Linux

Q: Describe below listed Commands?

• ls - list the files and directories in the current directory

ls

• cd - change the current directory

cd dir_name

• mkdir - create a new directory

mkdir rohan

• rmdir - remove a directory

rmdir rohan

• pwd - print the current working directory

pwd

• cp - copy files or directories

#We will copy a file called example.txt from the current directory to a directory called backup

cp example.txt backup/

• mv - move or rename files or directories

mv example.txt backup/

• rm - remove files or directories

rm example.txt

• touch - create a new empty file or update the timestamp of an existing file

touch shayan.txt

• cat - concatenate and display files

cat example.txt

• man - manual for a command

man ls

• htop - an interactive process viewer and system monitor

htop

• chmod - change the permissions of a file or directory

# The first digit represents the owner of the file/directory

# The second digit represents the group that the file/directory belongs to

# The third digit represents all other users

# 0 (no permission)

# 1 (execute only)

# 2 (write only)

# 3 (write and execute)

# 4 (read only)

# 5 (read and execute)

# 6 (read and write)

# 7 (read, write, and execute)

chmod 700 file.txt

chown - change the owner of a file or directory

chown new_owner example.txt

• tar - create or extract compressed archive files

# x: extract files from an archive

# t: list the contents of an archive

# r: append files to an existing archive

# z: use gzip compression

# j: use bzip2 compression

# cf: create file

#xf: extract file

tar cf archive.tar file1 file2 file3

• gzip - compress files

gzip file.txt

• gunzip - decompress compressed files

gunzip file.txt.gz

• ssh - connect to a remote server securely

ssh username@server_address

• scp - securely copy files between systems

scp myfile.txt user@remotehost:/home/user/

• ping - test network connectivity

ping google.com

• ifconfig - display or configure network interfaces

ifconfig

• netstat - display network connection information

netstat

• route - view or configure network routing tables

route [options] [add/delete/show]

• top - display system resource usage and processes

top

• ps - display information about running processes

ps aux

• kill - terminate a process

kill [PID]

• systemctl - control system services and settings

# Start the nginx service

systemctl start nginx

# Check the status of the nginx service

systemctl status nginx

# Stop the nginx service

systemctl stop nginx

• service - control system services

service apache2 start

• useradd - add a new user to the system

useradd harry

• passwd - change the password for a user

passwd harry

• userdel - delete a user from the system

userdel harry

• su - switch user to become another user

su john

• sudo - execute a command as another user or with elevated privileges

sudo

• uptime - display system uptime and load average

uptime

• df - display disk space usage

df

• du - display disk usage by file or directory

du

• mount - mount a file system

sudo mount /dev/sdb1 /mnt/usb

• umount - unmount a file system

sudo umount /mnt/usb

• date - display or set the system date and time

date

• whoami - display the current user name

whoami

• which - locate a program or command in the system path

ls

• finger - displays all the information about user

finger harry

• uname - display system information

uname

uname -a

• history - display a list of previously executed commands

history

• echo - display text or variables to the console

echo 'I need Tshirt from codeswear!'

• tee - redirect output to both a file and the console

$ ls | tee file.txt

• locate - locate any file on the system

locate file.txt

• sort - sort lines of text in a file or input

cat file.txt

banana

orange

apple

sort file.txt

apple

banana

orange

• uniq - remove duplicate lines from a file or input

cat file.txt

apple

orange

banana

apple

banana

uniq file.txt

apple

orange

banana

• head/tail - display the first/last few lines of a file or input

#display first 10 lines

head file.txt

#display last 10 lines

tail file.txt

                                                      ========================Linux OS====================

Q: Write difference between Linux and Unix.

Linux: It is an open-source and free-to-use Operating system that was first developed in 1991 by Linus Torvalds. It is specially designed to offer free and low-cost OS for personal computer users. It has very low hardware requirements and facilitates powerful support for networking. Different versions of Linux are known as variants. 

Example: Red Hat, Android, etc. 

Unix: It is a closed source OS derived from the original AT&T Unix and was first developed in the 1960s. It is not open source and is not free to use. It is generally capable of handling activities from multiple users at the same time. Furthermore, it is specially designed to be more portable, multi-user, and multitasking in a time-sharing configuration. Different versions of Unix are known as distros. 

Example: HP-UX, Solaris, etc. 

Q: What is the difference between BASH and DOS?

Ans:

BASH (Bourne Again Shell): It is basically a powerful command shell and scripting language that is being developed from the Bourne shell used on UNIX systems. 

It runs on multiple OS and new features are added regularly. It can read and execute commands from a file known as a shell script. 

DOS (Disk Operating System): It is basically an OS that runs from a hard disk drive. It was the first OS system used by IBM-compatible computers. It basically provides a command-line in which users are allowed to give instructions in the form of commands. 

BASH          DOS 

• In BASH, commands are case-sensitive.  In DOS, commands are not case-sensitive.
• In this, / character are directory separator 
• and \ acts as an escape character. In this, \ is a directory separator and / acts as a command argument delimiter.
• It can take input with its built-in “read” 
• command.                 It cannot take input during run time and one can only pass “/argument” during execution from the command line.

Q: How to create private DNS in Linux

Ans:

1. Navigate to etc/host file and add hostname with IP address

2. vi etc/host

 <IP address> <any hostname> 

3. save and close the file (:wq)

Q: where all user will stored in Linux

Ans:

ls /home/  will show all users

ls -la /home/<user name> will show all files related to that user

user/bin/  -> contains all commands for any user

Q: How to create SSH keypair(public /private key) ?

Ans: ssh-keygen -t rsa

Copy the public file /root/.ssh/id_rsa.pub & paste in Client /root/.ssh/authorized_keys file

Now try ssh from Ansible Master to Ansible Client

Q:How to install webserver on Linux

Ans:

Install httpd package on CentOS 7 or CentOS 6

[root@testvm ~]# yum install httpd -y

Start httpd service on CentOS 7.x

[root@testvm ~]# systemctl start httpd

Start httpd service on Boot on CentOS 7

[root@testvm ~]# systemctl enable httpd

Check httpd service Status on CentOS 7

[root@testvm ~]# systemctl status httpd

Go to document root of the web server

[root@testvm ~]# cd /var/www/html

Edit document root of the web server with your index file.

[root@testvm html]# vi index.html

Open Port 80 in Security Group on AWS Cloud Platform

Now Browse Your Public IP

Have Funnnnnn...!!!