1. LINUX

LINUX: Free and Open-source OS
OS: Operating system -- > communication blw user & system.

TYPES OF OS:
1. WINDOWS
2. LINUX
3. MAC OS

LINUX COMPONENTS:

1. KERNEL: Manages hardware components (CPU, MEMORY, etc --)
           The lowest level of OS.

2. DAEMON: Manage the Background Service (Lights, Sounds, schedule)
           While starting the system.

3. SHELL: Manage the User Inputs (Command, Script, programs)
          Takes input from the user and executes and gives the output.
           

LINUX OS FLAVOURS/DISTRIBUTIONS:

IPHONE: 14, 14+, 14 PRO, 14 PRO MAX,
VERSIONS: 14, 13, 12, 11

MAIN:
RedHat
Ubuntu  (75%)
Amazon Linux

MODES:
1. GUI: Its having the Dashboard
2. CLI: Command line interface (Works with commands only)

HISTORY:
1991 -- > Linus Torvalds -- > student from finland.
1991 -- > Want to create an OS that works like UNIX.
LINUX is Written in C Programming. (1972)
Firstly he wanted to name it as 'Freax' but later it became 'Linux'.
1992 -- > Linxu's initial version was released. 
TOTAL PROGRAMMING LANGUAGES: 700 +

OPEN SOURCE:
It is free no need to pay money.
It is available publically.
We can change the code.
we can give a copy of the code to other people.

ADVANTAGES:
It's free and open-source.
Multi-user based.
Fewer Bugs.
Better Performance.
It can be used for all programming languages.
It will hang very rarely.

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

DAY-02: SERVER & COMMANDS

MOBAXTERM LINK: https://download.mobatek.net/2312023031823706/MobaXterm_Portable_v23.1.zip

NOTE: Go to the path where you have keypair
CONNECT: SELECT THE SERVER -- > CONNECT -- > SSH CLINET -- > COPY TO TERMINAL
PASTE: 1. RIGHT CLICK 2. SHIFT + INSERT


COMMANDS:
ec2-user: default user       root: admin
*	: refers all in linux


sudo -i		: switch to root user form ec2-user
clear/ctrl + l	: to clear the screen
touch file1	: to create a file
ll/ls		: to list the files
ll -a / ls -a	: to list the hidden files
pwd		: to show the present working directory
cat file1	: to show the content in a file
more file1	: to show the content in a file
cat>file1	: to insert the content
enter, ctrl d	: to save the content
cat>>file1	: to insert the content more than one time.

cp file1 file2	: to copy the content from file1 to file2
mv file1 file5	: to rename file1 to file5
rm file2	: to remove file2
rm file4 -f	: to remove file4 forcefully
rm * -f		: to remove all files forcefully

touch java{1..5}: to create series of files
rm j* -f	: to remove all the files starting with j
wc file1	: to see number of lines, words & characters.

head file2	: to print top 10 lines
head -7 file2	: to print top 7 lines
head -5 file2	: to print top 5 lines

tail file2	: to print bottom 10 lines
tail -7 file2	: to print bottom 7 lines
tail -5 file2	: to print bottom 5 lines
sed -n '6,16p' file2 : to print form line numbers 6 to 16

FOLDERS = DIRECTORIES

mdkir dir1	: to create a folder
cd dir1		: to go inside the directory
cd ..		: to go back one directory
rmdir dir1	: to remove a directory

echo "hai raham" > file3
===============================================================


DAY-03:

STATIC: We can't modify
DYNAMIC: We can mofify

VI/VIM EDITOR: Used to edit files and insert content.
i: used to modify/insert content
esc: to get out from insert mode

3. SAVE MODE:

:w	: to save 
:q	: to quit 
:wq	: to save & quit
!	: forcefully

2. INSERT MODE:

A	: End of line
I	: Starting of line
O	: Create new line above existing line
o	: Create new line below existing line

1. COMMAND MODE:

yy	: copies single line
p	: paste single line
dd	: delete single line
u	: undo

nyy	: copies n lines
np	: pastes n line
ndd	: delete n lines
nu	: undo n times

gg	: top of file
shift+g	: bottom of file
:15	: to go to line 15
:set number: print lines inside the file

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

HARDWARE:

cat /proc/meminfo	: to show memory information
lsmem			: to show memory information
cat /proc/cpuinfo	: to show cpu information
lscpu			: to show cpu information
cat /etc/os-release	: to print flavoure


fdisk -l		: to show the ebs volume info
lsblk			: to show the ebs volume info

df			: to show the mount point
df -m			: to show the mount point in mb

free			: to show how much ram is available
free -m			: to show how much ram is available

yum install lshw -y	: to install the package 
lshw			: to show the hardware information.
====================================================================================================================


USERS: 
ec2-user: he is the default user.

root: he is the admin, he will have all permissions.
superuser: 
he is a normal user created by root user.
normal user -- > visudo -- > super user

useradd raham: to create a user
cat /etc/passwd: to see the users list.

user -- > GROUP & FOLDER

cat /etc/group: to see the groups list.
ls /home: to show user folder on home 
id raham: to show the user info
passwd raham: to assign password for user

NOTE: in linux password will not be visible.
password -- > more than 8 char. 
username should not be given as password.

To create super user:
1. create user (useradd raham)
2. password (passwd raham)
3. visudo -- > 100 -- > yy & p -- > root=raham

su - rajesh : to login to super user

NOTE: In linux if you are on non root use sudo command 


root -- > normal -- > visudo -- > super user 

logout or ctrl d used to exit from super user.


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

-rw-r--r-- 1 root root 0 Jun  8 16:02 file1


TYPE OF FILES:
-	: Regular file
b	: Blocked file
c	: Charcter file
d	: Directory
l	: link file

PERMISSION:

rw-r--r--
r	: read		: 4
w	: write		: 2
x	: executable	: 1

user	: rw-	: 4+2+0	: 6
group	: r--	: 4+0+0	: 4
others	: r--	: 4+0+0	: 4


chmod 777 file1
chmod 666 file2

1	: acl -- > access control list


chown raham file1: to make raham as owner to file1
chgrp raham file1: to make raham as group to file1
chown raham:raham file2 : to make raham user&group for file2
chown rajesh:raham file1: rajesh as user & raham as group


groupadd devops	: to create devops group
usermod -aG devops raham : to add raham user to devops group
usermod -aG aws raham : to add raham user to aws group

gpasswd --delete raham devops : to remove raham user form devops group
userdel raham : to delete raham user

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

DAY-05:


GREP : Global Regular Expression Print
to search for a particular word

grep is file1		: to search word is on file1
grep IS file1 -i	: to avoid the case sensitive
grep IS file1 -i -v	: to avoid the line which is having word is
cat file1 | grep is	: to search word is on file1
cat file1 | grep IS -i	: to avoid the case sensitive
cat file1 | grep IS -iv : to avoid the line which is having word is

| : is pipe sysmbol -- > to work with pipe we need to have 2 commands
here 1 st command output will be input of 2 nd command.

lscpu | grep cpu -i
lsmem | grep memory -i
dmesg | grep image -i


SED: Stream Editor -- > to replace words in a file.

%s/is/abc/ -- > to replace is with abc
sed '3c/abc/' file1  -- > to replce 3rd line in a file
sed 's/linux/unix/' file1-- > single word replace
sed 's/linux/unix/; s/session/class/' file1 -- > multi word replace
cat file1 -n -- > to print line numbers in a file
sed '=' file1 -- > to print line numbers in a file
sed -n '5,13p' file1 -- > to print line 5 to 13
sed -e '5,13p' file1 -- > to print line 5 to 13 double times

NETWORKING:
ip addr
ip addr show
hostname -i
ifconfig          -- > all the 4 commands used to show ip address

ping google.com -- > to get response form server
ping -c 4 google.com
netstat   --- > to show active internet connections
ps  -- > to check the process
kill -9 32555 -- > to kill a process
ps aux -- > to list process in ids

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

LINUX DIRECTORY SYSTEM:
FHS 


bin	: it stores all the binary files and also it stores the commands that had been executed by the user.
sbin	: it stores the commands that had been executed by the super user.
boot	: it contains boot images & boot files.
dev	: it contains all the device files
etc	: it contains all the host specific system configuration files.
lib	: it contains all the library files of the system.
lib64	: it contains all the library files of the system of 64 bit.
mnt	: it is used for the mounting purpose.
opt	: it stores all the file details of the 3 rd party when it installed.
proc	: it is used to see all the processing related files (Hardware details).
srv	: it stores all the service related information provided by system.
sys	: it stores any new changes that obtained while changing Hardware.
tmp	: it stores temperory files and have access to all.
usr	: it contains local system files which are continuing with the old system architecture.
var	: it stores all the system services.