1. Application deployment will happen on linux machines only

2. Tools will be installed on Linux machines only

   Ex: Docker, K8S, Jenkins, Nexus, SonarQube, ELK etc...

3. Application log files will be stored in linux machine only

=> It is a software which acts as mediator between user and computer

=> Users will communicate with computers using OS

=> Without OS we can't use any computer

=> OS provides platform to run our applications in computer

Ex: notepad, calculator, browser, tomcat, eclipse...

=> We have several operating systems in market

Ex: Windows, Linux, Mac, Android, IOS etc...	

=> Developed by Microsoft company (Bill Gates)

=> It is commercial OS (licensed)

=> It is single user based OS

=> Security features are very less in Windows

Note: We need to install anti-virus software to protect files

=> Windows is GUI based OS

=> Windows is recommened for personal use only

Ex: internet browsing, games, watch movies, attend online classes....

=> Linux community based OS

=> Linux is free & open source os

=> Linux is CLI based OS

=> Linux is multi user based OS

=> Security Features are very high in linux

Note: Anti-virus s/w is not required

=> Linux OS developed by "Linus Torvalds"

=> Linux is highly recommended to manage servers

Ex: App Severs, DB servers, Docker, Jenkis, K8S etc..

-> Linus Torvalds identified some challenges/issues in Unix OS

-> Linus Torvalds identified one OS which is matching with his ideas

		i.e Minux os	

-> Linus Torvalds used Minux OS code and made some changes and released into market was new OS

	(Li) nus + Mi (nux) ===> Linux

-> Linus Torvalds provided Linux OS code for free of cost

-> So many companies downloaded Linux OS source code and modified according to their requirement and released into market with their brand names those are called as Linux Distributions/ Linux Flavours.

-> We have 200+ Linux Distributions in the market.

Ex: Amazon Linux, Ubuntu, CentOS, RedHat, Debian, SUSE, Kali, Fedora....

Approach-1) Install Linux OS directley in computer

Approach-2) We can use Virtual Box and install Linux OS as Guest OS in Windows

Approach-3) Setup Linux VM in AWS Cloud (Recommended)

Step-1 : Login into AWS cloud account

Step-2 : Create EC2 Instance (Linux VM) (Amazon Linux)

	instance type : t2.micro (free tier eligible)

Step-3 : Connect with Ec2 instance using SSH Client

	  ( git bash/ mobaxterm / putty)

Step-4 : Practice Linux commands

👉 AWS account setup : https://www.youtube.com/watch?v=xi-JDeceLeI

👉 Linux Machine with Git Bash : https://www.youtube.com/watch?v=JMlQaTXvw5o

👉 Linux Machine with MobaXterm : https://youtu.be/uI2iDk8iTps?si=ZuZs0lQTxoRpbRMk

👉 Linux Machine with putty : https://youtu.be/GXc_bxmP0AA?si=HgSydrP89mPxv23s

=> Linux is CLI based OS

=> We will perform operations in linux vm using linux commands

whoami pwd date cal cal 2025

mkdir : Make directory

	mkdir ashokit
	mkdir java python aws devops

rmdir : Remove empty directory

	rmdir devops

ls : list the files of present working directory

		ls -l : Display in alphabetical order

		ls -lr : Display in reverse of alphabetical order

		ls -lt : Display files based on timestamp (latest on top)

		ls -ltr : Display old files on top & latest at bottom
		
		ls -la : display hidden files (.a)

cd : change directory (navigation)

		cd <dir-name> : go inside the directory

		cd .. : come out from directory	

touch : To create empty files

		touch f1.txt

		touch f2.txt f3.txt f4.txt	

cat : create file with data + append data to file + print file data

		cat > f1.txt : Create new file with data

		cat >> f1.txt : Append data to the exiting file data

		cat f1.txt		: Print file data from top to bottom

		cat -n f1.txt : print file data along with line numbers

rm : Remove files

		rm f1.txt : Remove the file

		rm -rf devops : remove non-empty directory

cp : copy the data from one file to another file

		cp f1.txt f2.txt

Note: To copy the data from multiple files we need to use cat command like below

		cat f1.txt f2.txt > f3.txt

mv : rename file/directory + move the file/directory

		mv linux.txt  linux-os.txt

		mv git.txt  devops/

=======================================================================

tac : Read file data from bottom to top (opposite of cat cmd)

		tac f1.txt

wc : word count

		wc f1.txt

rev : reverse the file data and print it

		rev f1.txt			

========================================

head : To display file data from top (default 10 lines)

			head app.log

			head -n 20 app.log

			head -n 25 app.log

tail : To display file data from bottom (default 10 lines)

			tail app.log

			tail -n 20 app.log

			tail -n 100 app.log

grep : grep stands for global regular expression print

Note : We will use this grep command for keyword search in file

			grep 'exception' app.log (print lines which contains given keyword)

			grep -i 'exception' app.log (ignore case sensitive)

			grep -n 'java' app.log (print lines along with line num)

			grep -v 'apache' app.log (print lines which don't have apache keyword)

=> vi (visual editor) it is default editor in linux machines

=> using 'vi' we can create new files and we can edit existing files also

	$ vi f1.txt

=> vi command is having 3 modes

a) command mode (just to open the file)

b) insert mode (to edit the file) ---> press 'i' in keyboard

c) esc mode (to comeout from insert mode) --> press 'esc' in keyboard	

## Save changes & close the file =>  :wq or :wq!

## Without saving changes close the file => :q!			

Note: vi command will open the file if it is already avilable otherwise it will create new file and it will open that file.

touch : Create empty file

cat : Create file with data

cp : copy one file data into another file

vi : create and open file for editing

cat : print file data from top to bottom

tac : print file data from bottom to top

rev : print each line in reverse order

head : print top 10 lines of file

tail : print last 10 lines of file

vi : open file

=> SED stands for stream editor

=> It is used to process file data

=> Using SED command we can perform operations on the file without opening the file.

sed 's/linux/unix/' linux-os.txt

sed 's/linux/unix/2' linux-os.txt

sed 's/linux/unix/g' linux-os.txt

sed -i 's/linux/unix/g' linux-os.txt

sed -i '2d' linux-os.txt

sed -i '4d' linux-os.txt

sed -i '$d' linux-os.txt

sed -i 'n,$d' linux-os.txt

sed -i '2,10d' linux-os.txt

$ sed -n '3,6p' linux-os.txt

$ sed '4i\i am from ashokit' linux-os.txt

$ sed '$a\i love linux' linux-os.txt

=> Linux is a multi user based OS

=> Multiple users can acces single linux machine and can perform multi tasking

Note: "ec2-user" is default user in amazon linux vm

Note: ec-user having sudo priviliges

Note: For every user we can create new account to access linux vm.

sudo useradd

sudo passwd

cat /etc/passwd

$ sudo su

$ cd ~

$ sudo userdel

$ sudo userdel --remove

$ sudo usermod -l

=> It is very important configuration file in linux machine.

=> Using this file we can control which user can run command as a superuser.

$ sudo cat /etc/sudeors

Note: We should be very careful while working with sudoers file. If we do any mistakes in sudoers file then system will be crashed.

########## Giving sudo previliges for user #######

$ sudo visudo

ALL=(ALL:ALL) ALL

=> After making changes to close sudoers file => ( CTRL + X + Y + Enter)

=> in sshd_config file , by default PassswordBasedAuthentication is no.

=> To enable password based authentication we need to set the value as yes.

$ sudo cat /etc/ssh/sshd_config

$ sudo vi /etc/ssh/sshd_config

Public IP : 43.204.143.144 username : loguser pwd: log@123

$ ssh uname@public-ip

Note: To connect with linux vm using username and password then passwordbasedauthentication must be enabled in that linux vm.

=> When we create user in linux, for every user one user group also will be created with the given username.

$ cat /etc/group

$ sudo groupadd

$ sudo usermod -aG

$ sudo gpasswd -d

=======================================

1. File permissions & ownership chomod & chown

2. Networking commands

3. Package Managers (s/w installation)

4. Linux Architecture

ec2-user => /home/ec2-user ==> f1.txt

raju => /home/raju ==> f1.txt

rani => /home/rani ==> f2.txt

ashok => /home/ashok ==> f3.txt

=> We can create several user accounts in single linux vm

=> Multiple users can connect to single linux vm at a time.

Note: One user can modify the file created by other user in linux vm.

=> To avoid this problem we will use file permissions in linux

=> In Linux, file permissions are divided into 3 types

	r => read
	w => write
	x => execute

=> A file/directory contains 3 sections of permissions

	user (owner) => u

	group => g

	others => o

=> We can see below permissions for a file & directory

		rwxrwxrwx f1.txt

				user having read + write + execute
				group having read + write + execute
				others having read + write + execute

		rw-r--r-- f2.txt

				user having read & write (no execute permission)
				group having only read
				others having only read
		
		rwxr-xr-x java

				user having read + write + execute
				group having read + execute
				others having read + execute

		r-xr----x sbms

			  user having read + execute
			  group having only read
			  others having only execute

=> To change file permissions we will use 'chmod' command

$ chmod u+x f1.txt

$ chmod g+w f1.txt

$ chmod o-x f1.txt

$ chmod o-rwx f1.txt

$ chmod g+rwx f1.txt

0 => No Permission 1 => Execute 2 => Write 3 => (2+1) => Write + Execute 4 => Read 5 => (4+1) => Read + Execute 6 => (4+2) => Read + Write 7 => (4+2+1) => Read + Write + Execute

$ chmod 765 f1.txt

	- user having all permissions
	- group having read + write
	- others having read + execute

$ chmod 456 f1.txt

	- user having only read
	- group having read + execute
	- others having read + write

=> To change file/directory ownership we will use 'chown' command

sudo chown new-owner file/directory

sudo chown :new-group file/directory

sudo chown new-owner:new-group file/directory

chmod => To change file/directory permissions

chown => To change owner/group

ping : To check connectivity

	$ ping www.google.com
	$ ping www.google.com
	$ ping 192.168.1.20

wget : It is used to download the files from internet

	$ wget https://dlcdn.apache.org/tomcat/tomcat-9/v9.0.91/bin/apache-tomcat-9.0.91.zip

curl : To send http request to server (api call)

	$ curl https://type.fit/api/quotes

ifconfig: To get IP address of our machine

	$ ifconfig

=======================================

whoami pwd date cal cal 2050 mkdir rmdir touch ls -ltr cat cp rm -rf mv tac head tail grep vi sed

useradd userdel usermod groupadd groupdel id

chmod chown

ping wget curl ifconfig

=> Package Managers are used to install softwares in linux machines

=> Package Managers are specific to linux distribution

	Amazon Linux + Red HAT : yum

	Ubuntu Linux + Debian : apt

#install git client s/w sudo yum install git -y

sudo yum install java

sudo yum install maven

=> Webserver is a software which is used to run websites

=> Websites are divided into 2 types

	1) static website (fixed content)

			ex : wikipedia

	2) dyanmic website (content will change based on user)

		  ex: gmail, facebook

=> For static websites execution we can use 'httpd' as webserver

=> For dynamic websites execution we can use 'tomcat' as webserver

sudo yum install httpd -y

sudo service httpd start

Note: httpd webserver runs on http protocol which is 80.

=> Access our webserver using EC2 VM public ip address in our browser.

cd /var/www/html

sudo vi index.html

=> systemctl is a command-line utility in Linux systems which is used to manage system services

=> Starting service => stopping service => restarting service => reloading service => enabling / disabling services

#check service status sudo systemctl status <service_name>

#start service sudo systemctl start <service_name>

#stop service sudo systemctl stop <service_name>

#re-start service sudo systemctl restart <service_name>

$ sudo hostname

$ exit

Note: Connect back to linux vm using ssh command.

To know the location of the package we have installed

whereis java

whereis maven

whereis git

=> find command is used to search files location

sudo find /home -name oops.txt

sudo find /home -type f -empty

sudo find /home -type d -empty

sudo find /home -mtime 30 -print

Deploy Spring Boot Application in Linux VM : https://www.youtube.com/watch?v=cRQPgbwOWq0

1. Why Linux for Java developers ?

2. What is OS & why ?

3. Windows Vs Linux

4. Linux History

5. Linux Distributions

6. Linux VM Setup

7. Linux commands

8. Working with directories & files

9. Working with editors (vi & sed)

10. Users & groups Management

11. sudoers file & sshd_config file

12. PasswordBasedAuthentication enable

13. File Permissions & Owership

14. Package Managers

15. Services management (systemctl)