rootsan technologies pvt ltd linux modul033

8/6/2019 Rootsan Technologies Pvt Ltd Linux Modul033

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Welcome to RedHat Linux

RH033


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Hardware Requirements

Pentium Pro or better with 256 MB RAMOr

64-bit Intel/AMD with 512 MB RAM

2-6 GB disk space

Bootable CD

Other processor architectures supported

Itanium 2, IBM Power, IBM Mainframe


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Lesson 1 Fundamentals of

Linux

IntroductionLinux is an open source operating system with

highly advanced features.

Topics

Brief History of Linux

Why is Linux?Linux Distributions


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Brief History of Linux

Linux was originally developed by LinusTorvald in 1991.

Linux is distributed under the GNU licenses.

GNU stands for Gnu Not UNIX, it is an opensource movement started by RichardStallman in the year 1984.

The main aim of GNU is to provide the O.Sand its source code freely.


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Why Linux?

Linux is an Open Source Software

Multi-user and multi-tasking

Supports most of modern PC hardware

Fully supported distribution


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Linux Distributions

To install Linux, choose a Linux Distribution

A distribution is the Linux kernel, plus aninstallation program, plus some set of

applications

There are four general distributions RedHat SuSE Mandriva Linux Debian


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Linux Distributions

The Red Hat and SuSE distributions are produced by

companies by the same names.

They aim at providing an easy installation procedure, andfor a pleasant desktop experience. They are also good asservers, sold in boxes, with an installation CD and printed

manual. Both can also be downloaded via the network.

Mandriva Linux (also known as Mandrake Linux) wasoriginated by Gael Duval.

Mandriva Linux is also notable for compiling its packages

with optimizations for Pentium-class and more advancedprocessors which are incompatible with older CPU versionssuch as 386 and 486.


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Linux Distributions

The Debian distribution is produced by avolunteer organization.

Its installation is less easy: You have to

answer questions during the installation theother distributions deduce automatically.Nothing complicated as such, but requiringunderstanding of and information abouthardware most PC users don't want to worryabout.

On the other hand, after installation, Debian


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Logging In and GeneralOrientation


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Module 2 Logging In and

General Orientation

IntroductionIn Linux, a terminal session starts by

logging in through the terminal. When theuser logs in for the first time, the user

account is set and provided with apassword.

Topics Typical terminal session Concept of Login and Logout Opening of Shell Prompt Command Line Format

Basic commands vi Editor


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A Typical Terminal Session

Provides login prompt to the user

Linux has two modes of terminals

Graphical User InterfaceCharacter User Interface

Linux has seven terminals by default (F1 F6)


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Logging In and Out

A Graphical login screen Graphical Logout Session


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Opening a Shell Prompt

Snapshot


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Command Line Format

Pattern of issuing the command

The commands are separated with optionsusing spaces and symbols.

The options are usually prefixed with thehyphen ( - )

Command line has three basic parts Command Options Arguments


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Shell Interpretation

Shell prompt accepts commands to perform various functions like:Execute commands

Variable assignment

Variable substitution

Filename generationI/O redirection

Pipelines

Command substitution

Interpretive Programming language


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Basic Commands

vi opens a text editor

rm remove files

mv move or rename the files

cp copy the files

rmdir removes the directory

pwd display present working

exit or logout leave the session

man command Read man pages on command


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vi Editor

vi (visual) editor was written in 1976 by BillJoy at the University of California, Berkeley.

vi uses a small amount of memory, which

allows efficient operation when the networkis busy.

vi is the only editor which provides basic textediting capabilities.

There are three modes of operation for vi.

They are: Command mode


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Usage of vi Editor

A text editor is a program used to edit files thatare composed of text which can be a

Simple regular text

The source code of a program orConfiguration file

The vi text editor


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Lab Exercises

Type vi editor and get the vi session


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Navigating the File Systems

d l i i h


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Module 4 Navigating the

File SystemsIntroduction

A file system is the methods and the data structures that anoperating system uses to keep track of files.

Topics

The Tree Structure

The File System Hierarchy

Path Names

Basic File System Commands

Create and Remove Directories


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Th T St t


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The Tree Structure

Linux File Structure

Example:/home/condron/source/xntp

Th Fil S t Hi h


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The File System Hierarchy

File System Hierarchy Standard (FHS)

The directories and files noted here are small subsets of those specifiedby the FHS document.

The /dev/ Directory

The /etc/ Directory

The /lib/ Directory

The /mnt/ Directory

The /opt/ Directory

The /proc/ Directory

The /sbin/ Directory

P th N


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Path Names

A PATH is an environment variable that is a

list of directories that the operating systemlooks in to find commands issued by theuser.

Example 1: # whereis ls

ls: /bin/ls /usr/share/man/man1/ls.1.gz

There are two types of path names

Relative Path

Absolute Path

Contd

P th N


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Path Names

Absolute path

Accessing a particular directory or file from the otherlocation, by typing the full details of path.

Absolute path starts with the root (/) directory. It

includes all directories and sub-directories. A relative path starts in your present working directory.

Relative path

Accessing a particular directory or file from samelocation, by typing the file or directory name.

In the case of relative path, the path does not start

with a slash.

B i Fil S t C d


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Basic File System Commands

pwd It displays the users present

working directory.

ls Lists the contents of the files

and directories

cd Changes and also opens thedirectory.

cat It combines files and print onthe standard output

find Command The find command

C t d R


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Create and Remove

Directories Creating directories

Use mkdir command to create a new directory

Syntax

# mkdir

Example: mkdir dir1

Removing directories There are two commands you can use for removing

directories. rmdir

rm -r

L b E i


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Lab Exercise

How will you create a new directory?

Use rm r to remove the existing directory.


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Managing Files

Mod le 5 Managing Files


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Module 5 Managing Files

Introduction

On a Linux system, everything is a file;if something is not a file, it is a process.

Topics

What is a File?

File CharacteristicsWhat can we do with Files?

What is a File?


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What is a File?

A file is a container for data or link to a

device.

Every file has a name and may hold datathat resides on a disk.

A file is a name and the associated data isstored on a mass storage device. It is a

stream of data bytes.

The different types of files are: Regular files

Can be text, data and drawings. Executable ro rams.

File Characteristics


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[root@localhost root]# ls -l

total 1872

-rw-r--r-- 1 root root 1134 Sep 28 12:31 anaconda-ks.cfg

drwxr-xr-x 3 root root 4096 Oct 3 15:29 Desktop

drwx------ 8 root root 4096 Oct 3 15:15 evolution

-rw-r--r-- 1 root root 47186 Sep 28 12:30 install.log

-rw-r--r-- 1 root root 3436 Sep 28 12:30 install.log.syslogdrwxr-xr-x 3 root root 4096 Oct 1 12:48 intro-linux

-rw------- 1 root root 1832960 Oct 1 12:42 intro-linux.html.tar

drwx------ 7 root root 4096 Oct 1 14:45 Mail

-rw-r--r-- 1 root root 51 Oct 3 12:44 new.txt

[root@localhost root]#


A file has several characteristics associated

with it. They can be displayed using the ls lcommand as shown below:

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Example:

-rw-r--r-- 1 root root 1134 Sep 2812:31 anaconda-ks.cfg0 1 2 3 4 5

6 7 The explanation of output is as follows:

File Type regular file d directory l link file c character special file b block special file p pseudo special file Permissions No. Of links to the File

Contd



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Owner

Group

File Size BytesTime Stamp

File Name

What can we do with Files?


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What can we do with Files?

A file is a collection of data, stored on disk

and that can be manipulated by listing thecontents in the directory, changing thelocations of files and directories, viewingfiles, creating and editing files, moving,copying and deleting files.

The user can also create directories, change

directories, delete directories and view PDFfiles.

A directory is also a file that acts as a folder

for other files.

Manipulating files and


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directoriesCopying files

Copying files and directories is done using the cp command. Thecp command is used to copy the files and directories from the specifiedsource to the specified destination. The user can copy a file into thedirectory, but under a different name.

Syntax

cp

Example: # cp file1 dir1

Removing files

The rm command is used to remove single files, rmdir toremove empty directories (Use ls -a to check whether a directory isempty or not). The rm command also has options for removing non-empty directories with all their subdirectories, read the Info pages fordifferent options of rm command.

Contd



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directoriesMoving and Renaming files

The mv command is used to move a file from its source to anylocation within the file structure.

Example of moving a file: # mv file1 /iiht/file1

Example of moving a file: # mv file1 /iiht/file1

The above example says, the file file1 is moved to a different directory iiht.

The mv command is also used to rename a file or a directory

Example of renaming a directory: # mv iiht dir1

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directoriesLinking filesA link is nothing more than a way of matching two or more file names to

the same set of file data. There are two ways to achieve this:

Hard link

Soft link

Hard link

Associates two or more file names with the same inode. Hard links sharethe same data blocks on the hard disk, while they continue to behave asindependent files.

Soft link or symbolic link (or symlink)

Soft link is a small file that is a pointer to another file. A symbolic linkcontains the path to the target file instead of a physical location on the hard disk.Since inodes are not used in this system, soft links can span across partitions.

Lab Exercise


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Lab Exercise

Create a directory by name testand create

the files file1 file2 and file3, createhardlinkfor file1 to new file data.

Differentiate deleting hard link files and softlink files.


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File Permission and Access

Module 6 File Permission


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Module 6 File Permission

and Access Introduction

Linux is a multi-user system where users can assigndifferent access permission to their files. Access permissionscan be set per file for owner, group and others on the basisof read (r), write (w) and execute permissions (x).

Topics File Permissions and Access

Types of Access

Who has to Access to a File?

Access Control Lists

Contd

File Permissions and Access


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Every file is owned by a particular user.

File permissions specifies who has the access to file andwhat type of access the user has.

On a Linux system, there is typically more than one userthat provides a mechanism known as file permissions(rwx), which protect user files from accessing by otherusers.

Types of permissions r read

w write

x execute

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read permission

The read permission lets a user read the contents of the file.For directories, read permission lets the user list the contents ofthe directory (using ls).

write permisisonThe write permission lets the user write and modify the file.

For directories, write permission lets the user create new files ordelete files within the directory.

execute permissionThe execute permission lets the user run the file as a program

or shell script (if the file is a program or shell script). Fordirectories, execute permission lets the user open the directory.


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Types of Access


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Types of Access

Default file permissions

By default, the Linux system assigns certain permissions to anewly created file. The maximum permissions that we can set for anordinary file is 666 and for directories and an executable files is 777.

The default file permission for an ordinary user is 664 and for

root it is 644.

Displaying the umask

The default umask file permissions for ordinary users are 002and for root it is 022.

where, 002 imply masking write permission for others and

022 implies masking write permission for the group and others.

Contd

Types of Access


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Displaying the umask

To display the default mask use the umaskcommand.

Example

# umask

Displaying the default umask value

Types of Access

Contd

Types of Access


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Changing the umask

To change the default umask use the command Syntax

# umask

Example: umask 004

Types of Access

Who has to Access a File?


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Access permission user(owner) group


The owner and the root have the main

access rights over a file.Example

First column gives the access permissions to theuser, group and others.

Second column shows the user or owner of thefile.

Third column shows the group to which the filebelongs.

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Changing permissions

chmod command

chmod changes the access permissions accordingto the options for directories and files.

Syntax

# chmod o+w


Contd



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The chmod command can be used with

alphanumeric or numeric options. Example of symbolic method

chmod u+rw,g-rwx,o-rwx file1 The above example, adds the read and write permission to the

user (owner) removes the read, write and execute permission

from the group to which the file belongs and removes the read,write and execute permissions for others.

Example of numeric method

# chmod 600 file1 6 indicates user (owner), 0 indicates group and the last number

0 indicates others.

Contd



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Changing ownership

chown command chown changes the owner and group of the file and

directory.

Syntax # chown

Example # chown user1 file1.txt

Contd



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Special File Permissions

There are three types of special file permissions

set user identity (SUID)

set group identity (SGID)

sticky bit


Contd



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Contd

SUID or setuid

It is represented by the character s in the user permission

field.

When this mode is set on an executable file, the other userscan login and run the executable file.

The roots id is set to the process.

Syntax

#chmod u+s

where,

u user

s - suid


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Sticky bit

If the sticky bit is set on directory, even others can read andwrite the data to the file, but can not delete the file except theowner.

Syntax

#chmod o+t

where,

o others

t - sticky bit

Example: # chmod o+t /tmp

Contd

Access Control Lists (ACLs)


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ACL is an object associated with a file and contains entries

specifying the access that individual users or groups ofusers have to the file.

It provides a simple way of granting or denying access for aspecified user or groups of users on single file at the same

time.

Using the chmod command the user can set permissions toowner, group or others.

Using ACL, the owner can set the different permissions on asingle file for different users.

Contd



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Contd

Setting ACL using Setfacl

setfacl - set file access control lists

Syntax setfacl u::




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Contd

Getting ACL using getfacl

The getfacl displays the file name, owner, thegroup, and the Access Control List (ACL).

Syntax

# getfacl



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Contd

o o ( )

Copying ACL

The acls can be copied to any files, for which thefiles get the same acl permissions from its sourcefile.

Syntax

getfacl | setfacl --set-file= -

where,

--set-file options set the acl of a file or a directory

Lab Exercise


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Change the permission of the following file

using chmod command.-rwx-rw-r-- file2.txt

From the following example change thepermissions to

User read, write, execute

Group read and execute Others - only execute


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Shell Basics


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What is a Shell?


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A shell manages the interaction between the

system and its users.A shell is a program which takes user input

(e.g. commands which you type) andtranslates them into instructions that theoperating system can understand.The shell allows the user to handle a system

in a very flexible way.

Contd

What is a Shell?


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Contd

Shell Features

Command history The command history buffer stores the commands you enter and

let you display them at any time.

Command aliases

The command aliases feature lets you abbreviate long commandlines or rename commands.

File name completion

The file name completion feature saves typing by allowing you to

enter a portion of the file name. When you press the tab/esc key,the shell will complete the file name for you.

Command line editing

This allows you to retrieve a previously entered command and editit.

What is a Shell?


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Contd

Types of shells

sh or Bourne Shell This is the basic shell, a small program with few features. This

shell does not support any of the shell features such ashistory, command line completion, command line editing.

bash or Bourne Again shell The standard GNU shell, intuitive and flexible. bash is the

standard shell for common users. This shell is a so-calledsuperset of the Bourne shell. This means that the BourneAgain shell is compatible with the Bourne shell: commands

that work in sh, also work in bash.

What is a Shell?


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Types of shells

csh or C shell: This shell has a syntax that resembles that of the highly popular C

programming language and thus preferred by programmers.

tcsh or Turbo C shell

This shell is based on csh but also has programmable filenamecompletion, command-line editing, a history mechanism and otherfeatures lacking in csh.

ksh or the Korn shell:

This shell is a superset of sh. It also features built-in arithmeticevaluation and advanced scripting capabilities similar to those foundin powerful programming languages such as awk, sed and perl.

Aliasing


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Contd

g

The command aliases allow the user to abbreviate long

command lines with small names easy to use and type.

Creating Aliases

To create aliases, use the alias command. The format of the aliascommand is:

Syntax

alias aliasname=command

The aliasname entry specifies the name you want to use.

The alias helps for alternate names for complicated commands.

Example:

[root@localhost root]# alias cls=clear

[root@localhost root]# cls

Aliasing


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Display Aliases

To display alias definitions, enter the followingcommand:

# alias

Remove Aliases To remove an alias for the current login session,

use the unalias command.

The general format of the unalias command is the

following: unalias

g

File Name Completion


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File name completion is one of the most useful features of

the Linux command line.

The shell lets you enter a portion of a file name orpathname at the shell prompt and the shell automaticallywill match and complete the name.

Example # vi us Press Enter

Then the entire file name will be completed as follows if itis unique name,

# vi user123.filnename.txt


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User profiles


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The user profile is a personalized settings of the user

and the shell script and gets executed whenever theuser logins.

The profile can be classified into:

System wide

The changes to system wide profile will effect the workenvironment of all users. These files are available in /etc.

User Specific

User specific profiles effect the work environment of only

that particular user and it stores in the home directory of each user.

What Happens At Login


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When a user logs into a system it executes the

start up scripts in the following sequence:/etc/profile sets the environmental variables andsettings for all users.

/etc/profile.d. runs the login script for all users.

~/.bash_profile - sets the environmental variables andsettings for particular user.

~/.bashrc - runs the login script for particular user.

/etc/bashrc - sets the environmental variables for bashshell.

Variables


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A variable is a label that has a value.

Variables are used to configure the shell.

To set a variable in the shell, use an equal sign toassign it a value. If the variable does not already exist,

it is created.

Example A new variable is defined as follows: $ MYVARIABLE=hello

To display the value of a variable, prefix the variablesname with a $ symbol.

Contd

Variables


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Types of Variables

There are two types of variables Shell variables or local variables

Environment variables

Shell variables or local variables are available only to the currentshell which is used to configure shell.

Environment variables are available to all shells and used toconfigure other commands. e keyboard arrows. To move up anddown in the history command shell. It helps to change the mainvariables like prompt settings, color settings by changing within theprofile to make effect for the entire settings.

Contd

Variables


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Display variable

set command is used to display the local andenvironment variables in a system.

env command is used to display onlyenvironmental variable.

There are two commonly used Variables Local variables

Environment variables

Contd

Variables


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Local variables

HISTFILESIZE - specifies the number of commands ofhistory to be saved when the shell exit.

COLUMNS- sets the width of the terminal.

LINES- sets the height of the terminal.

Environment variables HOME- path to the user home directory.

LANG- sets default language.

PWD- present working directory.

PATH- the path for the command locations. These variables are stored in the profile file (.bashrc).


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Module 8 Shell Advanced


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FeaturesIntroduction

In Linux systems, the shells are often referredto as command line interfaces. The shell capabilitiesprovide a configurable environment allowing the usersto modify commands and prompts.

Topics Shell Substitution Capabilities

Setting Shell Variables

Quoting Characters File Name Generationss

Shell Substitution Capabilities


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Substitution capabilities are used to speed

up command line typing and execution.

The shell substitutions are of three types:

Variable Substitution


Tilde Substitution

Contd



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Variable Substitution

Variable substitution is assigning the absolute pathof a file or directory to any variable. This allowsthe user to access the directory or file fromanywhere in the file hierarchy.

Syntax: =$

Example: myfile=$HOME/file1

Contd



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Command substitution is the mechanism used toreplace a command with its output, within thesame command line.

Syntax: =$(command)

Example: mydir=$ (pwd)

Contd



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Tilde Substitution

A tilde is replaced for the quick reference ofhome directory.

Syntax: ~

Example: ls ~



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The new variable can be created and assigned to an

existing environmental variable such as path.

The new value replaces the old value in theenvironment and the same can be displayed by

using the display value commands.Syntax

=

Example

myfile_name=/root/file1

Contd



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Displaying variable values

The variables can be displayed by using $.

It can be local variable (assigned by the user) or

environmental variable (default variable). All setting variables can be displayed by using thecommand set.

Quoting Characters


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There are some characters in the Unix system and

each has the meaning for the shell and is called asspecial characters. The special characters are:

-

$

#

*

< >

Quoting removes the special meaning of the above

characters. The quoting characters are: \ Backslash

Single quotes

Double quotes Contd

Quoting Characters


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Contd

Backslash ( \ )

Backslash removes the special meaning of thecharacter immediately following the backslash.

Quoting Characters


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Single quotes ( )

The single quote is used to preserve the literalvalue of special character enclosed within the quotes.

Contd

Quoting Characters


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Double quotes ( )

Double quotes removes the special meaning ofall the characters except \ , $ (variable name), $(command).

File Name Generation


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The file name generation has the timesaving feature for

typing the filenames. This feature is called file name

generation or filename expansion.

Advantages of file name generation

File name generating characters are interpreted by the shell.

The command operates on the generated file names. The shell will generate file names that satisfy the requested pattern.

File name generation is done before the command is executed.

The special characters that are interpreted by the shell forfile name generation are: ? Matches any single character except a leading dot

* Matches zero or more characters except a leading dot

Contd



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Usage of the special character ?

Contd



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Usage of the special character *

Lab Exercise


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Give one example on usage of single quotes

command with the variable substitution

Display the files which has 9 characters andwith the extension .jpg


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Input and Output Redirection

Module 9 Input and OutputRedirection


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Redirection Introduction

One important thing you have to know to understand I/O

redirection is file descriptors. There are three types of I/O, calleda file descriptor. They are standard input, standard output,standard error.

Topics Input Redirection

Output Redirection

Error Redirection

Filter

Pipes

Input Redirection


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The standard input (stdin) by default is any text

entered from the keyboard.

Standard input can be redirected through the use ofcommand line argument and redirection operators (like


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Output Redirection


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The default standard output (stdout) is the display

screen.

The command line programs automatically send theiroutput to the screen.

Standard output can be redirected through the use ofcommand line argument and redirection operators (like>).

The standard output can be redirected from the screento any file or to the printer.

Contd

Output Redirection


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Example of output redirection

# ls > list.file

Syntax# command > (file name

Error Redirection


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By default the standard error (stderr) displays on

the terminal and can be redirected into a file,printer and any other program.

Standard error can be redirected with the

standard error redirection operator (i.e 2>, 2>>).

The error messages can be redirected to any file,so that the error messages will not appear on the

screen and it is written to the file.

Contd

Error Redirection


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Example of error redirection

# ll myfile 2>error_message

Syntaxcommand (filename) 2> (filename)

Common RedirectionOperators


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Operators There are two common redirection operators

>

>>

> operator sends the input of command or file to theother file as standard input, overwriting the existingfile.

> > operator sends the input of command or file to the

other file as standard input, appending text to anexisting file, instead of overwriting the file.

Contd



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OperatorsUsage of > operator

Syntax# cat > (filename)

Contd



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Contd

Usage of the >> operatorOperators

Filters


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Filters take standard input and perform an operation upon it andsend the results to standard output.

Example for filters: grep root /etc/passwd

The grep command is used to filter the root user from the /etc/passwd

file.

Pipes


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A pipe is a mechanism for interprocess communication.

The data written to the pipe by one process can be readby another process. It is handled in a first-in, first-out(FIFO) order.

Pipes ( | ) let you redirected output from one commandto become input to another command.

Example: simple pipe with morels -l | more

Contd

Pipes


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The tee command

The tee command copies the standard input to standard outputand also to any files given with an argument.

This is useful when you want not only to send some data down apipe, but also to save a copy.

If a file being written which does not already exist, it is created.

If a file being written which already exists, the data contained isoverwritten unless the -a option (appends the standard input to

the given files rather than overwriting)

Contd


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Lab Exercise


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Filter and display the word blue from the file

my_sortfile

Sort and redirect the data from one file toanother


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Networking in Linux

Networking in Linux


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IntroductionA computer network is defined as a number of systems that

are connected to each other and exchange information across thenetwork connection. The system network is configured by settingthe IP address which is assigned by the system administrator.The IP address provides base services for transmitting databetween networks in TCP/IP (Transmission control

protocol/Internet protocol).

Topics

Network Connectivity

IP address Accessing Remote system

Transferring files

Internet configuration

Networking in Linux


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The Linux system can be connected to the network with the helpof network hardware.

Network hardware can be LAN (Local area network) card, cables,hub/switch or router. To configure the network for the system,TCP/IP (Transmission Control Protocol/Internet Protocol) addressis required from the system administrator.

The IP address can also be obtained from the DHCP (Dynamichost configuration protocol) server configured by the systemadministrator.

When the system is connected to the network, the resources canbe shared and data can be transferred among the systems.

The LAN services (telnet, SSH - Secure Shell, FTP File transferprotocol) enables the file transfer and remote login to the system.

IP Address


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An IP address is a 32 bit binary number usuallyrepresented as 4 decimal values, each representing 8

bits, in the range 0 to 255 (known as octets) separatedby decimal points.

Every system in network is assigned a uniqueidentifying number called IP address.

It is used in order to identify and communicate withdifferent systems present in the network.

The data is sent across the network and contains a

source and destination IP address.

Example:

10.10.1.240

130.130.1.10

192.168.1.200

IP Address


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Configuring IP address

The system can be a part of network byconfiguring the IP address. The IP address can be setby two options in CUI mode and GUI mode.

Static IP

Dynamic IP (DHCP)


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IP Address


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Static IP address in CUI mode

Configuration of the static IP address

Syntax

Type the command # netconfig (Press Enterkey) at the command prompt in the terminal window.

IP Address


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network service

Syntax# service network restart

IP Address


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# ifconfig

IP Address


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# ping

IP Address


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Dynamic IP address in CUI mode

Configuration of the dynamic IP address

Syntax

# netconfig (Press Enter key)

IP Address


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Static IP address in GUI mode

Network configuration in static IP

IP Address


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Dynamic IP address in GUI mode

DHCP settings

IP Address


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Host NameA hostname is the unique name assigned to each host

on the network. The hostname is used to identify a particularIP address. Hostnames are used by various naming systemslike telnet, ssh, FTP, GFTP, NIS and DNS.

There are three ways to resolve host names to IPaddresses on a Linux system:

/etc/hosts

DNS (Domain name service)

NIS (Network information service)

Contd

IP Address


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etc/hosts is a configuration file maintained locally on each hostto resolve hostnames to IP addresses. On a small network, it is

easy to maintain the name resolution of hostnames toaddresses. When adding or removing hosts, or reassigning IPaddresses, the user have to update the /etc/hosts file.

DNS (Domain name service) will resolve the host names into

IP addresses in a large network.

NIS (Network information service) provides a central point ofadministration for common configuration files like /etc/passwd,

/etc/hosts. It preserves the consistency of the configuration

files across all the systems on the network. It simplifiesconfiguration file updates considerably.

Accessing Remote System


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Systems in the network can be accessed remotely withhelp of network connectivity and using IP addresses in

two ways:

Telnet

SSH

Telnet

Telnet is a terminal program for TCP/IP networks such as the Internet.

The telnet program runs on your computer and connects your system tothe other system present in the network.

To start a telnet session, you must log in to other system by entering avalid username and password of the other system.

Contd



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Contd

telnet session

Syntax# telnet



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SSHSSH is a program for logging into a remote machine and

for executing commands on a remote machine

The root user can login through SSH and execute thesystem administrative command.

ssh command

Syntaxssh

Transferring files

Files can be transferred among various systems in


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Files can be transferred among various systems inthe network by using FTP, GFTP and SCP (secure

copy). FTP FTP (File transfer protocol) is a program that allows you to

transfer the files between computers present in the network. Itcan also transfer the files among different operating systems.

Example: Linux to Linux, Linux to Windows, Windows to Linux.

Syntax

# lftp

Transferring files


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GFTP

GFTP (Graphical file transfer protocol) is the toolused for uploading and downloading the files in agraphical mode.

GFTP (Graphical file transfer protocol)session

Contd

Transferring files


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SCP (secure copy)

The scp command is used to copy the files fromother system present in network.

Syntax

# scp :

Example: scp file1 192.168.1.171:/root


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Step 2: Proxy configuration

Contd



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Step 3: Setting the proxy IP and the port

number

Contd



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Contd

Step 4: Verifying the Internet connectivity


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C i i h h d


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Connection to internet through modem

Lab Exercise

H t fi th IP dd i CUI d ? A


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How to configure the IP address in CUI mode? Assumethat your system administrator or lab in-charge has given

you the IP Address as 192.168.1.60?

Check your system to be a part of network andcommunicate with other systems present in the work

Configure your system with Dynamic IP Address usingDHCP

Name the command to copy the files among the system

in the network with out using ftp?

Name the command to copy the files among the systemin the network with out using ftp?


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Process Control

Module 11 Process Control

I t d ti


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Introduction A process is a running occurrence of a program,including all variables and other conditions. It is anexecuting program.

Each process contains a system wide unique processnumber (PID- Process Identification).

Topics Identifying Process

Managing Process

Background Processing Putting Jobs in Background

The operating system will execute the processes by

Identifying Process


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The operating system will execute the processes bydefault and the user can also create a process.

The process can be identified which is in executionalong with its PID (process identification number).

Process creation

Processes are created with the fork system call (theoperation of creating a new process is called forking).

Example: vi

Contd

Vi i th i i

Identifying Process


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Viewing the process origin

The pstree command is used to display theprocess origin.

Contd

Identifying Process

Vie ing the c ent p ocess


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Viewing the current process

The ps command is one of the tools for visualizingprocesses. It displays the current working shell. Sinceps command does not give detailed information aboutthe process, the grep command in a pipe is used toselect a particular process out of the list of all

processes.

The bg command is used to check and

Managing Process


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The bg command is used to check and

move a job to background

Contd

Example for foreground

Managing Process


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Example for foreground

Contd

Managing Process

Process Scheduling


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Process Scheduling

The Linux kernel uses a process scheduler to decide which process

has to be executed first. It is done by using process priority.

Scheduling Priorities

Every process has a scheduling priority. The operating systemdetermines the priority of a process based on nice value method.

To calculate this priority is difficult, but users can affect the priorityby setting the nice value. The niceness value is the numberranging from -20 (highest priority) to 19 (lowest priority) It has adefault value of zero. Process with a high priority gets to run moreoften, while the low priority background tasks, run less frequently.

Contd

Priorities for programs

Managing Process


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Priorities for programs

The nice values of active processes can be viewed using

the ps command with the l or f option for long output.

Example for nice command:

The nice command is used to modify the default niceness

value. To set the niceness value to a different value, usethe n option:

Example:

Contd

Showing priorities of different process

Managing Process


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Contd

Showing priorities of different process

Managing Process

Usage of top command


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Contd

Usage of top command

The top program displays all the system and usersprocess priorities running in all the terminals.

The process running on your system is updated once inevery five seconds.

A process in the running state is highlighted.

Managing Process

Altering priorities of running programs


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Contd

Altering priorities of running programs

The users can reduce the priority of currentlyrunning jobs using the renice command. Only thesuperuser is permitted to move up the priority ofcurrently running processes.

Example of renice command

Managing Process

Terminating the process


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Contd

Terminating the process

The process is terminated when it receives asignal.

There are multiple signals that the user can send

to a process. The kill command is used to send a signal to aprocess.

The command kill -l shows a list of signals which

the user wants to terminate.

killall command will perform an orderly

Managing Process


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Contd

killall command will perform an orderly

shutdown of the process.

killing a process

Managing Process


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killing a process

Background Processing

A background process is the child of the process.


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A background process is the child of the process.

It refers to processes that are run with a relatively low priority,require little or no input, and produce a minimum of output.

The background is also used for long tasks that requiremassive amount of computation and thus CPU time.

Daemon (Disk and execution Monitor)

A daemon is a background process that is considered to runindependently, with little or no user interference.

Example: Apache web server http daemon (httpd)

Putting Jobs in Background

The shell offers a feature called job control which allows


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The shell offers a feature called job control which allowseasy handling of multiple processes. This mechanism

switches processes between the foreground and thebackground. Using this system, programs can also bestarted in the background immediately.

putting jobs in background

jobs command is used to verify the background process

Contd

Putting Jobs in Background

Suspending a process


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Suspending a process

A process can be suspended temporarily withoutbeing killed. Suppose that & symbol is missed outby mistake, use ^z and the process will besuspended.

The process still exists but is idling. To resume theprocess in the background type the bg command(background).

Lab Exercise

Create a process viwith filename and send the process to


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p pbackground and check background process

Check the background running process and bring it to the foreground

How to send running process to the background and bring it back tothe foreground?

Start a Process using find command with the priority of -18

Display and manage the priorities with the single command


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Offline File Storage


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Storage files to Media

Backing up of a system is the most major task to be


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g p y jperformed by a system administrator.

Computers have the major advantage of storing thedata, which makes it significant.

Backups are important because of the possibility ofloss of data.

The possibility of data loss can be by:

File system corruption

Accidental removal of files

Hardware failures

System crashContd

Backup Media



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Contd

p

The following are some of the methods of back up through

media floppy disks

Tapes

removable hard disks

rewritable CD-ROMs

Backup tools

tar

dd

Dump cpio


Backup using tar command


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Contd

An archiving program designed to store and extract files from an

archive file known as a tarfile. The tar is the most commonly usedcommand for the backup.

tar options

tar cvf (creating the tar file)

tar tvf (listing the contents of tar file)

tar xvf (extracting the contents of tar file)

where,

c create

t list

x extract

v verbose

f file

Backup using dd command



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Contd

p g

dd copies a file from source to destination. It copies aninput file (if) file and sends the result to the output file (of) whichconverts and formats according to the options.

Syntax

# dd if= of=

Exampledd if=bootdisk.img of=/dev/fd0


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Example:


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Contd

a pdump -0 f /home_dumps/mydumps /home

where,-0 - dump level (full backup)

-f - write a backup to file


Backup using restore command


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Contd

The restore command is used to view and restore the dumpfile.

Syntax:# restore -

Example: restore if mydumps

where,

-i is interactive restoration

-f is read backup from file

Backup using cpio command



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Contd

p g p

The cpio command is a tool for creating and extractingarchives, or copying files from one place to another,which contains other files and information about them,such as their file name, owner, timestamps, and access

permissions.

It handles a number of cpio formats as well as readingand writing tar files. The archive can be another file on

the disk, a magnetic tape, or a pipe.

cpio has three operating modes.



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Contd

copy-out mode, cpio copies files into an archive.

copy-in mode, cpio copies files out of an archive or liststhe archive contents.

copy-pass mode, cpio copies files from one directorytree to another, combining the copy-out and copy-in

steps without actually using an archive.

Syntax for creating the cpio file



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Contd

find (source file name) | cpio (options) > (target file name)

Example: find file1 | cpio -o > file1_back.cpio

Syntax for extracting the cpio file

cat | cpio (options)

Example:

cat file1_back.cpio | cpio idvm

where,

d make directories

i extract m modification time

o create

v verbose


Compression tools


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Contd

Zipzip is a compression and file packaging utility. The program is

useful for packaging a set of files for distribution, archiving files andsaving disk space by temporarily compressing unused files ordirectories. The zip program puts one or more compressed files into asingle zip archive, along with information about the files. An entiredirectory structure can be packed into a zip archive with a singlecommand.

Syntaxzip

Example:zip install install.log


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Gzip


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Contd

By default, gzip keeps the original file name and

timestamp in the compressed file. These are used whendecompressing the file with the N option. The mainadvantage of gzip over compress is it has a better

compression capacity than other compression tools.

Syntax

gzip

Example

gzip install.log

Gunzipd h f l d b k l



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Contd

gunzip decompress the files created by gzip. It takes a list

of files on its command line and replaces each file ending with.gz, -gz, .z, -z, _z or .Z and which begins with the correctnumber with an uncompressed file without the originalextension. gunzip also recognizes the special extensions .tgz and.taz as shortcuts for .tar.gz and .tar.Z respectively.

Syntax

gunzip

Example: gunzip install.log.gz


Bzip2b i 2 i bl k ti fil It t li t f fil


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Contd

bzip2 is a block-sorting file compressor. It expects a list of file

names to accompany the command-line tools. Each file is replacedby a compressed version of itself, with the nameoriginal_name.bz2. Each compressed file has the same modificationdate, permissions and when possible ownership as the correspondingoriginal, so that these properties can be correctly restored atdecompression time.

Syntaxbzip2

Example:bzip2 install.log


Bunzip2bunzip2 (or bzip2 d) decompresses all specified files bzip2


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bunzip2 (or bzip2 -d) decompresses all specified files. bzip2

attempts to guess the filename for the decompressed file from that ofthe compressed file. If the file does not end in one of the recognizedendings, .bz2, .bz, .tbz2 or .tbz, bzip2 gives an error message that itcannot guess the name of the original file, and uses the original namewith .out.

Syntaxbunzip

Example:

bunzip install.log.bz2

Backup any desired directory using tar command

Lab Exercise


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Compress the file mydata from the data directoryand uncompress into a new directory by name

backup usingzip and unzip commands

Backup the /tmp directory into a new directory byname tmp_backup using dump command

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