1 © 2001 John Urrutia. All rights reserved. Chapter 4 The LINUX Filesystem

2 © 2001 John Urrutia. All rights reserved. Topics The Hierarchical File System Directory and Ordinary Files Working With Directories Access Permissions Links

3 © 2001 John Urrutia. All rights reserved. Hierarchical File Systems  Structured like an upside-down tree  Grandparents at the top  Parents follow  Then Children Topics

4 © 2001 John Urrutia. All rights reserved. Child 1Child 2Child 3 Grandparent Parentauntuncle/Alice/Bobby/Carol/home/tmp/bin Hierarchical Structure / (aka root)

5 © 2001 John Urrutia. All rights reserved. Hierarchical File Systems Directories and ordinary files  Directories / sub-directories  Special files used for grouping  Ordinary Files  Contain the kitchen sink

6 © 2001 John Urrutia. All rights reserved. Directory assistance Directories provide an organized method to access ordinary files.  path –  A series of directory files traveling from the root to the ordinary file.  pathname –  The sequenced listing of directory names from the root to the ordinary file.

7 © 2001 John Urrutia. All rights reserved. Filenames  Max length 255 characters  A thru Z, a thru z, 0 thru 9 _.,  Some file systems limit these to 14 characters  Make them meaningful   IMd12CRU  OOicu812

8 © 2001 John Urrutia. All rights reserved. Filename Extensions Begins with a period  Generally are optional  Used by applications to identify specific file needed by the application  Examples: CPP TXT INI

9 © 2001 John Urrutia. All rights reserved. Invisible Files Must start with a period  Normally not displayed  Used by Unix for special purposes  Use “ ls –a ” to see these 

10 © 2001 John Urrutia. All rights reserved. Topics The Hierarchical File System Directory and Ordinary Files Working With Directories Access Permissions Links

11 © 2001 John Urrutia. All rights reserved. Creating a directory mkdir – utility creates a directory  The argument can either specify an absolute pathname or a relative pathname mkdir mydirectory  In this example “mydirectory” will be created under the current or working directory

12 © 2001 John Urrutia. All rights reserved. Directory file Two invisible files are created for each directory created  One is the pathname of the working directory named “ ”  Two is the pathname of the parent directory named “ ”  cat./Test.file  cat Test.file

13 © 2001 John Urrutia. All rights reserved. Path (to glory or destruction) Every file has a PATHNAME  Absolute Pathnames begin with the root (/)  Each directory in the hierarchy from the root to the file is separated by a slash

14 © 2001 John Urrutia. All rights reserved. Test.file Path example: /Alice/Bobby/Carol /home/tmp/bin // /home /Bobby Test.file /home/Bobby/Test.file

15 © 2001 John Urrutia. All rights reserved. Absolute & Relative Path Absolute path is fully qualified  cat /home/Bobby/Test.file Relative path is based on the working directory  pwd – Print Working Directory  /home/Bobby  cat Test.file

16 © 2001 John Urrutia. All rights reserved. The Working Directory You’re working directory is assigned by the login process. To access files in working directory simply refer to the filename no path is needed. Files outside your working directory require a pathname.

17 © 2001 John Urrutia. All rights reserved. Your Working Directory Generally you’re working directory will be  /home/userid

18 © 2001 John Urrutia. All rights reserved. Important Directories and Files The root - / (of all evil)  /root – Home directory for root  /boot – static files of the boot loader  /bin – files needed to boot the system  /sbin – /usr/sbin system admin. utilities  /dev – device files  /etc – admin. and configuration files

19 © 2001 John Urrutia. All rights reserved. Important Directories and Files  /tmp– temporary files  /home – user home directories  /lib – shared libraries  /mnt – mount point of temporary partitions  /tmp – temporary files  /usr – 2 nd major hierarchy – rarely change  /proc – kernel and process information

20 © 2001 John Urrutia. All rights reserved. Changing working directory pwd – displays your working directory cd - change directory  By default places you in your working directory (ie /home/userid)  cd ~ (will do the same thing) cd path/path1 – changes relative to your working directory

21 © 2001 John Urrutia. All rights reserved. Access Permissions Every file has access “permissions” associated with them.  r – read  w – write  x – execute

22 © 2001 John Urrutia. All rights reserved. Access Permissions Every ordinary file has three access groups.  Owner or User  User who created the file  Group  Users who are associated  Others  The rest of the world

23 © 2001 John Urrutia. All rights reserved. Access Permissions Directory file access “permissions”  r – read the directory  w – write the directory  x – search the directory

24 © 2001 John Urrutia. All rights reserved. Access Permissions Setting default “permissions”  umask 000  One digit each for U,G,O  Octal value representing the 3 bits RWXRWXRWX

25 © 2001 John Urrutia. All rights reserved. Directory Utilities chmod – change access mode u – User or owner g – group o – others + – add permission - – remove permission

26 © 2001 John Urrutia. All rights reserved. Directory Utilities mkdir – Make Directory  mkdir –p directory-list  The –p option creates the parent directory if it doesn’t exist  directory-list  One or more directories separated by space

27 © 2001 John Urrutia. All rights reserved. Directory Utilities rmdir – remove Directory  rmdir directory-list  directory-list  One or more directories separated by space

28 © 2001 John Urrutia. All rights reserved. Directory Utilities rm – remove  rm –r directory-list  The –r option removes recursively. All subdirectories are removed  directory-list  One or more directories separated by space

29 © 2001 John Urrutia. All rights reserved. Directory Utilities cd – change directory  cd directory  The directory (pathname) becomes the working directory

30 © 2001 John Urrutia. All rights reserved. Links aka – Also Known As  Creates an entry in the directory that point to an existing file or directory.  Doesn’t create a copy of the file

31 © 2001 John Urrutia. All rights reserved. Links – Hard and Symbolic Hard links  Behave just like a file  Cannot distinguish the original filename from the link  Cannot cross file systems  Directory links by superuser only

32 © 2001 John Urrutia. All rights reserved. Links – Hard and Symbolic Symbolic links  Indirect pointer to file or directory  Can be created by anyone  Can reside anywhere  Can become an orphan

33 © 2001 John Urrutia. All rights reserved. Link Utility ln – Make a link entry  ln [–s] filename linkname  ln [–s] file-list directory