Linux_Class.txt

AWS Account
===========
1.free account - 750hrs - 1 yrs
Debit/credit - 2/-rs
AWS

2. Putty software(puttygen also)

Optional - Puttygen

Linux - OS
=========
Server
Linux - command line

Linux Server
==========
Launch server
EC2 instnace/service/server

Elastic Compute cloud - EC2 - VM(Virtual Machine) server

EC2 - Instance
==============
7 steps

linux20april.pem

How to convert the privatekey
========================
puttygen - public we need private key(ppkfile)

how to connect the server
========================
linux-server(ec2-instnace) - public IP Address

21/04
=========
Linux
========
linux OS, Free open source os
Unix  - paid one, os

Linux
========
CentOS -
Ubuntu
SUSE Linux

Windows
=========
what is sudo -i?
=============
Sudo(Superuser do) allows a system administrator to give certailn users(or group of user) the ability to rum domr(or all) commands as root while logging all commnads and arguments

what is Root?
=============
Primary Hierarchy root and root directory of the entire file system hirerachy
1. Each single file and directory starts from the root directory
2. Only root user has the right to write under this directory
3. /root is toot user's home directory, which is not same as /
Linux
========
FSH - File System Hierarchy
=========
The Linux FSH defines the directory structure 

Folder/ Directory

pwd - present working directory

mkdir linux
ls
cd linux-demo

file -creation
================
touch file1

Note :
=====
In side directory you may have 100 files - directories are difined with "blue color"
In side file there no directories - files are defined with "white color"

Delete/Remove directory/folder
=============================
rm -rf dirname
or
rm -r firectory (type - y)

Delete/Remove files
============
rm -f filename

how to create multiple directories
=============================
mkdir d1 d2 d3

How to create parent directories
====================
To create parent directories using the mkdir command pass -p option
suppose the directory path /foo/bar/baz is to created even if /foo/bar directory is not existing 

Permissions and rights
================
A linux is a Multi-user  Operating system which can be accessed by many user simultaneously.
Hence this raises security conecrns as am going to restrict on the perticular user

2 levels

1. Ownership
2. Pemission

How to change the ownership for file level
========================================
The chown command change ownership of files and directories in a linux filesystem
to change the owner of a files/directory

syntax: chown  <ownername>(shobha)  <filename>(file.txt)

How to change the ownership for group of file
=================================
"chown" command is also used to the chnage group name of a file, like "chgrp" command
chown :shobhs file.txt

file name - file.txt

1.chown ec2-user

-rw-r--r-- 1 
  
-rw-    r--        r-- 1 (file - level)
user    group     others

Group:
=====
chown commands is also used to change group name of a file like, "chgrp" commands

synatx: chown <groupname> <filename>

chown :ec2-user file.txt

To recursively change ownership of directories and their contents
========================

synatx: chown -R root >filename>

mkdir test

 d          -rw-    r--        r-- 1
directory   users   group      others



2.chown -R root filename

-R = To recursively change ownership of directories and their contents

mkdir test
chown -R ec2-user:ec2-user test


How to chnage the Permission
========================
All file system object on Unix-like system have three main typesof permissions
read, write and execute access.
permissions are based upon 3 possible class
user, the usergroup and all system users

syntax: ls -lha

1. r: Read   	=4
2. w: Write	=2
3. x: Execution	=1


Permissions
==============
Read      - r   -  - 4
Write     - w   -  - 2
Execution - x   -  - 1
		   ====
                    7
Synatx: ls -lha

Example
===========
d	rwx		r-x		r-x

dir	(user)		(Group)		(Others)

task:
======

setting 442(rrw) permissions for the file of  file.txt(filename)


rwx		r-x		r-x
 r		r		w

file.txt rrw

chmod 442 file.txt


How to change the permissions & ownership recursively
==============================
to chnage the file access permissions you need to sue the chmod command. it has -R or -recursive option thar chnage files and directories recursively

mkdir dir5
cd dir5
touch file6 file7

dir5 - rwx 

d	rwx		r-x		r-x

dir	(user)		(Group)		(Others)

7	0		0

700 --(user)--(group)--(others)



file2 r r w

r--		r--		w--
 4		4		2
chmod 442 file2

permission with dire - anusha

d(rx) user(rx) group(rx) others

5	5	5 

chmod  -R 555 anusha

if you want give the permissions directory level(you should not entire inside the directory)


Linux/Unix Command
=========
1. File commands

ls - directory listing/ files listing
ls -al  - hidden files to be displyed
cd dir - change dir to dir
cd - change to home
rm file - delete file
rm -f filename - force remove file
rm -r dir -
rm -rf dir
cp file1 file2 - copy the file1 file2
cp -r dir1 dir2 - copy the dir1 dir2
mv file file2 - rename or move file1 dile2
touch file -
cat file - to see content inside file
more file - output the content of file
head file - output the first 10 lines of file
tail file -  output the last 10 lines of file
tail -f file - output the content of files as it grows, starting with the last 10 lines



2. Process managemnet

ps - display your current active process
top - display all running process
kill pid - kill process id pid
bg - list stopped or backgroundjobs; resume a stopped job in the background
fg - bring the most recent job into foreground
fg n - bring job n into foreground



3. File Permissions

chmod octal file -  chnage the permisiions of file of octal, which can be found separately for user, groups and world by adding

 4 - read(r)
 2 - write(w)
 1 - Execution(x)

Exmaple:
-
chmod 777
chmod 755


4. SSH
ssh user@host - connect to host as user
ssh -p port uset@host  - connect to host on port port as user


VIM Editor:
==========
Vim is powerfull text editor used in CLI(Command Line Interface).
Linux uses a lot of configuration files.
if you edit them and vim is a great tool do so, aletrnatively VIM is a command line editor

vim flie.txt
50 lines 
50 lines


vi editor
vim editor

It has 3 modes:
----
1. Command Mode
2. Insert Mode
3. Extended Mode

Note: when you open the vim editor , it will be in the command mode by default.

Insert Mode - i
Extended mode
----
save - esc:wq!
withoutsave- esc:q!

Command Mode
+++++++++++++++++
gg - to go to the beginning of the page
Shift+g - go to the end of the page
w - to move the cursor forward, word by word
b - to move the cursor backword, word by word
nw - to move the cursor forward to n words(5W)
nb - to move the cursor backend to n words(5W)
u - to undo last change(word)
Ctrl+u - to undo previous chnages (entire line)
Ctrl+r - to redo changes
yy - to copy a line
nyy - to copy n lines (5yy or 4yy)
p - to past line below the cursor position
P - to past line above the cursor positio
dw - delete the word letter by letter(like Backspace)
x - to delete the word letter by letter( delete key)
dd - to delete entire line
ndd - to delete n no.of positions from cursor positions(5dd)
/ - To search a word in the file


Insert Mode(edit mode):
+++++++++++++++
i - To begin Insert Mode
I - To insert beginning of line
a - To Append the next word's letter
A - To append at the end of the line
o - To insert a new line below the cursor positions
O - To insert a new line Above the cursor positions

Extended Mode(colon Mode)
++++++++++++
Esc+:w - To save the changes
Esc+:q! - to quit(without save)
Esc+:wq - to save and quit
Esc+:w! - To save forcefully
Esc+:wq! - To save and quite forcefully
Esc+:x - to save and quit
Esc+:X - to give password to the file and remove password
Esc+:20(n) - to go to line no 20 or n
Esc+:se nu - to set the line numbers to the file
Esc+:se nonu - To remove the set line number


Monitoring:
+++++++++++++++++++
- when you needs to see the running process on your linux in real time, you can have top as your tool that.

- top also displayes other info besides the running process 
top 
tasks - shows the numbe of process and their current state
%cpu- show CPU uilizaion details, user process, system process running, system Idle cpu.

Swap Memory in Linux:
===================
Swap space in Linux is used when the amount of physical memory (RAM) is full. If the system needs more memory resources and the RAM is full, inactive pages in memory are moved to the swap space.
 While swap space can help machines with a small amount of RAM, it should not be considered a replacement for more RAM.

zombie process in linux:
========================
Zombie processes in Linux are sometimes also referred to as defunct or dead processes.
 They're processes that have completed their execution, but their entries are not removed from the process table.

What is buff cache Linux?
========================
buff/cache is memory used by the Linux kernel buffers and page cache. 
You force clear buff/cache using the 'echo' command but observe it gradually increase again to 85% memory consumption.
 Shutting down the SAP NW application and/or database server. does not show buff/cache release any memory.

PID - ProcessID
USER - Effective UserID
PR - Dynamic Prority
NI - nice Value, also known as base priority
VIRT - Vitrual size of the task. This includes size of process executable binary, the data area and all the loaded shared libraries
RES - The size of RAM Currently consumed by the task, Swapped out portion of the task is not included
SHR - Some memory ares clould be shared b/w two or more task, this fileds reflects the shared area.
S - Task status
%CPU - the %CPU time dedicated to run the task since the last top's screen update
%MEM - the %Mem of RAM currently consumed by the task
TIME + - The total CPU time and task has been used since it started "+"sign means is displayed wih hundredth of second granularity.
  BY default, TIME/TIME+ desont account CPU Time used by the task's dead children
COMMAND-  Showing program names.

Kill userdetails
-------------
 kill -9 PID

Intracting with Top
================
M- 
P-
T- 
z - 
k - 
r- 
h

How do I find zombies on Linux?
===================
Image result for zombie in linux

How to find zombie processes?
D = uninterruptible sleep.
I = idle.
R = running.
S = sleeping.
T = stopped by job control signal.
t = stopped by debugger during trace.
Z = zombie.

Ping commnad
===========
packet internet Groper

ICMP - internet Control Messages
TTL - Time To Live
ping -c2 google.com


vmstat command:
================

vmstat (virtual memory stastics)
info about block IO and CPU 

Shortcut File commands
===============

wc -l : Prints the number of lines in a file.(filename)
wc -w : prints the number of words in a file.
wc -c : Displays the count of bytes in a file.
wc -m : prints the count of characters from a file.
wc -L : prints only the length of the longest line in a file.

Software Management
====================
its important role in installaling and configuring the softwares.

2 ways we can approach
1.rpm - Redhat package manager
2.yum - yellow dog update manager - (centos)

Ubuntu - apt-get

RPM:
========
RPM is a package managing system(collection of tools to manage software packages) - ex- git, maven, jenkins, python, java
RPM is powerful software mangement tools for installing, uninstall, verifying, querying and updating software packages.
RPM straight forward program to perform the above s/w management tasks.

synatx:

rpm -qa (where q stands for query, and a stands fo all)

rpm -qa python

installion syntax:
====
rpm -ivh package name


list out of package in linux server
==============
rpm -qa |grep -i python

grep - global regular expression print




yum 
=====
yellow dog update manager

yum install git -y


Repo:
clean
list

Networking Commands:
======================
Linux Networking Commands
ifconfig.
ip.
traceroute.
tracepath.
ping.
netstat.
ss.
dig.

Netwprk Configuration & Trouble Shooting
-----------------------
Networking - it is a connection b/w two or more machines to communicate with each other

#/etc/sysconfig/network-scripts/


ls /etc/sysconfig/network-scripts/


cat /etc/sysconfig/network:
---------------------

is a file whiich keep the information about the hostname assigned to the system. 
if you want to change the hostname permenently , you need to change the hostname in this file.

checking the IP Address
===========
ifconfig -a

DNS
----
Domain Name spacific

nslookup ipaddress/hostname
nslookup 


What is the difference between sudo and su command?
===================================
The main difference between Su and Sudo is that the Su command can interchange between superuser and root user if executed without prior additional options while the Sudo command provides single root privileges. 
Su demands the password of the root account while Sudo demands the password of the current user account

what is inode in linux?
=======================
What is an inode? By definition, an inode is an index node. It serves as a unique identifier for a specific piece of metadata on a given filesystem. 
Each piece of metadata describes what we think of as a file. That's right, inodes operate on each filesystem, independent of the others

Why is inode used?
===================
Inodes keep track of all the files on a Linux system. Except for the file name and the actual content of the file, inodes save everything else.
 It's like a file-based data structure that holds metadata about all of the files in the system.

what is softlink in linux?
======================
Soft links are similar to shortcuts, and can point to another file or directory in any file system. 
Hard links are also shortcuts for files and folders, but a hard link cannot be created for a folder or file in a different file system. 
These can be created in the following way on Linux and Mac operating systems.

what is hard link in linux?
=======================
Every file on the Linux filesystem starts with a single hard link. The link is between the filename and the actual data stored on the filesystem

what is hardening in linux?
========================
What is OS Hardening? Operating system (OS) hardening, a type of system hardening, is the process of implementing security measures and patching for operating systems, such as Windows, Linux, or Apple OS X, with the objective of protecting sensitive computing systems.

what is the difference between grep and find?
=====================================
The main difference between the two is that grep is used to search for a particular string in a file whereas find is used to locate files in a directory, etc. also you might want to check out the two commands by typing 'man find' and 'man grep'

what is the Linux Volumes
============================
A physical volume will be seen as /dev/sda, /dev/sdb; a physical disk that is detected by Linux. 
If we have two physical disks of 1TB each, we can create a volume group of almost 2TB amongst the two. From the volume group, we can create three logical volumes each of any-size not exceeding the total volume group size

What is the use of LVM in Linux?
==============================
LVM is used for the following purposes: Creating single logical volumes of multiple physical volumes or entire hard disks (somewhat similar to RAID 0, but more similar to JBOD), allowing for dynamic volume resizing.