Session 6 Files Systems: Hands-On

1. Nassau Community College ITE153 – Operating Systems Session 6Files Systems: Hands-On

2. File Systems (1) Nassau Community College ITE153 – Operating Systems • Essential requirements for long-term information storage: • It must be possible to store a very large amount of information. • The information must survive the terminationof the process using it. • Multiple processes must be able to access the information concurrently.

3. File Systems (2) Nassau Community College ITE153 – Operating Systems • Think of a disk as a linear sequence of fixed-size blocks and supporting reading and writing of blocks. Questions that quickly arise: • How do you find information? • How do you keep one user from reading another’s data? • How do you know which blocks are free?

4. File Naming Nassau Community College ITE153 – Operating Systems Some typical file extensions.

5. File Attributes Nassau Community College ITE153 – Operating Systems Some possible file attributes.

6. File Operations Nassau Community College ITE153 – Operating Systems • The most common system calls relating to files: • Append • Seek • Get Attributes • Set Attributes • Rename • Create • Delete • Open • Close • Read • Write

7. Nassau Community College ITE153 – Operating Systems Session 6Files Systems: Hands-On Commands

8. File & Directory Permissions Nassau Community College ITE153 – Operating Systems Unit Objectives: By the end of this unit, you will be able to: • Use the ls command to determine existing permissions on files and directories • Describe the significance of permission settings • Change permissions using the chmod command • Determine default permissions for new files and directories • Change the default permissions for new files and directories

9. Overview of Security Permissions Nassau Community College ITE153 – Operating Systems • View existing permissions using ls -l $ ls -l drwxr-xr-x 2 cajs office 32 nov 27 2002 06:33 DOCS - rw-r--r-- 1 cajs office 96 nov 27 2002 14:12 abc

10. Nassau Community College ITE153 – Operating Systems Permission Symbols

11. Changing Permisssions with chmod Nassau Community College ITE153 – Operating Systems • chmod SETTING NAME(s) • SETTING • Symbolic or Octal notation • Use symbols or octal numbers • $ chmod g+w my.file • $ chmod 664 my.file • NAME(s) • Name of file(s) or directory(s)

12. Symbolic Notation u user g group o other + add - subtract = set exactly r read w write x execute Symbolic setting examples u+r ugo+x g=r go+w ugo=rw g-w ug+w,o-r $ chmod settingfilename(s) Nassau Community College ITE153 – Operating Systems

13. Nassau Community College ITE153 – Operating Systems Practice Using Symbols

14. Octal Notation Common Octal Settings Directories 777 drwxrwxrwx 755 drwxr-xr-x 700 drwx------ Files 777 -rwxrwxrwx 644 -rw-r--r-- Shortcut Setting Value r 4 w 2 x 1 - 0 rwxrw-rw- is 766 rwx 4+2+1=7 rw 4+2+0=6 rw 4+2+0=6 Nassau Community College ITE153 – Operating Systems

15. Nassau Community College ITE153 – Operating Systems Practice With Octal

16. Default File & Directory Permissions Nassau Community College ITE153 – Operating Systems • The chmod command changes EXISTING file or directory permissions. • DEFAULT permissions • Used when new files or directories are created • For files: 666 • For directories: 777 • Default can be modified using the umask command

17. umask Settings Nassau Community College ITE153 – Operating Systems • umask uses Octal notation • To determine existing umask setting:$ umask • To change umask setting:$ umask 022 • File default becomes: -rw-r--r-- • Directory default becomes: drwxr-xr-x

18. Nassau Community College ITE153 – Operating Systems Common umask Settings

19. Hands-onExercises Nassau Community College ITE153 – Operating Systems

20. Nassau Community College ITE153 – Operating Systems Session 6vi Editor: Hands-On Commands

21. Basics of the vi Editor Nassau Community College ITE153 – Operating Systems By the end of this unit, you will be able to: • Describe the features of a text editor • List the modes of the vi editor • Use commands to move around a text file • Use input commands to enter text • Perform a global substitution • Escape to the shell • Create an abbreviation • Save your file • Exit the vi editor

22. vi Overview vi is a text editor No automatic formatting Not a word processor With vi, you can: Create text Edit text Delete text Search for text Much more… Nassau Community College ITE153 – Operating Systems

23. Inventor of vi Editor Nassau Community College ITE153 – Operating Systems • wrote the vi editor in a weekend, 1976 • largely responsible for managing the authorship of BSD UNIX • co-founded Sun Microsystems in 1982 • lives in Aspen

24. vi Modes Nassau Community College ITE153 – Operating Systems a, i, o... <enter> Input Command ex <esc> : $ $ vi filename

25. Moving the Cursor: Little Moves In Command Mode Moving by line:<enter> Moving by words:w W Moving by character:<space><backspace> Nassau Community College ITE153 – Operating Systems

26. Moving the Cursor: Big Moves In Command Mode Scroll up and down:<ctrl-u><ctrl-d> Move within the screen:H homeM middleL last Move to a specified line:6G Move to line sixG Move to the last line Where am I?<ctrl-g> Nassau Community College ITE153 – Operating Systems

27. Entering Text In Command Mode Type an Input command (i,a,o,O) Type the text you want to enter Press <esc> to return to CommandMode Input commands are relative to the cursor: Nassau Community College ITE153 – Operating Systems O a i o

28. Changing Text Nassau Community College ITE153 – Operating Systems • Change word: cw • Change 3 words: 3cw • Change current line: cc The change command: • Displays a $ at the end of the word(s) or line to be changed • Puts you into input mode • Use <esc> to return to command mode • A number before the command multiplies the action

29. Deleting Text Nassau Community College ITE153 – Operating Systems • Delete word dw • Delete 5 words 5dw • Delete current line dd • Delete current character x • A number before the command multiplies the action.

30. The Undo Command Nassau Community College ITE153 – Operating Systems • u Undo the last change • U Restores the current line (Even after several changes.)

31. Searching for Text Nassau Community College ITE153 – Operating Systems • In command mode type: /patternFor example: /edit • Searches forward in the file for the pattern ‘edit’. • Puts cursor on the ‘e’ in the first instance found • Type n (for next) to go to the next instance

32. Copying & Moving Text Nassau Community College ITE153 – Operating Systems • To copy text use vi’s yank command: • yw yanks (copies) one word • yy yanks (copies) one line • To move text use any of vi’s delete commands like dd, dw, x • To paste:p puts copied or deleted text back at the cursor

33. ex Mode Nassau Community College ITE153 – Operating Systems • From command mode a : (colon) puts you in ex mode • Some tasks in ex mode: • save(write) and quit (example: :wq!) • make global changes • create abbreviations • customize vi • many more….

34. Save & Quit Nassau Community College ITE153 – Operating Systems • Write and quit vi :wq • Write without quitting :w • Quit without saving :q! • Write to a new filename :w filename

35. Global Substitutions Nassau Community College ITE153 – Operating Systems • In ex mode - :[address]s/pattern/replacement/[g] • Examples: • :1, $s/Monday/Friday/g • :.,10s/his/hers/g • :18s/lunch/dinner • :1,.s/rabbits/bunnies/g

36. Abbreviations • :abbr UOS UNIX Operating System • When you type ‘UOS’ in input mode, vi will replace it with ‘UNIX Operating System’

37. Hands-onExercises Nassau Community College ITE153 – Operating Systems

38. Important URLs Nassau Community College ITE153 – Operating Systems • How Linux file permissions work- a little more info about file permissions • What is Umask and How To Setup Default umask Under Linux? – good explanation of umask command • Access Rights and File Security– good write-up on file security • The vi Editor (Wikipedia) – very good history of vi • Learning the vi Editor, Sixth Edition - this is the online (free) version

39. Homework Nassau Community College ITE153 – Operating Systems • Review the Slides • Keep Practicing Commands • Compare to what you have learned on Linux to Windows