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1
UNIT I
1
INTRODUCTION
Unit Structure
1.0 Objectives
1.1 Introduction
1.2 An Overview
1.2.1 History of Linux
1.2.2 Philosophy
1.2.3 Community
1.2.4 Distributions
1.3 How is the Linux operating system used?
1.4 How the Linux Operating System Works
1.5 Linux Kernel vs Distribution
1.6 Why learn Linux?
1.6.1 Importance of Linux in software ecosystem
1.6.2 web servers
1.6.3 Supercomputers
1.6.4 Mobile
1.6.5 Servers
1.7 Pros and Cons of Linux
1.8 Let us Sum Up
1.9 Unit End Questions
1.10 List of Re ferences
1.11 Bibliography
1.0 OBJECTIVES Introducing various tools and techniques commonly used by Linux
programmers, system administrators and end users to achieve their day -to-
day work in Linux environment.
1.1 INTRODUCTION Linux is similar to Unix. I t is coming under OS (Open source) and
community -developed operating system. Various devices like computers,
servers, mainframes, mobile devices, and embedded devices. Linux is
highly configurable. It depends on a modular design which provides
flexibility to users to customize their own versions of Linux. munotes.in

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2 Introduction 1.2 AN OVERVIEW Depending on the application, Linux can be optimized for different
purposes such as:
 Networking performance.
 Computation performance.
 Deployment on specific hardware platforms.
Users can choose different Linux distributions.
1.2.1 History of Linux:
In 1991, the Linux history started with the starting of a particular project
by the Finland student Linus Torvalds for creating a new free OS kernel .
The final Linux Kernel was remarked by conti nuous development
throughout the history since then.
o Linux was proposed by the Finland student Linus Torvalds in 1991.
o HP-UX ( Hewlett Packard ) 8.0 version was published.
o Hewlett Packard 9.0 version was published in 1992.
o FreeBSD 1.0 version and NetBSD 8 ver sion was released in 1993.
o Red Hat Linux was proposed in 1994. Caldera was detected by
Ransom love and Bryan Sparks and NetBSD 1.0 version published.
o HP-UX 10.0 version and FreeBSD 2.0 version was released in 1995.
o K Desktop Environment was established by Matthias Ettrich in
1996.
o HP-UX 11.0 version was released in 1997.
o The IRIX 6.5 version, i.e., the fifth SGI UNIX generation, Free BSD
3.0 version, and Sun Solaris 7 OS was released in 1998.
o The Caldera System agreement with professional services division
and SCO server software division was released in 2000.
o Linus Torvalds published the Linux version 2.4 source code in 2001.
o Microsoft filed the Trademark collection against Lindows.com in
2001.
o Lindows name was modified to Linspire in 2004.
o The first public ation of Ubuntu was published in 2004.
o The openSUSE project started a free distribution from the community
of Novell In 2005.
o Oracle published its Red Hat distribution in 2006. munotes.in

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3 Linux o Dell begun laptop distribution with Ubuntu which was pre -installed
on it in 200 7.
o Linux kernel version 3.0 was released in 2011.
o Linux -based android of Google insisted 75% of the market share of
the Smartphone, based on the number of phones exported in 2013.
o Ubuntu insisted on 20000000+ users in 2014.
1.2.2 Philosophy:
All operating systems have some philosophy. When Unix was being
developed in the late 1960s and early 1970s, the inventors were intent
upon building an operating system that was significantly different from the
operating systems that ante ceded. The idea of Unix was mar kedly
different from that of other operating systems. And the Linux philosophy
is relatively naturally deduced directly from the Unix philosophy.
1.2.3 Community:
A distribution is largely driven by its inventor and communities. Some
develop and fund their distributions on a levy base, Debian being a well -
known illustration. Others maintain a community interpretation of their
commercial distributions. Numerous Internet communities also give
support to Linux users. Utmost distributions and free software / op en-
source projects have IRC chatrooms or newsgroups. Online forums are
another means for support, with notable exempli cations
being LinuxQuestions.org and the various distribution specific support and
community forums, such as ones for Ubuntu, Fedora, and Gentoo. Linux
distributions host mailing lists: commonly there will be a specific topic
such as usage or development for a given list.
1.2.4 Distributions :
Other operating systems like Microsoft combine each bit of coding
internally and release it as a s ingle package. You have to choose from one
of the interpretations they offer.But Linux is different from them.
Different parts include kernel, shell utilities, X server, system
environment, graphical programs, etc. If you want, you can access the
codes of all these parts and assemble them yourself. But its not an easy
task seeking a lot of time and all the parts has to be assembled correctly.
Linux Distributions List:
Approximately an average of six hundred Linux distributors providing
different features.
1) Ubuntu:
 Came into Existence in 2004
 Used as Graphical Linux without the use of command line. munotes.in

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4 Introduction  Well known distribution
 Lot of pre -installed apps
 Easy to use
2) Linux Mint :
 Based on Ubuntu
 Uses repository software.
 Media codec and proprietary software ar e included
 It uses cinnamon and desktop instead of Ubuntu's unity desktop
environment
3) Debian :
 Came into existence in 1993.
 Most Stable Linux distribution .
 User Friendly .
 Every release is based on the name of the movie Toy Story.
4) Red Hat Enterprise / CentOS :
 Commercial Linux distributor.
 Red hat uses trademark law to prevent their software from being
redistributed.
 CentOS is a community project that uses red hat enterprise Linux
code
 It is a free version of RHEL
5) Fedora :
 Mainly focuses on free sof tware.
 Used ‘upstream’ software
 Less stable
Choosing a Linux Distro Distribution Why To Use Ubuntu It works like Mac OS and easy to use. Linux mint It works like windows and should be use by newcomers. munotes.in

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5 Linux Debian It provides stability but not recommended to a new user. Fedora If you want to use red hat and latest software. Red hat enterprise To be used commercially. CentOS If you want to use red hat but without its trademark. OpenSUSE It works same as Fedora but slightly older and more stable. Arch Linux It is not for the beginners because every package has to be installed by yourself.
1.3 HOW IS THE LINUX OPERATING SYSTEM USED? Every version of the Linux OS manages hardware resources, launches, and
handles applications, and provides some form of user interface.
The Linux OS can be found in many different settings, supporting many
different use cases. Linux is used in the following ways:
 Server OS : web servers, database servers, file servers, email servers
and any other type of shared server. Designed to support high -volume
and multithreading applications, Linux is well -suited for all types of
server applications.
 Desktop OS : for personal productivity computing. It is an OS and
freely available.
 Headless server OS : for systems that do not require a grap hical user
interface (GUI) or directly connected terminal and keyboard.
Headless systems are often used for remotely managed networking
server and other devices.
 Embedded device or appliance OS : needs less computing function.
It is used as as embedded OS f or a variety of application like
including household appliances, automotive entertainment systems
and network file system appliances.
 Network OS : for routers, switches, domain name system servers,
home networking devices and more. For example, Cisco that u ses the
Linux kernel.
 Software development OS : for enterprise software development.
Although many development tools have been ported to Windows or
other OSes, Linux is home to some of the most widely used open -
source software development tools. For example , git for distributed
source control; vim and emacs for source code editing; and compilers
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6 Introduction  Cloud OS : for cloud instances like Linux for cloud servers, desktops
and other services.
1.4 HOW THE LINUX OP ERATING SYSTEM WORKS The Linux OS follows a modular design that’s the key to its numerous
variations and distributions. All Linux distributions are based on Linux
kernel, but they can differ depending on factors such as:
 Kernel version: configured with mor e recent versions, to incorporate
newer features or with older versions to be more stable.
 Kernel modules: This is software that can be loaded and unloaded
into the kernel to extend functionality without rebooting. Kernel
modules are often used to support:
o device drivers, which use code that controls how attached devices
operate.
o file system drivers, which use code that controls how the kernel works
with different file systems; and
o system calls, which use code that controls how programs request
services fro m the kernel.
 Configuration options: It is compiled with configuration options set
to include only device or file system drivers are used for some
specialized distributions; for example, compiling a kernel for a
wireless device without any wired network de vice drivers.
The Linux kernel is the one thing that all systems running Linux have in
common. Linux works by:
 Loading and booting a Linux kernel.
 Kernel manages all system input and output. The system is initialized,
and processes can be started.
 As syste m processes are started, the system can be used for processes
that include network server functions, commands entered interactively
via command line, desktop applications or any application or
program.
When using Linux with a desktop environment as a GUI, Linux works
much an equivalent as any GUI -based OS. Applications and other
resources are often opened by clicking on icons, and files are
often moved, copied or deleted employing a mouse or trackpad
1.5 LINUX KERNEL VS DISTRIBUTION When we discuss Linux Op erating Systems, we
actually mention Whole OS or the Linux Distribution, not just the
Kernel. Technically Linux is that the Kernel of the OS. A kernel is that munotes.in

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7 Linux the core a part of any OS which basically handles Hardware. once
we use Linux kernel and add othe r important things just like the shell,
Various Libraries, GUI and other programs like Multimedia Apps etc.
Then we refer those systems as a Linux Distribution
which generally are often considered as complete OS. there's there are
dozens of Linux distribut ions available but few of them which are very
fashionable and widely used round the world.
1.6 WHY LEARN LINUX? Since Linux has many advantages and features to use it,
Some of them are as follows:
1. Free: Linux is License Free software.
2. Security (V irus Free with inbuilt Firewall protection): The
security aspect of Linux is much stronger; Inbuilt Firewall protection
is available hence Linux is not prone to viruses.
3. OpenSource: Linux is a opensource software hence source code is
open & easily ava ilable on internet.
4. Customizable: It is Customized with different types of hardware and
software
5. Flexibility: Linux is a flexible freeware operating system.
6. Cost: It is mostly free to obtain.
7. Linux is versatile: You can use Linux on virt ually anything you
develop
8. Linux is a community: You can work with other Linux developers to
share knowledge and learnings
9. Linux is very stable: Linux systems rarely crash, and when they do,
the whole system normally does not go down.
1.6.1 Impor tance of Linux in software ecosystem:
o GUI (Graphical User Interface)
o Multitasking: No of programs running at same time.
o Multiuser: Several users on the same machine at the same time
o Multiplatform: Number of processors at a time. runs on many
different C PUs, not just Intel.
o Multiprocessor: Kernel supports multiple independently thread of a
single process or multiple process.
o Multithreading: Has native kernel support for multiple independent
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8 Introduction o Linux runs in a protected mode on 386 machines. It has memory
protection between processes so that that one program can’t bring
whole system down.
o It supports virtual memory using paging i.e., separate partition or file
in file system created.
o Dynamically link ed shared libraries & static libraries.
o It is an open -source software hence all source code is available
including the kernel and all drivers.
o Multiple virtual consoles
o Linux has different filesystem depending upon file system like
FAT32, VFAT, NTFS or NFS, ext3, ext4, swap (RAM)
o It supports Network connectivity
o It supports Network Servers like It supports TCP/IP Networking
including FTP, Telnet, NFS, etc.
o It has Hardware Support
o Firewall Protection inbuilt available so that no outsider introducer can
attack on our System.
o It has its Own K -office Introduction to Linux 13
o Linux supports NetWare client and server with static Routing &
Dynamic Routing with the help of DHCP.
o Linux supports ‘Samba Server’ for connectivity of windows & Linux
file sharing.
o It Supports different Time Servers with send mail facility.
o It supports ftp & http services with Apache web server.
1.6.2 web servers:
o Economical: Linux is an open -source operating system, Its all
versions are available with lower price other than web s ervers., hence
Linux web servers are the best to choose for web hosting services.
o Flexibility: Linux provides a flexible hosting environment with
plenty of high -performance applications.
o High Up time: high up time decides how long a web server functions
well. Linux servers have high up -time because of its robust
performance and reliable.
o Stability and Performance: If hosting package includes Linux based
server, then performance is good of web servers. This operating
system is the most stable and doesn’t slow down over time or freeze munotes.in

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9 Linux up. Linux web servers don’t experience memory leaks and the up
times are often much better than other servers.
o Inexpensive Hosting: Linux is an open -source operating system,
which means it’s free to use.
o Multitasking: Linux s erver can run multiple programs
simultaneously and its enables programs to run continuously in the
background while user works with some other programs. Hence Linux
web servers to have multitasking capabilities.
1.6.3 Supercomputers:
 Customization: Linux o pen-source nature make source code available
to modify code or make customization of code with supercomputer
administration. Hence custom server implantation is possible.
 Less overhead, i.e., way faster: Linux does not require extra software
to update or u pgrade.
 No need for reboots.
 10,000 times more stable: Linux with supercomputers is more stable.
 Easier to automate with scripts .
 Easier backup facility available of Linux servers with
supercomputers .
1.6.4 Mobile:
 Google’s Android developers modified t he Linux kernel and created
Android operating system which is based on Linux ke rnel (core of
operating system).
 powered by the Linux kernel, which can be found on a wide range of
devices.
 Android is an open -source operating system which allows developers
to access unlocked hardware and develop new programs as they wish.
 Android manages processes and different Apps to keep minimum
power consumption.
1.6.5 Servers :
Linux servers are very powerful of their outstanding characteristics like
security, stabilit y, and flexibility. These Linux servers has in built web
servers and business applications which supports network administration
and web and database management services.

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10 Introduction Following are the Key features of Linux servers:
 High Level Security: Since secur ity is main concern hence Linux
servers provides high level of security with the help of firewall
protection and powerful system administration and file access system
to provide authorization.
 Ease of administration: Linux servers are easily administrated . They
can be controlled and managed remotely. It reduces cost because no
additional software setup for the administration is required.
 Supports multiple applications: Linux servers supports many software
applications because of its inbuilt technical stre ngth.
 Customization is easy.
 Reliable: These servers are very reliable as they offer consistent
services without any failures.
1.7 PROS AND CONS OF LINUX Some advantages of using Linux include:
 Open -source software
 Licensing cost is Nil.
 Reliability.
 Backward compatibility
 Many choices of distributions.
Some disadvantages of using Linux include:
 Lack of established standard.
 Support costs: Most enterprise Linux distributors like SUSE and Red
Hat offer support contracts. Depending on the circumstances, t hese
license fees can reduce savings significantly.
 Proprietary software. Desktop productivity software like Microsoft
Office cannot be used on Linux desktops, and other proprietary
software may be unavailable for Linux platforms.
 Unsupported hardware.
 Steep learning curve. Many users struggle to learn to use the Linux
desktop or Linux -based applications.
In some cases, the same Linux attribute can be either an advantage or
disadvantage. For example, having many options for customizing the
Linux OS is advan tageous for manufacturers looking for an embedded OS,
but it is a disadvantage for enterprises that want a desktop OS that can be
used by a wide range of end users. munotes.in

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11 Linux 1.8 LET US SUM UP Linux is an open -source operating system. As it is open source, it is
special and different from other operating systems, which means that you
can customize it by editing source code. It provides programming as well
as a graphical user interface. Linux is built by Linux Torvalds because
he wanted to create a free operating sys tem kernel that anyone can use.
Linux is a collection of operating systems that are based on Linux kernel .
The first version of Linux was released in the year 1991. The Linux
system is most commonly used for servers; however, it is available in
desktop ver sions as well.
Ubuntu, Devian, and Fedora are some popular Linux distributions. Also,
we have SUSE Linux Enterprise Server (SLES) and RedHat
Enterprise Linux for the commercial distribution of Linux. As it is open
source, we can modify the source code and make variations in the
operating system.
1.11 UNIT END QUESTIONS 1. Define what are different operating systems in market. Explain Linux
operating System in detail.
2. Explain features of Linux in detail .
3. Explain features of Linux in detail with di fferent Linux distributions.
4. Explain Linux Architecture with neat diagram.
5. What is Linux? Define History of Linux .
6. Explain about Philosophy of Linux .
7. What is Linux Community and state the names of Linux communities.
8. Explain Linux Te rminology .
9. Explain Linux different Distributions in detail.
10. Explain Linux k ernel vs different distribution.
11. Define different reasons Why we learn Linux .
12. Explain Importance of Linux in software ecosystem 1 .
13. Explain importance of L inux in web servers .
14. Explain importance of Linux in Supercomputers .
15. Explain importance of Linux in Mobile .
16. Explain importance of Linux servers . munotes.in

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12 Introduction 1.9 LIST OF REFERENCES 1. The Linux Programming Interface: A Linux and UNIX System
Programming Handbook 1st Edition by Michael Kerrisk.
2. How Linux Works, 2nd Edition: What Every Superuser Should
Know Second Edition by Brian Ward .
3. The Linux Command Line: A Complete Introduction 1st Edition by by
William E. Shotts Jr.
4. Fundamentals of Linux by Pelz Oliver .
1.10 BIBLIOGRAPHY 1. Linux Command Line and Shell Scripting Bible, 3rd Edition by
Richard Blum
2. Linux : The Complete Reference, Sixth Edition by Richard Petersen
3. How Linux Works, 2nd Edition: What Every Superuser Should
Know Secon d Edition by Brian Ward
4. The Linux Command Line: A Complete Introduction 1st Edition
by by William E. Shotts Jr.
5. Fundamentals of Linux by Pelz Oliver
6. https://www.javatpoint.com/lin ux-distributions
7. https://searchdatacenter.techtarget.com/definition/Linux -operating -
system
8. https://opens ource.com/resources/linux
9. https://www.linuxfoundation.org/tools/participating -in-open -source -
communities/
10. https://www.tutorialspoint.com/operating_system/os_linux.htm




*****
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13
2
INSTALLATION
Unit Structure
2.1 Introduction
2.2 Download the Linux distribution of your choice
2.3 Boot into the Live CD or Live USB
2.4 Try out the Linux distribution before installing
2.5 Start the installation process
2.6 Create a username and password
2.7 Set up the partition
2.8 Boot into Linux
2.9 Check your hardware
2.10 Start using Linux
2.11 Linux Structure
2.11.1 Linux operating system
2.11.2 Architecture of Linux system
2.12 Unit End Qu estions
2.13 List of References
2.14 Bibliography
2.0 INTRODUCTION Linux is the foundation of thousands of open -source operating systems
designed to replace Windows and Mac OS. It is free to download and
install on any computer. Because it is open source, there are a variety of
different interpret ation, or distributions, available developed by different
groups. Follow the guidelines for installing any version of Linux.
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14 Installation 2.2 DOWNLOAD THE LINUX DISTRIBUTION OF YOUR CHOICE. Still, consider trying a featherlight and easy to use distribution, similar as
Ubuntu or Linux Mint. Linux distributions (known as "distros") are
generally available for free to download in ISO format. You can find the
ISO for the distribution of your choice at the distribution’s website. This
format needs to be burned to a CD or USB stick before you can use it to
install Linux. This will produce a Live CD or Live USB.
 A Live CD or Live USB is a fragment that you can boot into, and
frequently contains a interpretation of the operating system that can be
run directly from the CD or USB stick.
 Install an image burning program or use your system’s built -in burning
tool if you are using Windows 7, 8, or Mac OS X. Pen Drive Linux and
UNetBootin are two popular tools for burning ISO files to USB sticks.


2.3 BOOT INTO THE LIVE CD OR LIVE USB Utmost computers are set to boot into the hard drive first, which means
you’ll need to change some settings to boot from your recently burned CD
or USB. Start by rebooting the computer.
 Once the computer reboots, press the key used to enter the menu. The
key for your system will be displayed on the same screen as the
manufacturer’s logo. Typical keys include F12, F2, or Del.
 For Windows 8 users,
 hold the Shift key and click restart. munotes.in

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15 Linux This will load the Advanced Start -up Options, where you can boot fr om
CD.
 For Windows 10 users,
 go to advanced boot and then "Restart Now."
 Once you're in the boot menu,
 select CD or USB.
Once you’ve changed the settings, save and exit the BIOS setup or boot
menu .


2.4 TRY OUT THE LINUX DISTRIBUTION BEFORE INSTALLING Live CDs and USBs can launch a "live environment", giving you the
capability to test it out before making the switch. It is not possible to
create files but can navigate around the interface.
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16 Installation
2.5 START THE INSTALLATION PROCESS. If you are trying distr o, then it can be launched from the application on the
desktop. If it is not distro, we can start the installation from the boot menu.


2.6 CREATE A USERNAME AND PASSWORD We need to create login information to install Linux:


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17 Linux 2.7 SET UP THE PARTITION Linux needs to be installed on a separate partition from any other OS on
your computer if you intend binary booting Linux with another OS. A
partition is a portion of the hard drive that is formatted specifically for that
operating system.
Ubuntu will set a partition automatically and Linux installation require at
least 20 GB
 If partitions are not given by installation process, then check the
formatted as EX4. If the copy of Linux you are installing is the only
operating system on the computer, you will mo st likely have to
manually set your partition size.


2.8 BOOT INTO LINUX After installation, computer will be rebooted. We can see a new screen.
“GNU GRUB” is a boot loader and handles Linux installation.
 If you install multiple distros on your computer, they will all be listed
here.

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18 Installation 2.9 CHECK YOUR HARDWARE Utmost H/W should work out of the box with your Linux distro, though
you may need to download some additional drivers to get everything
working.
 Some hardware requires proprietary drivers to work co rrectly in
Linux. This is most common with graphics cards.
 In Ubuntu, we can download proprietary drivers through the System
Settings menu.
 Select the Additional Drivers option, and then select the graphics
driver from the list. Other distros have specifi c methods for obtaining
extra drivers.
 You can find other drivers from this list as well, such as Wi -Fi
drivers.


2.10 START USING LINUX If installation is complete and verified if all H/W is working properly then
we are ready to start using Linux. Many popular programs can be installed
from their respective repositories.
2.11 LINUX STRUCTURE Let's first start with the basic knowledge of the Linux operating system.

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19 Linux 2.11.1 Linux operating system:
An OS can be defined as an interface between the computer hardware and
the user. OS is a group of software that handles the resources of the
computer and provides basic services for computer programs.
It is an essential component of system software. The objective is to
provide a platform for the user to run any p rogram efficiently. Linux is
one of the famous versions of the UNIX OS. It is coming under free open
source.
2.11.2 Architecture of Linux system:

Fig 1. Architecture of Linux System

The Linux operating system's architecture mainly contains some of the
components: the Kernel, System Library, Hardware layer,
System, and Shell utility .
1. Kernel: - The kernel is one of the core section of an operating system.
It is responsible for each of the major actions of the Linux OS. This
operating system contains dis tinct types of modules and cooperates with
underlying hardware directly. The kernel facilitates required abstraction
for hiding details of low -level hardware or application programs to the
system. There are some of the important kernel types which are ment ioned
below:
o Monolithic Kernel
o Micro kernels
o Exo kernels
o Hybrid kernels munotes.in

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20 Installation 2. System Libraries: These libraries can be specified as some special
functions. These are applied for implementing the operating system's
functionality and don't need code access rig hts of the modules of kernel.
3. System Utility Programs: It is responsible for doing specialized level
and individual activities.
4. Hardware layer: Linux operating system contains a hardware layer
that consists of several peripheral devices like CPU, HDD, and RAM.
5. Shell: It is an interface among the kernel and user. It can afford the
services of kernel. It can take commands through the user and runs the
functions of the kernel. The shell is available in distinct types of OSes.
These operating systems are categorized into two different types, which
are the graphical shells and command -line shells .
The graphical line shells facilitate the graphical user interface, while the
command line shells facilitate the command line interface. Thus, both of
these s hells implement operations. However, the graphical user interface
shells work slower as compared to the command -line interface shells.
There are a few types of these shells which are categorized as follows:
o Korn shell
o Bourne shell
o C shell
o POSIX shell
2.12 UNIT END QUESTIONS 1. How to Download the Linux distribution of your choice.
2. How to create a username and password.
3. How to set up the partition.
4. Briefly explain Linux structure
5. Short notes on Architecture of linux sytem
2.13 LIST OF REFERENCES 1. The Linux Programming Interface: A Linux and UNIX System
Programming Handbook 1st Edition by Michael Kerrisk
2. How Linux Works, 2nd Edition: What Every Superuser Should
Know Second Edition by Brian Ward
3. The Linux Command Line: A Complete Introduction 1st Edition by by
William E. Shotts Jr. munotes.in

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21 Linux 4. Fundamentals of Linux by Pelz Oliver.
2.14 BIBLIOGRAPHY 1. Linux Command Line and Shell Scripting Bible, 3rd Edition by
Richard Blum.
2. Linux: The Complete Reference, Sixth Edition by Richard Petersen.
3. How Linux Works, 2nd Edition: What Every Superuser Should
Know Second Edition by Brian Ward.
4. The Linux Command Line: A Complete Introduction 1st Edition
by by William E. Shotts Jr.
5. Fundamentals of Linux by Pelz Oliver.


*****

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22
3
LINUX STRUCTURE
Unit Structure
3.1 Introduction
3.2 What is Linux File System?
3.3 Linux File System Structure
3.4 Types of Linux File System
3.4.1 Ext, Ext2, Ext3 and Ext4 file system
3.4.2 JFS File System
3.4.3 ReiserFS File System
3.4.4 XFS Fi le System
3.4.5 Btrfs File System
3.4.6 Swap File System
3.5 Linux Boot Process
3.5.1 BIOS
3.5.2 MBR
3.5.3 GRUB
3.5.4 Kernel
3.5.5 Init
3.5.6 Runlevel programs
3.6 Shutdown
3.7 Very basic instructions to Linux Process
3.7.1 List processes
3.7.2 Verbose list (processes)
3.7.3 Kill by PID
3.7.4 Kill by name/keyword
3.7.5 List background jobs and resume background jobs
3.7.6 Bring the most recent job to the foreground
3.7.7 Bring a specific job to the foreground
3.8 Packaging Systems
3.8.1 High and low -level package tools
3.9 Graphical Vs Command line
3.10 Unit End Questions
3.11 List of References
3.12 Bibliography munotes.in

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23 Linux 3.1 INTRODUCTION A Linux file system is a structured collection of files, which may be in a
disk drive or a partiti on. Mostly a partition is a segment of memory and
contains some data. Our system may contain various partitions of the
memory. Generally, every partition contains a file system. Some reasons
for maintaining the file system are given below.
o Primarily the co mputer saves data to the RAM storage; it may lose the
data if it gets turned off.
o Data storage is preferred on hard drives as compared to standard
RAM as RAM costs more than disk space.
File system contains the following sections:
o The root directory (/)
o A specific data storage format (EXT3, EXT4, BTRFS, XFS and so
on)
o A partition or logical volume having a particular file system.
3.2 WHAT IS THE LINUX FILE SYSTEM? Linux file system is generally a built -in layer of a Linux operating system
which is used to handle the storage. Usually, it manages name of the file,
size of the file, date of creation and much more about a file.
3 Basic File Types are:
 Ordinary Files : Contains data, text, or program instructions.
 Directories : Directories are equivalent to folders.
 Special Files : Provides access to H/W
3.3 LINUX FILE SYSTEM STRUCTURE It has a hierarchal file structure which contains :
 a root directory and
 its subdi rectories.
 Linux file system contain s two -part file system software
implementation architecture



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24 Linux Structure

Fig 1. Linux File System Architecture

To interact with file system, Application Programming Interface is
required. API facilitates algorithm for arrangi ng files on a file system and
facilitates tasks such as creating, deleting, and copying the files. Linux
virtual file system provides a single set of commands for the kernel. It
requires the specific system driver to give an interface to the file system.
1.4 TYPES OF LINUX FILE SYSTEM Linux operating system installation offers many file systems like Ext,
Ext2, Ext3, Ext4, JFS, ReiserFS, XFS, btrfs, and swap .

Fig 2. Types of Linux File System

Let's understand each of these file systems in detail:

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25 Linux 3.4.1 Ext, Ext2, Ext3 and Ext4 file system :
Ext1 stands for Extended File System . It was primarily developed
for MINIX OS . Due to some limitations, this file system no longer used.
Ext2 is managing 2 terabytes of data.
Ext3 is developed through Ext2; it is an u pgraded version of Ext2 and
contains backward compatibility. The major drawback of Ext3 is that it
does not support servers because this file system does not support file
recovery and disk snapshot.
Ext4 file system is the fastest file system and compatibl e. It is the default
file system in linux distribution.
3.4.2 JFS File System :
JFS stands for Journaled File System , and it is developed by IBM for
AIX Unix . It is an alternative to the Ext file system. It can also be used in
place of Ext4, where stability is needed with few resources. It is a handy
file system when CPU power is limited.
3.4.3 ReiserFS File System :
ReiserFS is an alternative to the Ext3 file system. It has improved
performance and advanced features. In the earlier time, the ReiserFS was
used as the default file system in SUSE Linux. This file system
dynamically supports the file extension, but it has some drawbacks in
performance.
3.4.4 XFS File System :
XFS file system was considered as high -speed JFS, which is developed for
parallel I/O pro cessing. NASA still using this file system with its high
storage server (300+ Terabyte server).
3.4.5 Btrfs File System :
Btrfs stands for the B tree file system . It is used for fault tolerance, repair
system, fun administration, extensive storage configura tion, and more. It is
not a good suit for the production system.
3.4.6 Swap File System :
The swap file system is used for memory paging in Linux operating
system during the system hibernation. A system that never goes in
hibernate state is required to have swap space equal to its RAM size.


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26 Linux Structure 3.5 LINUX BOOT PROCESS The following are the 6 high level stages of a typical Linux boot process.




3.5.1 BIOS :
 BIOS stands for Basic Input/Output System .
 Performs some system integrity checks .
 Searches, loads, and executes the boot loader program.
 It looks for boot loader in floppy, cd -rom, or hard drive. You can
press a key (typically F12 of F2, but it depends on your system)
during the BIOS startup to change the boot sequence.
 Once the boot loader program is dete cted and loaded into the memory,
BIOS gives the control to it.
 So, in simple terms BIOS loads and executes the MBR boot loader.
3.5.2. MBR :
 MBR stands for Master Boot Record.
 It is located in the 1st sector of the bootable disk. Typically, /dev/hda,
or /de v/sda munotes.in

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27 Linux  MBR is less than 512 bytes in size. This has three components 1)
primary boot loader info in 1st 446 bytes 2) partition table info in next
64 bytes 3) mbr validation check in last 2 bytes.
 It contains information about GRUB (or LILO in old systems).
 So, in simple terms MBR loads and executes the GRUB boot loader.
3.5.3 GRUB
 GRUB stands for Grand Unified Bootloader.
 If you have multiple kernel images installed on your system, you can
choose which one to be executed.
 GRUB displays a splash screen, waits for few seconds, if you don’t
enter anything, it loads the default kernel image as specified in the
grub configuration file.
 GRUB has the knowledge of the filesystem (the older Linux loader
LILO didn’t understand filesystem).
 Grub configuration file is /b oot/grub/grub.conf (/etc/grub.conf is a
link to this). The following is sample grub.conf of CentOS.
#boot=/dev/sda default=0 timeout=5 splashimage=(hd0,0)/boot/grub/splash.xpm.gz hiddenmenu title CentOS (2.6.18 -194.el5PAE) root (hd0,0) kernel /boot/vmlinuz -2.6.18 -194.el5PAE ro root=LABEL=/ initrd /boot/initrd -2.6.18 -194.el5PAE.img
 As you notice from the above info, it contains kernel and initrd image.
 So, in simple terms GRUB just loads and executes Kernel and initrd
images.
3.5.4 Kernel :
 Mounts the root file system as specified in the “root=” in grub.conf
 Kernel executes the /sbin/init program
 Since init was the 1st program to be executed by Linux Kernel, it has
the process id (PID) of 1. Do a ‘ps -ef | grep init’ and check th e pid.
 initrd stands for Initial RAM Disk.
 initrd is used by kernel as temporary root file system until kernel is
booted and the real root file system is mounted. It also contains munotes.in

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28 Linux Structure necessary drivers compiled inside, which helps it to access the hard
drive p artitions, and other hardware.
3.5.5 Init :
 Looks at the /etc/inittab file to decide the Linux run level.
 Following are the available run levels
 0 – halt
 1 – Single user mode
 2 – Multiuser, without NFS
 3 – Full multiuser mode
 4 – unused
 5 – X11
 6 – reboot
 Init identifies the default initlevel from /etc/inittab and uses that to
load all appropriate program.
 Execute ‘grep initdefault /etc/inittab’ on your system to identify the
default run level
 If you want to get into trouble, you can set the default run leve l to 0 or
6. Since you know what 0 and 6 means, probably you might not do
that.
 Typically you would set the default run level to either 3 or 5.
3.5.6. Runlevel programs
 When the Linux system is booting up, you might see various services
getting started. Fo r example, it might say “starting sendmail …. OK”.
Those are the runlevel programs, executed from the run level
directory as defined by your run level.
 Depending on your default init level setting, the system will execute
the programs from one of the follo wing directories.
 Run level 0 – /etc/rc.d/rc0.d/
 Run level 1 – /etc/rc.d/rc1.d/
 Run level 2 – /etc/rc.d/rc2.d/
 Run level 3 – /etc/rc.d/rc3.d/
 Run level 4 – /etc/rc.d/rc4.d/
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29 Linux  Run level 6 – /etc/rc.d/rc6.d/
 Please note that ther e are also symbolic links available for these
directory under /etc directly. So, /etc/rc0.d is linked to /etc/rc.d/rc0.d.
 Under the /etc/rc.d/rc*.d/ directories, you would see programs that
start with S and K.
 Programs starts with S are used during startup . S for startup.
 Programs starts with K are used during shutdown. K for kill.
 There are numbers right next to S and K in the program names. Those
are the sequence number in which the programs should be started or
killed.
 For example, S12syslog is to start the syslog deamon, which has the
sequence number of 12. S80sendmail is to start the sendmail daemon,
which has the sequence number of 80. So, syslog program will be
started before sendmail.
3.6 SHUTDOWN The shutdown command brings down system in a secure w ay. All the
logged -in users are notified about the system shutdown.
Signal SIGTERM notifies all the processes that the system is going down,
so that processes can be saved and exit properly.
Command shutdown signals the init process to change the runlevel.
Runlevel 0 halts the system
Runlevel 6 reboots the system
Runlevel 1 is default state.
Five minutes before shutdown sequence starts, file /etc/nologin is created
when shutdown is scheduled for future which does not allow new user
logins.
If by any reason, command shutdown is stopped before signalling init, this
file is removed. It is also removed to change runlevel before signalling
init.
To run shutdown command root user access is required.
3.7 VERY BASIC INSTRUCTIONS TO LINUX PROCESS Anytime you run a pr ogram, you have created a process.
3.7.1 List processes:
To display currently active processes, use the ps command:
[tcarrigan@client ~]$ ps munotes.in

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30 Linux Structure PID TTY TIME CMD
2648 pts/0 00:00:00 bash
3293 pts/0 00:00:00 sleep
3300 pts/0 00:00:00 ps

Here you will get information about the active processes on your system.
You will want to pay attention to the PID (unique process ID),
the TIME (amount of time that the process has been running), and
the CMD (the command executed to launch th e process).
3.7.2 Verbose list (processes):
To see an incredibly detailed list of processes, you can use the ps
aux command.
 a - all users
 u - shows the user/owner
 x - displays processes not executed in the terminal (making the output
rather long)
You can see the command here (output edited for length):
[tcarrigan@client ~]$ ps aux
USER PID %CPU %MEM VSZ RSS TTY STAT START
TIME COMMAND
tcarrig+ 3293 0.0 0.0 215292 520 pts/0 T 13:41 0:00 sleep 500
root 3380 0.0 0.0 0 0 ? I 13:45 0:00 [kworker/1:1 -
mm_percpu_wq]
root 3381 0.0 0.0 0 0 ? I 13:45 0:00 [kworker/1:3]
root 3398 0.0 0.0 0 0 ? I 13:46 0:00 [kworker/3:2 -
ata_sff]
root 3481 0.0 0.0 0 0 ? I 13:50 0:00 [kworker/u8:2 -
flush -253:0]
root 3482 0.0 0.0 0 0 ? I 13:50 0:00 [kworker/0:1 -
events]
root 3483 0.0 0.0 0 0 ? I 13:50 0:00 [kworker/0:2]
root 3508 0.0 0.0 0 0 ? I 13:51 0:00 [kworker/3:0 -
ata_sff]
root 3511 0.0 0.0 18892 7732 ? S 13:52 0:00 systemd -
userwork
root 3512 0.0 0.0 18892 7656 ? S 13:52 0:00 systemd -
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31 Linux root 3513 0.0 0.0 18892 7656 ? S 13:52 0:00 systemd -
userwork
root 3566 0.4 0.0 432792 8024 ? Ssl 13:54 0:00
/usr/libexec/fprintd
tcarrig+ 3598 0.0 0.0 228208 3948 pts/0 R+ 13:54 0:00 ps aux
3.7.3. Kill by PID:
Inevitably, a process will get hung, and you will need to kill it. The more
time you spend at the CLI, the more likely it is you will need
the kill command. The most accurate way to identify a process is by
process ID (PID).
Use the following syntax:
[tcarrigan@client ~]$ kill PID
This command sends the SIGTERM signal. However, if you are dealing
with a stuck process, add the -9 option.
[tcarrigan@client ~]$ ps
PID TTY TIME CMD
2648 pts/0 00:00:00 bash
3293 pts/0 00:00: 00 sleep
4684 pts/0 00:00:00 sleep
40527 pts/0 00:00:00 sleep
40540 pts/0 00:00:00 ps
[tcarrigan@client ~]$ sudo kill -9 3293
[sudo] password for tcarrigan:
[1] Killed sleep 500
3.7.4 Kill by name/keyword:
Use the killall command to kill a process by name. This command will
kill all processes with the keyword/name that you specify.
The syntax is:
[tcarrigan@client ~]$ killall sleep
This would kill all sleep processes active on the system (the -9 option
works here as well ). Here is an example:
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32 Linux Structure PID TTY TIME CMD
2648 pts/0 00:00:00 bash
4684 pts/0 00:00:00 sleep
40527 pts/0 00:00:00 sleep
40540 pts/0 00:00:00 ps
[tcarrigan@client ~]$ killall -9 sleep
[2]- Killed sleep 500
[3]+ Killed sleep 500
These next two commands go hand in hand. They allow you to
move/manage background commands.
3.7.5 List background jobs and resume background jobs:
To list and manage background jobs, we w ill use the bg command. I
started a new sleep 500 process and then stopped it, sending it to the
background. Thus we see it listed when running bg below:
[tcarrigan@client ~]$ bg
[1]+ sleep 500 &
3.7.6 Bring the most recent job to the foreground:
To do th is, we are going to use the fg command. This brings the most
recently run job/process to the foreground. The following example is a
continuation of the above command. The sleep 500 process that is in the
background is now active in the background. Let's br ing it into the light...
[tcarrigan@client ~]$ fg
sleep 500
This command brings us to our final command in this list.
3.7.7 Bring a specific job to the foreground:
Use the fg command again, but select a specific job to bring to the
foreground (instead of the most recent). To do this, we are just going to
add the job/process name to the command.
[tcarrigan@client ~]$ fg XXXample
This brings job XXXample to the foreground.
3.8 PACKAGING SYSTEMS Almost all the software that is installed on a modern Linux syst em will be
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33 Linux through central repositories (which can contain several thousands of
packages, each of which has been specifically built, tested, and maintained
for the distribution) or be available in source code that can be downloaded
and installed manually.
Because different distribution families use different packaging systems
(Debian: *.deb / CentOS: *.rpm / openSUSE: *.rpm built specially for
openSUSE), a package intended for one d istribution will not be
compatible with another distribution. However, most distributions are
likely to fall into one of the three distribution families covered by the
LFCS certification.
3.8.1 High and low -level package tools:
In order to perform the task of package management effectively, you need
to be aware that you will have two types of available utilities: low-
level tools (which handle in the backend the actual installation, upgrade,
and removal of package files), and high -level tools (which are in c harge of
ensuring that the tasks of dependency resolution and metadata searching -
”data about the data” - are performed). DISTRIBUTION LOW-LEVEL TOOL HIGH -LEVEL
TOOL Debian and derivatives Dpkg apt-get / aptitude CentOS Rpm yum openSUSE Rpm zypper
Let us see the descrption of the low -level and high -level tools.
dpkg is a low -level package manager for Debian -based systems. It can
install, remove, provide information about and build *.deb packages but it
can’t automatically download and install t heir corresponding
dependencies.
apt-get is a high -level package manager for Debian and derivatives, and
provides a simple way to retrieve and install packages, including
dependency resolution, from multiple sources using the command line.
Unlike dpkg, apt -get does not work directly with *.deb files, but with the
package proper name.
aptitude is another high -level package manager for Debian -based
systems, and can be used to perform management tasks (installing,
upgrading, and removing packages, also handlin g dependency resolution
automatically) in a fast and easy way. It provides the same functionality as
apt-get and additional ones, such as offering access to several versions of a
package.
rpm is the package management system used by Linux Standard Base
(LSB)-compliant distributions for low -level handling of packages. Just munotes.in

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34 Linux Structure like dpkg, it can query, install, verify, upgrade, and remove packages, and
is more frequently used by Fedora -based distributions, such as RHEL and
CentOS.
yum adds the functionality of au tomatic updates and package management
with dependency management to RPM -based systems. As a high -level
tool, like apt -get or aptitude, yum works with repositories.
3.9 GRAPHICAL VS COMMAND LINE CLI is that the word form used for Command Line Interface. CLI
permits users to put in writing commands associate degree exceedingly
in terminal or console window to interact with an operating system. CLI
is a platform or medium wherever users answer a visible prompt by
writing a command and get the response from sy stem, for this users have
to be compelled to kind command or train of command for performing
the task. CLI is suitable for the pricey computing wherever input
exactitude is that the priority.
GUI stands for Graphical User Interface. GUI permits users to us e the
graphics to interact with an operating system. In graphical user interface,
menus are provided such as : windows, scrollbars, buttons, wizards,
painting pictures, alternative icons etc. It’s intuitive, simple to find out and
reduces psychological fea ture load. In GUI, the information is shown or
presented to the user in any form such as: plain text, videos, images, etc.
Let’s see that the difference between GUI and CLI: S.NO. CLI GUI 1. CLI is difficult to use. Whereas it is easy to use. 2. It consumes low memory. While consumes more memory. 3. In CLI we can obtain high precision. While in it, low precision is obtained. 4. CLI is faster than GUI. The speed of GUI is slower than CLI. 5. CLI operating system needs only keyboard. While GUI operating system need both mouse and keyboard. 6. CLI’s appearance can not be modified or changed. While it’s appearance can be modified or changed. 7. In CLI, input is entered only at command prompt. While in GUI, input can be entered anywhere on the screen. 8. In CLI, the information is shown or presented to the user in plain text and files While in GUI, the information is shown or presented to the user in any form such as: plain text, videos, images, etc. 9. In CLI, there are no menus provided. While in GUI, menus are provided. 10. There are no graphics in CLI. While in GUI, graphics are used. 11. CLI do not use any pointing devices. While it uses pointing devices for selecting and choosing items. munotes.in

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35 Linux 12. In CLI, spelling mistakes and typing errors are not avoided. Whereas in GUI, spelling mistakes and typing errors are avoided.
3.10 UNIT END QUESTIONS 1. What is Linux File System?
2. Briefly explain Linux File System Structure
3. Explain various types of Linux File System
4. Explain Linux Boot Process
5. Briefly explain about Packaging systems
6. Write difference between CUI and GUI
3.11 LIST OF REFERENCES 1. The Linux Programming Interface: A Linux and UNIX System
Programming Handbook 1st Edition by Michael Kerrisk
2. How Linux Works, 2nd Edition: What Every Sup eruser Should
Know Second Edition by Brian Ward
3. The Linux Command Line: A Complete Introduction 1st Edition by by
William E. Shotts Jr.
4. Fundamentals of Linux by Pelz Oliver
3.12 BIBLIOGRAPHY 1. Linux Command Line and Shell Scripting Bible, 3rd E dition by
Richard Blum
2. Linux: The Complete Reference, Sixth Edition by Richard Petersen
3. How Linux Works, 2nd Edition: What Every Superuser Should
Know Second Edition by Brian Ward
4. The Linux Command Line: A Complete Introduction 1st Edition
by by William E. Shotts Jr.
5. Fundamentals of Linux by Pelz Oliver


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36
UNIT II
4
GRAPHICAL DESKTOP
Unit Structure
4.1 Graphical Desktop
4.2 Session Management
4.3 Basic Desktop Operations
4.4 Network Management
4.5 Installing and Updating Software
4.6 Text editors: gedit, vi, vim, emacs, Graphics editors
4.7 Multimedia applications
4.1 GRAPHICAL DESKTOP The Linux Desktop Environment:
In the early days of Linux simple text interface to the Linux operating
system was available. This text interface allowed administrators to start
programs, control program operatio ns, and move files around on the
system.
But now due to Microsoft Windows awareness the Linux graphical
desktops are introduced.
The X Windows System:
X windows is designed for flexibility and there are various ways you can
configure it. on X windows you c an run most of the different video cards
available & different graphics cards. The X Windows software is the core
element in presenting graphics. It provides an graphics operations.
To run X -windows, the X free 86 server for appropriate system video card
has to be installed and configuration information provided about your
monitor, mouse and keyboard. This information resides in the
configuration file called /etc/xF86 config. The file uses technical
information that is best generated by an X -windows.
There are two basic elements that control your video environment — the
video card in your PC and your monitor. The X Windows software is a
low-level program that works directly with the video card and monitor in
the PC, and controls how Linux applications can present fancy windows
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37 Linux In the Linux world, there are only two software packages that can
implement it.
The XFree86 software package is the older of the two, and for a long time
was the only X Windows package available for Lin ux. As its name
implies, it’s a free open source version of the X Windows software.
A new package called X.org has come onto the Linux scene. It too
provides an open source software implementation of the X Windows
system. Both packages work the same way, c ontrolling how Linux uses
your video card to display content on your monitor. To do that, they have
to be configured for your specific system. During installation it
automatically happens.
The core X Windows software produces a graphical display environmen t,
but nothing else. There is no desktop environment allowing users to
manipulate files or launch programs. To do that, you need a desktop
environment on top of the X Windows system software.
The KDE Desktop:
The K Desktop Environment (KDE) was first relea sed in 1996 as an open
source project to produce a graphical desktop similar to the Microsoft
Windows environment. The KDE desktop incorporates all of the features
you are probably familiar with if you are a Windows user.
The KDE desktop allows you to plac e both application and file icons on
the desktop area. If you single -click an application icon, the Linux system
starts the application. If you single -click on a file icon, the KDE desktop
attempts to determine what application to start to handle the file.
The bar at the bottom of the desktop is called the Panel. The Panel consists
of four parts:
 The K menu: Similarly to the Windows Start menu, the K menu
contains links to start installed applications.
 Program shortcuts : These are quick links to start appli cations
directly from the Panel.
 The taskbar: The taskbar shows icons for applications currently
running on the desktop.
 Applets: These are small applications that have an icon in the Panel
that often can change depending on information from the applicatio n.





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38 Graphical Desktop


KDE Applications: KDE Applications Application Description amaroK Audio file player digiKam Digital camera software K3b CD-burning software Kaffeine Video player Koffice E-mail client Konqueror File and Web browser Kontact Personal information manager Kopete Instant messaging client
Application Description:
All of the Panel features are similar to what you would find in Windows.
Besides the desktop features, the KDE project has produced a wide area of
applications that run in the KDE environment.
The GNOME Desktop:
The GNU Network Object Model Environment (GNOME) is another
popular Linux desktop environment.
First released in 1999, GNOME has become the default desktop
environment for many Linux distributions (the most popular bei ng Red
Hat Linux).
While GNOME choose to depart from the standard Microsoft Windows
look-and-feel, it incorporates many features that most Windows users are
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39 Linux  A desktop area for icons.
 Two panel areas.
 Drag -and-drop capabilities.
GNOME deve lopers have also produced a host of graphical applications
that integrate with the GNOME desktop. As you can see, there are also
quite a few applications available for the GNOME desktop. Besides all of
these applications, most Linux distributions that use the GNOME desktop
also incorporate the KDE libraries, allowing you to run KDE applications
on your GNOME desktop.
Figure shows the standard GNOME desktop used in the Fedora Linux
distribution.


Other Desktops:
The downside to a graphical desktop environm ent is that they require a
fair amount of system resources to operate properly. In the early days of
Linux, a hallmark and selling feature of Linux was its ability to operate on
older, less powerful PCs that the newer Microsoft desktop products
couldn’t ru n on. However, with the popularity of KDE and GNOME
desktops, this hallmark has changed, as it takes just as much memory to
run a KDE or GNOME desktop as the latest Microsoft desktop
environment.
4.2 SESSION MANAGEMENT The screen or GNU screen is a termi nal multiplexer. Using this, you can
run any number of console -based -applications, interactive command
shells, course -based applications, etc. When screen is called, it creates a
single window with a shell in it (or the specified command) and then gets
out of your way so that you can use the program as you normally would.
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40 Graphical Desktop programs in them (including more shells), kill the current window, view a
list of the active windows, copy text betwe en windows, switch between
windows, etc.
Screen manages a session consisting of one or more windows each
containing a shell or other program. Furthermore, screen can divide a
terminal display into multiple regions , each displaying the contents of a
window. All windows run their programs completely independent of each
other. Programs continue to run when their window is currently not visible
and even when the whole screen session is detached from the user's
terminal. This is practical to prevent involuntary ssh timeout session.
1. Screen:
# screen
You can start a new window within the screen and also gives a name to
the window, for example aloft. It creates a session with identified by that
name. The name can be used to reattach at a later stage.
OnlyFans found er resigns from CEO position
# screen -S aloft
Note that you can do all your work as you are in the normal CLI
environment.
2. List all the screen processes:
As we are able to start new windows within the screen, it is possible to
display the currently ope ned screens including those running in the
background. It will list all the existing screen sessions.
# screen -ls
There is a screen on:
10437.aloft (Attached)
1 Socket in /var/run/screen/S -root.
3. Main command of screen:
Ctrl-a followed by c: create a n ew windows
Ctrl-a followed by w: display the list of all the windows currently opened
Ctrl-a followed by A: rename the current windows. The name will appear
when you will list the list of windows opened with Ctrl-a followed by w.
Ctrl-a followed by n: go t o the next windows
Ctrl-a followed by p: go to the previous windows
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41 Linux Ctrl-a followed by a number from 0 to X: go the windows n° X.
Ctrl-a followed by ": choose the windows into which to move on.
Ctrl-a followed by k: close the current windows (kill)
4. Show screen parameter:
You can list all screen's parameters for help. To do this, type Ctrl-
a followed by the character ?. It will display a list of all the commands.


5. Detaching session:
The best a dvantage of the screen command is the possibility to detach a
screen session. You can start a screen session on one computer at the
office, detach the session from the local terminal, go home, log into our
office computer remotely and reattach the screen s ession to our home
computer's terminal. During the intervening time, all jobs on your office
computer have continued to execute. This function is used to prevent the
lost of data which occur suddenly during dropped ssh connection.
To good understand what w e are talking about, let us take an example. We
launch an installation process.


Now we will detach the screen with Ctrl-a followed by d. We can check
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42 Graphical Desktop # screen -ls
There is a screen on:
12449.win (Detached)
1 Socket in /var/run/s creen/S -root.
It is possible to detach screen with screen -d command followed by the
screen id or its name. It means that you will need to open another windows
or console to detach the session if the current console have a process in
progress. You first ne ed to list current attached screen.
# screen -ls
There is a screen on:
13686.win200 (Attached)
1 Socket in /var/run/screen/S -root.
Now on a new terminal, enter the command below.
# screen -d 13686
or you can use the name
# screen -d win200
You will have a n output as below which indicates that the screen was
detached.
[remote detached from 13686.win200]
6. Split windows:
To have a global view of your work, you can need to split your windows
instead of having multiple windows. Ctrl-a followed by S or | split your
screen horizontally or vertically. It is possible to repeat the operation with
no limit. To move another windows, use Ctrl-a followed by Tab.
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43 Linux
When the cursor is on the bottom windows, you can create a new window
(Ctrl -a followed by c) or call an e xisting window (Ctrl -a followed by a
number).


To close a splitted windows, use Ctrl-a followed by X (Note that it is the
uppercase character).
7. Reconnect to a disconnected ssh session:
When you first log in,
run screen to start a screen session. You g et another shell, run commands
in that.
# screen -S remote_session
When you have finished, detach the screen session then logout to the ssh
[detached from 20995.remote_session]
You can list all the screen session first
# screen -ls
There are screens on:
20995.remote_session (Detached)
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44 Graphical Desktop 14134.mom (Detached)
3 Sockets in /var/run/screen/S -root.
Reconnect to your screen session and continue your work
# screen -d -r remote_ression
The screen command is most used for ssh session because it h elps to
continue your work after a disconnection without losing the current
processes in progress.
8. Scroll up in screen windows:
Since screen takes over managing your remote programs, you can't use
your terminal emulator's scroll features while running s creen. You must
use the Screen commands to access the scrollback buffer.
Use Ctrl-a followed by escape
Press the Up and Down arrow keys or the PgUp and PgDn keys to scroll
through previous output.


You can see where is my cursor on the screenshot. Each v irtual terminal
has its own scrollback buffer.
9 See the owner of each screen session:
The screen -ls or screen -list commands only show you your own screen
sessions even for root. As far as I know that's as good as it gets for screen
itself.
If you want t o see which screen sessions have been started by which users
look in each users directory in /var/run/screen/.


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45 Linux 4.3 BASIC DESKTOP OPERATIONS Desktop Browser Screen Layout
The Desktop Browser screen consists of a "[File] menu", "ribbon",
"windows", and "bars". Documents and folders can be searched on a
separate Search Screen.
[File] menu
Ribbon
Windows
Bars
Search Screen
[File] menu
The [File] menu contains the functions relating to Desktop Browser, such
as printing and scanning, and items regarding the configuration of all of
Desktop.


Ribbon:
The ribbon includes tabs with commands for performing operations on and
editing documents stored in libraries and commands for sending and
receiving faxes and printing materials.
Commands are grouped by function and located on tabs. You can switch
the displayed commands by clicking the tabs.
The following tabs are displayed on the ribbon of Desktop Browser by
default.
[Home]
[Fax]
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46 Graphical Desktop You can also click the following areas of the Navigation Window to
display commands related to the area on a tab.
My Tray: Displays the [Edit] tab of the My Tray tool.
Checkout Folder: Displays the [Operations] tab of the document
management tool.
Document Server Library: Displays the [Operations] tab of the doc ument
management tool.
Recycle Bin: Displays the [Manage] tab of the Recycle Bin tool.


NOTE:
You can hide or display the ribbon by clicking (Hide the Ribbon)/
(Display the Ribbon). For information on hiding/displaying the ribbon, see
the following.
Displaying/Hiding Ribbons
If you click (Open Manual), this manual is displayed.
When you use a wheel mouse, you can switch the tabs displayed on the
ribbon by rolling the wheel while above the ribbon.
Ribbons can be customized. For more information, see th e following.
Customizing Ribbons
For information on the Navigation Window, see the following.
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47 Linux Windows
Areas of the Desktop Browser screen mainly used for displaying content
are called "windows".
This section describes the "windows" of Des ktop Browser.
Navigation Window
File List View Window
Preview Window
Properties Window
You can resize Desktop Browser screen and other windows by
dragging with the mouse.
Navigation Window
The Navigation Window is used to organize multiple libraries and list
the folder structure inside libraries. It also enables you to list saved
search conditions.
The following content is displayed on the Navigation Window of
Desktop Browser.
[Libraries] tab: Displays a t ree view of libraries, checkout folders, and
My Tray folders.
[Search Conditions] tab: Displays the saved search conditions.


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48 Graphical Desktop File List View Window :
The File List View Window displays the content of the libraries and
folders selected on the Navigation W indow. You can change the File List
View Window to the list view or thumbnail view.
You can also add memos to documents on the File List View Window.

NOTE The list view can be displayed in ascending or descending order. The thumbnail view can be changed to [Large Thumbnail], [Medium Thumbnail], and [Small Thumbnail]. You can return the File List View Window to the previous display with
(Back), or move forward with
(Forward) on the address bar. For information on the address bar, see the following. Address Bar For more information on how to switch the display format of the File List View Window, see the following. Selecting from the File List View Window
Preview Window :
The Preview Window displays a preview of the docume nt selected on the
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49 Linux

NOTE You can switch between displaying/hiding the Preview Window. For more information, see the following. Displaying/Hiding the Preview Window For information on operating the Preview Window, see the following. Displaying Documents in the Preview Window
Properties Window :
The Properties Window displays the information (properties) of the
document or folder selected on the Navigation Window or File List View
Window.
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50 Graphical Desktop NOTE You can switch between displaying/hiding the Properties Window. For more information, see the following. Displaying/Hiding the Properties Window Bars
Areas of the Desktop Browser screen mainly used for operations and with
items arranged horizontally or vertically are called "bars".
This section describes the "bars" of Desktop Browser.
Address Bar
Simple Search Bar
Toolbar
Output Bar
Status Bar
Address Bar
The addre ss bar shows the path of a selected library, My Tray, or folder.
You can also click
(Back),
(Forward),
(Up),
(Refresh),
or
(Go) on the address bar to switch the view of the File List View
Window.

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51 Linux NOTE By clicking
(Refresh), the File List View Window display is updated. If you select the address bar,
(Refresh) changes to
(Go). If you click
(Go), the screen moves to the location entered in the address bar.
Simple Search Bar :
The simple search bar provides the bar for entering a keyword (s) and
performing a simple search.


Toolbar :
The toolbar enables you to set frequently used ribbon commands on the
toolbar.
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52 Graphical Desktop NOTE For information on the ribbon commands that can be set as buttons on the toolbar, see the following. Lists of Ribbon Commands/Toolbars The toolbar can be customized. For more information, see the following. Customizing Toolbars
Output Bar :
The output bar enables you to configure settings for linkage with
applications and devices and use them. You can also use it for specifying
shared folders and circulating documents.

NOTE The output bar can be customized. For more information, see the following. Changing the Color of Output Bar Buttons
Status Bar :
The status bar displays the number of files selected on the File List View
Window. If no files are selected, the status bar displays the total number of
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53 Linux


Search Screen
The Search Screen displays the results of searching from the simple search
bar.
The Search Screen also provides the items for configuring detailed search
conditions, performing a search, and saving search conditions .

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54 Graphical Desktop NOTE To display the Search Screen always in front of the Desktop Browser screen, click
(Display in Front of Browser) to make it
. Click it again to cancel. For information on searching for documents and folders in Desktop Browser, see the following. Searching for Documents/Folders
4.4 Network Management 4.4.1 TCP/IP Basics:
Remote Access with Linux : Remote Access with Linux can be performed
using TCP/IP or UUCP network protocols.
TCP / IP Remote Access operations: the TCP / IP remote commands
allow you to log in remotely to accounts on other system. You can also
copy files and execute linux commands on those systems. You can also
obtain information about other systems, such as who is currently logged
on. However, for your remote commands to work on a remote system, you
must first given access by that remote system. To provide such a access by
that remote syst em needs to have a .rhosts file that lists your system name
and login name. The various TCP / IP commands are as follows: All the
commands are preceded by alphabet r.
$ rwho: It displays all the users currently logged into the network
$ ruptime: It display s information about each system on your network.
The information shows how each system has been performing, whether a
system is up or down, how long, it has been up or down, the no of users on
the system etc.
$ ping: The ping command detects whether or not a system is up and
running. It takes the name of the system which you want to check as
argument.
Eg $ ping violet .
Output: violet is alive .
$ ping garnet
Output: no answer from garnet
Remote Access Permissions (rhosts): To control the access to our sys tem
(from other users who are using TCP/IP) we use rhosts file. To achieve
communication between you and others the rhosts file on both system
(yours and others) should have each others system name and login name.
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55 Linux allow people access to your account without giving out your password. To
deny access to a user, simply delete the user’s system name and login
name from your rhosts file
$ cat .rhosts
Output: garnet chris
Violet Robert
Remote Login : It is quite possible that we have no of account on different
systems in a network. If sitting on one system if we want to log into our
account on other system on a network then it can be done with rlogin
command. rlogin command takes system nam e as argument. $ rlogin
violet
As soon as we execute the rlogin command we are immediately prompted
for the password. During executing this command we have passed only the
system name but not the login name. This is because rlogin command
assumes that the login name on your local system is same as that login
name on the remote system.(login name on local system means the login
name of current system on which you are currently working). But suppose
that you are having different login name on remote system th en we use the
following command.
$ rlogin system -name – l login -name: (-l option is used to specify the
login name on remote system is different from the current system).
$ rlogin violet – l robert: (The user logs into the system violet using login
name ro bert).
Remote file copy (rcp): The rcp command is used to copy files to and
from remote and local systems. rcp is a file transfer utility that operates
like the cp command but across the network. The rcp command requires
that the remote system have your lo cal system name and login name in its
.rhosts file. The syntax is as follows:
$ rcp system -name:source file system -name:copy -file.
When copying to remote system, the copy file will be a remote file and
will require the remote system’s name. If the source file is one which is
present on your own system then it will not require the system name. For
e.g.
$ rcp abc violet:xyz . The file abc since it is present on your own system
it will not require the system name, only file name is sufficient. The file
abc is copied from the current system to violet system and named as xyz.
$ rcp violet:pqr jkl . The file pqr from violet system is copied to current
system and named as jkl.
Copying directories: The rcp command with –r option will copy the
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56 Graphical Desktop $ rcp –r source -directory remote -system -name:copy -directory
$ rcp –r vijay violet:vijay1 (vijay directory from current system is
copied to directory vijay1 on violet system)
$ rcp –r violet:manoj manoj1 (manoj directory from v iolet system is
copied to directory manoj1 on current system)
$ rcp –r violet: \*.c . (All files with .c extension is copied from violet
system to current directory on current or local system ( .))
$ rcp –r abc violet: \ . (Directory abc is copied from curren t system to
current directory of violet system).
The asterisk i.e. * and the dot are special shell characters which are
evaluated by your local system ( because you executing the shell
command), not by the remote system. If you want that the special
charac ters to be evaluated by the remove system, you must quote it (by
using backward slash).
Remote Execution : Some times we need to execute a shell script on
remote system, for which we use rsh command. The rsh command will
execute a command or shell script on remote system and display the
results on your system. Your system name and login name must, of
course, be in the remote system’s .rhosts file. The syntax of the command
is
$ rsh remote -system -name Linux -command
$ rsh violet ls /home/robert (listing all the contents of robert directory on
violet system)
$ rsh violet ls /home/robert > xyz (all the contents from robert directory
on violet system is redirected to xyz file on local or current system)
$ rsh violet ls /home/robert ‘ >’ xyz (If we use the quote s for redirection
operator then it becomes the part of Linux command evaluated on the
remote system. The working of the above command is same as that of
earlier command but the only difference is that the file xyz is formed on
remote system instead of curr ent system)
The same is true with all the Linux commands. For e.g. with pipes
$ rsh violet ls /home/robert | lpr ( piped to local or current printer)
$ rsh violet ls /home/robert ‘|’ lpr ( piped to remote system’s printer)
 TCP/IP commands:
(1) You can find ou t who is logged in, get information about a user an
another system.
$ rwho munotes.in

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57 Linux violet Rebert: tty I sept 10 10:34
garnet cris: tty 2 sept 10 29:22
(2) The ruptime command displays information about each system on
your network
$ ruptime
Violet up 11+04:10 8 users load 1:20 1:10 1:00 ruptime shows
whether a system is up or down, the number of users on the system,
and the average load on the system for the last 5, 10 and 15 minutes.
(3) The ping command detects whether or not a system is up and running.
The ping command takes as its argument the name of the system you
want to check.
$ ping violet  system number or name
violet is a line
(4) It is possible that you could have accounts on different systems in
your network. You can perform such a remote login using the rlogin
command takes as its argument a system name.
$ rlogin system -name -1 login name
For example, the user logs into a system called violet using the login name
Robert
$ rlogin violet -1 robert
password
The option –1 allows you to enter a different login name for the account
on the remote system. Because most people use rlogin to access accounts
they have on other systems with their own login name.
(5) To copy files to and from remote and local system, use the rcp
command that operates like the Cp command but acro ss a network
connection to a remote system. The rcp command begins with the
keyword rcp and has its arguments the source file and copy file
names.
$ rcp system -names : source -file system -name : copy file
When copying to a remote systems, the copy file will be a remote file and
require the remote system name. The source file is one on your own
system and does not require a system name. For e.g. The user copies the
file whether from his own system to the remote system violet and renames
the file Monday.
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58 Graphical Desktop In the next example, the user copies the file Wednesday from the remote
system violet to his own system and renames the file today.
$ rcp violet : Wednesday today.
(6) At times, you may need to execute a single command on a remote
system. The rsh command will execute a linux command on another
system and display the results on your own.
The rsh command takes two general arguments, a system name and a
Linux command.
The syntax is as follows:
$ rsh remote -system -name Linux -command
In the next example, the rsh command executes an IS command on the
remote system. Violet to list the files in the /home/Robert directory on
violet.
$ rsh violet ls/more/Robert
or
$ rsh violet Is/more/Robert> my files
This example shows you the list of files on the remote system and sends
them to standard output to local system.
4.4.2 Resolving Ip Addresses:
(1) TCP/IP Network Addresses:
TCP/IP address is organized into four segments consisting of numbers
separated by periods. This is called the IP address. Part o f this address is
used for network address, and the other part is used to identify a particular
host in the network. The network address identifies the network that a
particular host is a part of. Usually, the network part of the address takes
up the first three segments and the host takes the last segment. Altogether
this forms a unique address with which to identify any computer on a
TCP/IP network. For example, in the IP address 199.35.209.72, the
network part is 199.35.209 and the host part is 72. The h ost is a part of a
network whose own address is 199.35.209.0.
The IP address of the host, or host address is only one of several addresses
you will need in order to connect the host to a network in addition, you
will need a network address, or a network m ask or netmask. If you
provided them at that time, they will all be automatically entered into the
appropriate configuration files.

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59 Linux (2) Network Address:
You can easily figure out the network address using your host address. It
is a network part of your hos t address; with the host part set to 0.50 the
network address for the host address 199.35.209.72 is 199.35.209.0
Therefore system device the network address form the host address using
the netmask.
(3) Broadcast Address:
The broadcast address allows a system t o send the same message to all
systems on your network at once. As with the network address, you can
easily figure it out using your host address; it has the host part of your
address set to 255. The network part remains untouched. So the broadcast
address for the host address 199.35.209.72 is 199.35.209.255. (You
combine the network part with 255 in the host part.)
(4) Gateway Address:
Some networks will have a computer designated as the gateway to other
networks. Every connection to and from the network to ot her networks
passes through this gateway computer. If you are on this type of network,
you will have to provide the gateway address. If your network does not
have a gateway or you use a stand -alone system or dial into an Internet
Service Provider, you do n ot need a gateway address.
Usually a gateway address has the same network part of a hostname, with
the host part set to 1. The gateway address for the host address
199.35.209.72 may be 199.35.209.1.
(5) Nameserver Addresses:
Many networks, including the intern et, have computers that operate as
domain nameservers to translate the domain names of networks and hosts
into IP addresses. This makes your computer identifiable on a network,
using just your domain name rather than your IP address. You can also use
the d omain names of other system to reference them, so you don’t have to
know their IP addresses. You do, however have to know the IP addresses
of any domain nameservers for your network.
Even if you are using an internet service provider, you will have to know
the address of the domain nameservers that your ISP operates for the
internet.
(6) Netmask:
The netmask is used to derive the address of the network you are
connected to. The netmask is determined using your host address as a
template. All the numbers in the network part of your host address are set
to 255, and the host part is set to 0. This, then is your netmask. So the
netmask for the host address is 199.35.209.72 is 255.255.0. The network
part 199.35.209, has been set to 255.255.255 and the host part, 72 h as munotes.in

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60 Graphical Desktop been set to 0. Systems can then use your netmask to derive your network
address from your host address. They can determine what part of your host
address makes up your network address and what those numbers are.
(7) TCP/IP Configuration Files:
A set of con figuration files in the /etc directory, are used to set up and
manage your TCP/IP network. They specify such network information as
host and domain names, IP addresses, and interface options. It is in these
files that the IP address and domain names of oth er Internet hosts that you
want you access are entered. If you configured your network during
installation, you will already find that information in these files. The
netcfg program on your desktop and netconfig program on your command
line both provide an easy interface for entering the configuration data for
these files. File Function /etc/hosts Associates hostnames with IP addresses /etc/networks Associates domain names with network
addresses /etc/rc.d/init.d/inct Contain commands to configure your
network interface when you boot up /etc/HOSTNAME Holds the hostname of your system /etc/host.conf Resolves options /etc/resolu.conf Contains list of domain nameservers
(8) Identifying Hostnames: /etc/hosts:
Without the unique IP address that the TCP/IP net work uses to identify
computers, a particular computer could not be located. Since IP addresses
are difficult to use or remember, domain names are used instead. For each
IP address there is a domain name. When you use a domain name to
reference a computer on the network, your system translates it into its
associated IP address. This address can then be used by your network to
locate that computer.
The responsibility for associating domain names and IP addresses has
been taken over by domain nameservers. Ho wever, the hosts file is still
used to hold the domain names an IP addresses of frequently accessed
hosts. Your system will always check your hosts file for the IP address of
a domain name before taking the added step of accessing a nameserver.
The format of a domain name entry in the hosts file is the IP address
followed by the domain name, separated by a space. You will already find
an entry in your hosts file for “localhost” with the IP address 127.0.0.1.
Localhost is a special identification used by you r computer to enables
users on you’re your system to communicate locally with each other. The
IP address 127.0.0.1 is a special reserved address used by every computer
for this purpose. It identifies what is technically referred to as a loopback
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61 Linux (9) Network Name: /etc/networks:
The /etc/networks file holds the domain names and IP addresses of
networks that you are connected to, not to domain names of particular
computers. Every IP address consists of a network part and a host part.
The network part is t he network address you will find in the networks file.
You will always have an entry in this file for the network portion on your
computer’s IP address. This is the network address of the network, your
computer is connected to.
/etc/HOSTNAME:
The /etc/HOST NAME file holds your system’s hostname. To change your
hostname, you change this entry. The netcfg program allows you to
change your hostname and will place the new name in /etc/HOSTNAME.
Instead of displaying this file to find your hostname, you can use t he
hostname command.
$ hostname
turtle.trek.com
(1) Network Interfaces and Routes: ifconfig and route:
Your connection to a network is made by your system through a particular
hardware interface such as an Ethernet card or a modem. Data passing
through this i nterface is then routed to your network. The ifconfig
command configures your network interfaces and the route command will
route them accordingly.
Every time you start your system, the network interfaces and their routes
have to be established. You can h ave this done automatically for you when
you boot up by placing the ifconfig and route commands for each interface
in the /etc/rc.d/init.d/inet initialization fle, which is executed whenever
you start your system.
Ifconfig :
The ifconfig command takes as it s arguments the name of an interface and
an IP address as well as options. Ifconfig then assigns the IP address to the
interface. Your system now knows that there is such an interface and that
it references a particular IP address. In addition, you can spe cify whether
the IP address is a host of network address. You can use a domain name
for the IP address, provided the domain name is listed along with its IP
address in the /etc/hosts file. The syntax for the ifconfig command is as
follows.
# ifconfig inter face – host – net – flag address options.
The host – net – flag can be either – host or – net to indicate a host or
network IP address.
In the next example, the ifconfig command configures an Ethernet
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62 Graphical Desktop # ifconfig etho 204.32.168.56
The ifconfig command can have several options, which set different
features of the interface, such as the maximum number of bytes. It can
transfer (mtu) or the broadcast address. The up and down option activate
and deactivate the interface.
The ifconfig command is ver y useful for checking on the status of an
interface if you enter the ifconfig command along with the name of the
interface, information about that interface is displayed
# if config etho
Routing:
A packet that is part of transmission takes a certain route to reach its
destination. On a large network, packets are transmitted from one
computer to another until the destination computer is reached. The route
determines where the process starts and what computer your system needs
to send the packet to in order f or it to reach its destination. On small
network routing may be static, that is, the route from one system to
another is fixed. One system knows how to reach another, moving through
fixed paths. However, on larger networks and on the Internet, routing is
dynamic. Your system knows the first computer to send its packet off to,
and then that computer takes it from there, passing it on to another that
then determines where to pass it on to. For dynamic routing, your system
needs to know very little. Static rou ting however can become very
complex, since you have to keep track of all the network connections.
Your routes are listed in your routing table in the /proc/net/route file. To
display the routing table, enter route with no arguments.
# route
kernel routing table : Destination Gateway Fenmask flags metric Ref Use Iface Loopback * 255.0.0.0 U 0 0 12 Lo Pongol.train.com 255.255.255.0 U 0 0 0 0 etho The different fields are listed in the following table : Field Description Destination Description IP address of the route Gateway IP address or hostname of the gateway the route uses * indicates no gateway is used. Genmask The network for the route Flags Type of route: U = up, H = host, G = Gateway, D = dynamic, M = modifies. munotes.in

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63 Linux Metric Metric cost of rou te Ref Number of routes that depend on this one Window TCP window for Ax.25 networks. Use Number of times used Iface Type of interface this route uses
You should have at least one entry in the routing table for the loopback
interface. If not, you wi ll have to route the loopback interface using the
route command. The IP address for an interface has to be added to the
routing table before you can use that interface. You add an address with
the route command and the add option.
Route add address:
The ne xt example adds the IP address for the loopback interface to the
routing table.
route add 127.0.0.1
If your system is connected to a network, there should be at least one entry
in your routing table that specifies the default route. This is the route take n
by a message packet when not other route entry leads to its destination.
The destination for a default route is the keyword default.
Monitoring Your Network: Ping and Netstat:
With the ping program, you can check to see if you can actually access
another host on your network. Ping will send a request to the host for a
reply. The host then sends a reply back, and it is displayed on your screen.
Ping will continually send such a request until you stop it with a break
command, a Ctrl+C. you will see one repl y after another scroll by on your
screen until you stop the program. If ping can not access a host, it will
issue a message saying that the host is unreachable.
The netstat program provides real -time information on the status of your
network connections, a s well as network status and the routing table.
The netstat command with no options will list the network connections on
your system. First, active TCP connections are listed and then the active
domain sockets. The domain sockets contain processes used to set up
communications between your system and other systems. The various
fields are described in the following table. Field Description Proto Protocol used for the connection: TCP, UDP Recu-Q Bytes received but not yet used by the system Send-Q Bytes sent to remote system, but not yet confirmed as received. Local Address Local hostname and port number Foreign Address Remote hostname and port number assigned to a connection, port number can be connection type, such munotes.in

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64 Graphical Desktop as telnet or ftp. (State) State of connection to remote host ESTABLISHD, connection established SYN_SENT, trying to make connection SYN_REC, connection being created Fin_WAIT1, connection shutting down CLOSED, connection closed LISTEN, listening for remote connection UNKNOWN, unknown state
Domain socket:
Proto protocol for socket, usually unix
RefCnt number of processes currently in socket
Flag Type Mode Socket is access State State of the socket FREE, Socket is not used LISTENING, waiting for connection UNCONNECTED, no current connection CONNECTING, trying to make connection CONNECTED, currently connected DISCONNECTING, closing a connection Path Path name used by processes to access socket
You can use netstat with the –r option to display the routing table, and
netstat with the –i opti on displays the us are for the different network
interfaces. The following table explains the coded information.
# netstat –i
kernel interface table : Iface Mtu met Rx-OK Rx-ERR Rx-DRP Rx-OUR Tx-OK Tx-ERR Tx-DRP Tx-OVR flags LO 2000 0 0 0 0 0 58 0 0 0 BLRU MTU Maximum number of bytes for one transmission RX-OK Packets received with no errors RX-ERR Packets received with errors RX-DRP Packets dropped RX-OVR Packet overrun errors TX-OK Packets sent with no errors TX-ERR Packets sent with errors TX-DRP Packets dropped in transmission TX-OVR Packets dropped in transmission with overrun errors. munotes.in

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65 Linux Flags Interface Characteristics A Receives packets for multicast addresses B Receives broadcasts D Debugging is on I Loopback interface M Promiscuous mode N No trailers processed on packets O Address resolution protocol is off P Point-to-point interface R Interface is running U Interface is activated, up
Domain Name Service (DNS):
Each computer connected to a TCP/IP network such as the Inte rnet is
identified by its own IP address. An IP address is a set of four numbers
specifying the location of a network and of a host (a computer) within that
network. IP addresses are difficult to remember, so a domain name version
of each IP address is als o used to identify a host. A domain name consists
of two ports, the host name and the domain. The host name is the
computer’s specific name, and the domain identifies the network that the
computer is a part of. The combination of a hostname domain and
extension forms a unique name by which a computer can be referenced.
The domain can, in turn, be split into further sub -domains.
As you know, a computer on a network can still only be identified by its
IP address, even if it has a domain name. You can use a do main name to
reference a computer on a network, but this involves using the domain
name to look up the corresponding IP address in a database. The network
then uses the IP address, not the domain name, to access the computer.
As networks become larger, it becomes impractical and, in the case of the
Internet impossible for each computer to maintain its own list of all the
domain names and IP addresses. To provide the service of translating
domain addresses to IP addresses databases of domain names were
devel oped and placed on their own servers. To find the IP addresses of a
domain name, a query is sent to a name server that then looks up the IP
address for you and sends it back. In a large network there can be several
name servers covering different parts of the network. If a nameserver
cannot find a particular IP address, it will send the query on to another
name server that is more likely to have it. Nameservers can also provide
information such as the company name and street address of a computer or
even th e person maintaining it.
Nameservers are queried by resolvers. These are programs specially
designed o obtain addresses from nameservers.
4.4.3 Telnet:
What is Telnet? Telnet is a user command and an underlying TCP/IP
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66 Graphical Desktop administrator or another user can access someone else's computer
remotely. On the Web, HTTP and FTP protocols allow you to request
specific files from remote computers, but not to actually be logged on as a
user of that computer. W ith Telnet, you log on as a regular user with
whatever privileges you may have been granted to the specific application
and data on that computer.If you have an account on a host in local
network, you can use telnet with the hostname or IP address as argum ent:
$ telnet 192.168.35.12
Connected to 192.168.35.12
Login:
Now user can enter the Login name at this prompt and then the password
to gain access to the remote machine. After login you can work on any
command at remote location.
telnet> !ls –l
4.4.4 FT P:
ftp command can also be used with or without arguments.
ftp ip -address
After establishing a connection with the destination, ftp prompts for the
username and password. The local username is prompted as default and if
pressed enter, the system would have logged in as default. Termination of
ftp is done in two stages. Firstly one has to disconnect from the remote
machine with close and then quit ftp either with bye or quit. ftp has all the
basic facilities needed to handle files and directories On the remo te
machine like pwd, ls, cd, mkdir, rmdir, chmod. User can delete single file
with delete and multiple files with mdelete or rename a file(rename).
Transferring files:
For the purpose of transfer files can be seen as belonging to two types -
ascii and bina ry. All executables, graphics, word processing and
multimedia files belong to binary type. Uploading of files is done with put
for single file and for multiple files mput. For downloading get for single
file and mget for multiple files.
ftp displays the ft p> prompt when used without argument. Then
connection can be established with open command.
ftp works in two stages. First it makes a connection with a remote
machine. This is done by invoking ftp with the hostname or later with the
open command. After the connection has been established, ftp asks for the
username and password. To login after this user command is used along
with the username.
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67 Linux Anonymous ftp:
On the internet there are several sites which offer trial and public domain
software for downloadin g. Where a separate account is not there for every
user. These sites offer a special user account “anonymous” that has to be
used for logging in. these sites are known as anonymous ftp sites. User can
only download files from an anonymous site.
4.5 INSTALLING AND UPDATING SOFTWARE Most people are surprised to see that they have a running, usable computer
after installing Linux; most distributions contain ample support for video
and network cards, monitors and other external devices, so there is usually
no need to install extra drivers. Also common tools such as office suites,
web browsers, E -mail and other network client programs are included in
the main distributions. Even so, an initial installation might not meet your
requirements.
If you just can't fi nd what you need, maybe it is not installed on your
system. It may also be that you have the required software, but it does not
do what it is supposed to do. Remember that Linux moves fast, and
software improves on a daily basis. Don't waste your time trou bleshooting
problems that might already be resolved.
You can update your system or add packages to it at any time you want.
Most software comes in packages. Extra software may be found on your
installation CDs or on the Internet. The website of your Linux distribution
is a good place to start looking for additional software and contains
instructions about how to install it on your type of Linux, see Appendix A.
Always read the documentation that comes with new software, and any
installation guidelines the p ackage might contain. All software comes with
a README file, which you are very strongly advised to read.
4.5.1. What is RPM?
RPM, the RedHat Package Manager, is a powerful package manager that
you can use to install, update and remove packages. It allow s you to
search for packages and keeps track of the files that come with each
package. A system is built -in so that you can verify the authenticity of
packages downloaded from the Internet. Advanced users can build their
own packages with RPM.
An RPM packa ge consists of an archive of files and meta -data used to
install and erase the archive files. The meta -data includes helper scripts,
file attributes, and descriptive information about the package. Packages
come in two varieties: binary packages, used to en capsulate software to be
installed, and source packages, containing the source code and recipe
necessary to produce binary packages.

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68 Graphical Desktop Types of RPM Packages :
RPM packages come in two categories: source and binary.
A source RPM can always be recognized beca use the filename ends with
the string “.src.rpm“. In a source RPM are not only the original program
source code files but scripts that allow the code to be recompiled
automatically, to be installed automatically, and to be removed
automatically. There are no end -user executable files in a source RPM.
Usually, only developers are interested in a source RPM.
A binary RPM contains the end -user compoments of an RPM. Binary
RPM filenames identify the host architecture for the contents. For
example, the binary RP M file:
bash-3.1-16.1.x86_64.rpm
It contains files only usable on a 64 -bit Intel X86 architecture CPU. Other
common architecture values include “i386” for 32 -bit Intel hosts. Some
binary RPM’s may be installed on any CPU architecture because their
files wi ll work on any host; an example of these “.noarch.rpm” packages is
the “tzdata” RPM which contains information about world timezones. To
update your system with the latest version of a package, you will need the
most recent binary RPM for it.
RPM Naming Sc heme :
Each RPM package is contained in a single file. The filename has several
fields to fully identify the contents of the package. While the RPM tools
themselves do not rely upon the filename itself, you should understand the
filename convention to help you identify or download the proper package.
Here is an example RPM filename:
bash-3.1-16.1.x86_64.rpm
This RPM is for the BASH shell (“/bin/bash”). The filename is composed
of several parts:
[name] -[version] -[release].[arch].rpm
Where,
[name] is the name of the program or package. The [name] is usually
assigned by the program’s author. In our example, the developers decided
to name their product “bash” for reasons that seemed amusing to them.
version] identifies which edition of the software this RPM conta ins. The
[version] number is assigned by the program’s author. Using the number
allows one to determine which version of the author’s sources were used
to generate the RPM.
[release] provides the edition number of the RPM file itself and not the
version of the author’s source files. An updated RPM may be issued to
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69 Linux not have come from the original developer, so the RPM [release] gets
incremented instead of the [version].
[arch] describ es the contents of the RPM and tells whether this file
contains the product source (a “.src.rpm”), architecture -independent files
(a “.noarch.rpm”), or files which may only be installed on a particular host
type (a “.sh.rpm” will work only on a STRONGHOLD embedded
processor).
Installing and Removing Files
Note: Usually only one or of an RPM may be installed at once.
Later versions are usually installed using the “ -U” (update) RPM function
instead of the “ -i” RPM function. Common exceptions to the only -one
RPM rule are the kernel RPM’s. A system commonly has several versions
of kernels installed; RPM has a list of which RPM’s may have multiple
versions installed. To delete one version when several are installed, you
must fully -specify the package name and ver sion.
On the x86_64 architecture, it is common to have both the 32 -bit “.i386”
and the 64 -bit “.x86_64” RPM packages installed tosupport both 32 -bit
and 64 -bit applications. Normally, RPM does not display the architecture
of a package on a query but you ca n manually display it.
Installation and Removal :
# rpm -i --install (install new RPM; error if already installed)
# rpm -U --upgrade (delete existing RPM, if any; install new)
# rpm -F --freshen (update RPM only if package already installed)
# rpm -e --erase (remove, delete, expunge)
Common Options
Output: -v (verbose – file name), -h (hash)
Preconditions: –nodeps, –replacefiles, –force (BE CAREFUL HERE !!!)
Relocating: –excludepath, –prefix, –relocate, –badreloc, –root
URL Support: ftp, http
Examples:
# rpm -ivh binutils -2.11.90.0.8 -12.i386.rpm
# rpm -Uvh finger -0.17-9-i386.rpm
# rpm -Fvh ftp://updates.redhat.com/current/i386/*.rpm
# rpm -e diffutils
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70 Graphical Desktop Hint: Never, ever, use the “ -U” option to install a new kernel RPM. Th e “-
U” update function first deletes the current RPM from the system and then
attempts to install the new RPM. Any problem that prevents the new RPM
from installing will leave the system unbootable. This is not what you
want, so always use the “ -i” switch to install a kernel RPM.
Queries (Packages and/or Information) :
Use a query for information about installed packages. You may query
against all installed packages, or a single installed package. You may also
find out which RPM supplies a particular file.
# rpm -q [packages] [information]
# rpm -qa (all installed packages)
# rpm -q package_name
# rpm -qf (filename)
# rpm -qp (package filename)
Information
default (package name)
-i: general information
-l: file list
Examples:
# rpm -qa
# rpm -q kernel -i (inf ormation)
# rpm -q kernel -l (files contained in package)
# rpm -q kernel --requires (prereqs)
# rpm -q kernel --provides (capabilities provided by package)
# rpm -q kernel --scripts (scripts run during installation and removal)
# rpm -q kernel --changelog (revision history)
# rpm -q kernel -queryformat format (rpm --querytags for list of options)
Queries – Verification (Files) :
The RPM database contains many attributes about each and every file
installed by an RPM. You may verify the current status of the file against
the information cataloged by RPM when the package was installed.
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71 Linux # rpm -Va (verify all)
# rpm -Vf (filename)
# rpm -Vp (package filename)
4.6 TEXT EDITORS 4.6.1 Gedit
4.6.2 Vi
4.6.3 Vim
4.6.4 Emacs
4.6.5 Graphics editors
4.6.1 Gedit :
gedit is a full -featured text editor for the GNOME desktop environment.
You can use it to prepare simple notes and documents, or you can use
some of its advanced features, making it your own software development
environment.


Once gedit launches, you can start writing right away. To save your text,
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72 Graphical Desktop Tab-related Shortcut keys:


Shortcut keys for working with files:
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73 Linux Shortcut keys for editing files:


Replace text in gedit :
Open the Replace tool by clicking Menu button ▸ Find and Replace… or
press Ctrl+H.
Enter the text that you wish to replace into the Find field.
Enter the new, replacement text into the Replace with field.
Once you have entered the original and replacement text, you can add
extra parameters to the sear ch. You can also choose what you want to
replace:
To replace only the next match, click Replace.
To replace all occurrences of the searched -for text, click Replace All.
Print Preview:
Prior to printing your document, you can preview how the printed
documen t will look by using Print Preview. To preview the document:
Select File ▸ Print Preview. Alternatively, you can press Shift+Ctrl+P.
Printing To Paper:
You can print your documents to paper using a local or remote printer. To
print a file:
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74 Graphical Desktop Select the desired printer from the list of printers avail able.
You can preview the file using Print Preview and once you are satisfied
with the settings, click Print to send the file to printer.
Printing To File :
You can also use gedit to print to a file. To print your document to file of a
different format:
Select File ▸ Print ▸ Print to File.
Printing is enabled for the following file formats, you may select from:
Portable Document Format (.pdf)
PostScript (.ps)
Scalable Vector Graphic (.svg)
To print the document to file, click Print
Search for text:
The Find tool can help you find specific sequences of text within in your
file.
Finding text
Open the search window by clicking Menu Button ▸ Find… or pressing
Ctrl+F. This will move your cursor to the start of the search window.
Type the text you wish to search for in the search window.
As you type, gedit will begin highlighting the portions of text that match
what you have entered.
To scroll through the search results, do any of the following:
Click on the up or down facing arrows next to the search window.
Press the up ar row or down arrow keys on your keyboard.
Press Ctrl+G or Ctrl+Shift+G.
To close the search window, press either Esc or Enter. Pressing Esc will
return the cursor to where it was before you began your search. Pressing
Enter will return the cursor to the cur rent position in the search results.
Undo a recent action:
If you make a mistake while using gedit, you can undo it by pressing
Ctrl+Z.
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75 Linux Create a new file:
The easiest way to create a new file in gedit, is to click the Create a new
document button on the left side of the toolbar, or press Ctrl+T.
Any one of these actions will create a new file in the gedit window. If you
have other files open in gedit, the new file that you create will appear as a
new tab to the right of those files.
Open a file or set o f files:
To open a file in gedit, click the Open button, or press Ctrl+O.
This will cause the Open dialog to appear. Use your mouse or keyboard to
select the file that you wish to open, and then click Open. The file that
you've selected will open in a new tab.
To close the Open dialog without opening a file, click Cancel.
Save a file:
To save a file in gedit, click on the Save button on the right side of the
toolbar or just press Ctrl+S.
If you are saving a new file, a dialog will appear, and you can selec t a
name for the file, as well as the directory where you would like the file to
be saved.
Reopen a recently -used file:
By default, gedit provides easy access to five of your most recently -used
files. Here is how you can open a recently -used file:
Click t he Open button.
gedit will display a list of the five most -recently used files.
Select the desired file, and it will open in a new tab.
Ref : https://help.gnome.org/
4.6.2 vi/vim Editor:
In the Linux family, the VI editor is the most popular and classic text
editor. Here are some of the reasons why it is such a popular editor.
1) It's included in practically every Linux distribution.
2) It is compatible with a variety of systems and distributions.
3) It is user -friendly. Hence, millions of Linux users love it and use it for
their editing needs
Nowadays, there are advanced versions of the vi editor available, and the
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76 Graphical Desktop Modes of vi editor:
They are divided into three m ain parts:
Command Mode :
Insert Mode :
Escape Mode :


1. Command Mode:
Command Mode is the first screen of VI editor. It is case sensitive. Any
character that is typed during this mode is treated as a command. These
are character are not visible on the win dow. We can cut, copy, paste or
delete a piece of text or even move through the file in this mode
[ESC] used to enter the Command Mode from another mode (Insert
Mode)
2. Insert Mode:
We can easily move from Command mode à Insert mode by pressing ‘i’ or
‘Insert’ key from the keyboard. Characters typed in this mode is treated as
input and add text to your file
Pressing ESC will take you from Insert Mode -> Command Mode
3. Escape Mode
Press [:] to move to the escape mode. This mode is used to save the files &
execution of the commands
1. Open/ Create a File:
This will create a file with the name ‘filename’ or open the file with the
name ‘filename’ if already exists.
vi Filename
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77 Linux 2. Moving out of a file:
:q Quit out of a file
:q! Quit the file without saving the c hanges
:w Save the content of the editor
:wq Save the changes and quit the editor (*Combing the commands: q &:
w)
ZZ In command mode, this works similar to wq
3. Rename a File:
:w newFileName – This will rename the file that you are currently
working into ‘ne w filename’. A command is used in Escape Mode.
4. Move within a file:
To move around in a file without actually editing the content of a file we
must be in the Command mode and keep the below commands handy.
h Moves the cursor left one character position
l Moves the cursor right one character position
k Moves the cursor one line up
j Moves the cursor one line down .


Cursor Movement Keys:
5. Inserting or Adding Text
Following is the command used to put the editor in the insert mode. Once
the ESC is pressed it w ill take the editor back to command mode.
i Insert text before the cursor
I Insert at the beginning of the current line
a Append after the cursor
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78 Graphical Desktop o Open & places the text in a new line below the current line
O Open & places the text in a new line above the current line
6. Searching the Text:
Similar to the find & replace command in windows editor we have certain
Search & replace command available in the VI editor as well.
/string Search the mentioned ‘String’ in the forw ard direction
?string Search the mentioned ‘String’ in the backward direction
n Move to the next available position of the searched string
N Move to the next available position of the searched string in the
opposite direction
Cutting & Pasting Text:
These commands allow you to copy and paste the text
yy Copy (yank, cut) the current line into the buffer
Nyy or yNy Copy ‘N’ lines along with the current line into the buffer
p Paste / Put the lines in the buffer into the text after the current line
4.1.6.3 Ema cs:
GUI text editors and coding environments and are not used to a primarily
text-based program, running commands in the editor itself, and/or using
large amounts of keyboard shortcuts.
List of shortcuts
C-h C-h : help
C-g : quit
C-x b : switch buffers
C-x right : right -cycle through buffers
C-x left : left -cycle through buffers
C-x k : kill buffer
C-x 0 : close the active window
C-x 1 : close all windows except the active window
C-x 2 : split the active window vertically into two horizontal windows
C-x 3 : split the active window horizontally into two vertical windows
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79 Linux C-x C-f : open file
C-x C-s : save file
C-x C-w : save file as
C-space : set region mark
C-w : kill region
C-k : kill region between point and end o f current line
M-w : kill region without deleting
C-y : yank region from kill ring
M-y : move to previous item in the kill ring
M-Y : move to next item in the kill ring
C-_ : undo
C-s : search forwards
C-r : search backwards
M-% : query replace (‘space’ to replace, ‘n’ to skip, ‘!’ to replace all)
M-q : wrap text
C-left : move one word left
C-right : move one word right
C-up : move one paragraph up
C-down : move one paragraph down
home : move to the beginning of the line
end : move to the end of the line
page up : move up a page
page down : move down a page
M- : move to end of buffer
Opening Emacs:
When you first open Emacs, you will see a window that looks something
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80 Graphical Desktop


4.7 MULTIMEDIA APPLICATIONS 1) Miro Media Player:
Miro is one of the best multimedia player for Internet TV for Linux
Desktop. It was developed by the Participatory Culture Foundation. It
plays almost all audio and video formats.


Features:
Remembers last played position
Supports all major video formats including MPEG, DivX, AVI,
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81 Linux Also support Bit torrent file download.
2) VLC Media Player
VLC is a popular media player in Windows and also made available for
Linux Desktop Environment like Ubuntu too. It is a free and open source
multimedia player that supports most video formats.


Features:
Remembers last played position
Supports all major video formats including MPEG, DivX, AVI,
Quicktime, WMV, FLV etc.
Also support Bit torrent file download
3) UMP layer :
UMPlayer stands for Universal Media Player as it can play all kinds of
media formats and also platform independent. The user interface is
aesthetically pleasing, simple and easy to use. It is licensed under the
GNU license and is free to download. Y ou can also watch YouTube
videos on the UMPlayer.
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82 Graphical Desktop
Features:
Search and play YouTube Videos
Supports almost 270 media formats including AC3, AVI, WMV, Mp4,
MPEG, XVID etc.,
You can also record YouTube Videos using UMPlayer
Skinnable Interface
Rememb er media position
Localization support
4) DigiKam :
DigiKam is an advanced photo editing and management software
available for all major operating systems including Linux, Windows and
Mac OS. The people behind the creation of DigiKam are real professional
photographers who saw the need to developing an application that can
enable them to view, edit and organize their pictures and also tag and
share them with other people through social media.




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83
5
COMMAND LINE
Unit Structure
5.1 Command Line
5.2 Shell
5.3 Basic Commands
5.4 General Purpose Utilities
5.5 Installing Software
5.6 User management
5.7 Environment variables
5.8 Command aliases
5.9 Summary
5.10 Unit End Questions
5.11 List o f References
5.1 COMMAND LINE Once you start a terminal it will log in Linux console, you get access to the
shell (command line interface) CLI prompt. The prompt is your gateway
to the shell. This is the place where you enter shell commands.
The default prompt symbol for the bash shell is the dollar sign ($)
indicates the normal user & # sign indicates the Root user of the Linux.
This symbol indicates that the shell is waiting for you to enter text.
However, you can change the format of the prompt used by your shell. On
my Fedora Linux system, the bash shell prompt looks like this:
rich@1[~]$
On my Fedora Linux system, it looks like this:
[rich@testbox ~]$
You can change the prompt by ps1 & ps2 command. You can configure
the prompt to provide basic information about your environmen t. The first
example above shows three pieces of information in the prompt:
 The username that started the shell Like rich.
 The current virtual console number Like @1.
 The current directory (the tilde sign (~) is shorthand for the home
directory) i.e. Absou lte path of Home.

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84 Command Line Directory:
In this example: [rich@testbox ~]$ it provides similar information, except
that it uses the hostname (Like testbox) instead of the virtual console
number.
There are two environment variables that control the format of the
command line prompt:
 PS1: Controls the format of the default command line prompt
 PS2: Controls the format of the second -tier command line prompt.
The shell uses the default PS1 prompt for initial data entry into the shell. If
you enter a command that require s additional information, the shell
displays the second -tier prompt specified by the PS2 environment
variable.
ps2 variable holds the secondary prompt symbol which is used for
commands that takes several lines to complete.
The default secondary prompt is ‘ >’
The PS1 & P2s2 variables contains primary & secondary prompt symbols
PS1 has defaults symbol value is $, you can change the prompt symbol by
assigning a new set of character to the PS1 variable.
$ PS1 = “Hello>”
Hello> new prompt
i.e. prompt will change to Hello>.
There should not be blank space before & after ‘=’ symbol. The new
prompt should be closed within (” “) double quotes.
$ psl = “”
Primary symbol prompt change to  new prompt.
You are having specific prompt codes specified for prima ry symbol.
Example 2:
$psl = “\w>”
~> cd/user/doc
/usr/doc>
~ (tilde) sign will indicate current working directory absolute path
Example 3:
$ psl = “\t\!”
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85 Linux ps2:
Ps2 is a Secondary prompt it appears when 1st prompt value of the
command is incomplete by pressing ctr +Z to exit command $ echo “This
is incomplete command (Enter)
You can change the secondary prompt
$ ps2 = ‘^’
$ ps2 will change to ‘^’
$ ps2 = “@”
$ echo”
@
@
To display the cur rent settings for your prompts, use the echo command:
rich@1[~]$ echo $PS1
It displays the current primary prompt of the system.
(Eg. \u@\l[\W]\$)
rich@1[~]$ echo $PS2
It displays the secondary prompt of the system. (Eg. >)
rich@1[~]$
The shell uses speci al characters to signify elements within the command
line prompt. Following:
List shows the special characters that you can use in the prompt string.
Bash Shell Prompt Characters: Character Description \a The bell character \d Current date in the format ‘‘Day Month Date’’ \e The ASCII escape character \h The local hostname \H The fully qualified domain hostname \j The number of jobs currently managed by the shell \l The basename of the shell’s terminal device name \n The ASCII newline character \r The ASCII carriage return \s The name of the shell ie. Shell currently active \t The current time in 24-hour HH:MM:SS format munotes.in

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86 Command Line \T The current time in 12 -hour HH:MM:SS format \@ The current time in 12-hour am/pm format \u The username of the current user \v The version of the bash shell \V The release level of the bash shell \w The current working directory \W The basename of the current working directory \! The bash shell history number of this command ie. Current history number. \# The command number of this command \$ Use a dollar ($) sign if a normal user, or a pound sign (#) if the root user \nnn The character corresponding to the octal value
nnn \\ A backslash \[ Begins a control code sequence \] Ends a control code sequence
Notice that all of the special prompt characters begin with a backslash ( \).
The prompt contained both prompt characters and a normal character. You
can create any combination of prompt characters in your prompt. To create
a new prompt, just assign a new string to the PS1 variable:
[rich@testbox ~]$ PS1="[ \t][\u]\$ "
[14:40:32][rich]$
This new shell prompt now shows the current time( \t), along with the
username( \u), along with that $ sign indicates the normal user. The new
PS1 definition only lasts for the duration of the shell session. When you
start a new shell, the default shell prompt definition is reloaded.
5.2 SHELL The GNU/Linux shell is a special interactive utility.It is a program started
after you log on to the LINUX. It provides a command line interface or
shell between user & LINUX kernel. Hence it is called as fundamental
interface to O.S “Kernel”. The core of the shell is the command prompt.
The command prompt is the interactive part of the shell.
Typed ‘cmds are interpreted by the shell & send to the ker nel which in
turns open, closes, reads or writes files. The shell runs like any other
program under the LINUX system. A shell is simply a macro processor
that executes commands that you enter at the command prompt. A Linux
shell is understood to be both a command interpreter and a programming
language. You can enter the commands at the command prompt (#) and
the shell will run them. If you have several commands that you need to
run, you can put them in a special text file called a script file and the shell
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87 Linux There are quite a few Linux shells available to use on a Linux system.
Different shells have different characteristics, some being more useful for
creating scripts and some being more useful for managing processes. The
default shell used in all Linux distributions is the bash shell. The bash
shell was developed by the GNU project as a replacement for the standard
Unix shell, called the Bourne shell (after its creator).
Linux Shells:
There are no. of shells available for linux:
1. Bash shell (Bourne again shell)
2. C shell
3. Korn shell
4. Restricted shell
5. Bourne shell
6. Tcsh shell
7. A shell
8. Z shell
9. PDKSH shell (public domain kom shell)
There are various shell available for LINUX system:
1. Bourne shell:
a. It is fastest unix command processor available & i t is available on all
the unix sys.
b. It is most widely used shell at present for UNIX sys.
c. The executable file name is ‘sh’ & it is installed as /bin/sh. It is
developed by AT&T.
2. C shell:
 This is another and processor developed by William joy it gets it’ s
name from its programming language in syntax.
 This C shell is not compatible with bourne shell.
 The C shell was developed to provide a programming interface
similar to C programming language.
 The name of executable file is esh.
3. Korn shell or ksh shell :
 It was developed by David korn. It is also a product of AT&T.
 It contains the best feature of both the above shell i.e. C shell &
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88 Command Line  The executable file name is ksh.
 This is a public domain distribution for Red Hat called pdksh.
 The korn shell language is an interactive, complete, high level
programming language that can be used to write shell scripts and
programs.
 It is useful for writing applications with the development time being
less than most other programming languages.
 Ksh is call ed command line completion that means when you are
typing a command at the command line ksh will attempt to guess what
you are typing and type it for you.
 A programming shell compatible with the Bourne shell but supporting
advanced programming features lik e associative arrays and floating -
point arithmetic
4. Restricted shell:
When you want use of O.S. to have limited access to LINUX serve to
restricted shell is used & it is typically used for guest users who are not
part of system &insurance installation wher e users must be restricted to
work only in their own limited environment. These are called rsh shells.
5. Bash shell:
Bash is known as Bourne again shell. It was written by Stephen
Bourne. It is an enhancement of Bourne shell since bourne shell is
default sh ell of Unix which is already registerd hence Linux O.S legally
can’t use bourne shell of Unix. Hence this bourne shell is newly created
with modification in bourne shell of Unix hence it is called as bourne
again shell. It is a default shell of most Linux system. The Bash shell is
executed as /bin/bash.
A simple, lightweight shell that runs in low -memory environments.
6. Tcsh:
Tcsh stands for Tom’s C shell. Also known as Tc shell. It is
enhancement of C shell. The symbolic link available for Tcsh shell on
Linux is csh. You can execute Tcsh shell by typing either csh or tcsh.
At cmd prompt. The C & Tc shell are not compatible with bourne
shell.
A shell that incorporates elements from the C programming language
into shell scripts
7. A shell:
The A shell (ash) w as developed by “Kenneth alnquist”. It is light
weight bourne shell. It is usually suitable for computers that have very
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89 Linux 8. Z shell:
The Z shell can be executed by zsh. It has best features of T esh set
shell. Also it has features of korn shell& having large no. of utilities &
extensive documentation. It is designed for interactive use with a
powerful scripting language. An advanced shell that incorporates
features from bash, tcsh, and korn, provi ding advanced programming
features, shared history files, and themed prompts.
5.3 BASIC COMMANDS File Management becomes easy if you know the right basic command
in Linux. Following commands are the basic commands in linux.


ls Lists all files and directories in the present
working directory ls – R Lists files in sub -directories as well ls – a Lists hidden files as well ls – al Lists files and directories with detailed
information like permissions, size, owner, etc. cat > filename Creates a new file cat filename Displays the file content cat file1 file2 > file3 Joins two files (file1, file2) and stores the
output in a new fi le (file3) mv file “new file
path” Moves the files to the new location mv filename
new_file_name Renames the file to a new filename sudo Allows regular users to run programs with the
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90 Command Line 5.4 GENERAL PURPOSE UTILITIES Along with controlling hardware devices, operating system needs utilities
to perform standard functions, such as controlling files and programs.
The GNU organization (GNU stands for GNU’s not UNIX) developed a
complete set of Unix utilities, but had no kernel system to run them on.
Linux is developed by t housand of programmers hence GNU public
licensed s/w provides a programming development tools, editors & work
processors. Once Linux is installed you can start creating your own
program. Hence Linux is distributed freely under GNU i.e. general public
licen se (GPL) specified by free S/W foundation hence called as freeware.
These utilities were developed under a software philosophy called open
source software (OSS). Since it is an open source S/W hence source code
for application is freely distributed along w ith application over the internet
& easy to downward, upgrade & share. The concept of OSS allows
programmers to develop software and then release it to the world with no
licensing fees attached. Anyone can use the software, modify it, or
incorporate it int o his or her own system without having to pay a license
fee.
The core GNU Utilities:
The GNU project was mainly designed for Unix system administrators to
have a Unix -like environment available. The core bundle of utilities
supplied for Linux systems is c alled the coreutils package.
The GNU coreutils package consists of three parts:
 Utilities for handling files
 Utilities for manipulating text
 Utilities for managing processes
These three main groups of utilities each contain several utility programs
that ar e invaluable to the Linux system administrator and programmer.
5.5 INSTALLING SOFTWARE Instructions how to install new software in Linux: as this point is
exceptionally challenging and called -for among former Windows users.
The most common methods are be low:
Installing RPM packages
Installing DEB packages
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91 Linux Firstly, any Linux user should be aware of such thing as software
repositories. Repository is storage for packages (both source and binary)
accessible via Inte rnet to install any required software on your computer.
You can easily select which to use or even create your own one: the list of
connected repositories is stored here by default (examples for the most
popular utilities):
– YUM: in files repo in the dire ctory /etc/yum.repos.d/;
– APT: in file /etc/apt/sources.list and in the files in the directory
/etc/apt/source.list.d/.
#1) Redhat RPM is common for Linux free software package management
tool developed by Red Hat. This method is popular because users don ’t
need to compile the code by themselves. The software is ready to be
installed and you can find a brief instruction below.
As for RPM, user needs to perform the extraction of files by already
defined options (such as destination, name etc.) which are hid den within
the responsible utilities (rpm, yum). Installing RPM packages is fairly
straight forward. To install such software package, you can run the
following command: rpm -i RPMPackage.rpm.
An alternative tool here is yum: the main difference is automat ic upgrades
and package management (including necessary dependencies). YUM is
analog for APT (DEB packages) and manage repositories. Example: yum
install RPMPackage.rpm; yum update RPMPackage.rpm; yum remove
RPMPackage.rpm.
#2) Debian packages are almost t he same as RPM but for usage in Debian
GNU/Linux systems. Obviously, the extension of such packages are *.deb.
To install such packages (whether source or binary) use APT (Advance
Packaging Tool). This is package management system for Debian and also
inclu des a lot of different tools. So, installing new software will be quite
simple as well: just run the command apt -get install DEBPackage.deb. Just
for understanding the common flow, here is an example: apt -get update
DEBPackage.deb; apt -get remove DEBPackag e.deb.
#3) Tarballs is so -called archives distributed with the following extensions
“.tar.gz”, “.tar.bz2”, or “.zip” (there are even more regarding the type of
compression and archivers). Originally tarballs are used for programs
which are not compiled, i. e. they are presented as source code. That’s why
there significant differences how to install software this way. The main
idea here: if you cannot find your program in the repositories, just
download the source code from any open source program website and then
install it according simple instruction below.
To extract data form such tarballs we should use the corresponding
commands. Some variants are below:
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92 Command Line  for files ending in .tar.b z2, run: tar -jxvf ,
 for files ending in .zip, run: unzip .
As you got the point that the program has not been prepared for
installation one should perform the preparation procedure called pre -
installation configuration. J ust run ./configure and your system will be
checked for any necessary libraries or configurations required.
To fulfill test of your system, preparation of the package and make
installation instructions for the next step apply the following command
make.
To install the program from source code after preparation phase run make
install. Though, according to Linux forums, checkinstall is strongly
recommended here due to the problem with further updates of installed
software if using make install.
5.6 USER MANAG EMENT The /etc/passwd file:
/etc/passwd: all information except the password encryption is stored in
/etc/passwd. This file contains the password once. The encryption itself is
stored in /etc/shadow. There are 7 fields area present in the file and the
fields and their description is as follows:
 username – the name with which user logs in.
 password – no longer stores the password encryption but contains an
x.
 UID- the use’s numerical identification. No 2 users should have the
same UID.
 GID- the user’s numeri cal group identification. This number is also
the third field in the /etc/group.
 Comment - user details.
 Home directory - the dir where the user ends up on logging in. the
variable HOME is set by the login program by reading this field.
 Login shell – the fi rst program executed after logging in. this is
usually the shell. Login also set the variable shell by reading this
entry, and also fork -execs the shell process.
For every line in /etc/passwd, there’s a corresponding entry in
/etc/shadow. The relevant lin e in this file could look something like this:
Oracle:sdfsdfsdfsd:12032::::::::
The password encryption is shown in the second field.
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93 Linux /dev:
Devices are also files. One can open a device, read and write to it and then
close it like any other file. The func tions for doing all this is built into the
kernel for each and every device of the system. The same device can often
be accessed with several different filenames. All device files are stored in
/dev or in its subdirectories. The device files can be grouped into mainly
depending on the first char of the permission field. It does have the
following dirs., cdrom, default floppy drive, first hard disk, printer, tape
drive and terminal.
There are two kinds of devices exist block devices and char devices. For
both these types of devices, the device file exist in the /dev dir.
$ cat /etc/passwd
root:x:0:0:root:/root:/bin/bash
bin:x:1:1:bin:/bin:/sbin/nologin
daemon:x:2:2:daemon:/sbin:/sbin/nologin
adm:x:3:4:adm:/var/adm:/sbin/nologin
lp:x:4:7:lp:/var/spool/lpd:/sbi n/nologin
sync:x:5:0:sync:/sbin:/bin/sync
shutdown:x:6:0:shutdown:/sbin:/sbin/shutdown
mail:x:8:12:mail:/var/spool/mail:/sbin/nologin
uucp:x:10:14:uucp:/var/spool/uucp:/sbin/nologin
Under standing Linux File Permissions :
The root user account is the admini strator for the Linux system and is
always assigned UID 0. The Linux system creates lots of user accounts for
various functions that aren’t actual users. These are called system
accounts . A system account is a special account that services running on
the s ystem use to gain access to resources on the system. All services that
run in background mode need to be logged in to the Linux system under a
system user account.
These services often just logged in using the root user account if an
unauthorized person b roke into one of these services, he instantly gained
access to the system as the root user. To prevent this, now just about every
service that runs in background on a Linux server has its own user account
to log in with.
You probably noticed that the /etc/passwd file contains lots more than just
the login name and UID for the user. The fields of the /etc/passwd file
contain the following information:
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94 Command Line  The password for the user.
 The numerical UID of the user account.
 The numerical group I D (GID) of the user account.
 A text description of the user account (called the comment field).
 The location of the HOME directory for the user.
 The default shell for the user.
The password field in the /etc/passwd file is set to an x. This doesn’t mean
that all of the user accounts have the same password. In the old days of
Linux, the /etc/passed file contained an encrypted version of the user’s
password. However, since lots of programs need to access the /etc/passwd
file for user information, this became somewhat of a security problem.
Now, most Linux systems hold user passwords in a separate file (called
the shadow file, located at /etc/shadow ). Only special programs (such as
the login program) are allowed access to this file.
The /etc/shadow file:
The /etc/shadow file provides more control over how the Linux system
manages passwords.
Only the root or admin user has access to the /etc/shadow file, making it
more secure than the /etc/passwd file.
The /etc/shadow file contains one record for each user acco unt on the
system. A record looks like this:
rich:$1$.FfcK0ns$f1UgiyHQ25wrB/hykCn020:11627:0:99999:7:::
There are nine fields in each /etc/shadow file record:
(1) The login name corresponding to the login name in the /etc/passwd
file.
(2) The encrypted password.
(3) The number of days since January 1, 1970 that the password was last
changed.
(4) The minimum number of days before the password can be changed.
(5) The number of days before the password must be changed.
(6) The number of days before password expiration that the user i s
warned to change the password.
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95 Linux (8) The date (stored as the number of days since January 1, 1970) since
the user account was disabled.
(9) A field reserved for future use.
Using the shadow password system, it can control how often a user must
change his or her password, and when to disable the account if the
password hasn’t been changed.
Adding a new user:
The primary tool used to add new users to your Linux system is useradd .
This co mmand provides an easy way to create a new user account and set
up the user’s HOME directory structure all at once. The useradd command
uses a combination of system default values and command line parameters
to define a user account. To see the system defa ult values used on your
Linux distribution, enter the useradd command with the -D parameter:
# /usr/sbin/useradd -D
GROUP=100
HOME=/home
INACTIVE= -1
EXPIRE=
SHELL=/bin/bash
SKEL=/etc/skel
CREATE_MAIL_SPOOL=yes
/usr/sbin directory, which may not be in your PATH environment
variable. The -D parameter shows what defaults the useradd command
uses if you don’t specify them in the command line when creating a new
user account.
This example shows the following default values:
(1) The new user will be added to a comm on group with group ID 100.
(2) The new user will have a HOME account created in the directory
/home/loginname .
(3) The account will not be disabled when the password expires.
(4) The new account will not be set to expire at a set date.
(5) The new account will use the ba sh shell as the default shell.
(6) The system will copy the contents of the /etc/skel directory to the
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96 Command Line (7) The system will create a file in the mail directory for the user account
to receive mail.
The next -to-the-last value is interesting. T he useradd command allows an
administrator to create a default HOME directory configuration, then uses
that as a template to create the new user’s HOME directory. This allows
you to place default files for the system in every new user’s HOME
directory auto matically. On my Linux system, the /etc/skel directory has
the following files:
# ls -al /etc/skel
total 48
drwxr-xr-x 2 root root 4096 2001 -11-01 00:23 .
drwxr-xr-x 107 root root 12288 2007 -09-20 16:53
..
-rw-r--r-- 1 root root 33 2007 -02-12 10:18
.bash_logout
-rw-r--r-- 1 root root 176 2007 -02-12 10:18
.bash_profile
-rw-r--r-- 1 root root 124 2007 -02-12 10:18
.bashrc
The useradd command created the new HOME directory, using the files in
the /etc/skel directory.
Useradd Parameter Description:
-c comment Add text to the new user’s comment field.
-d home_dir Specify a different name for the home directory other than the
login name.
-e expire_date Specify a date, in YYYY -MM-DD format, when the
account will expire.
-f inactive_days Specify the number of days a fter a password expires
when the account will be disabled. A value of 0 disables the account as
soon as the password expires; a value of -1 disables this feature.
-g initial_group Specify the group name or GID of the user’s login group.
-G group . . . Speci fy one or more supplementary groups the user belongs
to.
-k Copy the /etc/skel directory contents into the user’s HOME directory
(must use -m as well).
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97 Linux -M Don’t create a user’s HOME directory (used if the default settin g is to
create one).
-n Create a new group using the same name as the user’s login name.
-r Create a system account
-p passwd Specify a default password for the user account.
-s shell Specify the default login shell.
-u uid Specify a unique UID for the acc ount.
Removing a user:
If you want to remove a user from the system, the userdel command is
what you need. By default, the userdel command only removes the user
information from the /etc/passwd file.
It doesn’t remove any files the account owns on the syst em.
If you use the -r parameter, userdel will remove the user’s HOME
directory, along with the user’s mail directory. However, there may still be
other files owned by the deleted user account on the system. This can be a
problem in some environments.
Here’s an example of using the userdel command to remove an existing
user account:
# /usr/sbin/userdel -r test
# ls -al /home/test
ls: cannot access /home/test: No such file or
directory
User Account Modification Utilities:
Command Description:
Usermod Edits us er account fields, as well as specifying primary and
secondary group membership passwd Changes the password for an
existing user chpasswd Reads a file of login name and password pairs, and
updates the passwords chage Changes the password’s expiration date chfn
Changes the user account’s comment information chsh Changes the user
account’s default shell Each of these utilities provides a specific function
for changing information about user accounts.
The following sections describe each of these utilities.
usermod:
The usermod command is the most robust of the user account modification
utilities. It provides options for changing most of the fields in the
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98 Command Line parameter that corresponds to the value you want to change. The
parameters are mostly the same as the useradd parameters (such as -c to
change the comment field, -e to change the expiration date, and -g to
change the default login group). However, there are a couple of additional
parameters that might come in handy:
 -l to change the login name of the user account
 -L to lock the account so the user can’t log in
 -p to change the password for the account
 -U to unlock the account so that the user can log in
The -L parameter is especially handy. Use t his to lock an account so that a
user can’t log in without having to remove the account and the user’s data.
To return the account to normal, just use the -U parameter.
passwd and chpasswd:
A quick way to change just the password for a user is the passwd
command:
# passwd test
Changing password for user test.
New UNIX password:
Retype new UNIX password:
passwd: all authentication tokens updated successfully.
#
If you just use the passwd command by itself, it’ll change your own
password. Any user in the syst em can change their own password, but
only the root user can change someone else’s password.
The -e option is a handy way to force a user to change the password on the
next log in. This allows you to set the user’s password to a simple value,
then force th em to change it to something harder that they can remember.
If you ever need to do a mass password change for lots of users on the
system, the
chpasswd:
The chpasswd command reads a list of login name and password pairs
(separated by a colon) from the sta ndard input, and automatically encrypts
the password and sets it for the user account.

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99 Linux chsh, chfn, and chage:
The chsh, chfn, and chage utilities are specialized for specific functions.
The chsh commandallows you to quickly change the default login shell f or
a user. You must use the full pathname for the shell, and not just the shell
name:
# chsh -s /bin/csh test
Changing shell for test.
Shell changed.
#
The chfn command provides a standard method for storing information in
the comments field in the /etc/pa sswd file. Instead of just inserting random
text, such as names, nicknames, or even just leaving the comment field
blank, the chfn command uses specific information used in the Unix finger
command to store information in the comment field. The finger comma nd
allows you to easily find information about people on your Linux system:
# finger rich
Login: rich Name: Rich Blum
Directory: /home/rich Shell: /bin/bash
On since Thu Sep 20 18:03 (EDT) on pts/0 from 192.168.1.2
No mail.
No Plan.
#
If you use the chfn command with no parameters, it queries you for the
appropriate values to enter in to the comment field:
# chfn test:
Changing finger information for test.
Name []: Ima Test
Office []: Director of Technology
Office Phone []: (123)555 -1234
Home Phone []: (123 )555-9876
Finger information changed.
# finger test:
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100 Command Line Directory: /home/test Shell: /bin/csh
Office: Director of Technology Office Phone: (123)555 -1234
Home Phone: (123)555 -9876
Never logged in.
No mail.
No Plan.
#
If you now look at the entry in the /etc/passwd file, it looks like this:
# grep test /etc/passwd:
test:x:504:504:Ima Test,Director of
Technology,(123)555 -
1234,(123)555 -9876:/home/test:/bin/csh
#
All of the finger information is neatly stored away in the /etc/passwd file
entry.
Finally, the chage command helps us manage the password aging process
for user accounts.
There are several parameters to set individual values, shown in Table 6 -4.
The chage date values can be expressed using one of two methods:
 A date in YYYY -MM-DD format
 A numerical value representing the number of days since January 1,
1970
One neat feature of the chage command is that it allows you to set an
expiration date for an account. Using this feature, you can create
temporary user accounts that automatic ally expire on a set date, without
your having to remember to delete them! Expired accounts are similar to
locked accounts. The account still exists, but the user can’t log in with it.
The change Command Parameters:
Parameter Description:
 d Set the number of days since the password was last changed.
 E Set the date the password will expire.
 I Set the number of days of inactivity after the password expires to
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101 Linux  m Set the minimum number of days between password changes.
 W Set the number of day s before the password expires that a warning
message appears.
5.7 ENVIRONMENT VARIABLES The bash shell uses a feature called environment variables to store
information about the shell session and the working environment (thus the
name environment variable s).
This feature also allows you to store data in memory that can be easily
accessed by any program or script running from the shell.
There are two types of environment variables in the bash shell:
(1) Global Variables.
(2) Local Variables.
(1) Global Environment Vari ables:
Global environment variables are visible from the shell session, and any
child processes that the shell spawns. Local variables are only available in
the shell that creates them. This makes global environment variables
useful in applications that sp awn child processes that require information
from the parent process.
To display the value of an individual environment variable, use the echo
command. When referencing an environment variable, you must place a
dollar sign before the environment variable n ame:
$ echo $HOME
/home/rich
Global environment variables are also available to child processes running
under the current shell session:
$ bash
$ echo $HOME
/home/rich
(2) Local Environment Variables:
Local environment variables, as their name implies, can be seen only in
the local process in which they are defined.
Set} example

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102 Command Line 5.7.1 Setting Environment Variables:
Once you start a bash shell (or spawn a shell script), you’re allowed to
create local variables that are visible within your shell process. You can
assign either a numeric or a string value to an environment variable by
assigning the variable to a value using the equal sign:
$ test=testing
$ echo $test
testing
If you need to assign a string value that contains spaces, you’ll need to use
a single quot ation mark to delineate the beginning and the end of the
string:
$ test=testing a long string
-bash: a: command not found
$ test=’testing a long string’
$ echo $test testing a long string
Note: It’s extremely important that there are no spaces between the
environment variable name, the equal sign, and the value. If you put any
spaces in the assignment, the bash shell interprets the value as a
separate command:
$ test2 = test
-bash: test2: command not found
Once you set a local environment variable, it’s ava ilable for use anywhere
within your shell process. However, if you spawn another shell, it’s not
available in the child shell:
$ bash
$ echo $test
$ exit
exit
$ echo $test
testing a long string
$
The test environment variable is not available in the child shell (it contains
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103 Linux Similarly, if you set a local environment variable in a child process, once
you leave the child process the local environment variable is no longer
available:
$ bash
$ test=testing
$ echo $test
testing
$ exit
exit
$ echo $ test
Setting Global Environment Variables:
Global environment variables are visible from any child processes created
by the process that sets the global environment variable. The method used
to create a global environment variable is to create a local envi ronment
variable, then export it to the global environment.
This is done by using the export command:
$ echo $test
testing a long string
$ export test
$ bash
$ echo $test
testing a long string
$
After exporting the local environment variable test, I starte d a new shell
process and viewed the value of the test environment variable. This time,
the environment variable kept its value, as the export command made it
global.
5.7.2 Removing Environment Variables:
If you can create a new environment variable, it ma kes sense that you can
also remove an existing environment variable. This is done by using the
unset command:
$ echo $test
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104 Command Line $ echo $test
Note: When referencing the environment variable in the unset command,
remember not to use the dolla r sign.
If you’re in a child process and unset a global environment variable, it
only applies to the child process. The global environment variable is still
available in the parent process:
$ test=testing
$ export test
$ bash
$ echo $test
testing
$ unset t est
$ echo $test
$ exit
exit
$ echo $test
testing
$
5.7.3 Default Shell Environment Variables:
Table shows the environment variables the bash shell provides that are
compatible with the original Unix Bourne shell. Variable Description CDPATH A colon-separated list of directories used as a search path for the cd command. HOME The current user’s home directory. IFS A list of characters that separate fields used by the shell to split text strings. MAILPATH A colon-separated list of multiple filenames for the current user’s mailbox. The OPTARG The value of the last option argument processed by the getopts command. PATH A colon-separated list of directories where the shell looks for commands. PS1 The primary shell command line interface prompt string. PS2 The secondary shell command line interface prompt string. munotes.in

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105 Linux MAIL The filename for the current user’s mailbox. The bash shell checks this file For new mail. bash shell checks each file in this list for new mail. OPTIND The index value of the last option argument processed by the getopts command
5.7.4 Setting the PATH Environment Variables:
The most important environment variable in this list is the PATH
environment variable.
When you enter a command in the shell command line interface (CLI), the
shell must search the system to find the program. The PATH environment
variable defines the directories it searches looking for commands. On my
Linux system, the PATH environment variable looks like this:
$ echo $PATH
/usr/kerberos/bin:/usr/lib/ccache: /usr/local/bin:
/bin:/usr/bin:/home/rich/bin
This shows that there are six directories where the shell looks for
commands. Each directory in the PATH is separated by a colon. There’s
nothing at the end of the PATH variable indicating the end of the director y
listing.
PATH environment variable without having to rebuild it from scratch. The
individual directories listed in the PATH are separated by a colon. All you
need to do is reference the original PATH value, and add any new
directories to the string.
This looks something like this:
$ echo $PATH
/usr/kerberos/bin:/usr/lib/ccache:/usr/local/bin:
/bin:/usr/bin:/home
/rich/bin
$ PATH=$PATH:/home/rich/test
$ echo $PATH
/usr/kerberos/bin:/usr/lib/ccache:/usr/local/bin:
/bin:/usr/bin:/home
/rich/bin:/home/rich/test
$ myprog
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106 Command Line 5.7.5 Locating System Environment Variables:
The Linux system uses environment variables to identify itself in
programs and scripts. This provides a convenient way to obtain system
information for your programs. The tri ck is in how these environment
variables are set.
By default bash checks several files for commands. These files are called
startup files . The startup files bash processes depend on the method use to
start the bash shell.
There are three ways of starting a bash shell:
(1) Default login shell at login time.
(2) Interactive shell that is not the login shell.
(3) Non-interactive shell to run a script.
(1) Default Login Shell at Login Time:
Linux system, the bash shell starts as a login shell. The login shell looks
for four d ifferent startup files to process commands from. The order in
which the bash shell processes the files is:
 /etc/profile
 $HOME/.bash profile
 $HOME/.bash login
 $HOME/.profile
The /etc/profile file is the main default startup file for the bash shell.
Whenever you log in to the Linux system, bash executes the commands in
the /etc/profile startup file.
The remaining three startup files are all used for the same function to
provide a user -specific startup file for defining user -specific environment
variables.
(2) Interactive Shell that is not the Login Shell:
If you start a bash shell without logging into a system (such as if you just
type bash at a CLI prompt), you start what’s called an interactive shell.
The interactive shell doesn’t act like the login shell, but it still provides a
CLI prompt for you to enter commands.
If bash is started as an interactive shell, it doesn’t process the /etc/profile
file. Instead, it checks for the .bashrc file in the user’s HOME directory.
The .bashrc file does two things.
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107 Linux Second, it provides a place for the user to enter personal aliases and
private script functions.
The common /etc/bashrc startup file is run by everyone on the system who
starts an interactive shell s ession.
(3) Non-interactive Shell:
The last type of shell is a non -interactive shell. This is the shell that the
system starts to execute a shell script.
This is different in that there isn’t a CLI prompt to worry about. However,
there may still be specific startup commands you want to run each time
you start a script on your system.
To accommodate that situation, the bash shell provides the BASH ENV
environment variable. When the shell starts a non -interactive shell
process, it checks this environment variab le for the name of a startup file
to execute.
If one is present, the shell executes the commands in the file.
5.7.6 Variable Arrays :
Feature of environment variables is that they can be used as arrays . An
array is a variable that can hold multiple values. Va lues can be referenced
either individually or as a whole for the entire array.
To set multiple values for an environment variable, just list them in
parentheses, with each value separated by a space:
$ mytest=(one two three four five)
$ echo $mytest
one
$
Only the first value in the array appears. To reference an individual array
element, you must use a numerical index value, which represents its place
in the array. The numeric value is enclosed in square brackets:
$ echo ${mytest[2]} three
Note: Environmen t variable arrays start with an index value of zero.
To display an entire array variable use the asterisk wildcard character as
the index value:
$ echo ${mytest[*]}
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108 Command Line Change the value of an individual index position:
$ mytest[2]=sev en
$ echo ${mytest[*]}
one two seven four five
$
use the unset command to remove an individual value within the array
$ unset mytest[2]
$ echo ${mytest[*]}
one two four five
$
$ echo ${mytest[2]}
$ echo ${mytest[3]}
four
This example uses the unset command to remove the value at index value
2. When you display the array, it appears that the other index values just
dropped down one. However, if you specifically display the data at index
value 2, you’ll see that that location is empty.
Remove the entire array just by using the array name in the unset
command:
$ unset mytest
$ echo ${mytest[*]}
5.8 USING COMMAND ALIASES A command alias allows you to create an alias name for common
commands (along with their parameters) to help keep your typing to a
minimum.
To see a list of the active aliases, use the alias command with the -p
parameter:
$ alias -p
alias l.=’ls -d .* --color=tty’
alias ll=’ls -l --color=tty’
alias ls=’ls --color=tty’
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109 Linux alias which=’alias | /usr/bin/which --tty-only --
readalias --
show-dot --show-tilde’
use an alias to override the standard ls command. It automatically provides
the --color parameter, indicating that the terminal supports color mode
listings.
Using the alias command:
[rich@testbox ~]$ alias li=’ls -il’
[rich@testbox ~] $ li
total 989292
360621 drwxrwxr -x 2 rich rich 4096 2007 -08-24
22:04 4rich
301871 drwxr -xr-x 4 rich rich 4096 2007 -09-18
08:38 Desktop
301875 drwxr -xr-x 2 rich rich 4096 2001 -11-01
01:10 Documents
301872 drwxr -xr-x 2 rich rich 4096 2001 -11-01
04:06 Downlo ad
Once you define an alias value, you can use it at any time in your shell,
including in shell scripts.
Command aliases act like local environment variables. They’re only valid
for the shell process in which they’re defined:
$ alias li=’ls -il’
$ bash
$ li
bash: li: command not found
5.9 SUMMARY This chapter consist of different types of shell in command line, How to
install rpm packages with the help of yum, different files when we create a
user, command with options, how to change password of the user us ing
passwd , different types of environment variables.
5.10 UNIT END QUESTIONS 1. Write a short note on following
Bash shell (Bourne again shell) munotes.in

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110 Command Line C shell
Korn shell
Restricted shell
Bourne shell
Tcsh shell
A shell
Z shell
2. How many GNU coreutils packag e are available? Explain any one of
them.
3. Differentiate rpm and yum.
4. Write the contain of /etc/passwd file.
5. Describe /etc/shadow file
6. Describe useradd Parameter
7. How to change password of the particular user.
8. Explain types of environment variables in the b ash shell.
9. Explain how to setup and removing Environment Variables.
10. Describe default Shell Environment Variables.
11. How COMMAND ALIASES used in command line
5.11 LIST OF REFERENCES 1) Unix Concepts and Applications by Sumitabha Das.
2) Official Ubuntu Book, 8t h Edition, by Matthew Helmke & Elizabeth K.
Joseph with Jose Antonio Rey and Philips Ballew, Prentice Hall



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111
6
LINUX DOCUMENTATION
Unit Structure
6.0 Objectives
6.1 Linux Documentation
6.2 Man pages, GNU info,
6.3 Help command,
6.4 More documentation sources
6.5 File Operations
6.6 Filesystem
6.7 Filesystem architecture
6.8 File types
6.9 File attributes
6.10 Working with files
6.11 Backup, compression
6.12 Summary
6.13 Unit End Questions
6.0 OBJECTIVES In this chapter In this chapter you will learn about:
 Linux Documentation m an pages, GNU info help command
 More documentation sources, File Operations , Filesystem, Filesystem
 Architecture, File types, File attributes, Working with
 Files, Backup and compression
6.1 LINUX DOCUMENTATION if you are new to LINUX operating system and having trouble dealing
with the command -line utilities provided by LINUX then you really need
to know first of all about the help command which as its name says help
you to learn about any built -in command.
help command as told before just displays information about shell built -in
commands. Here’s the syntax for it:
// syntax for help command
$help [ -dms] [pattern ...]
The pattern specified in the syntax above refers to the command about
which you would like to know and if it is matched with any shell built -in
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112 Linux Documentation then help prints the list of help topics for your convenience. And the d, m
and s here are options that you can use with the help command.
$help help
help: help [ -dms] [pattern...]
Display information about builtin commands.
Displays brief summaries of builtin commands. If PATTERN IS
specified, gives detailed help on all commands matching PATTERN,
otherwise the list of help topics is printed.
Options:
-d output short description for each topic
-m display usage i n pseudo -manpage format
-s output only a short usage synopsis for each topic matching
6.2 MAN PAGES, GNU INFO GNU Info accepts several options to control the initial node being viewed,
and to specify which directories to search for Info fi les. Here is a template
showing an invocation of GNU Info from the shell:
info [option]... [menu -item...]
The program accepts the following options:
--apropos=string
Specify a string to search in every index of every Info file installed on
your system . Info looks up the named string in all the indices it can find,
prints the results to standard output, and then exits. If you are not sure
which Info file explains certain issues, this option is your friend. Note that
if your system has a lot of Info file s installed, searching all of them might
take some time.
6.3 HELP COMMAND $help help
help: help [ -dms] [pattern...]
Display information about builtin commands.
Options for help command
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113 Linux option : It is used when you just want to get an overview abo ut any shell
built-in command i.e it only gives short description.
-m option : It displays usage in pseudo -manpage format.
-s option : It just displays only a short usage synopsis for each topic
matching.
6.4 MORE DOCUMENTATION SOURCES The commercial L inux distributions -for example, Red Hat, SuSE,
Mandrake, Xandros, and Linspire -supply excellent user manuals. Every
major Linux distribution provides a feast of online resources. Search
engines, user mailing lists, Usenet, and all sorts of Linux web sites also
supply a wealth of help and information.
6.5 FILE OPERATIONS The most basic feature of the shell is the ability to see what files are
available on the system. The list command (ls) is the tool that helps do
that.
Basic listing:
The ls command at its most basic form displays the files and directories
located in your current directory:
$ ls
4rich Desktop Download Music Pictures store store.zip test backup
Documents Drivers myprog Public store.sql Templates Videos.
$
Notice that the ls command produces the listing in alphabetical order (in
columns rather than rows). If you’re using a terminal emulator that
supports color, the ls command may also show different types of entries in
different colors. The LS COLORS environment variable controls this
feature. Different Linux distributions set this environment variable
depending on the capabilities of the terminal emulator.
If you don’t have a color terminal emulator, you can use the -F parameter
with the ls command to easily distinguish files from directories. Using the
-F parameter produces the following output:
$ ls -F
4rich/ Documents/ Music/ Public/ store.zip Videos/
backup.zip Download/ myprog* store/ Templates/
Desktop/ Drivers/ Pictures/ store.sql test
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114 Linux Documentation The -F parameter now flags the directories with a forward slash, to help
identify them in the listing. Similarly, it flags executable files with an
asterisk, to help you find the files that can be run on the system easier.
The basic ls command can be somewhat misleading. It shows the files and
directories contained in the current directory, but not necessarily all of
them. Linux often uses hidden files to store configuration information. In
Linux, hidden files are files with filenames that start with a period.
These files don’t appear in the default ls lis ting (thus they are called
hidden).
To display hidden files along with normal files and directories, use the -a
parameter.
Displaying File Information with different ls options:
(1) $ ls : This ls command is shortened form of list &
lists the file in yo ur directory. It works as’ dir’
command in Dos. (2) $ ls – l : This command will give listing of files in long
format with all permission i.e. reading, writing,
& executing with users & group info of life. (3) $ ls–al : This command will give listing of file with all
info along with all hidden files in long format. (4) $ ls -c : Sort by time of last modification. (5) $ ls -d : Directory List directory entries instead of contents, and don’t dereference symbolic links. (6) $ ls -F : Classify Append file-type indicator to entries. (7) $ ls -g : List full file information except for the file’s owner. (8) $ ls -G : No-group In long listing don’t display group names. (9) $ ls -n : Numeric-uid-gid Show numeric userid and groupid instead of names. (10) $ ls -o : In long listing don’t display owner names. (11) $ ls -r : Reverse Reverse the sorting order when displaying files and directories. (12) $ ls -u : Display file last access time instead of last modification time. (13) $ ls -v : sort=version Sort the output by file version. (14) $ ls – m : It lists all the files separated by commas. (15) $ ls – Y : It sorts the file name in columns horizontally. (16) $ ls – A : It lists all the files & directories without two directories 1). 2) .. (17) $ ls – C : It sorts the file in column vertically. (18) $ ls – F : It identifies directories links & executable files. (19) $ ls – s : It sorts file by size. (20) $ ls – color : It use color for identification. munotes.in

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115 Linux There are different wildcard characters an d Regular Expression
supported by ls command.
The ls command recognizes standard wildcard characters and uses them to
match patterns within the filter:
 A question mark (?) to represent one character.
 An asterisk (*) to represent zero or more characters.
The question mark can be used to replace exactly one character anywhere
in the filter string.
For example:
$ ls -l mypro?
-rw-rw-r-- 1 rich rich 0 2007 -09-03 16:38 myprob
-rwxr --r-- 1 rich rich 30 2007 -08-23 21:42 myprog
$
The filter mypro? matched two file s in the directory. Similarly, the
asterisk can be used to match
zero or more characters:
$ ls -l myprob*
-rw-rw-r-- 1 rich rich 0 2007 -09-03 16:38 myprob
-rw-rw-r-- 1 rich rich 0 2007 -09-03 16:40 myproblem
$
The asterisk matches zero characters in the myp rob file, but it matches
three characters in the myproblem file.
This is a powerful feature to use when searching for files when you’re not
quite sure of the filenames.
Ls supports the regular expressions Like the range of characters is
specified by [ ].
Following are some of examples of using Wild card chracters & Regular
expressions: 1. $ ls doc *: This command will give listing of files starting with Doc. 2. $ ls * day: This command gives listing of all files ending with day. 3. $ ls * .c: Listing of all files having extension ‘.c’ 4. $ ls doc ?: This command gives listing of all files having munotes.in

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116 Linux Documentation starting 3 characters as doc & followed by one single unknown character. 5. $ ls *.[co] : It displays the files having extension either c or o main.c arg.c main.o 6. $ ls doc[1A]: You can specify a set of characters as a range, rather than listing them one by one. The filename begining with doc followed by 1 or A. 7. $ ls doc[1-3]: It displays the files begin with pattern doc & ending in character 1 through 3.
Output of ls –l is as shown below:
$ $ ls –l File type File permission No.
of
links Owner
group Other Size in byte Date & time last modified file name – rwxrwxrwx 2 ABC
other “ 660 4096 2007-08-24 15:34 abc.doc d wxrwxrwx 3 XYZ
ABC “ 1250 “ d wxrwxrwx 1 ABC
other “ 950 “ xyz
The file type (such as directory (d), Ordinary file ( -), character device (c),
or block device (b)
The permissions for the file:
(1) Read  With this permission user can read the data or file, user can
not write into it.
(2) Write  With this permission user can write the data or file.
(3) Execute  With this permission user can execute the application.
The number of hard links to the file (Links of the file in same directory)
The username of the owner of the file.
The group name of the g roup the file belongs to.
The size of the file in bytes.
The time the file was modified last.
The file or directory namePart I.
The Linsux is divided into 3 groups owner, group and others.

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117 Linux 1) Owner:
It is the user who creates a particulars file called as own er of that file. The
owner is a person who has all rights on the files created by him and also
decides the rights of other user associated to that file. The owner group is
abbrivated as ‘u’
2) Group:
In a typical software development one large project is div ided among
different members of a team. So software developers requires that file
belonging their project should not accessible to other users hence they will
apply right to group users. It is abbreviated as ‘g’
3) Others:
All the users that are neither owne r nor engaged to with a group is called
as other normally guest user Abbrivated d as ‘o’.
The Linux Command Line:
The -R parameter is another command ls parameter to use. It shows files
that are contained within directories in the current directory. If mor e
number of directories are available then this can be quite a long listing.
Here’s a simple example of what the -R parameter produces:
$ ls -F -R
.:
file1 test1/ test2/
./test1:
myprog1* myprog2*
./test2:
GURE 3 -3
Notice that first, the -R parameter shows the contents of the current
directory, which is a file (file1) and two directories (test1 and test2).
Following that, it traverses each of the two directories, showing if any files
are contained within each directory. The test1 directory shows two files
(myprog1 and myprog2), while the test2 directory doesn’t contain any
files. If there had been further subdirectories within the test1 or test2
directories, the -R parameter would have continued to traverse those as
well. As you can see, for large directory structures this can become quite a
large output listing.
The complete parameter list
The ls command uses two types of command line parameters:
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118 Linux Documentation The single -letter parameters are always preceded by a sing le dash. Full -
word parameters are more descriptive and are preceded by a double dash.
Many parameters have both a single -letter and full -word version, while
some have only one type. These are some of parameters that are used with
ls command. Single Letter Full Word Description O In long listing don’t display owner names. R Reverse the sorting order when displaying files and directories. R Recursive List subdirectory contents recursively. S Size Print the block size of each file. S sort=size Sort the ou tput by file size. T sort=time Sort the output by file modification time. U Display file last access time instead of last
modification time. U sort=none Don’t sort the output listing. V sort=version Sort the output by file version. X List entries by l ine instead of columns. X sort=extension Sort the output by file extension
You can use more than one parameter at a time if you want to. A common
combination to use is the -a parameter to list all files, the -i parameter to
list the inode for each file, the -l parameter to produce a long listing, and
the -s parameter to list the block size of the files. The inode of a file or
directory is a unique identification number the kernel assigns to each
object in the filesystem. Combining all of these parameters creates the
easy-to-remember -sail parameter:
$ ls -sail
total 2360
301860 8 drwx ------ 36 rich rich 4096 2007 -09-03 15:12 .
65473 8 drwxr -xr-x 6 root root 4096 2007 -07-29 14:20 ..
360621 8 drwxrwxr -x 2 rich rich 4096 2007 -08-24 22:04 4rich
301862 8 -rw-r--r-- 1 rich rich 124 2007 -02-12 10:18 .bashrc
361443 8 drwxrwxr -x 4 rich rich 4096 2007 -07-26 20:31 .ccache
301879 8 drwxr -xr-x 3 rich rich 4096 2007 -07-26 18:25 .config
301871 8 drwxr -xr-x 3 rich rich 4096 2007 -08-31 22:24 Desktop
301870 8 -rw------- 1 rich rich 26 2001 -11-01 04:06 .dmrc
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119 Linux 360207 8 drwxrwxr -x 2 rich rich 4096 2007 -07-26 18:25 Drivers
301882 8 drwx ------ 5 rich rich 4096 2007 -09-02 23:40 .gconf
301883 8 drwx ------ 2 rich rich 409 6 2007 -09-02 23:43 .gconfd
360338 8 drwx ------ 3 rich rich 4096 2007 -08-06 23:06 .gftp
File Handling :
The bash shell provides lots of commands for manipulating files on the
Linux filesystem. This section walks you through the basic commands you
will nee d to work with files from the CLI (command level interface) for
all your file -handling needs.
 File:
(1) The file is container for storing information.
(2) A file’s size is not stored in the file, nor even it’s name. All file
attributes are kept in a separate area of the hard disk, not directly to
humans, but only to the kernel.
(3) UNIX treats directories and devices as file as well. A directory is
simply a folder where you store filenames and other directories. All
physical devices like the hard disk, memory, CD -ROM, printer and
modem are treated as files.
 Creating files:
(1) Using cat to create a file:
 Cat is also useful for creating a file.
 Enter the command cat, followed by the > (the right chevron)
character and the filename(for e.g. kiran):
$ cat > kiran
A > symbol f ollowing the command means that the output goes to the
filename following it. Cat used in this way represents a rudimentary
editor.
[Ctrl -d]
$ _ prompt returns
 $ cat >file1:
This command is used to create a new file known as file1.
To save this file ctrl +d option is used, ctrl+d indicate end of file mark ie
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120 Linux Documentation This command defines that redirect the contents from standard output ie.
Console to the newly created file named as file1.
 When the command line is terminated with [Enter], the prompt
vanishes. cat now waits to take input from the user. Enter the three
lines, each followed by [Enter]. Finally press [Ctrl+d] to signify the
end of input to the system. This is the eof character used by UNIX
systems and i s shown in the sty output.
 When this character is entered, the system understand that no further
text input will be made.
 The file is written and the prompt returned.
 cat is a versatile command. It can be used to create, display,
concatenate and append to files.
 $ cat kiran >> new:
This command is used to redirect the contents of file kiran to the
standard output and redirect these contents for appending (adding)
into file new. ie. kiran contents will be appended into the new. if new
is not created first t hen it will create the file new and redirect the
contents of kiran to new and if it is already created then it will append
the contents of kiran to new.
 $ cat < chirag >newfile:
This command is used to redirect the contents of file chirag to the
standard o utput and redirect these contents to the file newfile. ie.
chirag contents will be redirected ( overwritten ) to the newfile.
(2) Using touch command to create a file:
Every once in a while you will run into a situation where you need to
create an empty file. Sometimes applications expect a log file to be
present before they can write to it. In these situations, you can use the
touch command to easily create an empty file:
$ touch test1
$ ls -il test1
1954793 -rw-r--r-- 1 rich rich 0 Sep 1 09:35 test1
$
The Li nux Command Line:
The touch command creates the new file you specify, and assigns your
username as the file owner. Since I used the -il parameters for the ls
command, the first entry in the listing shows the inode number assigned to
the file. Every file on the Linux system has a unique inode number.
Notice that the file size is zero, since the touch command just created an
empty file. The touch command can also be used to change the access and
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121 Linux $ touch test1
$ ls -l test1
-rw-r--r-- 1 rich rich 0 Sep 1 09:37 test1
$
The modification time of test1 is now updated from the original time. If
you want to change only the access time, use the -a parameter. To change
only the modification time , use the –m parameter. By default touch uses
the current time. You can specify the time by using the –t parameter with a
specific timestamp:
$ touch -t 200812251200 test1
$ ls -l test1
-rw-r--r-- 1 rich rich 0 Dec 25 2008 test1
$
Now the modification time for the file is set to a date significantly in the
future from the current time.
Copying files:
Copying files and directories from one location in the filesystem to
another is a common practice for system administrators. The cp command
provides this featu re.
In it’s most basic form, the cp command uses two parameters: the source
object and the destination object:
cp source destination
When both the source and destination parameters are filenames, the cp
command copies the source file to a new file with the filename specified
as the destination. The new file acts like a brand new file, with an updated
file creation and last modified times:
$ cp kiran newfile
$ ls -il
total 0
1954793 -rw-r--r-- 1 rich rich 0 Dec 25 2008 kiran
1954794 -rw-r--r-- 1 rich rich 0 Sep 1 09:39 newfile
$
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122 Linux Documentation You’ll also notice that the modification time for the newfile file shows the
time that it was created.
cp: Copying a file:
(1) The cp (copy) command copies a file or a group of files. It creates an
exact image of the file on disk with a different name
(2) The syntax requires at least two filenames to be specified in the
command line.
(3) When both are ordinary files, the first id copied to the second:
cp chap01 unit1
(4) If the destination file(unit1)doesn’t exist, it will first be created
before copying takes place.
(5) If not, it will simply be overwritten without any warning from the
system.
(6) If there is only one file to be copied, the destination can be eit her an
ordinary or directory.
(7) You then have the option of choosing your destination filename.
(8) The following example shows two ways of copying a file to the
progs directory:
cp chap01 progs/unit1
chap01 copied to unit1 under progs
(9) cp is often used wi th the shorthand notation, . (dot), to signify the
current directory as the destination.
(10) For instance, to copy the file .profile from /home/chirag to your
current directory, you can use either of the two commands:
cp /home/chirag/.profile.profile Destinat ion is a file
cp/home/chirag/.profile. Destination is the current directory
(11) cp can also be used to copy more than one file with a single
invocation of the command.
In that case, the last filename must be a directory:
 You have already seen how the UNIX system uses the * to frame a
pattern for matching more than one filename.
 If there were only three filenames in the current directory having the
common string chap, you can compress the above sequence using the
* as a suffix to chap:
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123 Linux cp Options:
(a) Interactive copying ( -i) the –i(interactive) option warns the user
before overwriting the destination file. If unit1 exists, cp prompts for
a response:
$ cp –i chap01 unit1
(b) cp: overwrite unit1 (yes/no)? y
A y at t his prompt overwrites the file, any other responses leaves it
uncopied.
Copying directory structures ( -R) Many UNIX commands are capable of
recursive behavior. This means that the command can descend a directory
and examine all files in its subdirectories . The cp –R command behaves
recurvely to copy an entire directory structure.
cp –R progs newprogs newprogs must not exist
(3) Basic bash Shell Commands 3:
If the destination file already exists, the cp command will prompt you to
answer whether or not you want to overwrite it:
$ cp test1 test2
cp: overwrite `test2’? y
$
If you don’t answer y, the file copy will not proceed. You can also copy a
file to an existing directory:
$ cp test1 dir1
$ ls -il dir1
total 0
1954887 -rw-r--r-- 1 rich rich 0 Sep 6 09:42 test1
$
The new file is now under the dir1 directory, using the same filename as
the original. These examples all used relative pathnames, but you can just
as easily use the absolute pathname for both the source and destination
objects.
To copy a file to the cur rent directory you’re in, you can use the dot
symbol:
$ cp /home/rich/dir1/test1 .
cp: overwrite `./test1’?
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124 Linux Documentation $ cp -p test1 test3
$ ls -il
total 4
1954886 drwxr -xr-x 2 rich rich 4096 Sep 1 09:42 dir1/
1954793 -rw-r--r-- 1 rich rich 0 Dec 25 2008 test1
1954794 -rw-r--r-- 1 rich rich 0 Sep 1 09:39 test2
1954888 -rw-r--r-- 1 rich rich 0 Dec 25 2008 test3
$
Now, even though the test3 file is a complete ly new file, it has the same
timestamps as the original test1 file.
The-R parameter is extremely powerful. It allows you to recursively copy
the contents of an entire directory in one command:
$ cp -R dir1 dir2
$ ls -l
total 8
The Linux Command Line:
drwxr -xr-x 2 rich rich 4096 Sep 6 09:42 dir1/
drwxr -xr-x 2 rich rich 4096 Sep 6 09:45 dir2/
-rw-r--r-- 1 rich rich 0 Dec 25 2008 test1
-rw-r--r-- 1 rich rich 0 Sep 6 09:39 test2
-rw-r--r-- 1 rich rich 0 Dec 25 2008 test3
$
Now dir2 is a complete copy of dir1. Y ou can also use wildcard characters
in your cp commands:
$ cp -f test* dir2
$ ls -al dir2
total 12
drwxr -xr-x 2 rich rich 4096 Sep 6 10:55 ./
drwxr -xr-x 4 rich rich 4096 Sep 6 10:46 ../
-rw-r--r-- 1 rich rich 0 Dec 25 2008 test1
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125 Linux -rw-r--r-- 1 rich rich 0 Dec 25 2008 test3
$
TABLE 3 -6
The cp Command Parameters:
Parameter Description:
-a Archive files by preserving their attributes.
-b Create a backup of each existing destination file instead of
overwriting it.
-d Preserve
-f Force the overwriting of existing destination files without prompting.
-i Prompt before overwriting destination files.
-l Create a file link instead of copying the files.
-p Preserve file attributes if possible.
-r Copy files recursively.
-R Copy directories recursively.
-s Create a symbolic link instead of copying the file.
-S Override the backup feature.
-u Copy the source file only if it has a newer date and time than the
destination (update).
-v Verbose mode, explaining what’s happening.
-x Restrict the copy to the current filestytem.
Some Examples of cp command:
E.g. $ cp kiran /home/root/mydoc/kiran
copies Kiran file from current directory into specified path
E.g. $ cp file* /tmp
(copies multiple files to /tmp directory)
E.g. $ cp –i file1 fil e2
(copies file while copying it will prompt for coping)
cp : overwrite ‘file2’ ? y
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126 Linux Documentation (copies file while copying it will prompt for coping and creates the backup
file)
cp: overwrite ‘file2’ ? y
$ ls file*
file2 file2~
~ This sign shows the backup file of file2.
(4) Linking files:
If you need to maintain two (or more) copies of the same file on the
system, instead of having separate physical copies, you can use one
physical copy and multiple virtual copies, called links. A link is a
placeholder in a directory that points to the real location of the file.
ln: This command is used to link a file
Links  In linux you can use links to give the same file with two entirely
different names or to pretend that the file is in one locatio n in the file
system and in actual stored in an entirely different location.
Linking is useful when you have two different programs that look for the
same file in different places. So you need to make sure that the file is in
both locations.
There are two types of links:
(1) Hard Link.
(2) Soft Link.
(1) Hard Link:
A hard link is just another name for an existing file. The two files share
the same inode, so in reality they are same file.
This is different from a copy, where there are two separate files with
separate i nodes, taking up different blocks on the hard disk. The hard link
is to be performed in the same directory in which you are currently logged
in.
The inode is a special file that tells the kernel which blocks on the hard
disk holds the file because the har d link to a file is actually the same as the
original (target) file, you can’t tell which is the original file and which is
the hard link.
You can create Hard Link by the given command:
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127 Linux $ ln originalfile linkfile:
The link file should not be created first.
$ ln old new:
To check whether a link file is created properly or not
$ ls –I old new
old
new
since first field displays the inode number and second field display the
name of the file. I f the inode number of both the file is same then it is sure
that both files are linked.
it will create a file new which is link file of the original file old.
$ ln today tom1
$ ln today tom2
$ ls –l today tom1 file type file permissions no. of links owner group other size file name – rwx rwx rwx 2 ABC xyz “ 660 today – rwx rwx rwx 2 2 ABC xyz “ 660 tom1
Long listing format shows the number of links for the file today and tom1
as 2.
You can only create a hard link between files on the same physical
medium. You can’t create a hard link between files under separate
mount points. In that case, you’ll have to use a soft link.
Symbol Link:
A symbol link is different from a hard link in that it is special file type that
contains the name of the original fil e some what link a shortcut in
windows.
Symbolic link is also called as symlink.
A symbolic link file is created that contains a pointer to the original, target
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128 Linux Documentation $ ln –s original lnfile
$ ln –s abc.doc /kk/xy.doc
It will crea te symbolic link of abc.doc in the specified directory to a file
xy.doc. In this xy.doc should be created first. The linking can identified by
red blinking on the path of abc.doc when ls –l ie. long lisitng is to be
shown. The symbolic link is identified by file type field of ls –l option
which is indicated by l (l in lower case).
The inode number of symbolic link files are not same.
Symbol Link to a directory 
You can create a symbolic link to current directory to specified directory.
$ ln –s /home/chris/l etter gifts
$ cd gifts
$ pwd
/home/chris/letter
If you want to display the name of symbolic link cwd variable is used.
cwd is a special system variable names of directory which is symbolic
link.
$ pwd
/home/chris/letter
$ cwd
/home/chris/gifts
Difference between Hard Link and Symbolic Link: Symbolic Link Hard Link It contains/hold the pathname of the file to which it is linking. In hard link the linking is not possible in other directory the linking is performed in current root path only It can be created by ln with –s option. It is created directly by ln command. Symbolic link can be created from one directory to other directory. Hard links can not be created from one file system to other file system in other directory. Command is $ ln – s abc /home/xyz/veg Command is $ ln abc xyz The symbolic link is identified by l in file type field of long listing format. The Hard link is identified by number of links option in ls –l option. In symbolic link the inode In Hard link the inode number munotes.in

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129 Linux number of original file and linked file is not same. of original file and linked file is same. You can see the inode number by a command ls –i original linkfile
Renaming files:
In the Linux world, renaming files is called moving. The mv command is
available to move bot h files and directories to another location:
$ mv test2 test6
$ ls -il test*
1954793 -rw-r--r-- 2 rich rich 6 Sep 1 09:51 test1
1954888 -rw-r--r-- 1 rich rich 0 Dec 25 2008 test3
1954793 -rw-r--r-- 2 rich rich 6 Sep 1 09:51 test4
1954891 lrwxrwxrwx 1 rich rich 5 Sep 1 09:56 test5 -> test1
1954794 -rw-r--r-- 1 rich rich 0 Sep 1 09:39 test6
$
Notice that moving the file changed the filename but kept the same inode
number and the timestamp value. Moving a file with soft links is a
problem:
$ mv test1 test8
$ ls -il test*
total 16
1954888 -rw-r--r-- 1 rich rich 0 Dec 25 2008 test3
1954793 -rw-r--r-- 2 rich rich 6 Sep 1 09:51 test4
1954891 lrwxrwxrwx 1 rich rich 5 Sep 1 09:56 test5 -> test1
1954794 -rw-r--r-- 1 rich rich 0 Sep 1 09:39 test6
1954793 -rw-r--r-- 2 rich rich 6 Sep 1 09:51 test8
[rich@test2 clsc]$ mv test8 test1
The test4 file that uses a hard link still uses the same inode number, which
is perfectly fine.
However, the test5 file now points to an invalid file, and it is no longer a
valid link.
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130 Linux Documentation $ mv dir2 dir4
 The mv command renames (moves) files. It has two distinct
functions:
 It renames a file (or directory).
 It moves a group of files to a different directory.
 If the destination doesn’t exist, it will be created. For the above
example, mv simply replaces the filename in the existing directory
entry with the new name.
 Like cp, a group of files can be moved to a directory. The following
command moves three files to the progs directory:
mv chap01 chap02 c hap03 progs
 There’s a –i option available with mv also, and behaves exactly like in
cp.
Deleting files:
rm: Deleting Files
In Linux if you want to delete existing files. Whether it’s to clean up a
filesystem or to remove a software package, there’s always opportunities
to delete files.
Deleting is called removing. The command to remove files in the bash
shell is rm.
(1) The rm(remove ) command deletes one or more files.
(2) The following command deletes three files:
rm chap01 chap02 chap03
rm chap* could be dange rous to use!
(3) A file once deleted can’t be recovered. rm won’t normally remove a
directory, but it can remove files from one.
(4) You may sometimes need to delete all files in a directory as part of a
cleanup operation
The *, when used by itself, represents all files, you can then use rm like
this:
$ rm * All file gone!
$ _
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131 Linux
rm options:
 Interactive deletion ( -i): Like in cp, the –i(interactive) option makes
the command ask the user for confirmation before removing each file:
$ rm –i chap01 chap02 chap03
rm: remov e chap01 (yes/no)? ?y
rm: remove chap02 (yes/no)? ?n
rm: remove chap03 (yes/no)? [enter]
No response – file is not deleted.
A y removes the file, any other response leaves the file undeleted.
 Recursive deletion ( -r or -R): With the –r (or -R) option, rm
performs a tree walk – a thorough recursive search for all
subdirectories and files within these subdirectories. At each stage, it
deletes everything it finds. rm won’t normally remove directories, but
when used with this option, it will. Therefore, when you issue the
command
rm -r * Behaves partially like rmdir
 Forcing removal ( -f) rm prompts for removal if a file is write -
protected: The –f option overrides this minor protection and forces
removal. When you combine with the –r option, it could be the most
risky thing to do:
rm -rf * Deletes everything in the current directory and below
The basic form of the rm command is pretty simple:
$ rm -i test2
rm: remove `test2’? y
$ ls -l
total 16
drwxr -xr-x 2 rich rich 4096 Sep 1 09:42 dir1/
drwxr -xr-x 2 rich rich 409 6 Sep 1 09:45 dir2/
-rw-r--r-- 2 rich rich 6 Sep 1 09:51 test1
-rw-r--r-- 1 rich rich 0 Dec 25 2008 test3
-rw-r--r-- 2 rich rich 6 Sep 1 09:51 test4
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132 Linux Documentation $
Notice that the command prompts you to make sure that you’re serious
about removing the file.
Once you remove a file it’s gone forever. Now, here’s an interesting tidbit
about deleting a file that has links to it:
$ rm test1
$ ls -l
total 12
drwxr -xr-x 2 rich rich 4096 Sep 1 09:42 dir1/
drwxr -xr-x 2 rich ric h 4096 Sep 1 09:45 dir2/
-rw-r--r-- 1 rich rich 0 Dec 25 2008 test3
-rw-r--r-- 1 rich rich 6 Sep 1 09:51 test4
lrwxrwxrwx 1 rich rich 5 Sep 1 09:56 test5 -> test1
$ cat test4
hello
$ cat test5
cat: test5: No such file or directory
$
I removed the test1 fil e, which had both a hard link with the test4 file and
a soft link with the test5 file. Noticed what happened. Both of the linked
files still appear, even though the test1 file is now gone (although on my
color terminal the test5 filename now appears in red ). When I look at the
contents of the test4 file that was a hard link, it still shows the contents of
the file.
When I look at the contents of the test5 file that was a soft link, bash
indicates that it doesn’t exist any more.
Directory Handling :
 Creat ing Directories:
(1) mkdir command is used to create a new directory.
Syntax is mkdir

.
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133 Linux Example: mkdir Kiran
Kiran directory is created in the current root path.
(2) Directories and subdirectories are created with the mkdir (make
directory) command.
(3) You can create a number of subdirectories with one mkdir command:
mkdir kiran chirag abc
(4) The system creates a new directory and assigns it a new inode
number.
(5) The following command create s a directory tree:
mkdir college college/kiran college/chirag
Creates the directory tree:
This creates three subdirectories –college and two subdirectories under
college. The order of specifying the arguments is important; you obviously
can’t create a sub directory before creation of it’s parent directory for
instance, you can’t enter
$mkdir college/chirag college/kiran college
mkdir: failed to make directory “college/chirag”; No such file or directory
mkdir: failed to make directory “college/kiran”; No suc h file or directory
Note that even though the system failed to create the two subdirectories,
kiran and chirag, it has still created the college directory.
(6) Sometimes, the system refuses to create a directory:
$ mkdir malcalm
mkdir: failed to make directory “malcalm”; Permission denied
This can happen due to these reasons:
The directory malcalm may already exist.
There may be an ordinary file by that name in the current directory.
The permissions set for the current directory don’t permit the creation of
files and directories by the users.
Deleting Directories:
The basic command for removing a directory is rmdir:
Syntax : rmdir

$ rmdir Kiran munotes.in

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134 Linux Documentation Removes the directory Kiran.
The following Rules are to be followed while removing or deleting a
director y.
(1) The rmdir (remove directory) command removes directories. You
simply have to do this to remove the directory pis:
rmdir college directory must be empty
The rmdir command only works for removing empty directories.
(2) like mkdir, rmdir can also create and d elete more than one directory
in one shot.
(3) For instance, the directories and subdirectories that they were just
created with mkdir can be removed by using rmdir with a reversed set
of argument:
rmdir college/kiran college/chirag college
(4) The following dir ectory sequence used by mkdir is invalid in rmdir:
$ rmdir college college/kiran college/chirag
rmdir: directory “college”: Directory not empty
(5) This error message leads to two important rules that you should:
Remember when deleting directories:
(a) You can’t delete a directory with rmdir unless it is empty. In this case,
the college directory couldn’t be removed because of the existence of
the subdirectories, Kiran and chirag, under it.
(b) You can’t remove a subdirectory unless you are placed in a directory
which is hierarchically above the one you have chosen to remove.
(6) To illustrate the second cardinal rule, try removing the kiran directory
by executing the command from the same directory itself:
$cd kiran
$ pwd
/home/user/college/kiran
$rmdir /home/user/college /kiran
rmdir: directory “/home/user/college/kiran”: Directory does not exist.
(7) To remove the directory, you must position yourself in the directory
above Kiran (i.e. You should be out of that directory), i.e., move to
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135 Linux $ cd /home/user/college
$ pwd
/home/user/college
$ rmdir kiran
The mkdir and rmdir commands work only in directories owned by the
user.
Viewing File Contents :
We can view the contents of the file and how to view or how to peek
inside of them . There are several commands available for taking a look
inside files without having to pull out an editor.
 Viewing file statistics:
ls command with –l option is used to provide lots of useful information
about files in the long listing format. There’s sti ll some more information
that you can’t see in the ls command.
The stat command provides a complete rundown of the status of a file on
the filesystem:
$ stat kiran
File: "kiran"
Size: 6 Blocks: 8 Regular File
Device: 306h/774d Inode: 1954891 Links: 2
Acces s: (0644/ -rw-r--r--) Uid: ( 501/ rich) Gid: ( 501/ rich)
Access: Sat Sep 1 12:10:25 2009
Modify: Sat Sep 1 12:11:17 2010
Change: Sat Sep 1 12:16:42 2010
$
The results from the stat command show just about everything you’d want
to know about the file being examined, even down the major and minor
device numbers of the device where the file is being stored.
 Viewing the file type:
Stat command produces all status of the file, there’s still one piece of
information missing – the file type. Before you want to vi ew the contents
of the file, it’s needed to know what type of file it is, i.e. To identify
whether it is binary or octal or text or ascii or device or ordinary or link
file or shell script file or it is directory. For that file command is used. It munotes.in

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136 Linux Documentation has the ability to peek inside of a file and determine just what kind of file
it is:
$ file test1
test1: ASCII text
$ file myscript
myscript: Bourne shell script text executable
$ file myprog
myprog: ELF 32 -bit LSB executable, Intel 80386, version 1 (SYSV),
dynami cally linked (uses shared libs), not stripped
$ file Monday reports
monday: text
reports: directory
$ file today mydata
today: Ascii text
mydata: empty
The file command classifies files into three categories:
 Text files: Files that contain printable charac ters.
 Executable files: Files that you can run on the system.
 Data files: Files that contain nonprintable binary characters, but that
you can’t run on the system.
The linux file commands helps you to determine for what a file is used. It
examines a few lin es of files & tries to determine classification for it. The
file command is used to display the type of file.
The file cmd looks for a special keybwords or special numbers in those
first few lines only but it is not fully accurate. Hence OD’ cmd is used to
examine the entire file byte by byte ‘OD’ is the ‘octal dump’ which
performs the dump of a file & it prints every bite in its octal
representation.
File [directory name]
File OD: it prints the contents of file byte by byte either in octal chara cter
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137 Linux -d It O/Ps a decimal form of byte value. -x It O/Ps hexadecimal form of byte value. -o It O/Ps octal form of byte value.  Viewing the whole file:
If you hav e a large text file on your hands, you may want to be able to see
what’s inside of it.
There are three different commands in Linux to view the files contents.
 The cat command:
The cat command is a used for displaying all of the data inside a text file:
$ cat test1
hello
This is a test file.
That we’ll use to test the cat command.
$
Contents of the text file will be displayed, there are a few parameters you
can use with the cat command. The -n parameter numbers all of the lines
for us:
$ cat -n test1
1 hello
2
3 This is a test file.
4
5
6 That we’ll use to test the cat command.
$
when you’re examining scripts. If you just want to number the lines that
have text in them, the -b parameter is for you:
$ cat -b test1
1 hello
2 This is a test file.
3 That we’ll us e to test the cat command.
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138 Linux Documentation art I
If you need to compress multiple blank lines into a single blank line, use
the -s parameter:
$ cat -s test1
hello
This is a test file.
That we’ll use to test the cat command.
$
if you don’t want tab characters to appear, use the -T parameter:
$ cat -T test1
hello
This is a test file.
That we’ll use to^Itest the cat command.
$
The -T parameter replaces any tabs in the text with the ^I character
combination.
Using the more command to display a text file
For large files, the cat command is not advisable. The text in the file will
just quickly scroll off of the monitor without stopping more command will
this problem.
 The More Command:
The more command displays a text file, but stops after it displays each
page of data. At the bottom of the screen the more command displays a tag
showing that you’re still in the more application and how far along in the
text file you are. Like – more – This is the prompt for the more command
more command is also called as PAGING OUTPUT.
 The man c ommand displays its output a page at a time. This is
possible because it sends its output to a pager program. UNIX offers
the more pager (originally from Berkeley) which has today replaced
pg, the original pager of UNIX. Linux also offers more but less is its
standard pager.
 To view the file chap01, enter the command with the filename:
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139 Linux  You’ll see the contents of chap01 on the screen, one page at a time. At
the bottom of the screen, you’ll also see the filename and percentage
of the file that has been viewed:
– more – (17%)
 more has a couple of internal commands that don’t show up on the
screen when you invoke them.q, the command used to exit more, is an
internal command.
Navigation:
Irrespective of version, more uses the spacebar to scroll forward a page at
a time. You can scroll by small and large increments of lines or screens.
To move forward one page, use f or the spacebar And to move back one
page, use b
The Repeat Features:
 The Repeat factor: Many navigation commands in more , including f
and b, use a repeat factor. This is the term used in vi to prefix a
number to vi internal command use of the repeat factor as a command
prefix simply repeats the command that many times.
 This means you can use 10f for scrolling forward by 10 pages and
30b for scrolling back 30 pages just remember that the commands
themselves are not displayed on the screen – even for a moment.
 Repeating the last command ( ) more has a repeat command, the dot
(same command used by vi), that repeats the last co mmand you used.
If you scroll forward with 10f, you can scroll another 10 pages by
simply pressing a dot.
Searching for a Pattern:
You can perform a search for a pattern with / command followed by the
string. For instance, to look for the first while loop in your programs,
you’ll have to enter this:
/while Press [enter]also
You can repeat this search for viewing the next while loop section by
pressing n, and you can do that repeatedly until you have scanned the
entire file. Move back with b (using a repeat factor, if necessary) to arrive
at the first page.
The more Command Options Option Description:
H Display a help menu.
spacebar Display the next screen of text from the file.
z Display the next screen of text from the file.
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140 Linux Documentation d Display a half -screen (11 lines) of text from the file.
q Exit the program.
s Skip forward one line of text.
f Skip forward one screen of text.
b Skip backward one screen of text.
/expression Search for the text expression in the f ile.
n Search for the next occurrence of the last specified expression.
_ Go to the first occurrence of the specified expression.
! cmd Execute a shell command.
v Start up the vi editor at the current line.
CTRL -L Redraw the screen at the current location in the file.
= Display the current line number in the file.
 Repeat the previous command.

 The Less Command:
Less command is actually a play on words and is an advanced version of
the more command (the less command uses the phrase ‘‘less is more’’).
(a) It provides several features for scrolling both forward and backward
through a text file
(b) It provides some advanced searching capabilities.
(c) The less command is used to display the contents of a file before it
finishes reading the entire file. This is a drawback for both the cat and
more commands when using extremely large files.
(d) The less command operates much the same as the more command,
displaying one screen of text from a file at a time. Kj
(e) Less command provides additional information in its prompt, showing
the total number of lines in the file, and the range of lines currently
displayed.
(f) The less command supports the same command set as the more
command, plus lots more options. 3
(g) The less command recognizes the up and down arrow keys, as well as
the page up and page down keys. This gives you full control when
viewing a file.

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141 Linux


Internal commands of more and less:
More Less Action Spacebar or f Spacebar or f or z One page forward 20f - 20 pages forward B B One page backward 15b - 15 pages back [Enter] J or [Enter] One line forward - K One line back - P or 1g Beginning of file - G End of file /pat /pat Searches forward for expression pat N N Repeats search forward - ?pat Searches back for expression pat .(a dot) - Repeats last command V V Starts up vi editor !cmd !cmd Executes UNIX command cmd Q Q Quit H H View Help
 Viewing parts of a file:
If we want to view the contents which are located right at top or at bottom
of a file. Head & Tail command is used to achieve this.
Head:
Displays the first t en lines of a file, unless otherwise stated.
Syntax:
head [ -number | -n number] filename
-number The number of the you want to display. -n number The number of the you want to display. filename The file that you want to display the x amount of lines of.
Examples:
head -15 myfile.txt: Would display the first fifteen lines of myfile.txt.
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142 Linux Documentation Delivers the last part of the file.

Syntax:
tail [+ number] [ -l] [-b] [-c] [-r] [-f] [-c number | -n number] [file].
+number -number This option is only recognized if it is specified first. COUNT is a decimal number optionally followed by a size letter (`b', `k', `m') as in `-c', or `l' to mean count by lines, or other option letters (`cfqv'). -l Units of lines. -b Units of blocks. -c Units of bytes. -r Reverse. Copies lines from the specified starting
point in the file in reverse order. The default for
r is to print the entire file in reverse order. -f Follow. If the input-file is not a pipe, the program will not terminate after the line of the input-file has been copied, but will enter an endless loop, wherein it sleeps for a second and then attempts to read and copy further records from the input-file. Thus it may be used to monitor the growth of a file that is being written by some other process. -c number The number option-argument must be a decimal integer whose sign affects the location in the file, measured in bytes, to begin the copying: + Copying starts relative to the
beginning of the file. - Copying starts relative to the
end of the file. none Copying starts relative to the
end of the file. The origin for counting is 1; that is, -c+1 represents the first byte of the file, -c-1 the last. -n number Equivalent to -c number, except the starting location in the file is measured in lines instead of bytes. The origin for counting is 1; that is, -n+1 represents the first line of the file, -n-1 the last. File Name of the file you wish to display
Examples:
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143 Linux The above example would list the last 10 (default) lines of the file
myfi le.txt.
tail myfile.txt -n 100
The above example would list the last 100 lines in the file myfile.txt.
6.6 FILE SYSTEM As you can see from the shell prompt, when you start a shell session you
are usually placed in your home directory. Most often, you will want to
break out of your home directory and want to explore other areas in the
Linux system.
The Linux filesystem OR The File structure:
The linux file organizes into tree structure format connected set of
directories each directory contains either files or directories.
Directory perform 2 main functions:
1) A directory hold files.
2) Directory connects to other directories like a branch in a tree which
can be connected to other branches also
Files and directories are shown in the tree structure format. /Root/dev/bin/home/Kiran /Chirag/Angela/Report/ Letter
The tree can be shown by root at the top. Extending down from the root
are the branches. Each branch grows out of other branch but it can have
many lower branches it can said to be parent child structure. In the same
way ea ch directory is a subdirectory of one other directory i.e. each
directory is a child of parent directory. Root is identified by a forward
slash (/), within the root directory number of system directories are built,
root directory also contain home director y which contains the info of all
users in the system and each user home directory i.e. Chirag in turn
contains the directory which the user has made for his use.
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144 Linux Documentation /(Root)LSChmodCPtomABCUser 3Cat/Sbin/bin/boot /dev/etc/var /usr/libspoolsbinbinmanlibReportsLetters

Home Directories:
When you lo g on to system you are placed within home directory. The
name given to this directory by system is the same as your login name.
You can crate files in home directory also you can create more directories.
You can change to these directories and stores file in them. Same is true
for users on the system i.e. each and every users will have his own
directory identified by login name and user in turn can create their own
directories and subdirectories.
Path Name:
The full name of the directory to identify that di rectory is the path name.
The hierarchically nested relationship among directories forms path and
these path can be used to identify and reference any directory or file. A
path exist from ‘/’ i.e. root directly to home directory. /rootdevbinhomerobertABCreportsLettersFILEPathname:/home/roberPathname:/home/ABC/reportsPathname:/home/ABC/letter/file
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145 Linux While writing the pathname by listing of each directory the pathname is
separated by ‘/’. When we are writing any path starts with “/” indicate root
directory receiving directory name Root DirectoryHome DirectoryHome Directory (users)Users DirectoryE.g. /home/abc/letters
Traversing Directories:
The ch ange directory command (cd) is what you’ll use to move your shell
session to another directory in the Linux filesystem.
The format of the cd command is:
cd destination
The cd command may take a single parameter, destination, which specifies
the directory name you want to go to. If you don’t specify a destination on
the cd command, it will take you to your home directory.
The destination parameter, though, can be expressed using two different
methods:
 An absolute filepath
 A relative filepath
Pathnames are o f two types:
(1) Absolute path.
(2) Relative path.
Absolute path is complete pathname of a directory or file always begins
with root directory. The absolute filepath defines exactly where the
directory is in the virtual directory structure, starting at the root of the
virtual directory. Sort of like a full name for a directory.
E.g: /usr/lib/apache
(1) If the first character of a pathname is / , the file’s location must be
determined with respect to root (the first /). Such a pathname is called
an absolute pathname.
(2) When you have more than one / in a pathname, for each such / , you
have to descend one level in the file system.
Relative Pathnames:
You would have noted that in a previous example, we didn’t use an
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146 Linux Documentation Relative pa thname begins from your working directory working directory
is the one you are currently in. Relative filepaths allow you to specify a
destination filepath relative to your current location, without having to
start at the root. A relative filepath doesn’t start with a forward slash,
indicating the root directory. Instead, a relative filepath starts with either a
directory name (if you’re traversing to a directory under your current
directory), or a special character indicating a relative location to your
current directory location. The two special characters used for this are:
 The dot (.) to represent the current directory.
 The double dot (..) to represent the parent directory.
The double dot character is extremely handy when trying to traverse a
directory h ierarchy. For example, if you are in the Documents directory
under your home directory and need to go to your Desktop directory, also
under your home directory, you can do this:
rich@1[Documents]$ cd ../Desktop
rich@1[Desktop]$ /rootmarkrobertchirsMandayThankYouF2AbcdevbinhomereportsLetters weatherAbsoulte Pathname:/home/chirs/reports/mondayAbsoulte Pathname:[@root/chirs]/reports/monday

Sometimes the absolute path could be complex hence to refer absolute
path. You can use a special character tilde ‘  ‘ which represents absolute
path name of your home directory. Suppose currently you are in ‘thank
you’ directory and you want to see contents of ‘abc’ file by using absolute
path, so you can write $ cat ~ / abc. Hence tilde (~) will give you absolute
path as ‘/home/chris/letters/thankyou’, Same way if you are in chris
directory & you want to see contents of file F2 of Monday directory. So
you can use tilde sign (~) before using it check you absolute path by
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147 Linux can write $ cat ~/reports/Monday/F2. So it displays the contents of F2
Where tilde (~) indicates the path /home/chr is.
6.7 FILESYSTEM ARCHITECTURE The root directory that begins with linux file structure contains several
system directories. The system directory contains files and programs used
to run and maintain the system. Many directories contains other sub
director ies with programs for executing specific features of LINUX
e.g. /usr/bin
Contains various LINUX commands that user executes such as cp – for
copy and mv – for renaming or moving to other directory & the directory
/bin holds interfaces with different syste m devices such as printer or the
terminal also consist of the executable file for the commands. Directory Function (1) Root ‘/ ’ It begin file system structure call the root,
The root of the virtual directory. (2) /home Contains users home directory. (3) /bin The binary directory holds all standard
commands and utility programs (like Vi
editor), also executable files for the
commands. (4) /usr Holds those files & commands used by the system. This directory breaks down into several sub directories. The user-installed software directory. (5) /usr/sbin Holds system administration commands with its executable files. (6) /usr/lib It holds libraries for programming language (7) /usr/doc Holds linux documentations. (8) /usr/man Holds online manual man files i.e. Help files. (9) /usr/spool Holds spool files such as those generated for printing jobs, waiting printing jobs will be stored in spool directory. (10) /sbin Holds system administration command for booting of system. The system binary directory, where many GNU admin-level utilities are stored. (11) /var It holds the file that vary. Hence this directory has information about different utilities of linux e.g. /val/log. – directory contains files that stores operating system log files or error reports file. The variable directory, for files that change frequently, such as log files. (12) /dev Holds file interfaces for devices such as terminal and printers. It stores the device files for input and output hardware devices. (13) /etc Holds system configuration files and any other system files. This stores operating system related data which users and operating system needs to refer such as password file. munotes.in

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148 Linux Documentation (14) /tmp The temporary directory, where temporary work files can be created and destroyed. (15) /mnt The mount directory, another common place for mount points used for removable media. (16) /Lib The library directory, where system and application library files are stored. (17) /boot The boot directory, where boot files are stored.
6.9 FILE ATTRI BUTES You can decode the cryptic file permissions you’ve seen when using the ls
command. Here we will specify how to decipher the permissions.
Using File Permission Symbols:
The ls command displays the file permissions for files, directories, and
devices o n the Linux system:
$ ls -l
total 68
-rw-rw-r-- 1 rich rich 50 2007 -09-13 07:49
file1.gz
-rw-rw-r-- 1 rich rich 23 2007 -09-13 07:50 file2
-rwxrwxr-x 1 rich rich 4882 2007 -09-18 13:58
myprog
-rw-rw-r-- 1 rich rich 237 2007 -09-18 13:58
myprog.c
drwxrwxr -x 2 rich rich 4096 2007 -09-03 15:12
test1
drwxrwxr -x 2 rich rich 4096 2007 -09-03 15:12
test2
$
The first field in the output listing is a code that describes the permissions
for the files and directories.
The first character in the field defines the type of th e object, These are the
different options of file types.
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149 Linux  b for block devices
 n for network devices
After that, there are three sets of three characters. Each set of three
characters defines an access permission triplet:
 r for read permission for the object
 w for write permission for the object
 x for execute permission for the object
If a permission is denied, a dash appears in the location. The three sets
relate the three levels of security for the object:
 The owner of the object
 The group that owns the object
 Everyone else on the system
FI-rwxrwxr -x 1 rich rich 4882 2007 -09-18 13:58 myprog
The file myprog has the following sets of permissions:
 rwx for the file owner (set to the login name rich)
 rwx for the file group owner (set to the group name rich)
 r-x for everyone else on the system
These permissions indicate that the user login name rich can read, write,
and execute the file (considered full permissions). Likewise, members in
the group rich can also read, write, and execute the file. However, anyone
else not in the rich group can only read and execute the file; the w is
replaced with a dash, indicating that write permissions are not assigned to
this security level.
Default File Permissions:
The umask command sets the default permissions for any file or directory
you create:
$ touch newfile
$ ls -al newfile
-rw-r--r-- 1 rich rich 0 Sep 20 19:16 newfile
$
The touch command created the file using the default permissions
assigned to my user accou nt. The umask command shows and sets the
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$
Unfortunately, the umask command setting isn’t overtly clear, and trying
to understand exactly how it works makes things even muddier. The first
digit represents a special securit y feature called the sticky bit . The next
three digits represent the octal values of the umask for a file or directory.
To understand how umask works, you first need to understand octal mode
security settings. Octal mode security settings take the three rwx
permission values and convert them into a 3 -bit binary value, represented
by a single octal value. In the binary representation, each position is a
binary bit. Thus, if the read permission is the only permission set, the
value becomes r--, relating to a binary value of 100, indicating the octal
value of 4.
Octal mode takes the octal permissions and lists three of them in order for
the three security levels (user, group, and everyone). Thus, the octal mode
value 664 represents read and write permissions f or the user and group,
but read -only permission for everyone else.
The permission for a file is broken into three parts. Each group represents
a category and contains three slots representing the read, write and execute
permissions of the file.
The first group (rwx) has all three permissions. The file is readable, write
able and executable by the owner.
The second group (r -x) has a hyphen in the middle slot, which indicates
the absence of write permission by the group user of the file.
The third group ( r--) has the write and execute bit absent. The file
permissions are also categorized for the kinds of user ie it can be other/
guest user.
6.10 WORKING WITH FILES The chmod command is used for changing the permissions of a file.
Permissions can be changed by two ways:
(1) Binary Ma sking Method (Absolute Permission Method):
In this method binary 1 or 0 is assigned to the permissions
1  Assigning (Granting permission)
0  Removing (Revoking permission)
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151 Linux 7 5 1 Chmod 751 hello.txt
7 indicate (111) Owner has all three permissions (Read, Write,
Execute)
5 indicate (101) Group user has Read & Execute Permission.
1 indicate (001) Other or Guest User has Only Execute Permission.
2) Symbolic Masking Met hod (Relative Method of changing
permissions):
In this method symbols (Abbreviations) are used for assigning &
Removing Permissions:
r  Read
w  Write
x  Execute
g  group
o  Other
u  Owner
a  All users
+  Assinging a permission (plus sign)
-  Remov ing a permission. (minus sign)
Syntax:
chmod category operation permission filenames
category can be user, group or other
operation can be assign or remove
permission can be read, write and execute
Example:
Chmod g+rw hello.txt
Chmod a -wx xyz.txt
6.11 BAC KUP, COMPRESSION Compressing Data:
The zip utility allows you to easily compress large files (both text and
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152 Linux Documentation Linux contains several file compression utilities. While this may sound
great, it often lea ds to confusion and chaos when trying to download files.
Lists the file compression utilities available for Linux.
The compress file compression utility is not often found on Linux systems.
If you download a file with a .Z extension, you can usually instal l the
compress package (called ncompress in many Linux distributions) and
then uncompress the file with the uncompress command.
The gzip command compresses every file in the directory that matches the
wildcard pattern.
The zip utility:
The zip utility is c ompatible with the popular PKZIP package created by
Phil Katz for MS -DOS and Windows. There are four utilities in the Linux
zip package:
 zip creates a compressed file containing listed files and directories.
 zipcloak creates an encrypted compress file cont aining listed files and
directories.
 zipnote extracts the comments from a zip file.
 zipsplit splits a zip file into smaller files of a set size (used for
copying large zip files to floppy disks).

unzip extracts files and directories from a compressed zip file.
zip [-options] [ -b path] [ -t mmddyyyy] [ -n suffixes] [zipfile list]
[-xi list]
The default action is to add or replace zipfile entries from list, which can
include the special name - to compress standard input.
If zipfile and list are omitted, zip co mpresses stdin to stdout.
-f freshen: only changed files -u update: only changed or new files.
-d delete entries in zipfile -m move into zipfile (delete files).
-r recurse into directories -j junk directory names.
-0 store only -l convert LF to CR LF.
-1 compress faster -9 compress better.
-q quiet operation -v verbose operation.
-c add one -line comments -z add zipfile comment.
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153 Linux -x exclude the following names -i include only the following names.
-F fix zipfile ( -FF try harder) -D do not add directory entries.
-A adjust self -extracting exe -J junk zipfile prefix (unzipsfx).
-T test zipfile integrity -X eXclude eXtra file attributes.
-y store symbolic links as the link instead of the referenced file.
-R PKZIP recursion (see manual).
-e encrypt -n don �ft compress these suffixes.
$
The power of the zip utility is its ability to compress entire directories of
files into a single compressed file. This makes it ideal for archiving entire
directory structur es:
$ zip -r testzip test
adding: test/ (stored 0%)
adding: test/test1/ (stored 0%)
adding: test/test1/myprog2 (stored 0%)
adding: test/test1/myprog1 (stored 0%)
adding: test/myprog.c (deflated 39%)
adding: test/file3 (deflated 2%)
adding: test/file4 (stor ed 0%)
adding: test/test2/ (stored 0%)
adding: test/file1.gz (stored 0%)
adding: test/file2 (deflated 4%)
adding: test/myprog.gz (stored 0%)
$
This example creates the zip file named testzip.zip, and recurses through
the directory test,
Adding each file an d directory found to the zip file. Notice from the output
that not all of the files stored in the zip file could be compressed. The zip
utility automatically determines the best compression type to use for each
individual file.
When you use the recursion f eature in the zip command, files are stored in
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154 Linux Documentation Directory structure in the zip file. Files contained in subdirectories are
stored in the zip.
File within the same subdirectories. You must be careful when extracting
the files, the unzip command wil l rebuild the entire directory structure in
the new location.
File Compression:
If you are transferring the file across a N/W to save transmission time.
You can effectively reduce the size by creating a compressed copy of it.
Anytime you need file again de compress it.
$ gzip mydata
$ mydata.gz drip1
To compress a gzip file
$ gzip –d mydata.gz
To decompress a gzip
$ gunzip mydata.gz
$ ls
$ gzip 0 -cmydata preface>mufiles.gz sends compressed version of a file to
standard o/p each file listed is separately comp ressed extension will be gz.
-h displays help help listing
-l file list
$ gzip -l myfiles.gz
-r dir name
-v file list
-num
You can also zip with bzipz (Burrows -wheeler block sorting text
compression algorithm)
The file created with extension .bzz bzip co mmand compresses file in
block & enables you to specify their size.
$ bzipz mydata
$ ls
mydata bzz
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155 Linux $ zip mydata
$ zip –r reports
$ ls
$ unzip mydata.zip
mydata.zip
Archiving (tar):
The tar command is used to store backup transport & archive files. A tar
file can be made on tape drive or on local hard disk. tar command serves
many file together in a single tape or disk archive & can single tape or
disk archive & can restore individual file from the archive i.e. tar file is a
single file that contains the contents of many file also store file attributes
like file access permission the user, group, size time. The files in tar file
are called the members of that archive.
The tar utility creates archive for files & directories w ith tar you can
archive specific files, update them in the archive & add new files as you
want to that archive. You can even archive entire directories with all their
files & subdirectories all of which can be restored from archive.
The tar utility was ori ginally designed to create archives on tapes.
The term tar stands for tap archive , also you can create archives on any
device such as floppy disk or you can create an archive file to hold the
archive (for devices archiving is not possible in DOS only for f iles it is
possible)
The tar utility is ideal for making backups of your files or combining
several files into a single file for transmission across a N/W.
On Linux, tar is used to create archives on devices of files.
You can direct tar to archive files t o a specific device or a file by using ’f ’
option with the name of device or file.
The syntax for the tar command with f option
$ tar option f archive name tar Directory & file name
When creating a file for a tar archive, the file name is usually given t he
extension .tar
If directory name is specified for archive then all its subdirectories &
included files are in archive.
To create an archive use c option along with f option or file.
c creates on archive on a file or device
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$ tar cvf myarch.tar mydir:
v verbose mode which means that it displays detailed comments as the
operation proceeds like verification.
c creating a new archive file i.e. tar file display each file name is it
archive for verifying
f file i.e. specify the name of tar file or locatio n where it is to be created.
In this example the directory mydir & its all subdirectories are saved in the
fie myarch.tar
myarch.tar  name of archive to be created .
mydir  directory to be archived. Mydir Mymeeting Party Reports Weather Monday Friday
$ tar cvf myarch.tar mydir
mydir/
mydir/reports/
mydir/reports/weather
mydir/reports/Monday
mydir/reports/Friday
mydir/mymeeting
mydir/party
Command Execution tar options : Back up files to tape device or archive file tar option archive name file list : Backs up file to specific file or device specified as archive name, filelist, can be filenm or directory
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157 Linux t : lists the names of files in an archive r : append file to an archive u : Update an archive with new & changed files, adds only those files modified ֶ◌ they were archived or files not already present in archive w : waits for a confirmation from the user before archiving each file x : extracts files from an archive m : created a multiple volume archive that may be stored on several floppy drives f archive –nm : saves the tape archives to the file archive name
instead of the default tape device, when in this
option gives an archive name, the f opt ion
saves the tar archive in file of that name which
is specified as archive name f device –nm : Saves a tar archive to a device such as floppy
disk or tape /dev/fdo is the device name For
your floppy disk the default devices is held in
/etc/default/tar f ile v : Displays each filename an it is archived z : Compresses or decompresses archived files
using g zip
The user can extract the directories from the tape using X option. The xf
option extracts file from an archive file or device. The tar extension
operation generates all subdirectories.
xf option directs for to extract all the files & subdirectories form the tar
files.
myarch.tar
$ tar xvf myarch.tar
$ tar xvf myarch.tar
pathname denotes the relative pathnames. The above command creates the
root di rectory under the current directory if it does not already exist.
mydir/
mydir/reports
mydir/reports/weather
mydir/reports/Monday
mydir/reports/Friday
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158 Linux Documentation You can use r option to add files to an already created archive. The r
option appends the files to the archive
$ tar rvf myarch.tar mydocs:
The user appends the files in the myarch.tar archive. Here the directory
mydocs & its files are added to the myarch.tar archive.
If you want to do change or update to the previously created ar chived, you
can use u option to instruct tar to update the archive with an modified file.
The tar command compares the time of the last update for each archive
file with those in users directory & copies into the archive any files that
have been changed si nce they were last archived.
Any newly created files in these directories are also added to the archive
suppose mydir directory you have added two or 3 files & you want to
update that in tar .
$ tar uvf myarch.tar mydir
mydir/
mydir/gifts
To see tar archive file stored in archive tar without option
$ gzip mydata
$ gunzip mydata
Since tar files are capable of preserving files info. & directory structure tar
is commonly used to perform full & incremented backups of disks.
Whenever any file corrupt the chances of recovering it are higher if it is
uncompressed tar file as well as you cannot update compressed file.
$ tar –cvf trial.tar /root/test/* tar;
Removing leading ‘/’ from absolute path names in archieve
root/test/a out
root/test/m.c.
tar file will not stor e the leading slash (/) it removes the slash while
retrieving a file as the tar file does not store the absolute filename, it
restores the file with relation to your current directory & prevents
accidental overwriting of original data.
If you want absolute path to be stored use –p (capital P) option
# -tar - -absolute -paths -paths -cvf trial.tar/root/test/*
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159 Linux # -tar -p -cvf trial.tar/root/test/*
Storing the absolute pathnames we can created archive filename will long
names also instead of using only singl e character # tar –c –v -f
trial.tar/root/user/
# tar --create - - verbose - - file = trial.tar/root/user/*
Deleting files form an Archive:
use -delete option
# tar - - delete –f trial.tar tmp
# tar -tvf trial.tar
a.txt
m.c.
tmp will be deleted
Concatenat ing Tar.Archives
# tar –Af trial.tar script.tar
The above command adds all contents of script.tar archive to the trial.tar
archive. To backup the files to a specific device, specify the device as the
archive for a floppy disk, you can specify the floppy dr ive. Be sure use
Blank floppy otherwise any data previously placed on it will be erased by
this operation.
The user created an archive on floppy disk in the /dev/fdo device device &
copies into floppy disk all the files which all in mydir directory.
 $ tar cf /dev/fdo mydir:
To extract the backed up files on the hard disk in a device
$ tar xf /dev/fdo
If the files you are archiving take up more space than would be available
on a device such as floppy disk, you can create a for archive that uses the
multiple labels. The m option instruct for to prompt you for a new storage
component when the current one is filled when archiving to a floppy drive
with m option tar prompts you to put in a new floppy disk when one
becomes full. You can then save your tar archive on several floppy disks.
$ tar cmf /dev/fdo mydirect
To unpack the multiple disk archive i.e. to take the multiple floppy disk
data form floppy to hard disk.
Place the 1st one in the floppy drive, & then issue the following tar
command using both the x & m options. You are then prompted to put in
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160 Linux Documentation $ tar xmf /dev/fdo
The tar operation does not perform compression on archived files. if you
want to compress the archive files you can instruct tar to involve the gzip
utility to compress them with the lower case z option tar first uses gzip to
compress file before archiving them. The same z option involves gzip to
decompress them when extracting files.
$ tar czf myarch.tar.gz mydir
Normally an archive is created for trans ferring several files at one as one
tar file to shorten transmission time the archive should be as emall as
possible extention of zip files i.e. tar.gz
To view the contents of the compressed tar file
# tar tufz trial.tar.gz
# gzip myarch.tar
$ ls
$ myarch. targz
6.12 SUMMARY In this chapter we learn documentation and types of
compression utilities and file system architecture
6.13 UNIT END QUESTIONS 1. Write a short note on man pages, GNU info help command.
2. Write different file operation used in linux.
3. Write a short note on Filesystem.
4. Describe Filesystem architecture.
5. Describe different file system.
6. Write different file attributes
7. Explain 1. Backup 2.Compression
List Of References :
1) Unix Concepts and Applications by Sumitabha Das.
2) Official Ubuntu B ook, 8th Edition, by Matthew Helmke & Elizabeth K.
Joseph with Jose Antonio Rey and Philips Ballew, Prentice Hall

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161
UNIT III
7
SECURITY
Unit Structure
7.0 Objectives
7.1 Introduction
7.2 Understanding Linux Security
7.3 Uses of root
7.4 Sudo command
7.5 Working with passwords
7.6 Bypassing user authentication
7.7 Understanding ssh
7.7 Let Us Sum Up
7.8 Unit End Questions
7.9 List of References
7.0 OBJECTIVES In this chapter you will learn about:
 Basic of linux security under the use of sudo command and password
policies. Also the ssh -secure shell uses will enhance the linux
security.
7.1 INTRODUCTION This chapter introduces linux security measures regarding network criteria
by using ssh command features. The password policies which are
modified by using user management command. The sudo command which
are helping to manage all linux security and password policies.
7.2 UNDERSTANDING LINUX SECURITY  Security is a set of appropriate procedures to protect your data,
account against risks.
 Risks for Linux users are compromised account, system compromise,
infrastructure related issues, not good user and system ad ministration.
 One important task is to understand why we need to secure a system.
 Linux being treated as highly secure operating system, it has some
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162 Security  Causes of security problem in linux are local security, root security,
file system security .
 Security system is in two parts:
o Authentication: Responsible for ensuring that a user requesting access
to the system is really the user with the account.
o Access Control: Responsible for controlling which resources each
account has access to and what kin d of access is permitted.
Security Requirements :
 Authorization: Allowing authorized user to access data
 Authenticity: Verifying them.
 Confidentiality: Personal information not been compromised.
 Integrity: Data not been changed or modified.
 Availability: Ensure that data is available.
Linux Security Systems and Tools:
 Reason for Linux is less vulnerable to attack is in Linux file system
model. Files are handled differently in a Linux system. One way is
that each file on the system has the concept of permissi on built in.
These permissions separate who can use the file and how.
 Most of the files on a Linux system belong by default to ‘root’, or the
system administrator account. Within this category, no non -root user
can write to system files, and some programs which are risky security -
wise can additionally be restricted so that only root can run them.
 The user access levels also apply to any program that the user runs.
That is even if a user downloads and runs a malicious program, that
program inherits the user’ s permissions and so cannot do anything
that the user themselves could not do.
 Each file has the system’s file type identifier embedded in the file
itself instead of relying in an extension. Thus executables do not
necessarily have “.exe” at the end, and p lain text files do not need
“.txt” at the end. Thus one cannot fools the system by making an
executable file with a “.pdf” extension, since even if the user naively
double -clicks on the PDF file to open it for reading the system will
know that it’s really an executable program and refuse to run it.
Firewalls:
 Firewalls are network packet filters that are capable of blocking
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163 Linux  A firewall uses a set of rules which determines which traffic is
allow ed to pass and in which direction. These are normally used to
separate internal networks from external ones.
 Firewalls are often the first line defense against crackers and internet
worms, which can be blocked by denying the means of network
ingress.
7.3 U SES OF ROOT  Root is username or account who has access to all commands and
files referred to as root user or superuser.
 In Linux system two people can change the permission of a file or
directory.
o The owner of file
o The root user
 Root user is a superuser wh o can do anything on the system to
maintain the system.
 It’s actually a directory represented by “/”.
 It has number of sub directories such as bin,dev,home,lib etc.
 It has write permission i.e to modify files.
 Root user can start up or shut down the system and change operating
mode such as single user mode.
 It can add or remove users, file systems, back up and restore files.
 Create new process or kill process if required for running of system.
 Any user account’s password can be change
 Setting of system date and clock.
 Communicate with concurrent user.
 Set the limitations to the user account like creating number of files,
disk space allowed to user.
 Schedule services using cron.
 Configuration of networking services FTP, SSH etc.
7.4 SUDO COMMAND  Its “superuse r do” which allows user with proper permission to
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164 Security  In Ubuntu Linux by default root account is not configured
 Linux sudo command is used to give permission to any particular
command such as when user tries to install,remove and change piece
of software that user wants to execute.
 During installation of Ubuntu a default user is created and default user
is set up with sudo permission
 Sudo requires that users authenticate with a password.
 By default it is user’s password not th e root password. Attribute Description -v Prints version number and exist -l List will print out the commands allowed the user on the
current host -h Help prints a usage message and exist. -b Background runs the given command in background -K Sure k ill removes the user’s timestamp entirely -u User option to run the specified command as a user other
than root -s Shell option runs the shell specified -e Edit option indicates that instead of running a command
user wish to edit one or more files.
For example user wants to update the operating system by passing
command:
apt-get update
7.5 WORKING WITH PASSWORDS Password and authentication are important concepts when working in
Linux environment
Rules for Good Password:
 Choose different password: If y ou have a fear that your password has
been hacked them immediately change it.
 Choose uncommon password: Don’t choose common names of your
friends, relatives, pets etc.
 Use mixture characters: Use characters, numbers and special
characters in mixed form.
 Length of password: Minimum characters should be of 6 in length
 Don’t keep password written anywhere.

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165 Linux Password Security:
 As password is an important issue if at the time of login when we
enter user ID and password and if is accurate then login successes
otherwise it fails.
 It is important for users to secure passwords and it should be
unguessable.
 Recently Linux distribution includes passwd programs that do not
allow to set easily guessable passwords.
 It has one store area where password information is stor ed i.e.
/etc/passwd
 Linux file system is case -sensitive
 No person can regenerate original password string from the encryptd
string, thus password is secured.
7.6 BYPASSING USER AUTHENTICATION  Most of the system require access to private information
 It is p ossible to bypass authentication measure by tempering with
request and tricking the application into thinking that we are already
authenticated.
 In authentication mechanism we ask a user name and password at
login and password at login page, then allow aut horized users
unrestricted access to other web pages without any further checking.
 The problem is if users go directly to configuration pages, bypassing
authentication.
 For e.g. One user to run a command as another user without supplying
a password
 The sol ution to this is use sudo nopasswd tag. Which indicates to sudo
that no password is needed for authentication.
7.7 UNDERSTANDING SSH  ssh means secure shell was created to provide the best security when
we are accessing another computer remotely.
 ssh provid es better authentication facility, secure file transfer.
 ssh encrypts any communication between the remote user and a
system on your network.
 Two implementation of ssh are ssh1 which uses original ssh protocol
and ssh2 uses rewritten version of ssh protoco l.
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166 Security ssh Working:
 When you connect through ssh, you are in shell session, a text based
interface where we can interact with server.
 In ssh session, any commands that we type in local terminal are sent
through an encrypted ssh tunnel and executed on server.
 The ssh connection is implemented by client server model where
remote machine must be running a piece machine must be running a
pience of software for connection to be established.
 The user’s computer ha s a ssh client.
ssh Encryption and authentication:
 ssh secures connections by authenticating users and encrypting
transmissions.
 ssh first authenticates particular host,verifies it if is valid ssh host for
srcure communication.
Encryption:
 Public key encry ption in ssh authentication uses two keys: public key
and private key.
 Public key is used to encrypt data and private ey to decrypt it.
 For eg. When host sends data to a user on another system, the host
encrypts the authentication data with public key prev iously received
from that user.
 Data can be decrypted by user’s private key.
Authentication:
 ssh authentication is first carried out with the host and then with users.
 When a remote user receives the encrypted challenge, that user
decrypts the challenge wi th its private key.
 The remote user first encrypts a session identifier using its private
key.
 The encrypted session identifier is then decrypted by the account
using the remote user’s public key.
ssh Tools:
 sssh is implemented on Linux systems with openSS H.
 OpenSSH packages include general openSSH package, openSSH
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167 Linux  The following are the tools: Application Description Sshs ssh client Sshd ssh server Scp ssh copy command client Sftp ssh ftp client sftp-server ssh ftp server ssh-keygen utility for generating keys slogin remote login ssh-agent ssh authentication agent
7.7 LET US SUM UP Thus, we have studied the basic concepts of security and linux command
which is used to modify security measures. The uses of sudo command
and password policies are explained in chapter.
7.8 UNIT END QUESTIONS 1) What are the uses of root user in Linux system? Give the purpose of
sudo command.
2) Write any five privileges of administrator .
7.9 LIST OF REFERENCES 1) Unix Concepts and Applications by Sumitabha Das.
2) Official Ubuntu Book, 8th Edition, by Matthew Helmke & Elizabeth
K. Joseph with Jose Antonio Rey and Philips Ballew, Prentice Hall .



*****


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168
8
NETWORKING
Unit Structure
8.0 Objectives
8.1 Introduction
8.2 Basic introduction to Networking
8.3 Network protocols
8.4 Transferring files
8.5 Networking GUI.
8.6 LET US SUM UP
8.7 Unit End Questions
8.8 List of References
8.0 OBJECTIVES In this chapter you will learn about:
 Basic networking concepts and networking protocol.
 Transferring files through FTP, TELNET etc.
 Networking GUI .
8.1 INTRODUCTION This chapter introduces network concept through OSI layers and
protocols. The transferrin g files can be done by protocols like FTP,
TELNET etc. The interface for users provided by network command.
8.2 BASIC INTRODUCTION TO NETWORKING  All pieces of hardware and software programs speak different
languages.
 For communication between two computers we need a special
program in operating system that performs this function
 There are 7 layers of communication protocols which is known as
OSI(Open system Interconnection) links.
Goals of Computer Network:
 Sharing of Resources: Resources are been shared. F or e.g. one
printer is shared by different nodes of computers.
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169 Linux 8.3 NETWORK PROTOCOLS  Protocols are set of rules used for communication.
 Different types of Network Protocols are as follows:
o HTTP (Hypertext transfer protocol)
o FTP (File transfer protocol)
o TCP/IP
o UDP
o ICMP
o Mail Protocols POP3 and SMTP
 HTTP (Hypertext Transfer Protocol):
o HTTP has separate client and server components.
o Client request the server for a document and server respond by
sending it.
o The protocol is also stateless in that each connection is unaware of the
other.
o Life cy cle of connection using http is.
 The client contacts the source and opens a connection at port number
80.
 Client request the web server for some service. The request may
consist of request header followed by data sent by th e client.
 Server now sends a response which has response header, followed by
data.
 Server waits for more requests and finally closes the connection.
 FTP (File Transfer Protocol):
o FTP command is used to transfer files between hosts.
o Like telnet, ftp can als o be involved with or without the address
o FTP is simple and convenient protocol.
o FTP hostname by default will connect you to system, you must have a
login id to be able to transfer the files.
o ASCII and Binary files can be transferred.
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170 Networking  Data transfer: It transfer data from one place to another.
 Control transfer: It transfers control to another system and also
control activities of remote machine.
 FTP command uses various options: Tag Description -p Use passive mode for data transfer -i Interactive prompting during multiple file transfer -e Disables command editing and history support -d Enabling debugging
 TCP/IP:
o TCP ( Transmission Control Protocol) and IP (Internet Protocol)
are two different procedures that are often linked together. When
information is sent over the Internet, it is generally broken up into
smaller pieces or “packets”
o The use of packets facilitates speedy transmission since different parts
of message can be sent by different routes and then reass embled at the
destination.
o TCP is the means for creating the packets, putting them back together
in the correct order at the end, and checking to make sure that no
packets got lost in transmission. If necessary, TCP will request that a
packet be resent.
o Internet Protocol(IP) is the method used to route information to the
proper address. Every computer on the Internet has to have its own
unique address known as the IP address. Every packet sent will
contain an IP address showing where it is supposed to go.
 UDP:
o This protocol is used together with IP when small amounts of
information are involved.
o It is simpler than TCP and lacks the flow -control and error -recovery
functions of TCP. Thus it uses fewer system resources.
 ICMP:
o A different type of protocol is Int ernet Control Message Protocol
(ICMP).
o It defines a small number of messages used for diagnostic and
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171 Linux  Mail Protocols POP3 and SMTP:
o Email has its set of protocols and there are a diversity of it, both for
sending mail and for receiving mail.
o The most common protocol for receiving mail is Post Office Protocol
(POP) which is now in version 3 called POP3.
o Both SMTP and POP3 use TCP for managing the transmission and
delivery of mail across the Internet .
o The most common protocol for sending mail is Simple Mail Transfer
Protocol (SMTP).
o For reading mail there is Interactive Mail Access Protocol (IMAP).
 IP Address:
o Every host in the network has an address has an address called IP
address, used by other mac hines to communicate with it.
o It’s a series of four dots delimited numbers.
o The maximum value of each octect is 255.
o It uses Internet Protocol for communication. For example:
211.162.0.1
o TCP/IP application can address a host by its hostname as well as its IP
address:
telnet abc
ftp 211.162.0.1
o The network administrator makes the IP address unique in all
connected networks.
 DNS (Domain Name System)
o It is a distributed system which has three key concepts .
 A hierarchical organization of hostnames
 A distributed database for mapping
 Authorities at individual level
o Host belongs to domains which further belong to sub domain.
o Root at the top signified by . (dot)
o There are number of top level domains as shown in below fig 8.1
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172 Networking

Fig 8.1 Internet Domain Hierarchy
o In the hierarchy related to these dot -separated strings, in is above net
which is in turn above vsnl represents fully qualifies domain name.
o BIND (Berkeley Internet Name Domain) maintains the DNS -related
software that runs under Linux.
o Below table shows various internet domains : Domain Name Significance Int International organization Edu Educational Institution Gov Government Com Commercial organization Net Networking organization In India Biz Business
 Browsers:
o Browsers are the most used applications as it’s important to choose
stable browser that suits all your needs.
o Browsers can be light weight, command line, free to cross platform
and extremely extensible one.
o Best browsers in Linux are Firefox , chrome, opera, Pale Moon.
o It’s a HTTP client which accepts a URL from URL window and gets
the resource from the server.
8.4 TRANSFERRING FILES  Files that can be transferred are ASCII (text) and binary.
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173 Linux  Uploading -put commands sends signal file i.e abc.gif to remote
machine. We can copy multiple files with mput.mput behaves
interactively and has confirmation for every file which has to be
transferred.
 Downloading -To download use get and mget commands.
 ssh (Secure shell):
o ssh, or secure shell is a protocol used to securely log onto remote
systems.
o It is the most common way to access remote Linux and Unix -Like
servers.
o For Example command is:
ssh remote_host
o The remote_host is the IP address or domain nam e that we are trying
to connect. This command assumes that your username on the remote
system is the same as your username on your local system.
 telnet:
o telnet is terminal network.
o Popular client server application process for terminal services.
o telnet use in time sharing system.
o Responsible for establishing connection to the remote system.
o It provides two types of login :
1) Local Login
2) Remote Login
1) Local Login :
a. Many terminal users are connected to one CPU .
b. CPU allocates time slot to each terminal.





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174 Networking

2) Remote Login:
a. Used as client server system
b. User logins from remote places so that remote terminal can access
application program of another machine.
c. Server can communicate with one or more client.
d. Whenever client needs services it runs, request for the servi ces and
use it.


 Ping (Packet Internet Groper):
o Ping command is used for checking the network and also to test
connectivity between two nodes.
o It uses ICMP(Internet Control Message Protocol) to communicate to
other devices.
o Pinging a host does not requir e server process to run at other end.
o Ping command sends the ICMP ECHO_REQUEST packets to
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175 Linux o PING (packet Internet Groper) command is the best way to check
connectivity between two nodes in Local Area Network(LAN) or
Wide Area Network(WAN).
o Host name or IP address can be used along with ping command. Ping
uses the ICMP protocols mandatory.
o ECHO_REQUEST datagram to evoke an ICMP ECHO_RESPONSE
from a host or gateway.
Example:
1) Ping the host to see if it’s alive.
2) Increase ping Time Interval
Wait for 5 seconds before sending the next packet.
$ping –I 5 google.com
3) Send N packets and stop
$ping –c 4 google.com
4) Timeout –w
Ping –w option specifies the deadline to terminate the ping output. This
specifies the total number of seconds the ping command should send
packets to the remote host.
The following example will ping for 5 seconds. i.e ping command will exit
after 5 seconds irrespective of how many packets are sent or reciv
$ping –w 5 localhost
 Traceroute:
o Prints the route that packets take to a network host.
o Attempts to trace the route an IP packet would follow to some intenet
host with time to live then listening for an ICMP “time exceeded”
reply from a gateway.
traceroute command uses various options : Tag Description -help Display a help message and exit -d Enable socket level debugging -f Specifies with what TTL to start -v Print version information and exit -e Show ICMP extensions $traceroute google.com munotes.in

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176 Networking  Route:
o Route command is used to show manipulate the IP routing table.
o Primarily used to setu p route to specific host or network through
interface
route command uses various options :
Tag Description -A Use the specified address family -F Operate on kernel’s forwarding Information base routing table -C Operate on kernel routing cache -n Shows numerical addresses -net Target is network -del Delete route -add Add a new route
 Hostname:
o Hostname command shows or sets system hostname
o To display the system’s DNS name
o Hostname is usually set at system startup by reading the contents of
file which contains hostname.
o For example /etc/hostname
Hostname command uses various options: Tag Options -a Displays the alias name of the host -b Always set a hostname -d Displays the name of the DNS domain -F Read the hostname from the specified file -i Display the network address of the host name -f Display the FQDN (Fully Qualified Domain Name) -s Display the short host name -h Print a help message and exit
8.5 NETWORKING GUI  The network manager service dynamically detects and configures
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177 Linux  Network manager does not have its own graphical user interface.
 In Ubuntu the graphical configuration tool to configure network
interfaces is called network -admin
 System should include the network -manager -gnome package that is
able to run Network M anager’s GUI connection editor.
8.6 LET US SUM UP Thus, we have studied the basic concepts of network and linux command
which is used to perform communication among user over internet. The
uses of network protocol and commands are explained in chapter.
8.7 UNIT END QUESTIONS 1) Write a note on FTP.
2) What is the purpose of commands: - ssh, ping, hostname, telnet, route.
Give suitable example.
3) Define network protocol. Explain in detail HTTP.
8.8 LIST OF REFERENCES 1) Unix Concepts and Applications by Sumitabha Da s.
2) Official Ubuntu Book, 8th Edition, by Matthew Helmke & Elizabeth
K. Joseph with Jose Antonio Rey and Philips Ballew, Prentice Hall




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178
9
BASIC SHELL SCRIPTING
Unit Structure
9.0 Objectives
9.1 Introduction
9.2 Features and capabilities,
9.3 Syntax
9.4 Modifying files
9.5 Sed
9.6 awk command
9.7 File manipulation utilities
9.8 Dealing with large files and Text
9.9 String m anipulation
9.10 Boolean expressions
9.11 File tests
9.12 Case
9.13 Debugging
9.14 Regular expressions
9.15 Let Us Sum Up
9.16 Unit End Questions
9.17 List of References
9.0 OBJECTIVES In this chapter you will learn about:
 Basic of shell scri pting through environment variables, conditional,
looping statements and commands.
9.1 INTRODUCTION This chapter introduces shell scripting through variables, commands,
conditional and looping statements. The sed and awk commands are
supporting for file ma nipulation for analyzing data.
9.2 FEATURES AND CAPABILITIES  A shell scr ipt is defined as it plain text file with a set of Linux
command, flow of control and Input Outptut facilities. And it is
created by using any text editor like vi, emac etc.
 Shell scr ipt allows use of variable, file and directory management
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179 Linux  Shell script provides many features like loop, construct, array,
functions, logic with other utilities etc.
 Shell script allows reading input and parsing the co mmand line.
 Shell supports advanced features such as Functions and Arrays,
regular expressions.
 Easy to use and understand.
 It is much quicker than programming in any other languages.
9.3 SYNTAX Following is syntax basic structur e of shell script:
#!/bin/b ash (Shebang)
#(comments)
chmod +x scriptfilename (make script executable)
echo “ “ (to print message of variables contains)
./scriptfilename.sh (execute script)
Where,
#!/bin/bash: -It define which shell will be used to run the shell script.
#comments: -By using ‘#’ symbol you can pass the comments.
chmod +x scriptfilename.sh: -It define file is executable and tell to Linux
that file is executable.
./scriptfilename.sh: -It define execute the script
Examples,
1) To check your current shell use following command a s
echo $SHELL


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180 Basic Shell Scripting #we learn shell scripting
echo “This is my first program by using shell script”


Output :


Constructs:
Construct shell script you can use text editor such as vi or cat command .
vi command :
First type following vi command and rest of text as :





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181 Linux


Output:
We learn basic shell scripting, following are screen snaps for creating first
shell script program.


cat command:
First type following cat command and rest of text as :




When you finished your writing script press CTRL+D to save and then by
using chmod command give executable permission to file.


For execute file give command as ./demofile2.sh

Sometimes arguments are specified with shell procedure ten they are
assigned to special variable or propositional parameters.
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182 Basic Shell Scripting 2) $* The complete set of positional parameters as single string.
3) $# The number of arguments specified in command line.
4) $0 Name of executed command.
5) $? Exit status of the last command
6) $! PID of last command
Example :


When you finished your script press CTRL+D to save and By using
chmod command give executable permission to file.


Here we pass optional parameters as ashwini and 18889 as shown above.


9.4 MODIFYING FILES Consider a file studentinfo.txt which is already created and contains
information of student like Roll.No, Name, Class and PH.No. etc if you
want to add some text in studentinfor.txt file then it is modify by using vi
editor following key for modify the file. Name of Key Use of Key h It is used to move left one character l It is used to move right one character k It is used to move up one character J It is used to move down one character Also for modifying file you sed command which modify each line of line
and replace specified parts of the line.
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183 Linux 9.5 SED “sed” means stream editor. Sed command allows:
1) Performing basic text transformations on an input stream.
2) To modify each line of a file
3) To replace specified parts of the line.


Example
Conside r a file file.txt


If the file name “file.txt” and you want to change all occurrences of
VASHI to PAREL to the modified file to “file.txt then use the following
command.
Command:


Output:

sed is also frequently used to filter lines in a file or strea m.
Example:
If you only want see the lines containing “SA” you could use: munotes.in

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184 Basic Shell Scripting


Output :


Replacing or substituting string:
sed command is mostly used to replace the text in a file. The below simple
sed command replaces the word “UNIX” with “LINUX” in the fi le.


Output :


Here the “s” specifies the substitution operation. The “/” are delimiters.
The “Unix” is the search pattern and the “Linux” is the replacement string.
9.6 AWK COMMAND This command is used for processing or analyzing text files, in particu lar
data files that are organized by lines (rows) and columns.
Syntax:
awk ‘pattern {action}’ input -filename > output -filename
This command is worked as taking each line of the input file. And if the
line contains the pattern then apply the action to the l ine and write the
resulting line to the output -file.
If the pattern is omitted, the action is applied to all line.

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185 Linux Examples:


1) $awk ‘{print $1}’ file.txt > outputfie.txt :




This statement takes the element of the 1st column of each line and write s
it as a line in the output file “outputfile.txt”. As shown above
2) $awk ‘{print $2,$3}” file.txt > opfile.txt:

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186 Basic Shell Scripting In this command we pass the second, third column, with $2,$3. By default
columns are assumed to be separated by spaces or tabs, comma.
You can use regular expression as condition.
3) $awk ‘/15/{print $2}’ file.txt:
Here regular expression is string between the two slashes (‘/’). In this case
string “15”. It indicates that if a line contains the string “15”, the system
prints out the element at the 2nd column of that line.
4) If the table elements are numbers awk can run calculations on them
as in this example :


$cat awkfile.txt :


$awk ‘{print ($1 * $2) + $4}’ awkfile.txt :


9.7 FILE MANIPULATION UTILITIES 1. tac:
This command is used fo r file manipulation tac command is used for print
file in reverse (liat line first). That is this command prints the file in
reverse order with the last line first.






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187 Linux


Syntax: tac filename.txt
Example: consider a file file.txt
Command :


By using tac command file.txt display print in reverse.
2. rev:
This command is used for reverse the characters in every line. Difference
between tac command and rev command is -
rev command reverse each character of the line
tac command reverse each line of the fi le.
Syntax: rev filename.txt
Example: Consider a file file.txt


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188 Basic Shell Scripting Command:


By using rev command file.txt display reverse the characters in every line.
3. paste:
This command is used for merge file lines that means. This command
paste the line1 of file1 , line1 of file2,.. line1 of fileN. It will repeat the
same for all lines. Each file’s line is separated by tab.
Syntax: $paste filename1.txt filename2.txt filename3.txt
Example 1:
Consider a two file pastefile1.txt and pastefile2.txt are shown combined by
using cat co mmands:






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189 Linux Example 2:
Let us consider a file with the sample contents as below :


i) Join all lines in a file:


-s option of paste joins all the lines in a file. Since no delimiter is
specified. Default delimiter tab is used to separate the columns.
ii) Merge a file by pasting the data into 2 columns using colon
separator:


iii) Join all lines using the comma delimiter:


4. join:
This command is used for join lines of two files which is based on a
common field, this can specify by using field.
Syntax: $join –t’:’ -1 N -2 N file1 file2
Where ,
-t’:’ – it indicates that field separator
-1 N – it indicate that Nth field in 1st file
-2 N – it indicate that Nth field in 2nd file
file1 file2 – it indicate that files name that should be jo ined munotes.in

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190 Basic Shell Scripting Example: Consider two file joinfile.txt and joinfile1.txt


Now by using join command you join this two file joinfile.txt joinfile1.txt
Command :


Output :


9.8 DEALING WITH LARGE FILES AND TEXT To view and manipulate large log files use the follow ing command
1. To Display Specific Lines of a file use sed command:
Here to view specific lines you have to use line numbers.
Syntax: $ sed –n –e Xp –e Yp FILENAME
Where, Sed print all the lines by default -n output -e Command to be executed Xp Print line number X Yp Print line number Y FILENAME name of the file
Example :
1. $sed –n –e 50p –e 100p –e 100p /var/log/file :
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191 Linux ii) You can view the content of var/log/f ile from line number 100 to
300:
Syntax: sed –n M, Np FILENAME
Where, M Starting line number N Ending line number
$sed –n 100,300p /var/log/file
2. To display First N Lines of a file use head Command :
To displays only first 20 lines of /var/log/file
Syntax: head –n N FILENAME
$head –n 20 /var/log/file
3. Ignore last N lines of file use head command:
To shows how to ignore the last N lines, and display only the remaining
lines from the top of file.
To display all the lines of the /var/log/file except the last 50 lines.
Syntax: head –n N FILENAME
$head –n -50 /var/log/file
4. Display last N lines of the file use tail command
To displays only last 30 lines of /var/log/file.
Syntax: tail –n N FILENAME
$tail –n 30 /var/log/messages
9.9 STRING MANIPULATION We know that when you use $(dollar s ign) followed by variable name it
indicates that variable with its values which is known as parameter
expansion.
1. String:
This command is used to get the length of the given variable in your shell
script.


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192 Basic Shell Scripting Syntax: $(#string)
Example:






Output:


2. Position:
This command is used to extract a substring from a string. Character
substring from $sting starting from $position
Syntax: $(string:position)
$(string:position:length)
Example:




Output:


Where, First variable returns the substring from 6th position.
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193 Linux 3. Substring for shortest match:
To match shortest substring use following command :
Syntax:
1) ${string#substring}:
# - deletes the shortest match of $substring from front of $string
2) ${string%substring}:
% - deletes the shortest match of $substring from back of $string
Example :




Output :


Here first echo statement substring is ‘*’ matches the substring starts with
dot and # strips from the front of the string, so it strips the substring is
“substrings”
Second echo statement substring ‘*’ matches the substring starts with dot,
and % strips from back of the string, so it deletes the substring ‘.txt’
4. Substring for longest match:
To match longest $substring use f ollowing command
Syntax:
1) ${string##substring}
## - deletes the longest match of $substring from front of $string.
2) ${string%%substring}
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194 Basic Shell Scripting Example:




Output:


Here first echo stateme nt ##* match for ‘*’ longest match which matches
‘file.substrings’ so after striping it returns remaining txt.
Second echo statement %%* match for ‘*’ longest match which matches
‘subtrings.txt’ so after striping it returns ‘file’.
9.10 BOOLEAN EXPRESSIONS Following are Boolean operators used in shell script: Name of operator operator Use logical negation ! operator Display result as a true condition into false and vice versa logical OR -o operator Display if one of the operands is true then condition should be true logical AND -a operator Display if both the operands are true then condition should be true otherwise it should be false.
Example:

1) [ !false ] return it is true
2) [ $a –lt 20 –o $b –gt 100 ] return it is true
3) [ $a –lt 20 –a $b –gt 100] return it is false
Whete ‘lt’ means less than and ‘gt’ means greater than.

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195 Linux


Output :


9.11 FILE TESTS When you are using files in shell script, to do some file tests on your file
before using it.
File test allow :
1) Checking for existence of your file.
2) Your fi le is readable, writable or executable.
3) Type of the file.
File test is done by if clause .
Syntax:
if [ -option filename to be test ]
then,
--------------
else
---------------
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196 Basic Shell Scripting Following are some file test operators: File test operator name Use a It returns true if the file exists c It returns true if the file exists and is a character special file d It returns true if the file exists and is a directory e It returns true if the file exists f It returns true if the file exists and is a regular file p It returns true if the file exists and is a regular file r It returns true if the file exists and is readable s It returns true is the file exists and has a size greater than zero t It returns true if file descriptor is open and refers to a terminal w It returns true if the file exists and is writable x It returns true if the file exists and is executable
Example:
1. Shell script checks for existence of a regular file.


Output :


2. All the file test operators :
Consider a variable name is ‘file’ which holds an existing file name as
“/var/www/test/linux/test.sh” whose size is 100 bytes and has read, write
and execute permission off -




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197 Linux


Output:


Here read, write and execute permission off -hence output is obtained with
every else statements.
9.12 CASE munotes.in

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198 Basic Shell Scripting Case statement is similar to switch statement used in C. By using case
statement user can test simple values for integers and characters and
testing can be done by string pattern that can contains wild card char
actors (special characters)
Syntax:
Case expression in
pattern1)
Statement to be executed if pattern1 matches
;;
Pattern2)
Statement to be executed if pattern2 matches
;;
esac
case required at least one pattern
Finally case statements expand the expression and try to it against each
pattern. Here expression is compared against every pattern until match is
found and then the statements following the pattern matching is executed.
When statement part is executed until;; (double semicolon) which
indicates that program flow should jump to the end o f the entire case
statement. If there is no match, exit status of case is zero.
Example:
Once finished save it and exit.
For run above shell script use chmod com
mand as shown in below.
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199 Linux

Output:


9.13 DEBUGGING We know that with the x -option, run the entire script in debug mode.
Each command with its arguments is printed to standard output after the
commands have been expanded but before they are executed.
-x option is used to debug a shell script
Run the shell script using –x option
For e.g. $ -x scriptname.sh
Following are debugging options used for turn on or off with set
command.
set –x: it display command and their arguments as they are executed
set –v: it display shell input lines as they are read.
9.14 REGULAR EXPRESSIONS Regular express ions are special characters. It is used for search data,
matching patterns grep command is used to search for a specific string in a
file.
Following are some basic regular expressions symbols : munotes.in

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200 Basic Shell Scripting 1) It is used to replaces any character
2) ^ It is used for matches s tart of string
3) $ It is used for matches end of string
4) * It is used for matches up zero or more times the preceding character.
5) \ It is used for Represent special characters
6) () It is used for Groups regular expressions.
7) ? It is used for Matches up exactly on e character
8) \+ It is used for Matches one or more occurrence of the previous
character
9) \? It is used for Marches zero or one occurrence of the previous
character .
Examples:
1. Search for matches start of -
$ls –l | grep ^ -

2. Search for content that STARTS with ‘d’
$ls –l | grp ^ d


3. Search for content containing letter ‘r’
$cat test.sh | grep r munotes.in

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201 Linux


4. Search for content that STARTS with ‘e’
$cat test.sh | grep ^e


5. Select only those line that end with ‘e’
$cat test.sh | grep e$ munotes.in

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202 Basic Shell Scripting







6. Filter out all lines that contain character ‘o’
$cat test.sh | grep o


7. Searching for all characters ‘v’
$cat test.sh | grep v munotes.in

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203 Linux


8. Filter out lines where character ‘a’ proceeds characters ‘r’
$cat test.sh | grep “a \+r”


9.15 LET US SUM UP Thus, we have studi ed the basic concepts shell scripting. Test cases,
conditional, looping statements have been described briefly. The
debugging also explained.
9.16 UNIT END QUESTION S 1) Give the purpose of HOME, PS2, PS1, SHELL, USER shell
variables.
2) Define regular expressio n. What is the purpose of the following
regular expression characters: - ^ , $ , * , ?
3) Write a shell script to read a month number from the user and display
corresponding month name
4) List any three features of awk. Give its general syntax. Explain it with
two different examples
5) Write a shell script to accept 2 numbers from user and one operator.
Based on the operator entered perform addition, subtraction,
multiplication and division.
9.17 LIST OF REFERENCES 1) Unix Concepts and Applications by Sumitabha Das.
2) Official Ubuntu Book, 8th Edition, by Matthew Helmke & Elizabeth K.
Joseph with Jose Antonio Rey and Philips Ballew, Prentice Hall .



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204 Basic Shell Scripting *****
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