UNIX File System Layout

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 large 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

super block
boot block
data blocks
inode list
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

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 ..

5
foo.c
3
bar
mumble
6
to inode
to inode
unused space
to inode
4
Hard Links

• an inode can be linked from many different
  directory entries, i.e., it may have many names

5
foo.c
3
bar
mumble
6
to inode
inode 2714
reference count 2
5
Symbolic (Soft) Links

• a symbolic link is a special file that contains a
  pathname.

Hello, world
/usr/joe
foo
/usr/sue
/usr/joe/foo
bar
file content
inodes
directories