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Chapter 11

Chapter 11. File Sharing. Sharing Techniques. Duplicate files Common login Setting appropriate access permissions on shared files Common group for team members Sharing via links. Sharing via Links.

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Chapter 11

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  1. Chapter 11 File Sharing

  2. Sharing Techniques • Duplicate files • Common login • Setting appropriate access permissions on shared files • Common group for team members • Sharing via links

  3. Sharing via Links • A link is a connection between the file to be shared and the directory entries of the users who want to have access to this file • 2 types of links exist: • hard links • soft (symbolic) links

  4. Figure 11.1 (a) Logical structure of current directory; (b) contents of current directory

  5. Figure 11.1 (c) relationship among a directory entry, inode, and file contents

  6. Hard Links • A hard link is a pointer to the inode of a file • Established using the ln command • The link count of the file is incremented • Both the original file and the new entry point to the same inode • When deleted, the link count is decremented, and the file is only deleted if the resulting link count is zero

  7. Figure 11.2 Establishing a hard linkln Chapter3 Chapter3.hard

  8. ln command Syntax ln [options] oldfile newfile ln [options] old-file-list directory Options -f force creation (overwrite existing file) -n don’t force -s create soft(symbolic) link

  9. Figure 11.2 (c) hard link implementation by establishing a pointer to inode of the file

  10. Hard Link across directoriesln memo6.hard memos/memo6

  11. Hard Link across accountsln linuxbook/examples/demo1 ../bob/dir1sarwar must have x-permission for bob and wx-permission for dir1

  12. Limitations of Hard Links • Links cannot be established across file systems • If one of the files is moved to a different file system, it is copied instead, and the link counts of both files adjusted accordingly • Only superusers can create hard links to directories

  13. Soft (Symbolic) Links • Established using the ln -s command • The link count of the file is not incremented • The created file is of the special type “link” denoted by “l” in directory listings • The linked file is an actual file that contains the path to the original file • Symbolic links can be created across file systems • Symbolic links to directories can be created by any user

  14. Figure 11.5 Establishing a soft linkln -s Chapter3 Chapter3.soft

  15. Soft links in directory listing ln -s Chapter3 Chapter3.soft ls – il 52473 -rwxr--r-- 1 sarwar faculty 9352 May 28 23:09 Chapter3 52479 lrwxr--r-- 2 sarwar faculty 8 Oct 13 14:24 Chapter3.soft --> Chapter3

  16. Figure 11.5 (c) soft link implementation by establishing a “pointer” to (pathname of) the existing file in the link file

  17. Soft Link across accounts

  18. Types of Symbolic Links • absolute • relative • other_fs • messy • lengthy • dangling symlinks command used for examining and repairing links

  19. Drawbacks of Soft Links • If the original file is moved to a different location, it can no longer be accessed via the symbolic link (dangling link) • Extra space on disk and extra inode to store the link file • Extra time required for access to the original file: the link file has to be read first, then path followed to target file

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