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Session 6 Files Systems: Hands-On. File Systems (1). Essential requirements for long-term information storage: It must be possible to store a very large amount of information . The information must survive the termination of the process using it. - PowerPoint PPT Presentation
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Fall 2011Nassau Community College ITE153 – Operating Systems 1
Session 6Files Systems: Hands-On
• Essential requirements for long-term information storage: It must be possible to store a very large
amount of information. The information must survive the
termination of the process using it. Multiple processes must be able to access
the information concurrently.
File Systems (1)
Nassau Community College ITE153 – Operating SystemsFall 2011 2
• 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?
File Systems (2)
Nassau Community College ITE153 – Operating SystemsFall 2011 3
Some typical file extensions.
File Naming
Fall 2011 4Nassau Community College ITE153 – Operating Systems
Some possible file attributes.
File Attributes
Nassau Community College ITE153 – Operating SystemsFall 2011 5
The most common system calls relating to files:
File Operations
• Append• Seek• Get Attributes• Set Attributes• Rename
• Create• Delete• Open • Close• Read• Write
Nassau Community College ITE153 – Operating SystemsFall 2011 6
Fall 2011Nassau Community College ITE153 – Operating Systems 7
Session 6Files Systems:
Hands-On Commands
File & Directory Permissions
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
Fall 2011 8Nassau Community College ITE153 – Operating Systems
Overview of Security Permissions
• 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
d rwx r-x r-x
- rw- r-- r--
Directory orfile
User/owner
User’sGroup
Others
Fall 2011 9Nassau Community College ITE153 – Operating Systems
Permission Symbols
Readr
Writew
Executex
Directory List Add/deletefiles
ChangeDirectory
File DisplayContents
Edit Use ascommand
Fall 2011 10Nassau Community College ITE153 – Operating Systems
Changing Permisssions with chmod
chmod SETTING NAME(s)• SETTING
Symbolic or Octal notationUse symbols or octal numbers
$ chmod g+w my.file $ chmod 664 my.file
• NAME(s) Name of file(s) or directory(s)
Fall 2011 11Nassau Community College ITE153 – Operating Systems
Symbolic Notation
u userg groupo other+ add- subtract= set
exactlyr readw writex execute
Symbolic setting examplesu+rugo+xg=rgo+wugo=rwg-wug+w,o-r
$ chmod setting filename(s)
Fall 2011 12Nassau Community College ITE153 – Operating Systems
Practice Using Symbols
Before Command Line After
drwxrw---- chmod o+r dirName ?
-rw-rw-rw- ? -rwxrwxrwx
-r--r--r-- chmod ug+w,o-r fileName
?
drwx------ ? drwxrwx---
Fall 2011 13Nassau Community College ITE153 – Operating Systems
Octal Notation
Common Octal Settings
Directories
777 drwxrwxrwx755 drwxr-xr-x700 drwx------Files
777 -rwxrwxrwx644 -rw-r--r--
ShortcutSetting 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
Fall 2011 14Nassau Community College ITE153 – Operating Systems
Practice With Octal
Before Command Line After
drwxrw---- chmod 766 DirName ?
-rw-rw-rw- ? -rwxrwxrwx
-r--r--r-- chmod 660 fileName ?
drwx------ ? drwxrwx---
Before Command Line After
drwxrw---- chmod 766 DirName ?
-rw-rw-rw- ? -rwxrwxrwx
-r--r--r-- chmod 660 fileName ?
drwx------ ? drwxrwx---
Fall 2011 15Nassau Community College ITE153 – Operating Systems
Default File & Directory Permissions
• 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
Fall 2011 16Nassau Community College ITE153 – Operating Systems
umask Settings
• 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
Fall 2011 17Nassau Community College ITE153 – Operating Systems
Common umask Settings
umask Setting
Directory File
022 drwxr-xr-x -rw-r--r--
037 drwxr--r-- -rw-r-----
002 drwxrwxr-x -rw-rw-r--
umask Setting
Directory File
022 drwxr-xr-x -rw-r--r--
037 drwxr--r-- -rw-r-----
002 drwxrwxr-x -rw-rw-r--
Fall 2011 18Nassau Community College ITE153 – Operating Systems
Hands-onExercises
Fall 2011Nassau Community College ITE153 – Operating Systems 19
Fall 2011Nassau Community College ITE153 – Operating Systems 20
Session 6vi Editor:
Hands-On Commands
Basics of the vi Editor
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
Fall 2011 21Nassau Community College ITE153 – Operating Systems
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…
Fall 2011 22Nassau Community College ITE153 – Operating Systems
Inventor of vi Editor
• 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
Fall 2011Nassau Community College ITE153 – Operating Systems 23
vi Modes
$ vi filename
$
<esc>
a, i, o...
Input
Command
ex
<enter>
:Fall 2011 24
Nassau Community College ITE153 – Operating Systems
Moving the Cursor: Little Moves
In Command Mode
• Moving by line:<enter>
• Moving by words:w W
• Moving by character:<space><backspace>
Fall 2011 25Nassau Community College ITE153 – Operating Systems
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>
Fall 2011 26Nassau Community College ITE153 – Operating Systems
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 Command Mode
Input commands are relative to the cursor:
O
i a
o
Fall 2011 27Nassau Community College ITE153 – Operating Systems
Changing Text
• Change word: cw• Change 3 words: 3cw• Change current line: ccThe 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
Fall 2011 28Nassau Community College ITE153 – Operating Systems
Deleting Text
• Delete word dw• Delete 5 words 5dw• Delete current line dd• Delete current characterx• A number before the command
multiplies the action.
Fall 2011 29Nassau Community College ITE153 – Operating Systems
The Undo Command
• u Undo the last change• U Restores the current line
(Even after several changes.)
Fall 2011 30Nassau Community College ITE153 – Operating Systems
Searching for Text
• 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
Fall 2011 31Nassau Community College ITE153 – Operating Systems
Copying & Moving Text
• To copy text use vi’s yank command:• ywyanks (copies) one word• yyyanks (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
Fall 2011 32Nassau Community College ITE153 – Operating Systems
ex Mode
• 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….
Fall 2011 33Nassau Community College ITE153 – Operating Systems
Save & Quit
• Write and quit vi :wq• Write without quitting :w• Quit without saving :q!• Write to a new filename :w filename
Fall 2011 34Nassau Community College ITE153 – Operating Systems
Global Substitutions
• 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
Fall 2011 35Nassau Community College ITE153 – Operating Systems
Abbreviations
• :abbr UOS UNIX Operating System
• When you type ‘UOS’ in input mode, vi will replace it with ‘UNIX Operating System’
Hands-onExercises
Fall 2011Nassau Community College ITE153 – Operating Systems 37
Important URLs
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
Fall 2011Nassau Community College ITE153 – Operating Systems 38
Homework
Review the Slides Keep Practicing Commands Compare to what you have learned
on Linux to Windows
Fall 2011Nassau Community College ITE153 – Operating Systems 39