1. Chapter 11 File Sharing

2. Copyright © 2005 Pearson Addison-Wesley. All rights reserved. Objectives  To explain different ways of sharing files  To discuss the UNIX schemes and commands for implementing file sharing  To describe UNIX hard and soft (symbolic) links in detail and discuss their advantages and disadvantages  To cover the commands and primitives –*, ~, ln, ln –f, ln –s, ls –i, ls –l

3. Copyright © 2005 Pearson Addison-Wesley. All rights reserved. File Sharing  Duplicate Shared Files  Common Login for Members of a Team  Setting appropriate Access Permissions on Shared Files  Common Group for Members of a team  File sharing via Links –Hard Links –Soft/Symbolic Links

4. Copyright © 2005 Pearson Addison-Wesley. All rights reserved. File Sharing via Links Hard Links ln [options] existing-file new-file ln [options] existing-file-list directory

5. Copyright © 2005 Pearson Addison-Wesley. All rights reserved. File Sharing via Links (contd)

6. Copyright © 2005 Pearson Addison-Wesley. All rights reserved. File Sharing via Links (contd)

7. Copyright © 2005 Pearson Addison-Wesley. All rights reserved. File Sharing via Links (contd)

8. Copyright © 2005 Pearson Addison-Wesley. All rights reserved. File Sharing via Links (contd) Characteristics of Hard Links  No hard links across file systems  Only superuser can create hard links to directories

9. Copyright © 2005 Pearson Addison-Wesley. All rights reserved. Soft / Symbolic Links

10. Copyright © 2005 Pearson Addison-Wesley. All rights reserved. Soft / Symbolic Links

11. Copyright © 2005 Pearson Addison-Wesley. All rights reserved. Pros and Cons of Symbolic Links Pros –Can be establishes between files across file systems and to directories. –Files that symbolic links point to can be edited by any kind of editor without any ill effects Cons –If the file that the symbolic link points to is moved from one directory to another, it can no longer be accessed via the link –UNIX has to support an additional file type (the link type) and a new file has to be created for every link. –Slow file operations because for every reference to the file, the link file has to be opened and read in order to reach the actual file