In linux there the file access is based under three categories

 CurrentUser - Users in Group - Other Users

drwxr – CurrentUser can read, write and execute
xr – Users in Group can read and execute
x – Users can execute

 >>ls -l
-rw-r--r-- 1 root root    0 Apr 14 17:19 test.txt 

The test.txt file has only Read and Write access (rw) for Current User – Read access for Users in Group – Read access for other Users

 >>chmod u+x test.txt

Now the test.txt file has Execute access along with Read and Write as below

 >>ls -l
-rwxr--r-- 1 root root    0 Apr 14 17:19 test.txt

Giving Read wrtite to Group

 >>chmod g+r test.txt

Giving read right to Current User, Group Users and Other Users

 >>chmod a+r test.txt

Giving Execute right to Other Users

 >>chmod o+x test.txt

rwx – 111 7
r-x – 101 5
rw- – 110 6
rw- – 101 4
-wx – 011 3
-w- – 010 2
–x – 001 1
– 000 0

Example of binary format

 >>chmod 752  test.txt

Current User can rwx
Group User can r-x
Other User can -w-

Giving Multiple Permission for Multiple User Types at Once

 >>chmod u+r, o+x test.txt

How folders are organized
when you enter terminal the default location it takes is the location of the folder of the current user which
comes under /home/mugil(user logged In)

How to Login as a Root User

>> su

Logout of Root User

>> exit

Current Working Directory

>> pwd

Navigate Backward

>> cd ..
>> cd ../..

Navigate Forward

>> cd home/mugil

Home Directory

>> cd ~

Equivalent to Microsoft User Directory i.e My Documents

How to reset admin password

>> sudo passwd

How to Find Directory Files info

>> ls -l

Touch- Creates a Time Stamp

>> touch test.txt

If the file does not exist it creates new once else it updates just the time

Make new Directory

>> mkdir NewFolder

Moving File within folder that exist

>> mv test.txt NewFolder/

Copying File within folder that exist
Copies test.txt to NewFolder

>> cp test.txt NewFolder/

Copies test.txt to one folder above

>> cp test.txt ..

Deleting File that exist

>> rm test.txt 

Deleting File in folder that is not empty
-r recursive

>> rm -r NewFolder/

After installing apache in CentOS it would go to Apache 2 Test Page.

To locate this directory you need to go to /var/www/
In this directory you can create your file which you needs to run.

To set up Virtual Host navigate to /etc/httpd/conf/httpd.conf file

Open the file in gedit or editor of your preference.

Add the lines below

<VirtualHost *:80>
   DocumentRoot /var/www/sample/
   ServerName virtualhost1

The document root points out to sample older in www directory

The server name is virtual host name you type in URL

You should also add the code in /etc/hosts file    virtualhost1


Once this is done dont forget to restart apache server in terminal by typing service httpd.restart

Now you are ready to go now.Open the browser and type http://virtualhost1/


Install Apache Server in Terminal CentOS

 yum install httpd

Check Status of Apache Server

/etc/init.d/httpd status

Start Apache Server

/etc/init.d/httpd start

Start MySQL Terminal

/etc/init.d/service mysqld start

Check Status of MySQL

/etc/init.d/service mysqld status

What is Shell?

Computer understand the language of 0’s and 1’s called binary language.In eaarly days of computing, instruction are provided using binary language, which is difficult for all of us, to read and write. So in Os there is special program called Shell. Shell accepts your instruction or commands in English (mostly) and if its a valid command, it is pass to kernel.

Shell is a user program or it’s environment provided for user interaction. Shell is an command language interpreter that executes commands read from the standard input device (keyboard) or from a file.

Shell is not part of system kernel, but uses the system kernel to execute programs, create files etc.

Several shell available with Linux including:Bash, CSH, KSH, TCSH

To Find the list of Shells available in your system Type the below in your terminal

  cat  /etc/shells

Any of the above shell reads command from user (via Keyboard or Mouse) and tells Linux Os what users want.

To find the current shell you are using now use the below command

 echo $SHELL

what is Shell script?

Shell Script is series of command written in plain text file. Shell script is just like batch file is MS-DOS but have more power than the MS-DOS batch file.