Session3 Theory

8/11/2019 Session3 Theory

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Linux File System Directories

/ Begins the file system structurecalled the root.

/boot Hold the kernel image files and associated boot information and files.

/home Contains users home directories.

/sbin Holds administration-level commands and any commands used by the

root user.

/dev Holds file interface for devices such as the terminal and the printer.

/etc Holds system configuration files and any other system files.

/etc/opt Holds system configuration files for application in /opt

Directory Function


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/etc/X11 Holds system configuration files for the X Window System and its

applications.

/bin Holds the essential user commands and utility programs.

/lib Holds essential shared libraries and kernel modules.

/lib/modules Holds the kernel modules.

/mnt Used to hold directories for mounting file systems like CD-ROMs orfloppy disks that are mounted only temporarily.

/opt Holds added software applications (for example, KDE on some

distributions).

Directory Function


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/proc Process directory, a memory-resident directory containing files used to

provide information about the system.

/tmp Holds temporary files.

/usr Holds those files and commands used by the system; this directory

breaks down into several subdirectories.

/var Holds files that vary, such as mailbox and FTP files.

Directory Function



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Login screenEnter the user name


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PWD

PWD

Present working Directory

Display the absolute path of the current directory.


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The absolute path of the

root directory is displayed.

PWD



mkdir

mkdir :

Make directory (or) To create a directory

Syntax :

mkdir



mkdir

This will create a

directory advpro.



cd

cd

- Change directories

Syntax :

cd

cd ..

- To a directory one level up (parent directory)

cd -

- To your previous working directory

cd /

- To the / (slash) directory



cat

cat

it is the command to create and view files

Syntax:

cat [options] [filename]

cat > [filename] To create a file

cat < [filename] To view a file

cat >> [filename] To append text to a file



cat

As mentioned in the previous

slide. cat is used to create a file

The file is saved through ctrl -d

after typing the text


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touch

touch command is used to update the time stamps of a file.

touch is also used to create empty file.

Syntax : touch [filename]

touch can create multiple empty file too.

Syntax : touch [filename1] [filename2]


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Copy Command

cp : cp command is known for copying files and directories.

Syntax : cp [options] source destination

Options :

-r recursively copy an entire directory tree

-p preserve permissions, ownership, and time stamps

Example :

cp File1 File2


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mv : This command is used to move and renaming files and

directories

Syntax:

mv

Example

mv file1 file2 (now the file1 is changed to file2)

Move Command


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rm and rmdir command

rm : This command is used to remove files

Syntax:

rm

Example :

rm file1

rmdir : This command is used to remove directories.

Syntax:

rmdir Example :

rmdir linux


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The file command is used to check the file content.

Syntax :

file Example:

file f1 (f1 is a file. File will show the format)

file /dev/fd0 (The output shows that the fd0 is a

block special file)

File command


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vi & vim editor

Vi is known as the visual editor.

It is a standard editor under Linux and Unix system.

Vim is the improved version of vi editorVi have three modes of operation

Command mode

Insert mode

Esc mode


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File Repositioning

Press G, Cursor go to last line of a file.

Press 1G, Cursor go to first line of a file.

Press Ctrl+f, Cursor forward one full screen.

Press Ctrl+b, Cursor go back one full screen.

Press Ctrl+d, Cursor go down half a screen.

Press Ctrl+u, Cursor go up half a screen.


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Screen Repositioning

Press H, Cursor go to first line on screen.

Press M, Cursor go to middle line on screen.

Press L, Cursor go to last line on screen.

Press Z+Enter, Make current line is first line on screen.

Press - (hyphen) Make current line last line on screen.


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It is also possible to read a other file content in your current files.The following command help you :

Go to exmode in a vi editor

Syntax : r

Example :r /root/file1

While working in a editor we can copy the file content to another

file

Syntax : starting line, endingline w

Example : 1,20w file2Example : 21,40w >> file2

Advanced Reading and Saving


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Filtering

A powerful feature of vi is the ability to include into your document

the output of Linux commands.

For example if you want to display any command output in

your file see following syntax .!!command

The syntax will be working in exmod in editor.

For example to display date ,type following command in exmod.

!!date


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Sed Command

Sed command just like find and replace .

To display a file , the Sed command change the particular word in

standard input only , but not change original content of file.

Example of Sed command .

sed s/ram/raju/g /root/file1


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ex mode : search and replace

vi can perform search and replace operations much like sed

command.

Syntax:

ex mode:1,$s/searchname/replacename/g

1,$ - address starting from line one.

s - String of character

g - replace multiple matches in a

line


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It is also possible to read a other file content in your current files.

The following command help you :

Go to ex mode in a vi editor

Syntax : r

Example :r /root/file1

While working in a editor we can copy the file content to another

file

Syntax : starting line, ending line w

Example : 1,20w file2

Example : 21,40w >> file2

Advanced Reading and Saving


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Configuring VI and VIM

Number of configuration are available in vi editor, see some of

example .

:set number - shows a line number on the left margin in a vieditor

:set showmatch - when a right curly braces or a right paranthesis

is typed, a cursor will jump to the matching left curly braces or left

paranthesis.

:set all - it shows all configurations.


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Redirecting Input and Output

Output of a command is redirected to a file

Command > filenameExample ls -l > /root/file1

Example ls -i >> /root/file1

Output of file redirected to a command

Command < filename

Example - cat < file1

Error message of a command redirected to a file

Command 2> file1

Command 2>> file1

- Example ll L > file1


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tr translates the upper caseletters to lower case.Here

output of file v is redirected

as input to the tr command.



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2> redirects the

error messages to the

ex file.

Here we can see

redirected errormessages in the ex file.


i i


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Piping

Pipes is used to execute more than one command at a time. See

following command.

Syntax : command1 | command2Example: ls -l | more

It is also used to execute command result

Example: cat file1 | grep station


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Redirecting Both Standard Output And Error

If find command is executed, its output can be stored in file2. if

error occurs during execution, the error message is stored in file1.

For example:

find / -name passwd 2> file1 >file2

C d


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tee Command

tee is useful to save the output at various stages from a long

sequence of pipes.

Example: ls | tee a1 | ls

l | tee b2

The above example shows the types of ls commands and options are

used to store output to the files g1, g2 and g3.

d


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grep command

grep

- means general regular expression processor.

-it analyze the content of a file a line at a time, returning a line

that matches a pattern.


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awk command

An awk program searches for lines in a file and performs some

action on those lines.

Example:

awk /bash/ { print }/etc/passwd

Pi i


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Here the cat and

grep command are

executed in pipeline.

Piping

Fi d d


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Find command

Find:

To search files and directories in a specified path.

Syntax:

find [conditions] [action]

Condition:-name - to search a particular file

-user - lists the files owned byuser.

-perm - search a file depending

on permission.

Fi d d


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This command

searches the password

file from / directory.

Find command

Fi d d


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The above screen

shows the execution

of command

Find command

L t d


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Locate command

Locate:

To search or locate files and directories from the database.

It locate the files faster than the find command

Syntax:

locate [pattern]

L t d


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To search file

named test1 from

database.

Locate command

L t d


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All the files and

directories named test1is located and

displayed.

Locate command

X Wi d S t


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X Window System

It is the foundation for the graphical user Interface of Red Hat

Linux.

X applications communicate with a display via. The X protocol.

X is OS Independent.It is available on many platforms.

X P t l


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X Protocol

It hides the individual details of the OS and the underlying

hardware.

X protocol is a asynchronous network protocol for thecommunication between X client and X Server.

It defines how the graphical primitives are communicated

between X client and server.

M lti l D kt E i t


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Multiple Desktop Environments

The X Window System of Red Hat provides two Desktop Environments.

GNOME (GNU Network Object Modules Environment).KDE (K desktop Environment).

GNOME


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GNOME

It is the default desktop environment for Red Hat Linux.

It is Power full and easy-to-use desktop environment consisting

primarily of a panel and a set of GUI tools.GNOME is free and hence its source code can be downloaded form

the GNOME Web Site: www.gnome.org.

GNOME Interface


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GNOME Interface

The GNOME Interface consists of a Panel and a Desktop.

Panel appears as a long bar across the bottom of screen.

Panel holds Menus, Programs and Applets.

The Remainder Screen is the Desktop. Here you can place

directories, files or programs.

GNOME Desktop


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GNOME Desktop

GNOME Menus


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GNOME Menus

GNOME Menus


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GNOME Menus

KDE


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KDE

KDE provides an alternative desktop environment with full set ofintegrated network and internet applications.

Along with GNOME features, It also includes

Konsole : Highly configurable graphical terminal.

Konqueror : A file manager and web browser.

Kmail : A graphical email client.

Kdevelop : Integrated development.

KDE Desktop


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KDE Desktop

KDE Desktop


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KDE Desktop

KDE Desktop


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KDE Desktop

KDE Desktop


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KDE Desktop

Starting X Window


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Starting X Window

The X window start automatically, If so then a Graphical login

screen is prompted by the Display manager.

Alternatively use startx to get in to X window from non-

windowing console.


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Start X


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Start X

Desktop Selection


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Desktop Selection

To get in to the

previously used

desktop

Select failsafe in

case of anygraphical failure

To get the

default

desktop.

To get in to

GNOME

desktop. To get in to KDE

desktop.

KDE MODE


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KDE MODE

If you click yes the

KDE desktop is set asdefault desktop for

future sessions (or)

login

If you click No,

only the current

session is set to

KDE.

Switchdesk


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Switchdesk

To change the desktop

environment.

Switchdesk


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Switchdesk

To switch from kde to

gnome desktop

Switchdesk


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Thus we switched

into GNOME

desktop

Switchdesk

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