Session 6 Files Systems: Hands-On

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)


Some typical file extensions.

File Naming

Fall 2011 4Nassau Community College ITE153 – Operating Systems

Some possible file attributes.

File Attributes


The most common system calls relating to files:

File Operations

• Append• Seek• Get Attributes• Set Attributes• Rename

• Create• Delete• Open • Close• Read• Write



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


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


Permission Symbols

Readr

Writew

Executex

Directory List Add/deletefiles

ChangeDirectory

File DisplayContents

Edit Use ascommand


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)


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)


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---


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


Practice With Octal


drwxrw---- chmod 766 DirName ?


-r--r--r-- chmod 660 fileName ?



drwxrw---- chmod 766 DirName ?


-r--r--r-- chmod 660 fileName ?



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


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


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--


Hands-onExercises



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


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…


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


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>


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>


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


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


Deleting Text

• Delete word dw• Delete 5 words 5dw• Delete current line dd• Delete current characterx• A number before the command

multiplies the action.


The Undo Command

• u Undo the last change• U Restores the current line

(Even after several changes.)


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


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


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….


Save & Quit

• Write and quit vi :wq• Write without quitting :w• Quit without saving :q!• Write to a new filename :w filename


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


Abbreviations

• :abbr UOS UNIX Operating System

• When you type ‘UOS’ in input mode, vi will replace it with ‘UNIX Operating System’

Hands-onExercises


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


Homework

Review the Slides Keep Practicing Commands Compare to what you have learned

on Linux to Windows


Documents

Session 6 Files Systems: Hands-On