Session 6 Files Systems: Hands-On
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Transcript of Session 6 Files Systems: Hands-On
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Session 6Files Systems: Hands-On
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• 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)
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• 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)
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Some typical file extensions.
File Naming
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Some possible file attributes.
File Attributes
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The most common system calls relating to files:
File Operations
• Append• Seek• Get Attributes• Set Attributes• Rename
• Create• Delete• Open • Close• Read• Write
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Session 6Files Systems:
Hands-On Commands
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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
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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
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Permission Symbols
Readr
Writew
Executex
Directory List Add/deletefiles
ChangeDirectory
File DisplayContents
Edit Use ascommand
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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)
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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)
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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---
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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
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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---
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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
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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
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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--
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Hands-onExercises
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Session 6vi Editor:
Hands-On Commands
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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
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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…
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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
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vi Modes
$ vi filename
$
<esc>
a, i, o...
Input
Command
ex
<enter>
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Moving the Cursor: Little Moves
In Command Mode
• Moving by line:<enter>
• Moving by words:w W
• Moving by character:<space><backspace>
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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>
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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
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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
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Deleting Text
• Delete word dw• Delete 5 words 5dw• Delete current line dd• Delete current characterx• A number before the command
multiplies the action.
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The Undo Command
• u Undo the last change• U Restores the current line
(Even after several changes.)
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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
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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
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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….
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Save & Quit
• Write and quit vi :wq• Write without quitting :w• Quit without saving :q!• Write to a new filename :w filename
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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
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Abbreviations
• :abbr UOS UNIX Operating System
• When you type ‘UOS’ in input mode, vi will replace it with ‘UNIX Operating System’
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Hands-onExercises
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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
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Homework
Review the Slides Keep Practicing Commands Compare to what you have learned
on Linux to Windows
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