CS311

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CS311 Lecture 16 Outline

• File System inodes
• Note These lecture notes are not intended
  replace your notes. This is what I expect your
  notes to already look like, but with more
  explanation as needed.

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inodes

• Tutorial http//classes.engr.oregonstate.edu/eecs
  /summer2009/cs311/files/misc/inode.pdf
• Questions on inodes
• What is in an inode?
• How does the filesystem assemble all the blocks
  of a file?
• What is stored in a directory file?

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inodes

• To see inode number of files ls i
• File Types that we have studied include
  directory, regular, and symbolic (soft link).
• inodes are kept in an inode array on disk.
• Given the inode we just index into the array to
  the one we want.
• This is possible because inodes are all the same
  size.

Lecture 15
CS311 Operating Systems 1
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Links

• hard links ln existingFile newFile
• How does the above command relate to inodes?
• Ans Hard links have the same inode number.
  existingFile and newFile shares one inode.
• soft linksln -s existingFile newFile2
• How does the above command relate to inodes?
• Ans Soft links have their own inode number.
  newFile2 stores the path to existingFile

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Links

• link count is how many hard links point to them.
  Do not free up this inode until that goes down to
  0.
• What is an advantage of using soft links?
• Ans You can link across filesystems
• What is an advantage of using hard links?
• Ans Faster because you go directly to the right
  inode with no indirection.

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File system permissions

• file type regular
• r - you may read this file
• w - you may edit this file
• x - you may execute this file
• file type directory
• r - you may list the contents with ls
• w - you may add a file or rename a file
• x - you may search this directory for a specific
  filename

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Directory files

• filename / inode pairs are the only thing in the
  data blocks
• . and .. are valid filenames and refer to current
  directory and parent directory

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Examples

• What happens in the filesystem when we try to
  read this file?/nfs/stak/h/hacker/data.txt
• What do the inodes and datablocks look like after
  these commands?mkdir dirAcd dirAls .. gt
  listing lt- assume dirA is the only file in ..ln
  listing file1ln -s listing file2

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