the list of filenames in the directory and the inode associated with each file.  All file [[Metadata (computing)|metadata]] is kept in the inode.