22649807 linux lecture sem1

8/8/2019 22649807 Linux Lecture Sem1

http://slidepdf.com/reader/full/22649807-linux-lecture-sem1 1/282



Operating Systems

Computers have two fundamentalcomponents:

Hardware: Physical components inside acomputer

Software: Set of instructions or programsthat understand how to use the hardware

of the computer in a meaningful way



3

Operating Systems (continued)

Hardware components include:Processor (CPU)

Physical memory (RAM)Hard disk, floppy disk, and CD-ROM

drives

Sound and video cards

Circuit boards

November 17, 2009



4


Two different types of programs are executedon a computer:Applications

Operating system (OS) softwareDevice Driver: Software containing instructions

that the OS uses to control and interact with aspecific type of computer hardware

User Interface: An application program thatallows the user to interact with the OS andother application programs

November 17, 2009



5

Operating Systems (continued)Operating system: Software program

Set of instructions between hardware andsoftware

Way user communicates with computer

Processing of application programs

All input/output of computer

Controls/manages resources and users

November 17, 2009



6


The role of operating system software

November 17, 2009



Unix/Linux History

Unix first version created in Bell Labs-1969

Write Unix system in C language-1973 by Denis Ritchie

AT&T licenses source code for low cost, Trademarkes Unixname, licensees must create new name for their operating

systems

Many Unix Flavors:, IBM-AIX, Solaris,UnixWare, HP-UX

7November 17, 2009



Unix PrinciplesMultiuser, Multitasking

Configuration data stored in text

Ability to chain programs together toperform complex tasks

Working with Wide variety of

computersHigh Level of Security

8November 17, 2009



GNU Project / FSF

GNU (Gnu Not Unix) Project startedin 1984 (R. Stallman)

Goal: create “free” Unix cloneBy 1990, nearly all required users

applications created (gcc, emacs,..)

Free Software FoundationNon-profit organization that managesGNU project

November 17, 2009 9



GPL- GNU General PublicLicense

Primary license for Open SourceSoftware

Encourages free softwareAll enhancements and changes to

GPL software must also be GPL

Often called “copyleft”“all rights reversed”

November 17, 2009 10



GPL- GNU General PublicLicense-2

freedom to run the program, for anypurpose.

freedom to modify the program tosuit your needs.freedom to redistribute copies, eithergratis or for a fee.

freedom to distribute modifiedversions of the program, so that thecommunity can benefit from yourimprovements

11November 17, 2009



Linux OriginsLinus TorvaldsFinnish college student in 1991 create

Linux kernel

Code was made available over theinternet for freeCoders world wide took part in developing

the OS

When Linux Kernel combined withGNU applications, complete free Unix-like OS appears (GNU/Linux OS)




Why LinuxLinux and GNU software are distributed

under the terms of the GNU Public LicenseAgreement (GPL)

Linux is continually being developed byindividuals throughout the world

Skilled programmers can submit additionsand improvements to the Linux OS toLinux Development Team over the internet




Why LinuxApplications are developed that are

both free and commercialLinux is for Intel based platforms,

Power PC, Alpha-based Linux is forIntel based, multiprocessorcompatibility (SMPs)Fully supportedMany distribution

(redhat,suse,fedora,ubuntu ...)

14November 17, 2009



Red Hat Enterprise Linux

Custom version of recent Linuxkernel

Utility and applicationsInstallation and configuration

software

Support available

15November 17, 2009



Installing Red Hat LinuxPartitioning Hard disksPrimary Partition + Swap partition

Installation method

Network ConfigurationIP ,Netmask, Gateway, Hostname +Domain

name +Name Server

Configuring Boot manager (LILO, Grub)Select Package




Hard disk partitioning

hda: Primary Master IDE

hdb: Primary Slave IDE

hdc: Secondary Master IDE

hdd: Secondary Slave IDE

sda: First hard on SCSI bus (or SATA).

sdb: Second hard on SCSI bus (orSATA).




Hard disk partitioning-2Primary Partitions: 1,2,3,4

Logical Partitions: 5,6,7…

hdxy IDEsdxy SCSI, or SATAx (name of hard disk)

y (partition number )Example: hda2,hdb5,sda6

18November 17, 2009



Hard disk partitioning-3

HeadHead

SectorSector

CylindersCylinders

Track Track

SectorsSectors

19November 17, 2009




• Series of Sectors addressed by(CHS)

• First sector name MBR: MasterBoot Record contain:

• Boot program

• Partition Table:4 Primary partitions1 2 3 4

MBR Partition 1 Partition 3Partition 2 Partition 4





1 2 3 4

Primary

Partition 1

A 2 FAT32 2000

2001 FAT16 3500

3501 EXT2 6000

6001 NTFS 8000

Status Start FS End

0000

1BEh

1FEh

Partition

Table

Boot

Program

Primary

Partition 2

Primary

Partition 3

Primary

Partition 4





1 2 3 4

MBR

Boot Sectors

Primary

Partition 2

Primary

Partition 3

Primary

Partition 4

Primary

Partition 1

M

B

R

P. P. 1

Type: FAT32

P. P. 2

Type: Extended

P. P. 3

Type: Ext2

P. P. 4

Type: NTFS





M

B

R

D: E: F:C:

P1: FAT32 P2: Extended

MB

R

D: E: F:C:

P1: FAT32 P3: Extended

/ Swap

P2: EXT3

< 1024

23November 17, 2009



Installing VMWare and using a

virtual machine to install Linux

24

Download VMWare(http://vmware.com/download/server/)

Apply for license keys(http://register.vmware.com/content/registration.html)

November 17, 2009



Begin the installation



Accept the license terms




Customize




Choose desired features andinstallation path




Disable AutoRun

Note: Windows XP requires extra steps here




Disable each auto-run type inXP




Ready to install!




This may take a while

Note: You may need to temporarily disable yourVirus Shield (mcsheild.exe hogs processor tickswhile VMWare installs)


Enter one of the serial number



Enter one of the serial numberyou applied for in the step

above.




Finished!




Connect to the new VMWareinstance




Check settings




Select a directory on a drivewith plenty of free space




Create a new virtual machine




Choose Linux




Give it a name




Using NAT is easiest




8 GB is plenty




VMWare will now create a newspace for the Virtual Machine




New Guest OS setup complete




Confirm NAT is selected

This works best, especially when the Host OS is using DHCPNovember 17, 2009 45

R d i ll OS



Ready to install OS

Insert your install CD (DVD) and start the virtual machine




Installation Mode

New or Upgrade

from whereCD

HTTP, FTP, NFS, Hard disk

Kickstart

47November 17, 2009

St ti th I t ll ti



48

Starting the Installation(continued)

Beginning a Red Hat installation

Linux-OS

St ti th I t ll ti



49


Press F2 at Welcome screen to getinstallation options

Check media for errors prior to installation

Optional, but recommended

Linux-OS

St ti th I t ll ti



50


Viewing installation options

Linux-OS

Ch i th L



51

Choosing the Language,Keyboard, Mouse, and Monitor

Keyboard model and layout automaticallydetected

Check “Emulate 3 Button” if mouse does

not have third buttonMost monitors automatically detectedIf not, try to locate on list of monitor models or

use generic model with correct horizontal andvertical sync

Incorrect monitor settings can damagemonitor

Linux-OS

K b d M d M it



52

,Keyboard, Mouse, and Monitor(continued)

Selecting an installation language

Linux-OS

K b d M d M it



53


Verifying keyboardconfiguration

Linux-OS

K b d M d M it



54


Figure 3-6: Selecting a mouse

type Linux-OS

,Ke board Mouse and Monitor



55


Verifying monitor configuration

Linux-OS



56

Specifying the Installation Type

Personal DesktopGUI environment and common applications

Workstation

Same as Personal Desktop plus administrativeand network tools

ServerSeveral server services

Custom

Linux-OS




57

Specifying the Installation Type(continued)

Figure 3-8: Choosing an installation

type Linux-OS



58

Hard Disk Partitioning

Filesystems can be accessed if attached(mounted) to a directory

Minimum of two partitions

Partition for root directoryPartition for virtual memory (swap memory) Area on hard disk used to store information normally

residing in physical memory (RAM)

Automatic or manual partitioning

Linux-OS




59

Hard Disk Partitioning(continued)

Common Linux filesystems and sizes

Linux-OS




60


Figure 3-9: Choosing a disk partitioning

method Linux-OS




61


Different types of filesystemsExt2: Used on most Linux computers

Ext3: Performs journaling

Vfat: Compatible with Windows’ FAT filesystemREISER: Performs journaling

Journaling: Keeps track of the informationwritten to the hard drive

Disk Druid: Graphical partitioning program

Linux-OS




62


The Disk Druid partitioning utility

Linux-OS




63


Figure 3-11: Creating a newpartition

Linux-OS



64

Configuring the Boot Loader

Boot loader: Program started by BIOS ROMLoads kernel into memory

Can also boot other existing OSs

GRand Unified Bootloader (GRUB): Bootloader configured during Fedora Linuxinstallation

Dual booting: Choose OS to boot at startup

Linux-OS




65

Configuring the Boot Loader(continued)

Figure 3-12: Configuring a bootloader

Linux-OS




66


Boot loader usually resides on the MBR oron first sector of / or /boot partition

Kernel parameters: Information passed to

Linux kernel via the boot loaderLarge Block Addressing 32-bit (LBA32):

Enables Large Block Addressing in bootloaderFor large hard disks not fully supported by the

BIOS

Linux-OS




67


Configuring advanced boot loader options

Linux-OS

Configuring the Network and



68

Configuring the Network andFirewall

Specifying a network configuration

Linux-OS




69

Configuring the Network andFirewall (continued)

Will NIC be activated at boot time?

Manual IP configurationSet IP address, Netmask, host name, gateway, primary

domain name space (DNS)

Automatic IP configuration via DHCP

Firewall prevents traffic from entering computerCustomize which traffic is allowed through

Linux-OS




70

Configuring the Network andFirewall (continued)

Configuring a firewall

Linux-OS

Choosing a System Language



71

Choosing a System Languageand Time Zone

Selecting additional language support

Linux-OS

Choosing a System Language



72

Choosing a System Languageand Time Zone (continued)

Choosing a time zone

Linux-OS



73

Creating the Root User

Authentication: Users log in via valid username and password

Configure two user accounts

Administrator account (root) Full rights to system

Regular user account

Linux-OS




74

Creating the Root User(continued)

Setting a root password

Linux-OS



75

Selecting Packages

Figure 3-19: Selecting

packages Linux-OS



76

Installing Packages

Figure 3-19: Package

InstallationLinux-OS



77

Completing the Firstboot Wizard

Complete the installationLicense agreement

Graphics settings

User accounts and authenticationInstall additional software

Log in with user account for daily tasks

Shadow password: stored in separate DB

from user accountsMD5: password encryption method

Linux-OS




78

Completing the Firstboot Wizard(continued)

Setting the date and time

Linux-OS




79


Configuring screen resolution and colordepth

Linux-OS




80


Creating a regular user account

Linux-OS




81


Configuring user informationLinux-OS




82


Configuring authentication

Linux-OS

Installing Linux: Installation



83

Installing Linux: InstallationMethods

FTP serverHTTP Web serverNFS server

Packages on hard diskBoot from first Red Hat (Fedora) Linux CD-

ROM

Performing the Installation: Starting



84

Performing the Installation: Startingthe Installation (continued)

Beginning a Red Hat installation

Performing the Installation: Starting



85

Performing the Installation: Startingthe Installation (continued)

Press F2 at Welcome screen to getinstallation options

Check media for errors prior to installation

Optional, but recommended

Choosing the Language Keyboard



86

Choosing the Language, Keyboard,Mouse, and Monitor

Keyboard model and layoutautomatically detected

Check “Emulate 3 Button” if mouse

does not have third buttonMost monitors automatically detectedIf not, try to locate on list of monitor models

or use generic model with correct horizontaland vertical sync




87

Choosing the Language, Keyboard,Mouse, and Monitor (continued)

Selecting an installation language




88


Verifying keyboard configuration




89


Selecting a mouse type

Choosing the Language, Keyboard,



90


Verifying monitor configuration



91


Personal DesktopGUI environment and common applications

Workstation

Same as Personal Desktop plus administrativeand network tools

ServerSeveral server services

Custom




92

Specifying the Installation Type(continued)

Choosing an installation type



93


Filesystems can be accessed if attached(mounted) to a directory

Minimum of two partitions

Partition for root directoryPartition for virtual memory (swap memory) Area on hard disk used to store information normally

residing in physical memory (RAM)

Automatic or manual partitioning




94

g(continued)

Common Linux filesystems and sizes




g(continued)

Choosing a disk partitioning method




96

g(continued)

The Disk Druid partitioning utility



98


Boot loader: Program started by BIOS ROMLoads kernel into memory

Can also boot other existing OSs

GRand Unified Bootloader (GRUB): Bootloader configured during Fedora Linuxinstallation

Dual booting: Choose OS to boot at startup




99

g g(continued)

Configuring a boot loader




100

g g(continued)

Boot loader usually resides on the MBR oron first sector of / or /boot partition

Kernel parameters: Information passed to

Linux kernel via the boot loaderLarge Block Addressing 32-bit (LBA32):

Enables Large Block Addressing in bootloaderFor large hard disks not fully supported by the

BIOS




101

g g(continued)

Configuring advanced boot loader options




102

Firewall

Specifying a network configuration




103

g gFirewall (continued)

Will NIC be activated at boot time?

Manual IP configurationSet IP address, Netmask, host name, gateway, primary

domain name space (DNS)

Automatic IP configuration via DHCP

Firewall prevents traffic from entering computerCustomize which traffic is allowed through




104

g gFirewall (continued)

Configuring a firewall

Choosing a System Language and



105

g y g g Time Zone

Selecting additional language support

Choosing a System Language and



106

g y g g Time Zone (continued)

Choosing a time zone



107


Authentication: Users log in via valid username and password

Configure two user accounts

Administrator account (root) Full rights to system

Regular user account




108

(continued)

Setting a root password



109

Selecting Packages

Selecting packages



110

Installing Packages

Package Installation



111


Complete the installationLicense agreement

Graphics settings

User accounts and authentication

Install additional software

Log in with user account for daily tasks

Shadow password: stored in separate DB

from user accountsMD5: password encryption method




112

(continued)

Setting the date and time




113

(continued)

Configuring screen resolution and color depth




114

(continued)

Creating a regular user account




115

(continued)

Configuring user information




116

(continued)

Configuring authentication

L l L i



Local Login

Text mode login at Virtual consolesMultiple non-GUI logins are possible through the

use of virtual consoles

There are by default 6 available virtual consolesAvailable through Ctrl-Alt-F[1-6]

Graphical loginIf X is running, it is available as Ctrl-Alt-F7

November 17, 2009 117

Li G hi l E i t



Linux Graphical Environments

XFree86: standard X windows System

GNOME – Desktop environment based on the

GTK+ toolkitKDE – Desktop environment based on the Qt

toolkit

November 17, 2009 118

Shells, Terminals, and theK l



119

Kernel

Shells, terminals

C Li t i l



120

Common Linux terminals

R i C d



121

Running Commands

Command-line terminal may be accessedfrom GUI environmentCommand prompt:

Root user: #Regular user: $

R i C d



Running Commands

Command have the following syntax:command [options] [arguments]

Each item is separated by a space

Case sensitive

Options modify the command’s behavior

Arguments are filenames or otherinformation needed by the command

Separated commands with semicolon (;)Example: date;cal

November 17, 2009 122

Ch i Y P d



Changing Your Password

Password should be changed after first login

From the Red Hat menu, choose

Preferances

PasswordFrom a terminal, use passwd

November 17, 2009 123

Shutting Down the LinuxS t



124

System

Commands to halt and reboot the Linux operatingsystem

The Filesystem HierarchySt d d



125

Standard

Filesystem Hierarchy Standard (FHS):Standard set of directories for Linux andUNIX systemsFile and subdirectory contents

Gives Linux software developers ability to locatefiles on any Linux system Create non-distribution–specific software

The Filesystem HierarchyStandard (continued)



126

Standard (continued)

: Linux directories defined by FHS

The Filesystem HierarchyStandard (continued)



127

Standard (continued)

Linux directories defined by FHS

Linux File HierarchyC t



128

Concepts

The Windows filesystem structure

The Linux filesystem structure

Linux File Hierarchy Concepts



Linux File Hierarchy Concepts

November 17, 2009 129

Directories maycontain plain filesor other directories

Leads to a treestructure for thefilesystem

Root directory: /

/

tmpusersbin

doug rocket

cs2204joke.txt

lab2.txtlab1.txt

Listing Directory Contents



g yList the content of a current directory or a specified

directoryUsage:

ls [options] [files or dirs]

• Example:

• ls

• ls /home

• ls –l

• ls -a

130

The Home Directory



The Home Directory

Every user has a home directory, typically under/home

Contain user-specific configuration files as well asuser data

Represented by the ~ character

November 17, 2009 131

Absolute pathnames



Absolute pathnames

Absolute pathnames begin with a slash (/)

Complete “road map” to file location

Can be used anytime you wish to specify a filename

November 17, 2009 132

Relative pathnames



Relative pathnames

relative pathnames do not begin with a slash (/)

Specifies location relative to your current working

directory

Can be used as a shorter way to specify a file name

November 17, 2009 133

th



pathnames

November 17, 2009 134

Separate directories by /

Absolute path

start at root and followthe tree

e.g. /users/doug/joke.txtRelative path

start at workingdirectory

.. refers to level above;

. refers to working dir. If /users/doug/cs2204 is

working dir, this referto the same file asprevious one

joke.txt

/

tmpusersbin

doug rocket

cs2204

lab2.txtlab1.txt

Changing Directory



Changing Directory

pwd displays the absolute path to the currentdirectory

cd changes directories- To an absolute path: $ cd /home/issa/work

- To relative path:$ cd project/docs

- To a directory one level up: $ cd ..

- To your directory home: $ cd

- To your previous working directory: $ cd -

November 17, 2009 135

File names



File names

File names may be up to 255 charactersAll characters are valid, except the “/”It may be unwise to use certain special characters in

filename

File names are case-sensitiveExample: MAIL, Mail, mail, and mAil

Again, possible, but may not be wise

November 17, 2009 136

Getting Command Help



137


Linux distributions contain manycommands

Manual pages: Most common form of documentation for Linux commands“man” pages

At command prompt, type “man” followed by acommand name

Contain different sections



138

Manual page section numbers





Examples

man ls

man 5 passwd (5 for section)

man passwd

November 17, 2009 139

Other Help Utilities



Other Help Utilities

command --help The whatis same as man –f

The apropos same as man –k

info Text based with sections organized by subject Command is info section_name

Gnome documentation

November 17, 2009 140

Copying files and Directories



Copying files and Directories

cp – copy files and directoriesUsage:

cp [options] file destinationMore than one files may be copied at a time if the

destination is a directorycp [options] file1 file2 dest

November 17, 2009 141

Copying Files and Directories:Th D i i



The Destination

If the destination exists and is a directory, thecopy is placed there with the same name

If the destination exist and is a file, the copyoverwrites the destination file

If the destination does not exist, the copy iscreated with that name

142

Moving and Renaming



Files and Directories

mv – move and/or rename files and directories

Usage:

mv [options] file destination

More than one files may be moved at a time if thedestination is a directory

mv [options] file1 file2 dest

143

Moving and Renaming Files and



Directories: the Destination

If the destination exists and is a directory, the sourcefiles or directory is moved there with the same name

If the destination exist and is a file, the source file ismoved to that filename, overwriting the file

If the destination does not exist, the source file ordirectory is renamed with that name

144

Removing and Creating Files



Removing and Creating Files rm – remove files

Usage:

rm [options] filenames -i interactive

-r recursive (when removing directory) -f force

touch – create empty files or update filestamps

145



Determining File Content



Determining File Content

Files can contain many types of data

Check file type before opening to determineappropriate command or application to use

Syntaxfile [options] filename (s)

November 17, 2009 147

Viewing an Entire Text File



Viewing an Entire Text File

Syntax

cat [options] [file …]

Contents of the files are displayedsequentially with no break

Files display “concatenated”

November 17, 2009 148

Viewing Files One ScreenfulAt Ti



At a Time

Syntax

less [options] [filename]

Display the contents of a text file one screen at a time

less is the pager used by man Syntax

more [options] [filename]

November 17, 2009 149

bash Introduction



Bourne shell (sh) –original UNIX shell writtenby Steven Bourne at AT&T

bash “Bourne Again shell “ Developed forGNU project

bash The de facto standard Linux shell

Backward – compatible with Bourne shell (sh)– the original (standard) UNIX shell.

November 17, 2009 150

bash Heritage

C shell (csh) – written by bill joy at UC Berkeley



( ) y j y yAdded many features such as command completion,

history and job controlKorn shell (ksh) – written by David Korn at AT&T

Bourne Again Shell (bash) Implements many of the extra features found in csh, ksh

Command line completionCommand line editing

Command line history

Sophisticated prompt control

November 17, 2009 151

File GlobbingGlobbing is wildcard expansion:



g p * matches zero or more characters

? matches any single character [a-z] matches a range of characters

[^a-z] matches all except the range

Example

$ls /usr/bin/b*

$ls /usr/bin/?b*$ls a[0-9]

$ls [!Aa]*

152

The Tab key



The Tab key

Type <TAB> key to complete command line:For the command name, it will complete a command

name

For an argument, it will complete a file name

Examaple:slo<TAB>

slocate

ls myf<TAB>

November 17, 2009 153

history

b h t hi t f d ’ t d



bash stores a history of commands you’ve entered,

which can be used to repeat commandsUse history command to see a list of

“remembered” commands: $ historyUse bang character !

!x execute last command begin with x!2 execute command no 2

!! Execute Last command

154

History-2



Use the up and down arrow keys to scrollthrough previous commands

Type <CTRL-R> to search for a commandin command history

(reverse-i-search)`’: To recall last argument from previous

command:

<ESC>. Or <ALT-.>

November 17, 2009 155

Command Editing Tricks



<Ctrl-a> move to beginning of line<Ctrl-e> move cursor to end of line

<Esc>f move cursor to beginning of next

word<Esc>b move cursor to beginning of

previous or current word

<Ctrl-u> delete to beginning of line

<Ctrl-k> delete to end of line

156

Command Editing Tricks



Editing Modes

By default, bash uses emacs-style keybindings for command editing

Type set –o vito change key bindings to vi-style

Make vi the default by adding the commandabove to $HOME/.inputrc

November 17, 2009 157

Tilde



Hidden file begin with . for listing them use ls -a Tilde (~)Refer to your home directory:

$ cat ~/.bashrc

May refer to another user’s home directory:$ ls ~issa/.bashrc

158

The bash Shell



Variable

A variable is a label that has a valueVariables are resident in memory

Tow types: local and environment

Local variables are used only by the shell

Environment variables are passed onto othercommands and shells.

set to display all variables env display environment variables

November 17, 2009 159

Local Variable

C i ll ll



Conventionally all upper-case

Setting variable value$ CREDIT=300

$ echo $CREDIT

Common Local VariablesHISTFILESIZE determine how many command to be

saved in the history file on logout

COLUMN sets the width of the terminal

LINES sets the height of terminalsPS1 sets the prompt

November 17, 2009 160

Environment variables



Shell variables exist only in current shellinstance

Environment variables passed to subshells

Shell variables can be exported intoenvironment

$ CREDIT=300; export CREDIT

November 17, 2009 161

Common Environment variables



HOME Path to user’s home directory

LANG Identification of default languageprogram should use

PWD User’s current working directory

EDITOR default editor program

LESS options to pass to the command less

TERM terminal type

November 17, 2009 162

Environment variables



PATH colon separated list of locations wherecommands can be found

which command (not variable) showing path

of executable$which ls

Path to command can also be given explicitly

$ /bin/ls /etc$ ./ls /etc

November 17, 2009 163

Aliases



Aliases

Aliases let you create shortcuts to command

$ Alias dir=‘ls –laF’

Use alias to see all set aliases To see alias value: $ alias dir

$ alias dir=‘ls –laF’

November 17, 2009 164

Variable and String



Parameter/Variable: $Substitute the value of variable in a command line

$ cat $HOME/.bash_profile

$ echo $PATH

Curly braces: { }A string is created for every pattern inside the braces

regardless if any file exist

$ rm hello.{c,o}

November 17, 2009 165

Command and Math



Command output: ` ` or $() substitute output from a command in a command line

$ echo “Hostname: `hostname`”

$ echo $(date)

Arithmetic: $[ ]Substitute result of arithmetic expression in a

command line

$ echo Area: $[ $x * $y ]

November 17, 2009 166

Protecting from Expansion:B k l h



BackslashBackslash ( \ ) is the escape character and makes

the next character literal

$ echo Your cost: \$5.00

Used as last character on line to continue commandon next line:

$ echo “This long string will be echoed \

back as one long line”

This long string will be echoed back as one longline”

November 17, 2009 167

Protecting from Expansion:Q



Quotes

Single quotes (‘) inhibit all expansion

Double quotes (“) inhibit all expansion except

$ (dollar sign) including $()

` (back tick), command substitution

\ (backslash),single character inhibition

! (exclamation point), history substitution

November 17, 2009 168

Shell Startup Script



November 17, 2009 169

Shell Startup Script



November 17, 2009 170

Startup Script: order of execution



November 17, 2009 171

/etc/profile



November 17, 2009 172

/etc/profile.d



/etc/profile.d

November 17, 2009 173

~/.bash_profile and ~.bashrc



November 17, 2009 174

~/.bash_logout



November 17, 2009 175

Overview of vi and vim



Overview of vi and vim

vi: the “visual editor”, standard Linux andUnix editor

vim: the “vi improved” standard Red Hateditor

On Red hat operating systems, the vi command invokes vim

Derived from earlier Unix editorsed->ex->vi->vim

November 17, 2009 176

Starting of vi and vim



Starting of vi and vim

To start vim : vi filenameIf the file exists, the file is opened and the content

are displayed

If the file doesn’t exists, vi create it when theedits are saved for the first time

November 17, 2009 177

Three Modes of vi and vim



Command modeCursor movement

Change, delete, yank, put

Insert mode Type in new text

Return to command mode with <ESC>

Ex mode

Configuring, exiting, savingSearch and replace

November 17, 2009 178





November 17, 2009 179

command

mode

insert

mode

last line

Mode or Ex mode

iESC :

wrong command

Cursor MovementInsert mode



Insert modeh left, j down , k up , l rightw word ahead, b word back

Arrow keys also work

a append after the cursor

i insert before the cursorA append to end of line

I insert at beginning of line

o open a line below

O open a line above

November 17, 2009 180

Command mode



<esc> takes you from insert mode backto command mode

cc change line, dd delete line, yy yank(copy) line

cw change word, dw delete word, yw yank word

Use p or P to put (paste) copied or deleteddata

November 17, 2009 181

Undoing Changes



Undoing Changes

u undo most recent change

U undo all changes to current line since thecursor landed on the line

<Ctrl-r> redo last “undone” change

November 17, 2009 182

Searching for Text



Searching for Text

/text search downwards for “text”

?text search Upwards for “text”

n continue search in the same directionN continue search in the opposite direction

November 17, 2009 183

Saving and Exiting: ex mode



:wq save changes

:q or q! abandon changes

:w save without exit

:e! abandon changes without exit

:wq! Forcing save changes

:w! Forcing save without exit

November 17, 2009 184

A few tricks



A few tricks5dd delete 5 line (a number can precede any

of the tow character change, delete, yank, orput command

x delete a characterrc replace a character with c

R replace character for character until

<esc>

November 17, 2009 185

Users



Every user of the system is assigned aunique User ID number

User’s names and uid are stored in

/etc/passwdUser are assigned a home directory and a

program that is run when they log in (usuallyshell)

Users cannot read, write or execute eachothers’ files without permission

November 17, 2009 186

Groups



p

User’s are assigned to groups with uniquegroup ID number (gid)

gids are stored in /etc/group

Each user is given their own private group They can also be added to other groups to gain

additional access

all users in a group can share files that

belong to the group

November 17, 2009 187



User and Group ID Numbers



User names map to user ID numbers

Group names map to group ID numbers

Data stored on the hard disk is stored numerically

Authentication information is stored in plain text files:/etc/passwd

/etc/shadow

/etc/group

November 17, 2009 189

System Users and Groups



Server programs such as web or printservers typically run as unprivileged users,not as root

Examples: mail, lp, nobodyRunning programs in this way limits the

amount of damage any single program cando to the system

November 17, 2009 190

Changing Your Identity



To change your password, run passwdInsecure passwords are rejected

To start a new shell as a different user:susu –

su username

su - username

November 17, 2009 191

The Linux Security Model



Users and groups are used to controlaccess to files and resources

Users log in to the system by supplying

their user name and passwordEvery file on the system is owned by auser and associated with a group

Every process has an owner and group

affiliation , and can only access theresources its owner or group can access

November 17, 2009 192



Linux Process Security



When a process accesses a file the userand group of the process are comparedwith the user and group of the fileIf the user matches, the user permissions apply

If the group matches, but the user doesn’t, thegroup permissions apply

If neither match, the other permission apply

November 17, 2009 194

Examining Permissions



File permissions may be viewed using ls$ ls –l /bin/login-rwxr-xr-x 1 root root 19080 Apr 1 18:26 /bin/login

File type and file access permission aresymbolized by a 10-character string

November 17, 2009 195



File Permission Types



Four symbols are used when displayingpermission:

r : permission to read a file or list a directory’scontentw : permission to write to a file or create and

remove files from a directory

x : permission to execute a program file orchange into a directory and do long listing of thedirectory

- : no permission (in place of the r, w, or x)

November 17, 2009 197

File Permission Types



November 17, 2009 198

Examining Directories



The first character in the long listingdistinguish directories (d) from regular files(-)

$ ls –ld /bindrwxr-xr-x 2 root root 4096 Apr 1 18:26 /bin

$ ls –l /bin/df -rwxr-xr-x 1 root root 4096 Apr 1 18:26 /bin/df

Others file types indicators exist

November 17, 2009 199



Examining group Permissions



Characters 5,6, and 7 in the access modeidentify group permissions

$ ls –l README-rw-rw-r-- 1 issa teachers 9080 Oct 1 8:26 README

This file can be read and written by

people in group teachers, but it cannot beexecuted.

November 17, 2009 201

Examining Other Permissions



Characters 8,9, and 10 in the access modeidentify permissions for others:

$ ls –l README-rw-rw-r-- 1 issa teachers 9080 Oct 1 8:26 README

This file can be read by people outsidegroup teachers, but it cannot be changed

or executed

November 17, 2009 202

Changing PermissionsSymbolic method



y

To change access mode :

$ chmod [-R] mode file…

Changes the access mode of files and directories

-R option: Change permission to directory and allfiles and subdirectory inside it content

November 17, 2009 203

Changing PermissionsSymbolic method



y

November 17, 2009 204

Examples: try this examplechmod u+x file (or dir) , chmod o-w file(or

dir)

chmod g+wx,o=r file (or dir)chmod u=rwx file (or dir)

Changing PermissionsNumeric method



Uses a three-digit mode numbersFirst digit specifies owner’s permission

Second digit specifies group permission

Third digit represents other’s permission

Permissions are calculated by adding :

November 17, 2009 205

Changing PermissionsNumeric method



Examples:chmod 755 file1 (dir1)

chmod 666 file1(dir1)

November 17, 2009 206

umaskOnly applies to newly created files and directories



Used to alter the permissions on all new files anddirectories by taking select default file and directorypermissions awayWill never be used to modify the permissions of existing files

and directories

Read and write for all is the default (666) for files and777 for directory

Non-privileged user’s umask is 0002 and the root’sumask is 0022

November 17, 2009 207

umask



Non-privileged user’s umask is 0002 andthe root’s umask is 0022File will have permissions of 664

Default Mode 666

umask -002New File Mode 664

November 17, 2009 208



209

Performing a umask 007 calculation

Special Permissions



Special permissions: a fourth permission set (inaddition to user/group/other), Applicable in fourcases:SUID (set user ID) for an executable, Processes are

granted access to system resources based on userwho owns the file.

SGID (set group ID) for and executable, Same withSUID except group is affected.

SGID a directory: Files created in that directory willhave their group set to the directory's group.

November 17, 2009 210

Special Permissions



The sticky bit was used on files in the pastto lock them in memory Today, the sticky bit performs a useful

function only on directories:

Sticky bit for a directory, If set on a directory,then a user may only delete files that he ownsor for which he has explicit write permissiongranted, even when he has write access to the

directory. (e.g. /tmp )

Special Permissions



November 17, 2009 212

Setting Special Permissions(continued)



213

Representing special permissions in the mode



214

Numeric representation of regular and special

permissions

SUID Permissions(example)When you login, your login shell process’ values are your user



ID and group IDE.g., if you run passwd (owned by root), THE user ID is your ID, not

root; then how can it update /etc/passwd file owned by root ?

SUID bit enables this functionality

When an executable file with set user ID (SUID) permission is executed,command run with permission of the owner of the command, not

executor of the commandFile permission of /usr/bin/passwd is r-s--x—x

The SUID can only be applied to binary compiled programs

November 17, 2009 215

Files sytsems



Disk drives are divided into partitionsPartitions are formatted with filesystems

alloying users to store dataDefault filesystem: ext3, The Third Extended

Linux Filesystems

Other common filesystems: ext2 , msdos, FAT, NTFS Iso9660(typically used for CDs)

November 17, 2009 216

Files sytsems(continued)



217

Filesystem has three main structuralsections:Superblock: Contains general information

about the filesystem e.g., number of inodes and data blocks

Inode: Describes a file or directory

Data blocks: Data making up contents of a file

InodeAn inode tables contains a list of all files in an ext2 or ext3



filesystemAn inode (index nodes) is an entry in the table, containing

information about a file (the metadata), including:File type, permission, link count, UID, GID

The file’s size and various time stamps

Pointers to the file’s data blocks on disk

One inode is associated with each file.

The system uses inodes as the definition of a file.

November 17, 2009 218

Directory



The computer’s reference for a file is theinode number

The human way to reference a file is by

file nameA directory is a mapping between the

human name for the file and thecomputer’s inode number

November 17, 2009 219

5 apples

4 oranges7 home

2 .

cp and inode



The cp command: allocates a free inode number, placing a new

entry in the inode table

Create a directory entry, referencing the file

human file name to the inode numberCopies data into new file

November 17, 2009 220

mv and inode



If the destination of the mv command ison the same file system as the source, themv command:Creates a new directory entry, with the news

file nameDeletes the old directory entry with the old file

name

Has no impact on the inode table (except for a

time stamp) or the location of the data on thedisk: no data is moved!

November 17, 2009 221

rm and inode



The rm command:Decrement the link count, thus freeing the

inode number to be reused

Places data bocks on the free list

Removed the directory entry

Data is not actually removed, but will beoverwritten when the data blocks are used

by another file

November 17, 2009 222

Linking Files



223

Symbolic link: One file is a pointer orshortcut to another

Hard link: Two files share the same data

Symbolic (or Soft) links



ls –i for displaying inode numberA symbolic link point to another file

ls –l display the link name and the

referenced file$ ls –l pf lrwxrwxrwx 1 issa issa 11 Oct 1 8:26 ps/etc/passwd

File type: l for symbolic link

Syntax

ln –s filename [linkname]

November 17, 2009 224



225

The structure of symbolically linked files

Hard linksDo not work with networked file systems, any



Do not work with networked file systems, anymounted devices, or any other file system

Only exist on same disk and partition as originalfile

One physical file on the filesystemEach link references the file’s inode

File is present in the filesystem as long as atleast one link remain

Syntaxln filename [linkname]

November 17, 2009 226

Hard links



To see which files are linked—check inodenumbers

Two files with same inode numbers—identical files

Any changes made to one file - reflected insecond file (true because files are linked)

To create links to files in differentdirectories first give read, write, andexecute permissions to other users

November 17, 2009 227



The structure of hard linked files

locate Command



Fastest way to search for file/s in entiredirectory tree locate looks in pre-defined database

Wildcards can be used with locate command

If database not updated cannot locatefiles even if files are in system

find command



find commandLocates specific file or group of files Does not rely on a database Searches directory tree for files

meeting criteria specifiedSearches recursivelyWildcards can be used in filename

statement

Ch 2 230

find command



Syntaxfind <dirs> [conditions] [action]

Recurses down in file tree in dirs

Optionally executes command oneach line of output

<Ctrl> + C is quick way to break

into command and stop it fromexecuting

November 17, 2009 231

some find options



Ch 2 232

Finding Examples



Example:find . -printfind all files in the current directory (and all

subdirectories) & display the results

find . -name “*.c” -printfind all files in the current directory (and all

subdirectories) with the extension .c & displaythe results

November 17, 2009 233

Finding Examples



find / -name myfile -print This command tells the find command to

look inside the / directory and everysubdirectory to look for a file or directorywith the name myfile and to display each

match it finds

find . -name “foo*” -amin -10 -print This command tells the find command to

look inside the current directory and everysubdirectory to look for a file with namebegin with foo that have been accessed inthe last 10 minutes and to display eachmatch it finds

Finding and processing Files



-exec action execute a command Syntax

find <dirs> [conditions] -exec cmd {} \;

“Found” files are passed to cmd as arguments{} is a place holder for the filename

The escaped semicolon delimit the generatedcommands

Finding Examples



Example: (for student)

find . -size +5000k

find . -name "*.tmp" -exec rm {} \;

November 17, 2009 236

whereis Command



ls, locate, and find commandsused to locate files of interest

whereis commandlocates/displays locations of aprogram, source, and manual pagesfor a specific command

Ch 2 237

whereis Command



whereis command

Faster than find command since

search path is built in More specific than locate command Searching for files that are

programs

whereis



KEY CONCEPTS: Most binary Command programs

located in the /usr/bin directory Most documentation located in

/usr/share/man directory Cannot execute a command unless it

is in your search path

Must have permission to execute acommand

File Compression



Results in smaller file size

Text files can be compressed up to75%

Binary files usually don’t compressmuch

File Compression



gzip Compresses a file or files Compressed file renamed filename.gz Syntax: gzip [options] [files]See option: –l -d

gunzip Uncompresses a file or files

Takes all of gzip’s options Syntax: gunzip [options] [files]

File Compression



bzip2 Compresses file/files Compressed file renamed to filename.bz2

Syntax: bzip2 [options] [filenames . . . ]

bunzip2 Used to uncompress file/files Syntax: bunzip2 [options] [filenames . . .]

File Compression



zcatReads compressed files compressed

with gzip and writes them to

standard output Identical to gunzip –c

Syntax: zcat [options] [files]

File Compression



Sample compression commands (forstudent)

gzip termcapgzip -v termcap

gunzip -c termcap.gz | wc –l

gunzip termcap

November 17, 2009 244

File Compression



KEY CONCEPTS: file no longer exist in home directory with

original name To see size of file when uncompressed pipe

output from zcat to wc commandFile seen in red—compressed/archived file Can see contents of .gz file (must be text

file) with zcat command

Archiving Tools



Tape archive (tar) utility: One of oldest andmost common backup utilitiesCan create archive in a file on a filesystem or

directly on a device

Accepts options to determine location of archiveand action to perform on archive



Archiving Tools

S



Syntax:tar [options] [tarfile] [other-files]

tar cvf archive_name filesc create a new archive

v produce verbose messages

f archive_name is the name of new file

Options do need a leading dash

November 17, 2009 248

Inspecting Archives

S t



Syntax

tar tf archive_name.tar

tar tvf archive_name.tar

First form display a list of all files in the archive

The v cause a long listing of each file in the

archive

November 17, 2009 249

Extracting an Archive

S t



Syntax

tar xvf archive_name.tar

The archive will be extracted in the current

directoryChange to the target directory first

Files maintain their hierarchy relative tothe current directory

Compressing archives

Oft t hi



Often tar archive are compress

tar can compress/uncompress archives

Compression switches- use during creation

and extraction z for gzip compression

j for bzip2 compression

November 17, 2009 251

tar with Compression



November 17, 2009 252

file1

sub-

directory

.tar .tar.gz

tar gzip

tar to Unformatted Floppies

Fl i d lik t d i



Floppies can used like tape drivesLow level format required

File system not needed

Use tar to write to the floppy/dev/fd0 is the destination

Floppy cannot be mounted

Example:

$ tar czvf /dev/fd0 mydir

November 17, 2009 253

Standard Input and Output



Linux provides three I/O channel toprocesses

Standard input (0): keyboard is defaultStandard output (1): terminal windows is

default

Standard error (2) : terminal windows is default

Redirecting Input and Output

d d i d b



standard input, output, and error can bereconnected to alternate locationsShell redirection operators allow standard I/O

channels to be redirected to/from a filePipes allow standard I/O channels to connected

to the input or output of programs

Redirecting Output

d d di i d d



In order to study redirecting standardoutput, and error, we will use the find command.

find /etc –name passwd This command will search for all files

named passwd in /etc and its subdirectory

By default both the standard output andstandard error are displayed on the screen.

November 17, 2009 256

Redirecting Standard Output

R di ti t d d t t ith



Redirecting standard output with >find /etc –name passwd > findresult

standard error is still displayed on the screen.

If the target file of file redirection with >already exists, the existing file will beoverwritten

To append data to an existing file, use >> to

redirect instead of >

November 17, 2009 257

Redirecting Input and Output



Redirecting Standard Error

R di t t d d ith 2



Redirect standard error with 2>

Example : redirect standard error to a file:find /etc –name passwd 2> finderrors

Standard outputs still displayed on thescreen.

To append data to an existing file, use 2>>to redirect instead of 2>

November 17, 2009 259

Redirecting Standard Error

Can redirect standard error to a



Can redirect standard error to adevice called /dev/null

Example: Redirecting error

message in find command

find / -iname gedit 2> /dev/null

November 17, 2009 260

Redirecting Both StandardOutput and Error

Redirection of standard output and standard error



Redirection of standard output and standard errorcan be performed simultaneouslyfind /etc –name passwd 2> error > result

Each I/O channel can be redirected to different files,or the same file: find /etc –name passwd > alloutput 2>&1

Or find /etc –name passwd &> alloutput

November 17, 2009 261

Redirecting Input

Redirect standard Input with <



Redirect standard Input with <Some commands only operate on standard inputtr doesn’t accept filenames as arguments- it require its

input to be redirected from somewhere

tr ‘A-Z’ ‘a-z’ < .bash_profile This command will translate the uppercase character in

bash_profile to lowercase

November 17, 2009 262

Using pipes To connectprocesses

Pipes (the | character) let you redirect output



Pipes (the | character) let you redirect outputfrom one command to become input to anothercommandls /usr/lib | less

The mail command takes the message contentsas standard inputls –l | mail –s “here the listing” issa

November 17, 2009 263

tee

Let you tee a pipe: redirect output to a file



Let you tee a pipe: redirect output to a filewhile still piping it to another program

set | tee set.out | lessOutput from set command is written to file

set.out while also being piped to less

November 17, 2009 264

teeLet writing to output and simultaneously date | tee file1 file2



date | tee file1 file2

Thu Jun 10 11:10:34 CEST 2007 cat file1

Thu Jun 10 11:10:34 CEST 2007cat file2

Thu Jun 10 11:10:34 CEST 2007uptime | tee -a file2

11:10:51 up 21 days, 21:21, 57 users, load average: 0.04, 0.16, 0.26cat file2

Thu Jun 10 11:10:34 CEST 2007

11:10:51 up 21 days, 21:21, 57 users, load average: 0.04, 0.16, 0.26

String Processing Toolshead



head command display first few line (default : 10lines) of text in a filehead /tmp/output.txt

Use –n or --lines parameter to change numberof line displayedhead –n 20 /tmp/output.txt

266

String Processing Toolstail



tail command display last few line (default : 10 lines) of text in a filetail /etc/passwd

Use –n or --lines parameter to change number of line

displayedtail –n 5 /etc/passwd

Use –f to follow the end of a text file as it changestail –f 5 make.out

Used to watch log files

267

String Processing Toolswc

“ d t” l t li d h t



“word count” – also counts lines and characterswc story.txt

39 237 1901 story.txt

Use –l for only line count

Use –w for only word count

Use –c for only character count

268

String Processing Toolssort

S i i l fil h d



Sort text to stout –original file unchanged

sort [option] file(s)

Common option:

-r Reverse sort to sort descending

-n Numeric sort

-f Ignore case of characters in strings

-u unique (remove duplicate lines in output)

-t ‘x’ Use x as field separator

-k pos1 sort from field pos1

269


$ cat b



$ cat bfishdoganimalbird

$ sort -r bfishdogbirdanimal

270


S t i fil t t



Sort numeric file as text$ cat c5412 this line should go last

998 this line should go second

50 this line should go first

999 this line should go third

$ sort c50 this line should go first

5412 this line should go last



271


Sort numeric file as numbers



Sort numeric file as numbers$ cat c5412 this line should go last


50 this line should go first


$ sort -n c50 this line should go first



5412 this line should go last

272

String Processing Toolsuniq

R i d li li i fil



Remove successive, duplicate lines in a file

Can use in conjunction with sort to remove allduplicated (or use sort –u)

Use –c to count number of occurrences of duplicate data

273

String Processing Toolsuniq



274

Just sorted:

$ cat a | sort

birdbird

dog

dog

fish

fishfly

sort | uniq:

$ cat a | sort | uniq

birddog

fish

fly

String Processing Toolscut

Di l ifi l f fil d t



Display specific column of file data

cut –f4 result.dat

Common option:-f Specifies field or column

-d Specifies field delimiter (default is TAB)

cut –f3 –d: /etc/passwd

-c Cuts by characterscut –c2-5 /usr/share/dict/words

275


Example output second word on each



Example – output second word on eachline:Delimiter: space “ “

Fields: 2$ cat athe quick brown fox

jumped over a quick brown fox

$ cut -f 2 -d ' ' aquick

over

276


Example – output characters 1-3 5 7-end



Example output characters 1 3, 5, 7 end$ cat a

the quick brown fox

jumped over a quick brown fox

$ cut -c 1-3,5,7- atheqick brown fox

jume over a quick brown fox

Example for student:cut –f1 -d: /etc/passwd | sort -r | less

277

String Processing Tools

tr

tr command:



tr command: Translates and/or deletes characters from

standard input, writing to standard output Takes input only from standard input

Syntax is tr [options] string1 [string2]Example:tr ‘A-Z’ ‘a-z’ < .bash_profile

This command will translate the uppercase

character in bash_profile to lowercase

278

String Processing Toolspaste

t li f fil



paste - merge line of files

Syntax:Paste file1 file2

Most useful when combining files withcolumns of information

279

Version Comparison withdiff

Compares two files for differences



Compares two files for differences

diff area.c /tmp/area.c

33c33

< x = y + 2;----

> x = y +4;33c33 indicated line where files differ

< indicates line in first file> indicates line in second file

280

Formatting aDocument with pr

pr utility program: Converts text files into a paginated



pr utility program: Converts text files into a paginated,columned version If no files specified, pr read standard

input By default, pr formats files into single-

column pages of 66 lines To print in formatted form—pipe

formatted document to lpr Syntax: pr [options] [arguments]

Ch 7 281

Formatting aDocument with pr

22649807 linux lecture sem1

Documents