UNIX File System Layout

Yukon Chang, Fall 1996 Operating System (II) Chapter 11 Supplement Slide 1

UNIX File System Layout boot block contains bootstrap code that is read into the

machine to boot the operating system super block describes the state of a file system, how lar

ge it is, how many files it can store, where to find free space on the file system, etc

inode list is a list of inodes (explained later) data blocks store file data and administrative data

data blocksinode listsuperblock

bootblock

Yukon Chang, Fall 1996 Operating System (II) Chapter 11 Supplement Slide 2

Inodes (Index Nodes) inodes exist in a statis form on disk, it consists of

• file owner (individual owner and group owner)• file type (regular, directory, character/block device, ...)• access permission (r-xr-x---)• access and last modify time (of file and inode)• number of links to the file• pointers to data blocks• file size

see Fig. 11.7 on the textbook

Yukon Chang, Fall 1996 Operating System (II) Chapter 11 Supplement Slide 3

Directory Block notably missing from inode information is the file name file name is kept in a directory entry of directory block the first two entries in a directory have names . and ..

toinode

5 foo.c 3 bar mumble6

toinode

toinode

unusedspace

Yukon Chang, Fall 1996 Operating System (II) Chapter 11 Supplement Slide 4

Hard Links an inode can be linked from many different directory e

ntries, i.e., it may have many names

toinode

5 foo.c 3 bar mumble6

inode2714 reference count = 2

Yukon Chang, Fall 1996 Operating System (II) Chapter 11 Supplement Slide 5

Symbolic (Soft) Links a symbolic link is a special file that contains a

pathname.

directories

/usr/joe

/usr/sue

foo

bar

inodesfile

content

/usr/joe/foo

Hello, world