Important Linux Commands You Should Know

Important Linux Commands You Should Know
Manjunath.R
#16/1, 8th Main Road, Shivanagar, Rajajinagar, Bangalore560010, Karnataka, India
*Email: manjunath5496@gmail.com
"The only true wisdom is in knowing you know nothing."
− Socrates
(A Pocket Guide For Beginners)

Disclaimer
© Copyright 2019 Manjunath.R
Despite my best efforts to assure the accuracy of the material in this book, I do not accept
and hereby disclaim any liability to any party for any loss, damage, or disruption caused by
mistakes or omissions, whether caused by negligence, accident, or any other cause.
For any suggestions or concerns, please write to me: manjunath5496@gmail.com
This work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike
4.0 International License.
(CC BY-NC-SA 4.0)
Under the terms of the cc-4.0-by license, you may:
 Share – copy and distribute the content in any form or media
 Remix, alter, and build upon the content for any non-commercial objective
As long as you comply by the conditions of the license, the licensor cannot revoke these rights.
You have to
 Provide proper recognition;
 Cite the license by including a link to it (https://creativecommons.org/licenses/by-nc-sa/4.0/);
and
 Specify whether (and if so, which) changes were made from the original.

Dedication
I dedicate this book to every individual, programmer, teacher, educational institutions and
enterprise corporations in every country of the world for their immense contributions towards the
process of creating, designing, deploying and supporting software…

Acknowledgements
Without the amazing work of some renowned programmers, their creativity, and their inventiveness in the
field of software programming, this book would not have been accomplished. I would like to use this
opportunity to thank my dearest friend and well-wisher "Lawrence" for his unwavering support during
the COVID crisis and for giving me access to all the resources I needed to finish this book. I want to
express my gratitude to my family for their support and encouragement as I wrote this book, especially to
my mother, who has been a tremendous source of inspiration in my life. I owe a lot of gratitude to my
mother for teaching me how to be perseverant and strong in life. Finally, I want to emphasize how crucial
patience is when writing a book or taking on any other project in life.

Foreword
I'm neither the proprietor of a well-known publishing house or a top IT firm with hundreds of in-
house programmers who could easily produce anything I needed. I am a self-employed software
engineer who is passionate about what I do, and believe me when I say that a lot of work and
effort went into compiling this comprehensive edition. I'll be overjoyed if it helps even a few
others reach their ideal positions in their professions.
Thank You
− Manjunath.R

A Complete Introduction to the Linux Command Line

Introduction
Want to use a Linux-based, open-source Unix-like operating system to increase the productivity
and efficiency of your everyday computing? You can get ideas, strategies, and tips on how to do
the task in this book. This book's main objective is to make system administration on Linux
machines simple by giving you all the information you need. This book takes a task-oriented
approach to system administration; as a result, it is structured around the requirements of a
system administrator rather than the characteristics of the Linux operating system.
The command-line interface is one of the nearly all well built trademarks of Linux. There exists
an ocean of Linux commands. Although, this to the end of time creates a problem: by all of so
copious commands accessible to manage, you don't comprehend where and at which point to fly
learning them, especially when you are learner. If you are facing this problem, and are peering
for a painless method to begin your command line journey in Linux, you've come to the right
place, as in this book, we will launch you to a hold of well liked and helpful Linux commands:
 You can copy, move, and remove files and folders
 Identify any network connectivity issues.
 Modify the ownership and permissions of files and folders.
 Manage, add, and create users and groups.
 Use "su" and "sudo" to securely access the root account.
 Create and modify text files without a graphical editor, and a lot more things.
This book is heavily focused on Linux system administration. It will make an effort to explain how to use
the command line interface more effectively. How does everything work? What is its scope? What
method of use is ideal? However, by giving the reader a strong foundation in the use of the command line,
a necessary tool for any significant system administration activity, it will set them up for further
exploration of a command-line executable software or utility. There is no quick route to Linux wisdom.
The command line is difficult to learn and requires significant effort. It's not that it's so difficult; rather,
it's that it's so big. On a typical Linux system, you can use literally a plethora of programs via the
command line. Be forewarned: learning the command line is not something you should take lightly. On
the other hand, as 90% of cloud infrastructure and hosting services use Linux, mastering the Linux
command line is quite advantageous.

Have Fun!
"All the best people in life seem to like LINUX."
−Steve Wozniak
Remember that a command line is an interface that receives lines of text and converts them into instructions for
your computer while you go through this book. A graphical user interface (GUI) is simply a command-
line application abstraction. For instance, a command is carried out every time you click the "X" to close a
window. Make sure to install Linux on your computer before diving into the most popular commands.
Note:
 Linux version used: CentOS Linux release 7.3.1611 (Core)

17 Principles of the philosophy of UNIX
 Principle of Modularity: A system should be composed of several components that are
joined, collaborate well, and have clearly defined functions
 Principle of Clarity: Clearness is better than smartness
 Principle of Composition: Create software that can communicate with other software
 Principle of Separation: Programming mechanisms and rules should be kept distinct.
Keep front-end interfaces and back-end engines separate
 Principle of Simplicity: Build for simplicity and only add complexity where necessary
 Principle of Parsimony: Only write a large program when it is clear by demonstration
that nothing else will work
 Principle of Transparency: Design with visibility in view to simplify analysis and
troubleshooting
 Principle of Robustness: Transparency and ease of use produce robustness
 Principle of Representation: Create programs easier to understand for any programmer
involved in the project so that it can be maintained
When offered the choice, programmers should choose to
complicate the data rather than the procedural logic of
the software because complex data is simpler for us to
understand than complex logic

 Principle of Least Surprise: Developers should be encouraged to create user-friendly,
intuitive products
 Principle of Silence: Allow programmers and other programs to get the data they require
from a program's output without having to interpret unnecessary extensive and detailed
 Principle of Repair: Programmers should create software that fails in a way that is simple
to identify and diagnose
 Principle of Economy: Project development costs should be minimized
 Principle of Generation: Programmers should develop abstract, high-level programs that
produce code rather than writing code by hand to decrease human error and save time
 Principle of Optimization: Before you can optimize it, get it working. Software should
be developed and tested before being masterfully crafted by developers
 Principle of Diversity: Make programs flexible, enabling their use in ways other than
those that their creators intended
 Principle of Extensibility: Increase the usefulness and lifespan of the developer's written
code

Better skills come with increased learning.
Your main focus as a novice should be on becoming familiar with the ins and outs of
operating system architecture as well as discovering shortcuts and time-saving techniques.

CentOs is a wonderful option if you use Windows and want to learn Linux because it is one
of the best Linux distributions for beginners. Your first few days using CentOs won't be that
odd. But you must learn how to utilize Linux's command line interface if you want to
experience its full capabilities. You will initially experience some difficulty learning several
instructions. Although employing the instructions won't make you a genius, it will assist you in
carrying out certain fundamental tasks. Here are the most basic CentOs commands for new
users to ensure a smooth start. Let's get right into it!

Linux Commands
Description:
Display system date and time.
Command:
date
Description:
Display calendar.
Command:
cal
"... being a Linux user is sort of like living in a
house inhabited by a large family of carpenters
and architects. Every morning when you wake
up, the house is a little different. Maybe there
is a new turret, or some walls have moved. Or
perhaps someone has temporarily removed the
floor under your bed."
~ Unix for Dummies, 2nd Edition
1

371
Description:
Display date, time and calendar.
Command:
date & cal
Description:
Display August month 2016 year calendar.
Command:
cal 8 2016
Description:
Used to clear the terminal window.
Command:
clear
Description:
Exit from the terminal window.
Command:
exit
386
2

372
Description:
Display free and used system memory.
Command:
free
Description:
Display free and used system memory in bytes.
Command:
free -b
Description:
Display free and used system memory in kilobytes.
Command:
free -k
Description:
Display free and used system memory in megabytes.
Command:
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373
free -m
Description:
Change user password.
Command:
passwd
Description:
Power-off the machine.
Command:
shutdown
Description:
Power-off the machine immediately.
Command:
shutdown -h now
Description:
Power-off the machine after 10 minutes.
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Command:
shutdown -h +10
Description:
Print current working directory.
Command:
echo $PWD
Description:
Print previous working directory.
Command:
echo $OLDPWD
Description:
Executes the 11th command in command history.
Command:
!11
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5

375
Description:
Reveals your command history.
Command:
history
Description:
Power off or reboot the Operating system.
Command:
sudo reboot
Description:
Display the IP address of the host.
Command:
ip address
Description:
List the size of files and directories.
Command:
ls -s
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376
Description:
View mounted file systems.
Command:
mount
Description:
Display the information of disk usage of files and directories.
Command:
du
Description:
Tells you how long the system has been running.
Command:
uptime
Description:
Set current date as 02 Nov 1988.
Command:
391
7

Description:
Set current time as 12:11:02 IST.
Command:
Description:
View Specific Disk Partition in Linux.
Command:
fdisk -l /dev/sda
Description:
Lists all files and directories in the present working directory.
Command:
ls
Description:
Report the process information.
377
392
8
date --set 1998-11-02
date --set 12:11:02

378
Command:
ps
Description:
Display disk usage.
Command:
df
Description:
Display disk usage in gigabytes, megabytes, or kilobytes.
Command:
df -H
Description:
Delete every file and every directory.
Command:
rm -r *
393
9

379
Description:
Provides a quick overview of the currently running processes.
Command:
top
Description:
The system performs an immediate reboot.
Command:
reboot
Description:
Terminate processes without having to log out or reboot.
Command:
kill
Description:
Change the current working directory.
Command:
cd
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10

380
Description:
Create a new session on the system.
Command:
login
Description:
List open files.
Command:
lsof
Description:
List USB devices.
Command:
lsusb
Description:
Check the status of the network services.
Command:
395
11

381
service network status
Description:
Start the network service.
Command:
service network start
Description:
Stop the network service.
Command:
service network stop
Description:
Restart the network service.
Command:
service network restart
Description:
Report information about the users currently on the machine and their processes.
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12

382
Command:
w
Description:
Display the current directory.
Command:
pwd
Description:
Displays CPU architecture information (such as number of CPUs, threads, cores, sockets, and
more).
Command:
lscpu
Description:
Displays the number of processing units available to the current process.
Command:
nproc
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13

383
Description:
The system performs an immediate reboot.
Command:
init 6
Description:
Power-off the machine.
Command:
init 0
Description:
List files by date.
Command:
ls -lrt
Description:
Report information about storage devices such as hard disks, flash drives etc.
Command:
lsblk
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14

384
Description:
Show exit status of previous command.
Command:
echo $?
Description:
Lists a few useful info commands.
Command:
info
Description:
Prints current year's calendar.
Command:
cal -y
Description:
Check the status of all the services.
Command:
399
15

385
service --status-all
Description:
Display time in hh:mm:ss.
Command:
date +%T
Description:
Tells when the user last logged on and off and from where.
Command:
last -1 username
Description:
Sort files and directories by extension name.
Command:
ls -X
Description:
Display the manual for the pwd command.
400
16

386
Command:
man pwd
Description:
Displays information about running processes in the form of a tree.
Command:
pstree
Description:
Resets your terminal.
Command:
reset
Description:
Displays What date is it this Friday.
Command:
date -d fri
401
17

387
Description:
Displays the size of each individual file.
Command:
du -a
Description:
Display information about the Advanced configuration and power Interface.
Command:
acpi
Description:
Takes you two folders back.
Command:
cd ../..
Description:
Takes you to the previous directory.
Command:
cd -
402
18

388
Description:
Displays a list of shell built-in commands.
Command:
help
Description:
Lists your last logins.
Command:
last yourusername
Description:
Create a new directory called myfiles.
Command:
mkdir myfiles
Description:
Remove the directory myfiles.
Command:
403
19

389
rmdir myfiles
Description:
Disable password for a specific user "root1".
Command:
passwd -d root1
Description:
Switch to user "root1".
Command:
sudo su root1
Description:
Exit from the terminal window.
Command:
logout
Description:
Creates a user "root1".
404
20

390
Command:
useradd "root1"
Description:
Assign password to user "root1".
Command:
passwd "root1"
Description:
Repeats the last command.
Command:
!!
Description:
Display Who you are logged in as.
Command:
whoami
405
21

391
Description:
Display the login name of the current user.
Command:
logname
Description:
Report the name of the kernel.
Command:
uname
Description:
Print the kernel version.
Command:
uname -v
Description:
Print the operating system.
Command:
uname -o
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392
Description:
Report the machine hardware name.
Command:
uname -m
Description:
Print version information and exit.
Command:
uname --version
Description:
Print the kernel release.
Command:
uname -r
Description:
Report the network node hostname.
Command:
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uname -n
Description:
Display all port connections (both TCP and UDP).
Command:
netstat -a
Description:
Display only TCP (Transmission Control Protocol) port connections.
Command:
netstat -at
Description:
Display only UDP (User Datagram Protocol) port connections.
Command:
netstat -au
Description:
Display all active listening ports.
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394
Command:
netstat -I
Description:
Display all active listening TCP ports.
Command:
netstat -It
Description:
Display all active listening UDP ports.
Command:
netstat -lu
Description:
Reveal all the information about the current user (user id, username, group id, group name etc.).
Command:
id
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395
Description:
Reveal all the information about the user "root1" (user id, username, group id, group name etc.).
Command:
id root1
Description:
Print the machine's architecture.
Command:
arch
Description:
Display the list of available fonts.
Command:
fc-list
Description:
Create two directories (myfiles, files).
Command:
mkdir myfiles files
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396
Description:
install apache (CentOS).
Command:
yum install httpd
Description:
install apache (Ubuntu).
Command:
apt install httpd
Description:
upgrade apache (CentOS).
Command:
yum update httpd
Description:
upgrade apache (Ubuntu).
Command:
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397
apt update httpd
Description:
uninstall apache (CentOS).
Command:
yum remove httpd
Description:
uninstall apache (Ubuntu).
Command:
apt remove httpd
Description:
Display usage summary for the command (date).
Command:
date --help
Description:
List active connections to/from system.
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28

398
Command:
ss -tup
Description:
List internet services on a system.
Command:
ss -tupl
Description:
Display all active UNIX listening ports.
Command:
netstat -lx
Description:
Display all the active interfaces details.
Command:
ifconfig
413
29

399
Description:
Display information of all network interfaces.
Command:
ifconfig -a
Description:
Compare the contents of two files (1.txt, 2.txt).
Command:
diff 1.txt 2.txt
Description:
Tells you how many lines, words, and characters there are in a file (1.txt).
Command:
wc 1.txt
Description:
Compresses file (1.txt), so that it take up much less space.
Command:
gzip 1.txt
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400
Description:
Uncompresses file (1.txt) compressed by gzip.
Command:
gunzip 1.txt
Description:
Examine the contents of the file (1.txt).
Command:
cat 1.txt
Description:
Display calendar.
Command:
ncal
Description:
Removes the file (1.txt).
Command:
415
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401
rm 1.txt
Description:
Rename a file named 1.txt to 0.txt.
Command:
mv 1.txt 0.txt
Description:
Replace the contents of 0.txt with that of 1.txt.
Command:
cp 1.txt 0.txt
Description:
Create a empty file (test.txt).
Command:
touch test.txt
Description:
Print the last 10 lines of a file (1.txt).
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402
Command:
tail 1.txt
Description:
Print N number of lines from the file (1.txt).
Command:
tail -n N 1.txt
Description:
Prints the number of words in a file (1.txt).
Command:
wc -w 1.txt
Description:
Prints the number of characters from a file (1.txt).
Command:
wc -m 1.txt
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403
Description:
Prints the length of the longest line in a file (1.txt).
Command:
wc -L 1.txt
Description:
Print information about usb ports, graphics cards, network adapters etc.
Command:
lspci
Description:
View contents of a file (1.txt).
Command:
less 1.txt
Description:
Display calendar (last month, current month, and next month).
Command:
cal -3
418
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404
Description:
Compare the contents of three files (1.txt, 2.txt, 3.txt) line by line.
Command:
diff3 1.txt 2.txt 3.txt
Description:
Compare two files (1.txt, 2.txt) line-by-line.
Command:
comm 1.txt 2.txt
Description:
Perform byte-by-byte comparison of two files (1.txt, 2.txt).
Command:
cmp 1.txt 2.txt
Description:
Prints the CRC checksum and byte count for the file "myfiles.txt".
Command:
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405
cksum myfiles.txt
Description:
Append contents of files (1.txt, 2.txt) into one file (0.txt).
Command:
cat 1.txt 2.txt > 0.txt
Description:
Append contents of files (1.txt, 2.txt, 3.txt) into one file (0.txt).
Command:
sed r 1.txt 2.txt 3.txt > 0.txt
Description:
Command:
sed h 1.txt 2.txt 3.txt > 0.txt
Description:
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406
mkdir test
cd test
pwd
touch test1.txt
Command:
sed -n p 1.txt 2.txt 3.txt > 0.txt
Shortcuts:
|
|
ctrl+c
ctrl+z
|
|
Halts the current command
Stops the current command
|
|
|
| ctrl+d
|
| Logout the current session
|
|
|
|
ctrl+w |
|
Erases one word in the current line |
|
| ctrl+u | Erases the whole line |
| ctrl+r | Type to bring up a recent command |
Description:
Writes contents of a file (0.txt) to output, and prepends each line with line number.
Command:
nl 0.txt
Description:
Create a empty file (test1.txt) inside a directory (test).
Command:
421
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407
Description:
Gather information about hardware components such as CPU, disks, memory, USB controllers
etc.
Command:
sudo lshw
Description:
Gather information about file system partitions.
Command:
sudo fdisk -l
Description:
Displays the line (good morning) in which the string (good) is found in the file (1.txt).
Command:
grep good 1.txt
Description:
Append contents of files (1.txt, 2.txt, 3.txt) into one file (0.txt) using for loop.
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408
###
| Command | Description
|: | :
| vi | Open vi editor
| i | Go to Insert mode
| |
| a =20; b =64; |
| print (a + b); |
| Hit Escape to return to Normal mode.
| :w hello.py | Save text
|
|
|
|
|
|
|
|
|
| :q | Quit |
| python hello.py |Print the output:84 |
Command:
for i in {1..3}; do cat "$i.txt" >> 0.txt; done
Description:
Search for files (test.txt, test1.txt, test2.txt, test.php, test.html) in a directory as well as its sub-
directories.
Command:
find test*
Description:
Displays status related to a file (1.txt).
Command:
stat 1.txt
Description:
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409
Download the file (file.txt) from url "http: //website.com/files/file.txt".
Command:
wget http://website.com/files/file.txt
Description:
Display host's numeric ID in hexadecimal format.
Command:
hostid
Description:
Display file type of the file (myfiles.txt).
Command:
file myfiles.txt
Description:
Create a file (myfiles.txt) containing a text (Hello World).
Command:
echo 'Hello World' > myfiles.txt
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410
echo "Hello world!" >> 1.txt
echo "this is 2nd line text" >> 1.txt
echo "last line!" >> 1.txt
Description:
Create a file (myfiles.txt) containing a text (Hello World).
Command:
printf 'Hello World' > myfiles.txt
Description:
Display IP address of the hostname.
Command:
hostname -i
Description:
Add a new line of text to an existing file (1.txt).
Command:
Description:
Displays a single line description about a command (cal).
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412
427
Command:
ping google.com
Description:
Find the location of source/binary file of a command (cal).
Command:
whereis cal
There are 2 ways to use the command:
 Numeric mode
 Symbolic mode
Numeric mode Permission Type Symbolic mode
0 No Permission ---
1 Execute --x
2 Write -w-
3 Execute + Write -wx
4 Read r--
5 Read + Execute r-x
6 Read + Write rw-
7 Read + Write + Execute rwx
[manju@localhost ~]$ ps -ef | grep sshd
root 988 1 0 06:14 ? 00:00:00 /usr/sbin/sshd
manju 3501 3461 0 06:24 pts/0 00:00:00 grep --color=auto sshd
# Check if the SSH server (sshd) is running
# Overwrite existing file
$ echo "Albert Einstein" > 1.txt
# Append a second line
$ echo "Alan Turing" >> 1.txt
43

cd /etc && ls
# Execute ls after cd /etc
rm myfiles.txt && echo success || echo failed
[manju@localhost ~]$ echo This is the $SHELL shell
This is the /bin/bash shell
[manju@localhost ~]$ echo This is $SHELL on computer $HOSTNAME
This is /bin/bash on computer localhost.localdomain
[manju@localhost ~]$ echo The user ID of $USER is $UID
The user ID of manju is 1000
[manju@localhost ~]$ echo My home directory is $HOME
My home directory is /home/manju
env LANG=C bash -c 'ls test[a-z].txt'
testa.txt testb.txt testc.txt
env LANG=en_US.UTF-8 bash -c 'ls test[a-z].txt'
testa.txt testA.txt testb.txt testc.txt testC.txt
Print 'success' if myfiles.txt is
removed and print 'failed' if it is
not removed
[manju@localhost ~]$ bash -c 'echo $SHELL $HOME $USER'
/bin/bash /home/manju manju
[manju@localhost ~]$ env -i bash -c 'echo $SHELL $HOME $USER'
/bin/bash

[manju@localhost ~]$ prefix=John
[manju@localhost ~]$ echo Hello ${prefix}Dalton and ${prefix}Humphrys
Hello JohnDalton and JohnHumphrys
echo 'a=5;echo $a'
[manju@localhost ~]$ touch myfiles.txt
[manju@localhost ~]$ cat myfiles.txt
Hello World
[manju@localhost ~]$ !to
touch myfiles.txt
echo $(a=5;echo $a)
5
a=5;echo $a
[manju@localhost ~]$ echo $HISTSIZE
1000
The number of commands that are stored in memory in
a history list while your bash session is ongoing
[manju@localhost ~]$ echo $HISTFILE
/home/manju/.bash_history Holds the name and location
of your Bash history file

echo $HISTFILESIZE
1000
[manju@localhost ~]$ ls *ile1.txt
file1.txt
[manju@localhost ~]$ ls f*ile1.txt
file1.txt
[manju@localhost ~]$ ls f*1.txt
file1.txt
[manju@localhost ~]$ ls file?.txt
file1.txt file2.txt file3.txt
[manju@localhost ~]$ ls fil?1.txt
file1.txt
[manju@localhost ~]$ ls fil??.txt
[manju@localhost ~]$ ls file??.txt
file23.txt file34.txt
How many commands can be stored in the .bash_history file

[manju@localhost ~]$ ls test[5A].txt
testA.txt
[manju@localhost ~]$ ls test[A5].txt
testA.txt
[manju@localhost ~]$ ls file[!5]*.txt
file123.txt file1.txt file23.txt file2.txt file34.txt file3.txt
[manju@localhost ~]$ ls file[!5]?.txt
file23.txt file34.txt
[manju@localhost ~]$ ls [a-z]ile?.txt
[manju@localhost ~]$ ls [A-Z]ile?.txt
[manju@localhost ~]$ echo *
*
[manju@localhost ~]$ echo '*'
*
[manju@localhost ~]$ echo "*"
*
[manju@localhost ~]$ ls [a-z]*[0-9].txt
file123.txt file1.txt file23.txt file2.txt file34.txt file3.txt
List all .txt files starting with a
letter and ending in a number

ls ?????
# List all files that have exactly five characters
ls [fF]*[3A].txt
# List all .txt files that start with f or F and end with 3 or A
ls f[iR]*[0-9].txt
# List all .txt files that start with f have i or R as second character and end in a number
ls [!f]*.txt
# List all .txt files that do not start with the letter "f"
[manju@localhost ~]$ echo Einstein2 | sed 's/2/36/'
Einstein36
[manju@localhost ~]$ echo Einstein36 | sed 's/Einstein/Hilbert/'
Hilbert36
[manju@localhost ~]$ echo Hawking6 Lucy8 | sed 's/Hawking/Lucy/'
Lucy6 Lucy8
[manju@localhost ~]$ echo Lucy3 Lucy6 | sed 's/Lucy/Hawking/g'
Hawking3 Hawking6

[manju@localhost ~]$ who | cut -d' ' -f1 | sort
manju
manju
[manju@localhost ~]$ who | cut -d' ' -f1 | sort | uniq
manju
grep bash /etc/passwd | cut -d: -f1 | sort > bu.txt
# Place a sorted list of all bash users in bu.txt
who | cut -d' ' -f1 | sort > users.txt
# Place a sorted list of all logged on users in users.txt
ls /etc | grep conf
# List of all filenames in /etc that contain the string "conf" in their filename
ls /etc | grep -i conf | sort
Display a sorted list
of logged on users
Display a sorted
list of logged on
users − but every
user only once
[manju@localhost ~]$ grep bash /etc/passwd
root:x:0:0:root:/root:/bin/bash
manju:x:1000:1000:su,root,yopp,hhhhh:/home/manju:/bin/bash
Display a list of all bash user accounts on this computer
Display a sorted list of all files in /etc
that contain the case insensitive string
"conf " in their filename

59
import os
os.system('ls')
List all the files and directories in the
current directory
import subprocess
subprocess.call ('ls')
428
90% of the public cloud workload is run on Linux distros.
The first ever Linux kernel just occupied only 65 KB.
import os
os.system('linux command')
import subprocess
subprocess.call ('linux command')
All of the 500 fastest supercomputers run Linux.
Execution of the linux command "ls" using the python program
44

Command:
last reboot
Description:
Show system reboot history
Command:
dmesg
Description:
Displays the messages from the kernel ring buffer (a data structure that records
messages related to the operation of the kernel)
Command:
cat /proc/cpuinfo
Description:
Display CPU information
429
45

Command:
cat /proc/meminfo
Description:
Display memory information
Command:
Description:
Display PCI (Peripheral Component Interconnect) devices
Command:
Description:
Display USB devices
430
46
lspci -tv
lsusb -tv

Command:
free -h
Description:
Display free and used memory (-h for human readable, -m for MB, -g for GB)
Command:
mpstat 1
Description:
Display processor related statistics
Command:
vmstat 1
Description:
431
47

Display virtual memory statistics
Command:
iostat 1
Description:
Display Input / Output statistics
Command:
watch df -h
Description:
Execute "df -h" command, showing periodic updates
Command:
Description:
432
48
ps -ef

Display all the currently running processes on the system
Command:
ip a
Description:
Display all network interfaces and IP address
Command:
dig wikipedia.org
Description:
Display DNS information for domain (wikipedia.org)
Command:
host wikipedia.org
Description:
433
49

Display the IP address details of the specified domain (wikipedia.org)
Command:
netstat -nutlp
Description:
Display listening Transmission Control Protocol (TCP) and the User Datagram
Protocol (UDP) ports and corresponding programs
Command:
rpm -qa
Description:
List all installed packages
Command:
yum list installed
Description:
List all installed packages (CentOS)
Command:
434
50

yum info httpd
Description:
Display description and summary information about package "httpd" (CentOS)
Command:
du -ah
Description:
Display disk usage for all files and directories in human readable format
Command:
du -sh
Description:
Display total disk usage off the current directory
Command:
435
51

cd /etc
Description:
Change to the /etc directory
Command:
ps -A
Description:
List the status of all the processes along with process id and PID
Command:
int main()
{
printf("Hello worldn"); Hello.c
return 0;
}
436
52
#include <stdio.h>
gcc Hello.c

Description:
Compile the C program saved in Hello.c file
Command:
int main()
{
std::cout << "Hello world!"; Hello.cpp
return 0;
}
Description:
Compile the C++ program saved in Hello.cpp file
Command:
tty
Description:
Displays the file name of the terminal connected to standard input
437
53
#include <iostream>
g++ Hello.cpp

Command:
public static void main(String [] args) {
System.out.println("Hello, World!"); MyClass.java
}
}
Description:
Compile the Java program saved in MyClass.java file using javac compiler
Command:
od -b myfiles.txt
Description:
Displays the contents of myfiles.txt file in octal format
Command:
od -c myfiles.txt
438
54
public class MyClass {
javac MyClass.java

Description:
Displays the contents of myfiles.txt file in character format
Command:
od -An -c myfiles.txt
Description:
Displays the contents of myfiles.txt file in character format but with no offset
information
Command:
csplit myfiles.txt 13 62 101
Description:
If the file myfiles.txt has 123 lines, the csplit command would create four files: the xx00 file
would contain lines 1−12, the xx01 file would contain lines 13−61, the xx02 file would contain
lines 62−100, the xx03 file would contain lines 101−123
Command:
439
55

md5sum myfiles.txt
Description:
Prints a 32-character (128-bit) checksum of myfiles.txt file using the MD5 algorithm
Command:
more myfiles.txt
Description:
Displays the content of myfiles.txt file
Command:
sha1sum myfiles.txt
Description:
Prints SHA1 (160-bit) checksum of myfiles.txt file
Command:
SHA 1 → Secure Hash Algorithm 1
440
56

shred myfiles.txt
Description:
Overwrites the myfiles.txt file repeatedly − in order to make it harder for even very
expensive hardware probing to recover the data
Command:
cat myfile.txt
01. Einstein
02. Newton
03. Maxwell
04. Tesla
05. Edison
tac myfile.txt
05. Edison
04. Tesla
03. Maxwell
02. Newton
01. Einstein
Description:
Print the lines of myfile.txt in reverse (from last line to first)
441
57

Command:
Description:
Delete repeated lines in the file (myfiles.txt).
Command:
Description:
Displays a list of system services and whether they are started (on) or stopped
(off) in run levels 0−6
Command:
Description:
Power-off the system
442
uniq myfiles.txt
chkconfig --list
halt -p
Command:
xdg-open myfiles.txt
Description:
Open a file (myfiles.txt).
58

Command:
lastlog
Description:
Prints the details of the last login (login-name, port and last login time)
Command:
lastlog -t 1
Description:
Displays the login information (1 day ago)
Command:
lastlog -u manju
Description:
Display lastlog information for a particular user (manju)
443
59

Command:
cat /etc/passwd
more /etc/passwd
less /etc/passwd
getent passwd
Description:
List all users on Linux
Command:
tail -5 /etc/passwd
head -5 /etc/passwd
444
60

Description:
List last 5 users on Linux
List first 5 users on Linux
Command:
wall "The system will be shutdown in 10 minutes."
Description:
The message (The system will be shutdown in 10 minutes.) will be broadcasted to
all users that are currently logged in
Command:
chage -l manju
Description:
List the password and its related details for a user (manju)
445
61

Command:
chage -M 10 manju
Description:
Set Password Expiry Date for an user (manju)
Command:
chage -E "2020-07-30" manju
Description:
Set the Account Expiry Date for an User (manju)
Command:
chage -I 10 manju
Description:
Force the user (manju) account to be locked after 10 inactivity days
446
62

cat /etc/hostname
→ localhost.localdomain
hostname
→ localhost.localdomain
nmtui
# Configure a network interface IPv4 address
yum check-update
# Check whether any updates are available for your installed packages
yum search httpd
# Find any packages containing the specified keyword "httpd"
ls /etc
# List the contents of /etc
ls /bin /sbin
# List the contents of /bin and /sbin
ls -al ~
# List all the files (including hidden files) in the home directory
ls -lh /boot
# List the files in /boot in a human readable format
Display the hostname of the system

mkdir ~/mydir
# Create a directory "mydir" under home directory
cd /etc ; mkdir ~/mydir
# Change to the /etc directory and create a directory "mydir" under home directory.
rm -i file.txt
rename .txt .backup *.txt
# Renames all .txt files replacing.txt with .backup
rm: remove regular empty file ‘file.txt’?
If we type "yes"
file.txt is removed
If we type "no"
file.txt is not removed
ls
file.txt cod.txt conf.txt
rename file FILE *
ls
FILE.txt cod.txt conf.txt
file /bin/cat /etc/passwd /usr/bin/passwd
Display the type of file of /bin/cat, /etc/passwd and /usr/bin/passwd

Command:
ftp 192.168.42.77
Description:
Connect to an FTP server at remote server IP address "192.168.42.77"
Command:
Description:
Lists all the peers connected at various interfaces along with their MAC
Addresses and IP addresses
Command:
dnsdomainname
Description:
447
63
arp -a

Display the system's DNS domain name
Command:
domainname
Description:
Display the name of the domain your machine belongs to
Command:
echo 'Hello World!' | base64
Output: SGVsbG8gV29ybGQhCg==
Description:
Encode text (Hello World!) to base64
Command:
echo 'SGVsbG8gV29ybGQhCg==' | base64 -d
Output: Hello World!
Description:
448
64

Decode (SGVsbG8gV29ybGQhCg==) to text (Hello World!)
Command:
Description:
Build font information cache files
Command:
cat 1.txt
Einstein
Newton
Albert
fmt 1.txt
Einstein Newton Albert
Description:
Formats text in a single line
449
65
fc-cache -f -v

df -h | sort -rnk 5 | head -3 |
awk '{ print "Partition " $6 "t: " $5 " full!" }'
awk 'BEGIN { FS=":" } { print $1 "t" $5 }' /etc/passwd
# Display all the users on your system
ls *.xml
1.xml 2.xml
ls *.xml > list.txt
[manju@localhost ~]$ cat list.txt
1.xml
2.xml
for i in `cat list.txt`; do cp "$i" "$i".md ; done
Partition /boot : 51% full!
Partition / : 29% full!
Partition /run : 2% full!
[manju@localhost ~]$ ls
12.txt 2.xml.md Documents file34.txt Music Pictures tree.cpio
13.txt 3.txt Downloads file3.txt mydi Public users.txt
145.txt all echo FILE.backup mydir SHOW Videos
1.txt allfiles.txt file file.md mydir1 Templates
1.xml bu.txt file123.txt first.bash myfiles.txt test
1.xml.md Desktop file1.txt first.txt myFILEs.txt.xz testA.txt
2.txt DICT file23.txt foo1.txt newdir testB.txt
2.xml dir file2.txt list.txt nohup.out text

[manju@localhost ~]$ df -h /
Filesystem Size Used Avail Use% Mounted on
/dev/sda3 18G 5.2G 13G 29% /
Check the actual
used space on the
current root device
less /proc/modules
# Display information about what kernel−modules are loaded on your system
[manju@localhost ~]$ free −tm
total used free shared buff/cache available
Mem: 999936 511156 73480 8572 415300 284236
Swap: 2097148 0 2097148
Display the memory usage including
totals in megabytes
[manju@localhost ~]$ date --date="3 months 1 day ago"
Mon Jul 18 23:17:47 PDT 2022
[manju@localhost ~]$ date -d "3 days"
Fri Apr 22 23:20:01 PDT 2022
Print the date 3 months and 1 day ago from the current date
Print the date 3 days in the future from now
Hello World
[manju@localhost ~]$ cat myfiles.txt | tr 'H' 'A' > myfilesB.txt
[manju@localhost ~]$ cat myfilesB.txt
Aello World

Command:
Description:
List the files in the current directory
Command:
Description:
Copy the files ending with .txt or .md to the user's home directory
lsattr
cp {*.txt,*.md} ~
[manju@localhost ~]$ fgrep 'He' myfiles.txt
Hello World Look for the string "He" in the file "myfiles.txt"
[manju@localhost ~]$ grep --color -i Hello myfiles.txt
Hello World
Hello World
ls file*
# List all files in the current directory starting with "file"
ls *file
# List all files in the current directory ending with "file"

cat phy.txt
Albert Einstein was a German-born theoretical physicist, widely acknowledged to
be one of the greatest physicists of all time. Einstein is known for developing
the theory of relativity, but he also made important contributions to the
development of the theory of quantum mechanics.
fmt -w 1 phy.txt
Albert
Einstein
was
a
German-born
theoretical
physicist,
widely
acknowledged
to
be
one
of
the
greatest
physicists
of
all
time.
Einstein
is
known
for
developing
450
66

the
theory
of
relativity,
but
he
also
made
important
contributions
to
the
development
of
the
theory
of
quantum
mechanics.
cat phy.txt
Albert Einstein was a German-born theoretical physicist, widely acknowledged to
be one of the greatest physicists of all time. Einstein is known for developing
the theory of relativity, but he also made important contributions to the
development of the theory of quantum mechanics.
fold -w 20 phy.txt
Albert Einstein was
451
67

a German-born theor
etical physicist, wi
dely acknowledged to
be one of the great
est physicists of al
l time. Einstein is
known for developing
the theory of relat
ivity, but he also m
ade important contri
butions to the devel
opment of the theory
of quantum mechanic
s.
Command:
traceroute google.com
Description:
Prints the route that a packet takes to reach the Google (172.217.26.206) host
from the local machine
Command:
cat 1.txt
452
68

Einstein
Newton
Albert
gzip 1.txt
zcat 1.txt.gz
Einstein
Newton
Albert
Description:
View the contents of zipped file
Command:
zdiff 1.txt.gz 2.txt.gz
Description:
Compare the contents of two zipped files (1.txt.gz, 2.txt.gz)
453
69

Command:
ss | less
Description:
List all connections
Command:
ss -aA tcp
Description:
Filter out TCP (Transmission Control Protocol) connections
Command:
ss -aA udp
Description:
Filter out UDP (User Datagram Protocol) connections
454
70

Command:
ss -lnt
Description:
Display only listening sockets
Command:
ss -ltp
Description:
Print process name and PID
Command:
ss -s
Description:
Print summary statistics
455
71

Command:
ss -tl6
Description:
Display only IPv6 connections
Command:
ss -tl -f inet
Description:
Display only IPv4 socket connections
Command:
ss -t4 state established
Description:
Display all IPv4 TCP sockets that are in connected state
456
72

Command:
pmap 3244
Description:
View the memory map of a process with Process ID (3244)
Command:
apropos -r 'remove file'
Description:
Find command that removes file
Command:
apropos editor
Description:
Display information about the editing programs that are available on a system
457
73

Command:
apropos pstree
Description:
Provide information about the pstree command (which displays the names of the
processes currently on the system in the form of a tree diagram)
basename /etc/passwd
Output: passwd
basename /usr/local/apache2/conf/httpd.conf
The apropos command is useful when you know what you want to do, but you have no idea what command
you should be using to do it. If you were wondering how to locate files, for example, the commands
apropos find
and
apropos locate
would have a lot of suggestions to offer.
458
74

Output: httpd.conf
echo a b c d e f| xargs
Output: a b c d e f
echo a b c d e f| xargs -n 3
Output: display only 3 items per line
a b c
d e f
Command:
env
Description:
Print out a list of all environment variables
Command:
459
75

printenv HOME
Description:
Print HOME variable value
cat score.txt
Albert-30
John-50
William-80
Stephen-20
Justin-40
cut -d- -f2 score.txt
30
50
80
20
40
cut -d- -f1 score.txt
Albert
John
William
Stephen
Justin
460
76

cat 1.txt
Hello World
cat 2.txt
Computer Program
paste 1.txt 2.txt
Hello World Computer Program
cat 1.txt
Hello World
cat 2.txt
Computer Program
join 1.txt 2.txt
Hello World Computer Program
461
77

Command:
rev 1.txt
Description:
Reverse lines of a file (1.txt)
cat 3.txt
22
33
11
77
55
sort 3.txt
11
22 sorts numeric values in 3.txt file and displays sorted output
33
55
77
462
78

cat 1.txt
Hello World
cat 1.txt | tr "[a-z]" "[A-Z]"
convert from lower case to upper case
HELLO WORLD
cat 5.txt
zz
zz
yy
yy
yy
xx
uniq 5.txt
zz removes duplicate lines and displays unique lines
yy
xx
463
79

cat 6.txt
Einstein
Newton
Tesla
nl 6.txt
1 Einstein numbers the lines in a file (6.txt)
2 Newton
3 Tesla
Command:
ls -l *.txt
Description:
Lists the files with .txt extension
The thing with Linux is that the developers themselves are actually customers too: that has
always been an important part of Linux.
Linus Torvalds
464
80

ls /proc/bus/
# List the contents of the /proc/bus/ directory
[manju@localhost ~]$ dmesg | grep "irq 1[45]"
[ 2.269581] ata1: PATA max UDMA/33 cmd 0x1f0 ctl 0x3f6 bmdma 0x1060 irq 14
[ 2.269585] ata2: PATA max UDMA/33 cmd 0x170 ctl 0x376 bmdma 0x1068 irq 15
echo Albert > 1.txt ; echo Einstein > 2.txt
cat 1.txt
Albert
cat 2.txt
Einstein
Find irq's allocated at boot time
cat /proc/ioports
# List system's IO ports
[manju@localhost ~]$ s=01234567890abcdefgh; echo ${s:7}
7890abcdefgh
[manju@localhost ~]$ cd /home/manju; echo $PWD
/home/manju
[manju@localhost ~]$ cd ..; pwd
/home
[manju@localhost home]$ echo $-
himBH

[manju@localhost home]$ w | cut -d " " -f 1 - | grep -v USER | sort -u
manju
12.txt allfiles.txt echo file3.txt mydi Pictures text
13.txt bu.txt file FILE.backup mydir Public tree.cpio
145.txt Desktop file123.txt file.md mydir1 SHOW users.txt
1.txt DICT file1.txt first.bash myfiles.txt Templates Videos
2.txt dir file23.txt first.txt myFILEs.txt.xz test
3.txt Documents file2.txt foo1.txt newdir testA.txt
all Downloads file34.txt Music nohup.out testB.txt
Users currently connected
[manju@localhost ~]$ echo ""

[manju@localhost ~]$ echo Al{ber,an,er}t
Albert Alant Alert
[manju@localhost ~]$ echo ${Albert:=Einstein}
Einstein
[manju@localhost ~]$ echo $[5*5]
25

ls -ldh * | grep -v total |
awk '{ print "Size is " $5 " bytes for " $9 }'
Size is 135K bytes for 12.txt
Size is 13M bytes for 13.txt
Size is 0 bytes for 145.txt
Size is 20 bytes for all
Size is 13M bytes for allfiles.txt
Size is 11 bytes for bu.txt
Size is 6 bytes for Desktop
Size is 0 bytes for DICT
Size is 6 bytes for dir
Size is 6 bytes for Documents
Size is 6 bytes for Downloads
Size is 0 bytes for echo
Size is 0 bytes for file
Size is 0 bytes for file123.txt
Size is 45 bytes for mydir
Size is 47 bytes for mydir1
Size is 12 bytes for myfiles.txt
Size is 68 bytes for myFILEs.txt.xz
Size is 0 bytes for FILE.backup
Size is 3 bytes for file.md
Size is 13 bytes for first.bash
Size is 13 bytes for first.txt
Size is 66 bytes for foo1.txt
Size is 6 bytes for Music
Size is 31 bytes for mydi
Size is 6 bytes for newdir
Size is 148 bytes for nohup.out
Size is 6 bytes for Pictures
Size is 6 bytes for Public
Size is 0 bytes for SHOW
Size is 6 bytes for Templates
Size is 6 bytes for test
Size is 0 bytes for testA.txt
Size is 0 bytes for testB.txt
Size is 25 bytes for text
Size is 512 bytes for tree.cpio
Size is 12 bytes for users.txt
Size is 6 bytes for Videos

Linux Unix
Free to use (open source) Licensed Operating System (closed source)
Linux is just the kernel Unix is a complete package of Operating System
Bash (Bourne Again SHell) is default shell for Linux Bourne Shell is default shell for Unix
Portable and is booted from a USB Stick Unportable
Source code is accessible to the general public Source code is not accessible to anyone
Uses Graphical User Interface with an optional
Command Line Interface
Uses Command Line Interface
Command:
Description:
Print the Default shell of user
Command:
Description:
Display the name of the currently running process ($0 is the name of the running process).
If you useit inside of a shell then it will return the name of the shell. If you use it inside of a
script, it will return the name of the script
echo $SHELL
echo $0
81

466
Command:
Description:
Print all files and folders − similar to ls command
Command:
Description:
Print the process ID of the current shell ($$ is the process ID of the current shell)
Command:
echo *
ps -p $$
Output:
PID TTY
3352 pts/0
TIME CMD
00:00:00 bash
sudo du -a Documents/ | sort -n -r | head -n 5
# List 5 biggest files from directory "Documents"
82

Description:
List shells
Command:
Description:
Display the files in the current folder that start with the letter "m".
Command:
Description:
List last logins of users and what happened such as "shutdown" or "crash" etc.
Command:
467
cat /etc/shells
echo m*
last
Command:
echo ~
Description:
Print your home folder path
83

bzip2 -k phy.txt
Description:
Compresses but does not deletes the original file
phy.txt → phy.txt.bz2
Command:
bzip2 -d phy.txt.bz2
Description:
Decompresses the compressed file (phy.txt.bz2)
phy.txt.bz2 → phy.txt
Command:
bzcat phy.txt.bz2
468
84

Description:
Display the contents of compressed file (phy.txt.bz2)
Command:
bunzip2 phy.txt.bz2
Description:
Decompresses the compressed file (phy.txt.bz2)
Command:
crontab –l
Description:
Display current logged-in user's crontab entries
cat /dev/null > phy.txt
469
85

cp /dev/null phy.txt
echo "" > phy.txt
echo > phy.txt
Description:
Empty the content of a file (phy.txt)
Command:
nohup ping google.com &
Description:
Ping google.com and send the process to the background
Command:
470
86

nohup ping google.com > log.txt &
Description:
Save the ping logs to log.txt
pgrep -a ping
Output:
3858 ping google.com
kill 3858
pgrep -a ping
Output:
Command:
ls -la /home
471
87

Description:
Display the contents of /home
Command:
sudo shutdown 2
Description:
Power-off the machine after 2 minutes
Command:
shutdown -c
Description:
Cancel the shutdown process
Command:
pr 36.txt
472
88

Description:
Display the contents of the file (36.txt) one page after the other
Command:
Description:
Display all current terminal settings
Command:
ls -1
Description:
List files one per line
Command:
473
89
stty -a

yes John
Description:
Outputs a string (John) repeatedly until killed
Command:
vdir
Description:
List files and directories in the current directory (one per line) with details
Command:
who -b
Description:
Print when the system was booted
# Open phy.txt with nano
474
90

nano phy.txt
# Open phy.txt with vim
vim phy.txt
Command:
ls -al *.txt
Description:
Display all .txt files, including its individual permission.
w --ip-addr
Command:
uname -i
Description:
Display the platform of hardware
Command:
uname -p
Description:
Display the type of processor
Command:
cat /proc/interrupts
Description:
Display the interrupts
91

# Displays information regarding the users currently on the machine, login time, IDLE time,
TTY and CPU time
Output:
11:12:10 up 1:29, 2 users, load average: 0.02, 0.04, 0.10
USER TTY FROM LOGIN@ IDLE JCPU PCPU WHAT
manju :0 :0 02:43 ?xdm? 3:30 0.65s gdm-session-worker [pa
manju pts/0 :0 11:01 2.00s 0.10s 0.01s w --ip-addr
w –short
# Omits CPU time and login information
Output:
11:11:46 up 1:28, 2 users, load average: 0.02, 0.04, 0.11
USER TTY FROM IDLE WHAT
manju :0 :0 ?xdm? gdm-session-worker [pam/gdm-password]
manju pts/0 :0 2.00s w --short
Command:
findmnt
Description:
Display a list of currently mounted file systems
Command:
476
92

ip addr show
Description:
List IP addresses and network interfaces
Command:
netstat -pnltu
Description:
List active (listening) ports
Command:
Description:
Display systemd, kernel and journal logs
Command:
477
93
journalctl

sudo systemctl status network
Description:
Display the status of network service
Command:
sudo systemctl start network
Description:
Start the network service
Command:
sudo systemctl stop network
Description:
Stop the network service
Command:
478
94

sestatus -b
Description:
Display the current state of Booleans
Command:
getenforce
Description:
Reports whether SELinux is enforcing, permissive or disabled
setenforce 0
Security-Enhanced Linux (SELinux) is a security architecture for Linux systems that allows
administrators to have more control over who can access the system
479
95

getenforce
Output:
Permissive
setenforce 1
getenforce
Output:
Enforcing
 Enforcing - SELinux security policy is enforced.
 Permissive - SELinux prints warnings instead of enforcing.
 Disabled - No SELinux policy is loaded.
480
96

[manju@localhost ~]$ let a="36 + 5" ; echo $a
41
[manju@localhost ~]$ let a="20 + 50/10" ; echo $a
25
[manju@localhost ~]$ let a="20 - 50/10" ; echo $a
15
[manju@localhost ~]$ let a="20 * 50/10" ; echo $a
100
[manju@localhost ~]$ grep PASS /etc/login.defs
# PASS_MAX_DAYS Maximum number of days a password may be used.
# PASS_MIN_DAYS Minimum number of days allowed between password changes.
# PASS_MIN_LEN Minimum acceptable password length.
# PASS_WARN_AGE Number of days warning given before a password expires.
PASS_MAX_DAYS 99999
PASS_MIN_DAYS 0
PASS_MIN_LEN 5
PASS_WARN_AGE 7
[manju@localhost ~]$ grep ^PASS /etc/login.defs
PASS_MAX_DAYS 99999
PASS_MIN_DAYS 0
PASS_MIN_LEN 5
PASS_WARN_AGE 7

Command:
Description:
List all local user accounts in column
Command:
Description:
Create a directory "mydir1" and create a file "myfiles1.txt" in it
Command:
Description:
Create a file "file.md" and give only read access to others
cut -d: -f1 /etc/passwd | column
mkdir ~/mydir1 ; touch ~/mydir1/myfiles1.txt
echo hi > file.md ; chmod 744 file.md
[manju@localhost ~]$ ls -l $(which sudo)
---s--x--x. 1 root root 130776 Nov 5 2016 /bin/sudo

Command:
sestatus
Description:
Display the current status of the SELinux that is running on your system
Command:
Description:
Display full listing of processes on your system
Command:
sar
Description:
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97
ps -aef

Display System Activity Report
Command:
ulimit
Description:
Report the resource limit of the current user
Output:
Unlimited The current user can consume all the resources the current system supports
2 types of resource limitation:
 Hard resource limit: The physical limit that the user can reach.
 Soft resource limit: The limit that is manageable by the user (its value can go up to the
hard limit)
Command:
482
98

ulimit -a
Description:
Report all the resource limits for the current user
Command:
Description:
Check the maximum stack size of the current user
Command:
Description:
Check out the max scheduling priority of the current user
483
99
ulimit -s
ulimit -e

Command:
Description:
Display the maximum number of user processes
Command:
Description:
Check out the size of virtual memory
Command:
Description:
Check out how many file descriptors a process can have
484
100
ulimit -u
ulimit -v
ulimit -n

Command:
man limits.conf
Description:
Display the in-depth information on the limits.conf configuration file
Command:
sar -V
Description:
Display the sar version
Command:
sar -u 2 5
Description:
Report CPU details total 5 times with the interval of 2 seconds
485
101

Command:
sar -n DEV 1 3 | egrep -v lo
Description:
Report about network interface, network speed, IPV4, TCPV4, ICMPV4 network traffic and errors
Command:
sar -v 1 3
Description:
Report details about the process, kernel thread, i-node, and the file tables
Command:
sar -S 1 3
Description:
Report statistics about swapping
486
102

Command:
sar -b 1 3
Description:
Report details about I/O operations like transaction per second, read per second, write per second
Command:
sudo systemctl status firewalld
Description:
Display the status of the firewalld
Command:
sudo systemctl start firewalld
Description:
Start the firewalld service
487
103

Command:
firewall-config
Description:
Start the graphical firewall configuration tool
firewall-cmd
Command:
firewall-cmd --list-all-zones
Description:
List all zones
Command:
firewalld is a firewall management tool for Linux operating systems
488
104

firewall-cmd --get-default-zone
Description:
Check the currently set default zone
Command:
firewall-cmd --list-services
Description:
Display currently allowed service on your system
Command:
firewall-cmd --list-ports
Description:
List the ports that are open on your system
Command:
489
105

firewall-cmd --zone=work --list-services
Description:
List services that are allowed for the public zone
Command:
mtr --report google.com
Description:
Provides information about the route that Internet traffic takes between the local
system and a remote host (google.com)
Command:
sudo yum install samba
Description:
install Samba (CentOS)
490
106

Command:
sudo firewall-cmd --add-service samba –permanent
Description:
Add Samba service to firewalld
Command:
zip q.zip q.txt
Description:
Create a zip file (q.zip)
Command:
Samba is client/server technology that implements network resource sharing across
operating systems. With Samba, files and printers can be shared across Windows,
Mac and Linux/UNIX clients.
491
107

unzip q.zip
Description:
Unzip a zip file (q.zip)
zipcloak q.zip
-----------------------------------------------------------------------------
# zipcloak prompts you for a password, and then ask you to confirm it:
Enter password:
Verify password:
...if the passwords match, it encrypts q.zip file
----------------------------------------------------------------------------
unzip q.zip
# When you try to unzip the q.zip file, it prompts you for the password before
allowing you to extract the file (q.txt) it contains
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108

Command:
zgrep -l "Einstein" *
Description:
Display the names of the files with the word (Einstein) present in it
Command:
zipsplit -n 1048576 q.zip
Description:
Split q.zip file to create a sequence of zipfiles (q1.zip, q2.zip…..) − each no larger
than 1048576 bytes (one megabyte)
You could concatenate (q1.zip, q2.zip…..) into a new file, w.zip, with the
command:
cat q*.zip > w.zip
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109

Command:
mtr google.com
Description:
Test the route and connection quality of traffic to the destination host google.com
Command:
route
Description:
Display IP routing table of a Linux system
Command:
nmcli dev status
494
110

Description:
View all your network devices
Command:
nmcli con show
Description:
Check network connections on your system
Command:
Description:
List all TCP ports (sockets) that are open on a server
Command:
495
111
ss -ta

ss -to
Description:
Display all active TCP connections together with their timers
Command:
type -a alias
Description:
Check Bash Aliases in Linux
# Difference between %B and %b is, %B will print full month name while %b will print abbreviated month
name.
echo "We are in the month = $(date +%b)"
# Difference between %Y and %y is %Y will print 4 digits while %y will print the last 2 digits of the year.
echo "We are in the year = $(date +%Y)"
echo "We are in the year = $(date +%y)"
496
112

echo "We are in the month = $(date +%B)"
# Difference between %A and %a is, %A will print full Weekday name while %a will print abbreviated weekday
name.
echo "Current Day of the week = $(date +%A)"
echo "Current Day of the week = $(date +%a)"
echo "Date using %D = $(date +%D)"
echo "Date using %F = $(date +%F)"
echo "current time in 24 hour format = $(date +%T)"
echo "current time in 12 hour format = $(date +%r)"
# Print yesterday's date and time.
echo "Yesterday = $(date -d "Yesterday")"
# Print Tomorrow date and time.
Date using %D = 08/15/21
Date using %F = 2021-08-15
current time in 24 hour format = 01:27:46
current time in 12 hour format = 01:27:47 AM
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113

echo "tomorrow = $(date -d "tomorrow")"
# Find what is the date and time before 10 days from now.
echo "Before 10 days = $(date -d "tomorrow -10 days")"
# Find last month and next month
echo "Last month = $(date -d "last month" "%B")"
echo "Next month = $(date -d "next month" "%B")"
# Find last year and next year
echo "Last Year = $(date -d "last year" "+%Y")"
echo "Next Year = $(date -d "next year" "+%Y")"
Command:
ls -lai /
Description:
Get the number of inodes of files in a directory (root directory)
Command:
sudo du --inode /
Description:
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114

Get the total number of inodes in the root directory
Command:
ss -o state established '( sport = :http or sport = :https )'
Description:
Get the list of all clients connected to HTTP (Port 80) or HTTPS (Port 443)
Command:
ss -tn src :80 or src :443
Description:
List the numerical port numbers
Command:
sudo yum install putty
Description:
499
115

Install PuTTy on CentOS
Command:
sudo watch netstat -tulpn
Description:
Watch TCP and UDP Open Ports in Real-Time
Command:
sudo watch ss –tulpn
Description:
Watch TCP and UDP Open Ports in Real-Time
Command:
timeout 5s ping google.com
500
116

Description:
Timeout a ping command after 5 seconds
Command:
yum install curl
Description:
Install curl on CentOS
Command:
Description:
List all UDP Connections
Command:
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117
ss -ua

Description:
List all Listening UDP Connections
Command:
ss -p
Description:
Display the Process IDs related to socket connections
Command:
ss -4
Description:
Display IPv4 and IPv6 Socket Connections
502
118
ss -lu

Command:
ss -6
Description:
Display IPv6 connections
Command:
ss -at '( dport = :22 or sport = :22 )'
Description:
Filter Connections by Port Number
"The only way to learn a new programming language is by writing
programs in it."
−Dennis Ritchie
503
119

[manju@localhost ~]$ echo {a..z}
a b c d e f g h i j k l m n o p q r s t u v w x y z
[manju@localhost ~]$ echo {z..a}
z y x w v u t s r q p o n m l k j i h g f e d c b a
[manju@localhost ~]$ echo {05..12}
05 06 07 08 09 10 11 12
12 11 10 9 8 7 6 5
12 11 10 09 08 07 06 05
[manju@localhost ~]$ echo {x..z}{1..3}
x1 x2 x3 y1 y2 y3 z1 z2 z3
[manju@localhost ~]$ echo {0..10..2}
0 2 4 6 8 10
[manju@localhost ~]$ for i in {a..z..5}; do echo -n $i; done
afkpuz
005 006 007 008 009 010
mkdir 20{09..11}-{01..12}
# Create directories to group files by month and year

[manju@localhost ~]$ ls *.txt; echo $_
12.txt 1.txt 2.txt abc.txt my.txt phy.txt
13.txt 24.txt 3.txt marks.txt names.txt mphy.txt
[manju@localhost ~]$ cut -d, -f2,1 <<<'Albert,Bob,John'
Albert,Bob
Bob
Bob,John
[manju@localhost ~]$ x="W X Y Z"; echo "$x"
W X Y Z
[manju@localhost ~]$ x="W X Y Z"; echo $x
W X Y Z
echo $x and echo "$x" yield different results
Quoting a variable preserves whitespace

[manju@localhost ~]$ let x=20+7; echo "The value of "x" is $x."
The value of "x" is 27.
[manju@localhost ~]$ x=100; let "x += 1"; echo "x = $x"
x = 101
[manju@localhost ~]$ x="a+b+c"; IFS=+; echo $x
a b c
[manju@localhost ~]$ x="a-b-c"; IFS=-; echo $x
a b c
[manju@localhost ~]$ x="a,b,c"; IFS=,; echo $x
a b c
The "+" sign will be interpreted as a separator
The "- " sign will be interpreted as a separator
The "comma" will be interpreted as a separator
free | grep Mem | awk '{ print $4 }'
# Display the unused RAM memory
du -ach
# Display (disk) file usage
readelf -h /bin/bash
# Display information and statistics about a designated elf binary
[manju@localhost ~]$ expr 5 * 2 + 3
13 # 10 + 3
[manju@localhost ~]$ expr 5 * ( 2 + 3 )
25 # 5 * 5

[manju@localhost ~]$ echo -e "033[4mAlbert Einstein.033[0m"
Albert Einstein.
[manju@localhost ~]$ echo -e "033[1mAlbert Einstein.033[0m"
Albert Einstein.
[manju@localhost ~]$ echo -e 'E[34;47mAlbert Einstein'; tput sgr0
Albert Einstein
[manju@localhost ~]$ echo -e 'E[33;44m'"Albert Einstein"; tput sgr0
Albert Einstein
[manju@localhost ~]$ echo -e 'E[1;33;44m'"Albert Einstein"; tput sgr0
Albert Einstein
[manju@localhost ~]$ x=2; y=3; echo $((2*$x + 3*$y))
13
[manju@localhost ~]$ x=2; y=3; echo $((2*x + 3*y))
13
[manju@localhost ~]$ let x=2+3 y=3+2; echo $x $y
5 5

Command:
sdiff phy.txt score.txt
Description:
Show Difference between Two Files (phy.txt and score.txt)
Command:
history -c
Description:
Delete or clear all the entries from bash history
Command:
ping -c 5 www.google.com
Description:
The ping test will stop after sending 5 packets
504
120

# count number of lines in each .txt file
ls *.txt | xargs wc -l
# count number of words in each .txt file
ls *.txt | xargs wc -w
# count number of characters in each .txt file
ls *.txt | xargs wc -c
# count lines, words and characters in each .txt file
ls *.txt | xargs wc
Command:
lslogins –u
Description:
Displays user accounts
505
121

Command:
systemctl list-units --type=service
Description:
List all loaded services on your system (whether active; running, exited or failed)
Command:
systemctl --type=service
Description:
List all loaded services on your system (whether active; running, exited or failed)
Command:
systemctl list-units --type=service --state=active
506
122

Description:
List all loaded but active services
Command:
systemctl --type=service --state=active
Description:
List all loaded but active services
Command:
systemctl list-units --type=service --state=running
Description:
List all running services (i.e., all loaded and actively running services)
Command:
507
123

systemctl --type=service --state=running
Description:
List all running services (i.e., all loaded and actively running services)
#scan a single port
nc -v -w 2 z 192.168.56.1 22
# scan multiple ports
nc -v -w 2 z 192.168.56.1 22 80
# scan range of ports
nc -v -w 2 z 192.168.56.1 20-25
Command:
cat /etc/resolv.conf
Description:
Find out your DNS Server IP address
508
124

Command:
less /etc/resolv.conf
Description:
Find out your DNS Server IP address
Command:
findmnt --poll --mountpoint /mnt/test
Description:
Monitor mount, unmount, remount and move actions on a directory (i.e., on /mnt/test)
Command:
uptime -p
Description:
Check Linux Server Uptime
509
125

Command:
uptime –s
Description:
Check Linux Server Starting Time
Command:
uptime –h
Description:
Display uptime's version information
Command:
grep -o -i Justin score.txt | wc –l
Description:
Count the number of times "Justin" appears in the file (score.txt)
510
126

Command:
crontab -r
Description:
Delete all crontab jobs
ADD=$(( 1 + 2 ))
echo $ADD
3
MUL=$(( $ADD * 5 ))
echo $MUL
15
SUB=$(( $MUL - 5 ))
echo $SUB
10
DIV=$(( $SUB / 2 ))
echo $DIV
5
MOD=$(( $DIV % 2 ))
echo $MOD
1
511
127

Command:
expr length "This is myw3schools.com"
Description:
Find the length of a string (This is myw3schools.com)
echo '3+5' | bc
8
awk 'BEGIN { a = 6; b = 2; print "(a + b) = ", (a + b) }'
(a + b) = 8
Command:
factor 10
Description:
Decompose an integer (10) into prime factors
512
128

Command:
ps -e
Description:
Display every active process on a Linux system
Command:
ps -x
Description:
Display User Running Processes
Command:
ps -fU manju
Description:
513
129

Display a user's processes by user name (manju)
Command:
ps -fu 1000
Description:
Display a user's processes by real user ID (RUID)
Command:
ps -U root -u root
Description:
Display every process running with root user privileges (real and effective ID)
echo -e "The following users are logged on the system:nn $(who)"
manju :0 Aug 15 03:31 (:0)
manju pts/1 Aug 15 03:32 (:0)
514
130

Command:
sh <(curl https://nixos.org/nix/install) --daemon
Description:
Install Nix Package Manager in Linux
Command:
locale
Description:
View System Locale in Linux
Command:
Description:
515
131
locale -a

Display a list of all available locales
cat score.txt
Justin-40
cat score.txt | tr [:lower:] [:upper:]
JUSTIN-40
cat score.txt | tr [a-z] [A-Z] >output.txt
cat output.txt
JUSTIN-40
cat domainnames.txt
www. google. com
www. fb. com
www. mactech. com
cat domainnames.txt | tr -d ''
www.google.com
www.fb.com
www.mactech.com
Remove the
spaces in the
domain names
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132

cat domainnames.txt
www.google.....com
www.fb.com
www.mactech.Com
cat domainnames.txt | tr -s ''
www.google.com
www.fb.com
www.mactech.Com
echo "My UID is $UID"
My UID is 0
echo "My UID is $UID" | tr " " "n"
My
UID
is
0
echo "myw3schools.com =>Linux-Books,Src,Tutorials" | tr " " ":"
myw3schools.com:=>Linux-Books,Src,Tutorials
Command:
A space into a " : " character
517
133

!sud
Description:
Re-execute previously used command
Command:
!sudo
Description:
Re-execute previously used command
Command:
cut -d: -f1 < /etc/passwd | sort | xargs
Description:
518
134

519
Generate a compact list of all Linux user accounts on the system
Command:
Description:
View multiple compressed files (phy.txt.gz and myfiles.txt.gz)
Command:
Description:
Find all php files in a directory
Command:
zcat phy.txt.gz myfiles.txt.gz
find . -type f -name "*.php"
mkdir /tmp/DOCUMENTS
# Create a directory 'DOCUMENTS' under "/tmp" directory
135

find . -type f -perm 0777 -print
Description:
Find all the files whose permissions are 777
Command:
find / -type f ! -perm 777
Description:
Find all the files without permission 777
Command:
find / -perm /g=s
Description:
Find all SGID set files
Command:
520
136

521
find / -perm /a=x
Description:
Find all Read-Only files
Command:
Description:
Find all Executable files
Command:
find / -perm /u=r
[manju@localhost ~]$ echo "ALBERT" | awk '{print tolower($0)}'
albert
Convert text from upper case to lower case
137

521
find . -type f -name "*.txt" -exec rm -f {} ;
find . -type f -name "*.mp3" -exec rm -f {} ;
Description:
Find and remove phy.txt File
Command:
Description:
To find and remove multiple .txt files
Command:
Description:
find . -type f -name "phy.txt" -exec rm -f {} ;
[manju@localhost ~]$ echo "Phone number: 55602369" | tr -cd [:digit:]
55602369
Get the digits from string
138

521
find /tmp -type d -empty
find /tmp -type f -name ".*"
To find and remove multiple .mp3 files
Command:
Description:
Find all Empty Directories
Command:
Description:
File all Hidden Files
Command:
[manju@localhost ~]$ echo "Phone number: 55602369" | tr -d [:digit:]
Phone number:
Remove all digits from string
139

find / -mtime 50
Description:
Find Last 50 Days Modified Files
Command:
find / -atime 50
Description:
Find Last 50 Days Accessed Files
Command:
find / -cmin -60
Description:
524
140

Find Changed Files in Last 1 Hour
Command:
Description:
Find Modified Files in Last 1 Hour
Command:
Description:
Find Accessed Files in Last 1 Hour
Command:
find / -mmin -60
find / -amin -60
Command:
type cat
Description:
Identifies whether the "cat" command is a shell built-in command, subroutine, alias, or keyword.
525
141

find / -size 50M
Description:
Find all 50MB files
Command:
find / -type f -size +100M -exec rm -f {} ;
Description:
Find and Delete 100MB Files
Command:
find / -type f -name *.mp3 -size +10M -exec rm {} ;
Description:
Find all .mp3 files with more than 10MB and delete them
526
142

ls -l --color
# List the files in current directory (with colorized output)
info df
# Loads the "df "info page
ls /usr/include
# List the Header files for compiling C programs
ls /usr/local
# List the Locally installed files
ls /usr/bin/d*
# List all files whose names begin with the letter "d" in the /usr/bin directory
[manju@localhost ~]$ ls [a-h]*
all DICT file1 file2 file34.txt file.md foo1.txt
allfiles.txt echo file123.txt file23.txt file3.txt first.bash
bu.txt file file1.txt file2.txt FILE.backup first.txt
[manju@localhost ~]$ ls .b*
.bash_history .bash_logout .bash_profile .bashrc
[manju@localhost ~]$ touch hello.cpp; touch hello.f99
[manju@localhost ~]$ ls *.?[9p]?
hello.cpp hello.f99

ls /usr
# List the /usr directory
ls ~ /usr
# List the user's home directory and the /usr directory
[manju@localhost ~]$ echo f*
file file1 file123.txt file1.txt file2 file23.txt file2.txt file34.txt file3.txt
file.md first.bash first.txt foo1.txt
[manju@localhost ~]$ echo f*.txt
file123.txt file1.txt file23.txt file2.txt file34.txt file3.txt first.txt foo1.txt
sudo vim myfiles.txt
# Open a file "myfiles.txt" using Vim editor
[manju@localhost ~]$ for ((i=0;i<8;i++)); do echo $((i)); done
0
1
2
3
4
5
6
7
Display any file beginning with "f"
Display any file beginning with "f" followed by
any characters and ending with ".txt"

Command:
cat /proc/sys/fs/file-max
Description:
Find Linux Open File Limit
Command:
ulimit -Hn
Description:
Check Hard Limit in Linux
Command:
ulimit -Sn
Description:
Check Soft Limits in Linux
527
143

Command:
timedatectl status
Description:
Display the current time and date on your system
Command:
timedatectl list-timezones
Description:
View all available timezones
Command:
timedatectl list-timezones | egrep -o "Asia/B.*"
timedatectl list-timezones | egrep -o "Europe/L.*"
timedatectl list-timezones | egrep -o "America/N.*"
528
144

Description:
Find the local timezone according to your location
Command:
timedatectl set-timezone "Asia/Kolkata"
Description:
Set your local timezone in Linux
Command:
swapon --summary
Description:
View a summary of swap space usage by device
Command:
529
145

cat /proc/swaps
Description:
Check swap usage information
# start recording of Linux terminal
script history_log.txt
Script started, file is history_log.txt
exit
Script done, file is history_log.txt
Command:
dir -shl
Description:
530
146

List files and their allocated sizes in blocks
Command:
less /proc/sys/dev/cdrom/info
Description:
Display information about CD-ROM
while true; do date >> date.txt ; sleep 5 ; done &
cat date.txt
Mon Aug 16 03:05:36 PDT 2021
Mon Aug 16 03:05:41 PDT 2021
Mon Aug 16 03:05:46 PDT 2021
Mon Aug 16 03:05:51 PDT 2021
"Don't write better error messages, write code that doesn't need them."
− Jason C. McDonald
531
147

[manju@localhost ~]$ echo hello > 1.txt
[manju@localhost ~]$ echo world > 2.txt
[manju@localhost ~]$ echo program > 3.txt
[manju@localhost ~]$ cat 1.txt
hello
world
program
[manju@localhost ~]$ cat 1.txt 2.txt 3.txt
hello
world
program
[manju@localhost ~]$ cat 1.txt 2.txt 3.txt >all
[manju@localhost ~]$ cat all
hello
world
program
ls -lrS /etc
# List the biggest file in /etc
strings /usr/bin/passwd
# Display the readable character strings from the /usr/bin/passwd

cat /etc/passwd >> myfiles.txt
# Create a file named myfiles.txt that contains the contents of myfiles.txt followed by the contents of /etc/passwd
[manju@localhost ~]$ ls /etc/*.conf
/etc/asound.conf /etc/kdump.conf /etc/radvd.conf
/etc/autofs.conf /etc/krb5.conf /etc/request-key.conf
/etc/autofs_ldap_auth.conf /etc/ksmtuned.conf /etc/resolv.conf
/etc/brltty.conf /etc/ld.so.conf /etc/rsyncd.conf
/etc/cgconfig.conf /etc/libaudit.conf /etc/rsyslog.conf
/etc/cgrules.conf /etc/libuser.conf /etc/sestatus.conf
/etc/cgsnapshot_blacklist.conf /etc/locale.conf /etc/sos.conf
/etc/chrony.conf /etc/logrotate.conf /etc/sudo.conf
/etc/dleyna-server-service.conf /etc/man_db.conf /etc/sudo-ldap.conf
/etc/dnsmasq.conf /etc/mke2fs.conf /etc/sysctl.conf
/etc/dracut.conf /etc/mtools.conf /etc/tcsd.conf
/etc/e2fsck.conf /etc/nfsmount.conf /etc/updatedb.conf
/etc/fprintd.conf /etc/nsswitch.conf /etc/usb_modeswitch.conf
/etc/fuse.conf /etc/ntp.conf /etc/vconsole.conf
/etc/GeoIP.conf /etc/numad.conf /etc/wvdial.conf
/etc/host.conf /etc/oddjobd.conf /etc/yum.conf
/etc/idmapd.conf /etc/pbm2ppa.conf
/etc/ipsec.conf /etc/pnm2ppa.conf
Display configuration files located in /etc
ls /dev/sd*
/dev/sda /dev/sda1 /dev/sda2 /dev/sda3 Display SATA device files

echo Hello || echo Hi ; echo World
echo $USER
# $USER
echo -e "2+2t=4" ; echo -e "12+12t=24"
echo Hello ; echo World
2+2 =4
12+12 =24
Hello
World
echo Hello && echo World
Hello
World
Hello
World
rm myfiles.txt && echo It worked! || echo It failed!
It worked!
rm files.txt && echo It worked! || echo It failed!
rm: cannot remove ‘files.txt’: No such file or directory
It failed!
pwd ; pwd
/home/manju
/home/manju
Execute the pwd command twice

a=$(pwd)
echo "Current working directory is : $a"
/home/manju
Command:
echo *.jpeg
Description:
Print all .jpeg files
Command:
echo 'linux' | fold -w1
Description:
Break down a word (linux) into individual
532
148

l
i
n
u
x
Command:
find . -user root
Description:
Output the files with respect of the user (root) owned files in the current directory
Command:
strace pwd
Description:
Trace a command (pwd) execution
533
149

534
Command:
Description:
Display specific User (manju) process details
top -u manju
3 characteristics of big data:
 Volume — How much data is there?
 Variety — How diverse is different types of data?
 Velocity — At what speed is new data generated?
[manju@localhost ~]$ netstat -plunt
# print all listening ports
[manju@localhost ~]$ netstat -plunt | grep 8080
# check if server is listening on port 8080 or not
[manju@localhost ~]$ netstat -s
# list statistics of all ports
150

Hello World
[manju@localhost ~]$ cat myfiles.txt | tr ' ' 'n'
Hello
World
find /etc > 12.txt
# Find all files in /etc and place the list in 12.txt
find . -newer file1.txt
# Find files that is newer than file1.txt
[manju@localhost ~]$ date +'%A %d-%m-%Y'
Tuesday 19-04-2022
[manju@localhost ~]$ date -d '2022-04-01 + 2000000000 seconds'
Thu Aug 16 03:33:20 PDT 2085
find . -name "*.txt"
# Find files that end in .txt in the current directory and all subdirectories
find /etc -type f -name '*.txt' | wc -l
# Print the number of .txt files in /etc and all its subdirectories
Hello World
[manju@localhost ~]$ grep -E 'o*' myfiles.txt
Hello World
[manju@localhost ~]$ grep -E 'o+' myfiles.txt
Hello World

[manju@localhost ~]$ echo Albert Einstein | sed 's/Albert/&&/'
AlbertAlbert Einstein
[manju@localhost ~]$ echo Albert Einstein | sed 's/Einstein/&&/'
Albert EinsteinEinstein
[manju@localhost ~]$ echo -e 'AlberttistScientist'
Albert is Scientist
[manju@localhost ~]$ echo -e 'AlberttistScientist' | sed 's_s_ _g'
Albert is Scientist
[manju@localhost ~]$ echo Albert | sed 's_(Alb)_1ert_'
Albertert
[manju@localhost ~]$ echo Albert | sed 's_(Alb)_1ert 1_'
Albert Albert
Hello World
[manju@localhost ~]$ cat myfiles.txt | sed 's/ll?/A/'
HeAo World

echo Albert `echo -n Einstein`
Hello World
[manju@localhost ~]$ cat myfiles.txt | sed 's/l{2}/A/'
HeAo World
Albert Einstein
[manju@localhost ~]$ test 50 -gt 15 ; echo $?
0
[manju@localhost ~]$ test 5 -gt 15 ; echo $?
1
[manju@localhost ~]$ test 5 -lt 15 ; echo $?
0
[manju@localhost ~]$ test 50 -gt 15 && echo true || echo false
true
[manju@localhost ~]$ test 5 -gt 15 && echo true || echo false
false
True: 50 is greater than 15
False: 5 is not greater than 15
True: 5 is lesser than 15

[manju@localhost ~]$ a=2; b=a; eval c=$$b; echo $c
2
[manju@localhost ~]$ [ 50 -gt 15 ] && echo true || echo false
true
[manju@localhost ~]$ [ 5 -gt 15 ] && echo true || echo false
false
[manju@localhost ~]$ [ 100 -gt 10 -a 100 -lt 150 ] && echo true || echo false
true
[manju@localhost ~]$ [ 100 -gt 10 -a 100 -lt 15 ] && echo true || echo false
false
[manju@localhost ~]$ date
Tue Apr 19 02:55:39 PDT 2022
[manju@localhost ~]$ date --date="1 week ago"
Tue Apr 12 02:55:05 PDT 2022

Command:
uname –or
Description:
Find Out Linux Kernel Version
Command:
uname -a
Description:
Print linux system information
Command:
cat /proc/version
Description:
Display some of your system information including the Linux kernel version
535
151

Command:
cat /etc/centos-release
Description:
Find Out Linux Distribution Name and Release Version
Command:
fuser .
Description:
Displays the PIDs of processes currently accessing your current working directory
Command:
536
152

fuser -v -m .bashrc
Description:
Determine which processes are accessing your ~.bashrc file
Command:
sudo fuser --list-signals
Description:
Displays all the possible signals that can be used with the fuser tool
Command:
sudo fuser -k -HUP /boot
Description:
Sends the HUP signal to all processes that have your /boot directory open
537
153

Command:
538
Description:
List all the files with the file permissions, the number of links to that file, the owner of the file, the group of the
file, the file size in bytes, the file's last modified datetime and the file name
Command:
Description:
Shutdown the system at 23:55 today
Command:
Description:
Run updatedb at 23:55 today
ls -al
Creates and updates the database of file
names used by locate
echo "shutdown -h now" | at -m 23:55
echo "updatedb" | at -m 23.55
# Everyone can now read the file
chmod a+r myfiles.txt
# Everyone can now read and write the file
chmod a+rw myfiles.txt
# Others (not the owner, not in the same group of the
file) cannot read, write or execute the file
chmod o-rwx myfiles.txt
154

Command:
539
Description:
Execute command "ls -al" and print the result to the standard output
Command:
Description:
Display the top 15 processes sorted by memory use in descending order
Command:
Description:
Redirect the output to a file (report.txt) for later inspection
echo $(ls -al)
top -b -o +%MEM | head -n 22
top -b -o +%MEM | head -n 22 > report.txt
155

Command:
ps -eo pid,ppid,cmd,%mem,%cpu --sort=-%mem | head
Description:
Check Top Processes sorted by RAM or CPU Usage in Linux
Command:
find . -type f ( -name "*.sh" -o -name "*.txt" )
Description:
Find all files in the current directory with .sh and .txt file extensions
Command:
find . -type f ( -name "*.sh" -o -name "*.txt" -o -name "*.c" )
Description:
Find all files in the current directory with .sh, .c and .txt file extensions
540
156

Description:
Find files edited more than 3 days ago.
Command:
find . -type f -mtime +3
Description:
Find files edited in the last 24 hours.
Command:
find . -type f -mtime -1
Description:
Find files that have more than 100 characters (bytes) in them.
Command:
find . -type f -size +100c
947
157

Description:
Find files bigger than 100 KB but smaller than 1 MB.
Command:
find . -type f -size +100k -size -1M
Description:
Deletes all the files edited in the last 24 hours.
Command:
find . -type f -mtime -1 -delete
Description:
List all files including hidden files.
Command:
948
158

ls -a
Description:
List Files and Directories with "/" Character at the End.
Command:
ls -F
Description:
List Files in Reverse Order.
Command:
ls -r
Description:
Sort Files by File Size.
949
159

Command:
ls -lS
Description:
List Files with an inode number.
Command:
ls -i
Description:
Check the version of the ls command.
Command:
ls --version
Description:
List files under directory /tmp.
950
160

Command:
ls -l /tmp
Description:
Display UID and GID of files and directories.
Command:
ls -n
Description:
Find all 30 MB files.
Command:
find / -size 30M
951
161

Description:
Find files with sizes between 100 - 200MB.
Command:
find / -size +100M -size -200M
Description:
List directories larger than 20 KB.
Command:
find / -type d -size +20k
Description:
Find empty files and directories.
Command:
find ./ -type f -size 0
952
162

Description:
List files modified within the last 17 hours.
Command:
find . -mtime -17 -type f
Description:
*** List directories modified within the last 10 days.***
Command:
find . -mtime -10 -type d
Description:
List all files modified between 6 and 15 days ago in the home directory.
Command:
953
163

find /home -type f -mtime +6 -mtime -15
Description:
Display files with permission 777.
Command:
find -perm 777
Description:
List files owned by a user (manju).
Command:
find /home -user manju
Description:
Find all text files owned by user "manju".
954
164

Command:
find /home -user manju -iname "*.txt"
Description:
Find and list files and directories together with their permissions.
Command:
find -name "*.conf" | ls -l
Description:
List directories only.
Command:
ls -d */
Description:
List multiple files on a single line.
955
165

Command:
ls --format=comma
Description:
View the process of a specific user "manju".
Command:
ps -u manju
Description:
Execute a previous command starting with a specific letter "c".
Command:
!c
956
166

Description:
Display BIOS information (You need elevated permissions to run this).
Command:
dmidecode -t 0
Description:
Display CPU information (You need elevated permissions to run this).
Command:
dmidecode -t 4
Description:
View all the system logs.
Command:
gnome-system-log
957
167

Description:
Identify SSH Client Version.
Command:
ssh -V
Description:
Display total connect time of users.
Command:
ac –d
Description:
Display connect time for all the users.
Command:
958
168

ac -p
Description:
Diaplay connect time report for a specific user "manju".
Command:
ac -d manju
Description:
Display the modules compiled inside Apache.
Command:
httpd -l
Description:
*** View Processes Owned by Current User.***
959
169

Command:
ps U $USER
Description:
Display the information about the filesystem Type.
Command:
df -Tha
Description:
Display Active Connections with Process ID and Program Name.
Command:
netstat -tap
Description:
Display RAW network statistics.
960
170

Command:
netstat --statistics --raw
LILO (Linux Loader)
Linux User Mode
Command Line Interface
Graphical user interface
Load Linux into memory and start the OS
The maximum length for a filename under
Linux is 255 bytes.
Logical Volume Manager (LVM)
Manage hard drives and other
storage devices on linux
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171

[manju@localhost ~]$ PS1="Please enter a command: "
Please enter a command: date
Thu Apr 21 20:51:19 PDT 2022
Please enter a command: cal
April 2022
Su Mo Tu We Th Fr Sa
1 2
3 4 5 6 7 8 9
10 11 12 13 14 15 16
17 18 19 20 21 22 23
24 25 26 27 28 29 30
Please enter a command:
[manju@localhost ~]$ ls /var/spool
abrt abrt-upload anacron at cron cups lpd mail plymouth postfix
[manju@localhost ~]$ ls /usr/share/man
ca en hu ko man1x man3p man5 man7 man9 pl ro tr zh_TW
cs es id man0p man2 man3x man5x man7x man9x pt ru uk
da fr it man1 man2x man4 man6 man8 mann pt_BR sk zh
de hr ja man1p man3 man4x man6x man8x overrides pt_PT sv zh_CN
/var/spool holds spooled files such as those
generated for printing jobs and network transfers
/usr/share/man holds the online Man files
ps -aux | grep 'httpd'
# Check for the httpd process

[manju@localhost ~]$ ls /etc/gdm
custom.conf Init PostLogin PostSession PreSession Xsession
ls /etc/gconf
# List the GConf configuration files
ls /usr/share/gnome
# List the files used by GNOME applications
[manju@localhost ~]$ ls /etc/sysconfig
atd firewalld libvirt-guests qemu-ga samba
authconfig grub man-db radvd saslauthd
autofs init modules raid-check selinux
cbq ip6tables-config netconsole rdisc smartmontools
cgred iptables-config network readonly-root sshd
console irqbalance network-scripts rpcbind sysstat
cpupower kdump nfs rpc-rquotad sysstat.ioconf
crond kernel ntpd rsyncd virtlockd
ebtables-config ksm ntpdate rsyslog virtlogd
fcoe libvirtd pluto run-parts wpa_supplicant
ls /etc/rc.d
# List the system startup and shutdown files
[manju@localhost ~]$ ls /etc/init.d
functions netconsole network README
List the contents of GDM configuration directory
List the system configuration files
/etc/init.d holds network scripts to start up
network connections

Important features of Linux Operating System
+
+
Swap space
 Free and Open Source
 Portable and More secure
 Robust and Adaptable
Linux Kernel
Manage RAM memory.
Manage the processor time.
Manage access and use of the various peripherals that are connected to the computer.
The core interface between a computer's
hardware and its processes
A space on a hard disk that is used when the amount of
physical memory (RAM) is full
172

[manju@localhost ~]$ cd /etc
[manju@localhost etc]$ pwd
/etc
[manju@localhost etc]$ cat /etc/hosts
127.0.0.1 localhost localhost.localdomain localhost4 localhost4.localdomain4
::1 localhost localhost.localdomain localhost6 localhost6.localdomain6
chmod u+w myfiles.txt
# Add user write privileges
chmod u-w myfiles.txt
# Remove user write privileges
chmod g+w myfiles.txt
# Add group write privileges
chmod g=r myfiles.txt
# Allow only the group read privileges
chmod o+x myfiles.txt
# Add execute privileges for others
chmod a+x myfiles.txt
# Add execute privileges for everyone
chmod a=xr myfiles.txt
# Allow read and execute only to everyone
/etc/hosts contains hostnames with their ip address
chmod go-r myfiles.txt
# Remove group and others read privileges

ps -L 3315
# List all threads for a particular process (with process ID 3315)
ps aux --sort pmem
# Check the memory status
awk '/Hello/' myfiles.txt
# Find "Hello" in myfiles.txt
awk -F: '{ print $1 }' /etc/passwd | sort
# Display a sorted list of the login names of all users
awk 'END { print NR }' myfiles.txt
# Counts lines in myfiles.txt
[manju@localhost ~]$ awk 'BEGIN { for (i = 1; i <= 7; i++) print int(101 * rand()) }'
24
29
85
15
59
19
81
Prints seven random numbers from zero to 100
ls -lg *.txt | awk '{ x += $5 } ; END {print "total bytes:" x }'
# Prints the total number of bytes used by all .txt files

Random-access memory Virtual memory
The internal memory of the CPU for storing
data, program and program result.
A storage area that holds the files on your hard drive
for retrieval when a computer runs out of RAM
Process States in Linux:
 Ready: a new process is created and is ready to run.
 Running: The process is being executed.
 Wait: The process is waiting for input from the user.
 Completed: The process has completed the execution.
 Zombie: The process is terminated but information regarding the process still exists
and is available in the process table.
Cron Anacron
A service that enables us to run scheduled jobs
in Linux/Unix systems every minute.
A service that only enables us to run scheduled jobs
in Linux/Unix systems on daily basis.
Command:
Description:
View system defined cron jobs
Command:
cat /etc/crontab
netstat --listen
173

Description:
Check which ports are in listening in Linux Server
Service Default Port
DNS 53
SMTP 25
FTP 20 (Data transfer), 21 (Connection established)
SSH 22
DHCP 67/UDP (dhcp server), 68/UDP (dhcp client)
squid 3128
Hard Link
A mirror copy of the original file
Soft Link
A symbolic link to the original file
Network Interface Card teaming is the process of combining
multiple network cards together for performance, load balancing
and to increase uptime.
Contains the original content
of the file
Does not contain the actual
content but contains the location
of the original file
174

ls /bin
# List the binaries and other executable programs
ls /boot
# List the files needed to boot the operating system
ls /dev
# List the device files − typically controlled by the operating system and the system administrators
ls /etc
# List the System configuration files
ls /lib
# List the System Libraries
ls /lib64
# List the System Libraries (64 bit)
ls /proc
# List the information about running processes
ls /sbin
# List the System administration binaries
ls /var/log
# List the Log files
mkdir mydir{1,2,3,4,5}
Create 5 new directories:
 mydir1
 mydir2
 mydir3
 mydir4
 mydir5

[manju@localhost ~]$ ls -l myfiles.txt
-rw-r--r--. 1 manju nath 12 Apr 19 20:22 myfiles.txt
find . -mtime +1 -mtime -3
# Display files that are more than 1 day old − but less than 3 days old in the current directory
find . -name "s*" –ls
# Find files that start with the letter "s" and perform the command "ls" on them
find . -size +3M
# Find files that is larger than 3 megabytes
[manju@localhost ~]$ cat myfile.txt
ffff
b
eee
cc
[manju@localhost ~]$ cat myfile.txt | sort
b
cc
eee
ffff
Display the permissions for the file "myfiles.txt"
[manju@localhost ~]$ touch file1; touch file2
[manju@localhost ~]$ ls file{1,2}
file1 file2
[manju@localhost ~]$ NUMLOGINS=$(who | grep $USER | wc -l)
[manju@localhost ~]$ echo You have $NUMLOGINS login sessions
You have 2 login sessions

Command:
Description:
Remove read write and execute permissions on the file "myfiles.txt" for the group and others
Command:
Description:
Give read and write permissions on the file "myfiles.txt" to all
Command:
Description:
Repeats the third most recent command
chmod go-rwx myfiles.txt
chmod a+rw myfiles.txt
!-3
[manju@localhost ~]$ echo $OSTYPE
linux-gnu
The current operating system you are using

Command:
Description:
Check Inodes on File system
Command:
Description:
Find Inode number of File (myfiles.txt)
Command:
Description:
Check ACL (Access control list) configured on a file (myfiles.txt)
df -i /dev/sda1
ls -il myfiles.txt
getfacl myfiles.txt
SSH (Secure Shell or Secure Socket Shell) is a network protocol that gives users and
system administrators a secure way to access a computer over an unsecured network.
175

3 standard streams in Linux:
Command:
Description:
Check information of disk usage of files and directories on a machine.
Command:
Text terminal
Keyboard
Display
Program
Standard input
(stdin)
Standard output
(stdout)
Standard error
(stderr)
du -sh /var/log/*
ldd /bin/cp
176

Description:
Display dependencies of the "cp" command.
Command:
Description:
Display dependencies of the "cp" command with details.
Command:
Description:
Display unused direct dependencies of the "cp" command.
ldd -v /bin/cp
ldd -u /bin/cp
177

[manju@localhost ~]$ date; cal
Thu Apr 21 19:44:12 PDT 2022
April 2022
1 2
3 4 5 6 7 8 9
10 11 12 13 14 15 16
17 18 19 20 21 22 23
24 25 26 27 28 29 30
[manju@localhost ~]$ date && cal
Thu Apr 21 19:44:21 PDT 2022
April 2022
1 2
3 4 5 6 7 8 9
10 11 12 13 14 15 16
17 18 19 20 21 22 23
24 25 26 27 28 29 30
[manju@localhost ~]$ ls *.c
hello.c vim.c
date command is executed
followed by a cal command
cal command is executed
only if the date command is
successfully executed
[manju@localhost ~]$ ls *.[co]
hello.c hello.o vim.c
-gt Greater than
-lt Lesser than
-ge Greater than or equal to
-le Lesser than or equal to
-eq Equal to
-ne Not equal to

[manju@localhost ~]$ a=`ls *.c`; echo $a
hello.c main.c vim.c
[manju@localhost ~]$ test 50 -ge 15 && echo true || echo false
true
[manju@localhost ~]$ test 50 -ge 50 && echo true || echo false
true
[manju@localhost ~]$ test 20 -le 50 && echo true || echo false
true
[manju@localhost ~]$ test 20 -le 20 && echo true || echo false
true
[manju@localhost ~]$ test 30 -eq 30 && echo true || echo false
true
[manju@localhost ~]$ test 320 -eq 30 && echo true || echo false
false
[manju@localhost ~]$ test 30 -ne 30 && echo true || echo false
false
[manju@localhost ~]$ test 320 -ne 30 && echo true || echo false
true

cd /home
# Takes you to the home directory
cd ..
# Takes you one folder back
Command:
cat /proc/mounts
Description:
Display the mounted file system
Command:
cat /proc/net/dev
Description:
Display network adapters and statistics
Command:
telinit 0
Description:
Shutdown the system
ls * [0-9] *
Display the files and folders that contain numbers 0 to 9
178

iconv -l
# Display the lists of known ciphers
ls -lSr | more
# Display the size of the files and directories ordered by size
du -sk * | sort -rn
# Display the size of the files and directories ordered by size
Command:
ls -lh
Description:
Display permissions
Command:
yum list
Description:
List all packages installed on the system
Command:
yum clean packages
Description:
179
Clean all the saved packages

ip link show
# Display the link status of all interfaces
ps -eafw
# Display Linux tasks
lsof -p $$
# Display a list of files opened by processes
Command:
yum clean all
Description:
Clean all cached information
Command:
yum clean headers
Description:
Clean package headers
Command:
yum clean metadata
Description:
Clean Metadata
180

Command:
find /var -atime -90
Description:
Find files in the /var directory that have not been accessed in the last 90 days
Command:
find / -name core -exec rm {} ;
Description:
Search for core files in the entire directory tree and delete them as found without
prompting for confirmation
Command:
Description:
Check current run level of a Linux server
181
who -r

Bash script:
for i in *linux*; do rm $i; done
Description:
Delete all the files in the current directory that contains the word "linux"
Command:
awk '{print}' myfiles.txt
Description:
Display the content of file (myfiles.txt)
# Wait for 5 seconds
sleep 5s
# Wait for 5 minutes
sleep 5m
# Wait for 5 hours
sleep 5h
# Wait for 5 days
sleep 5d
Sleep commands used to introduce
wait time in scripts
182

Command:
ln myfiles.txt hardF1
Description:
Create hard-link to myfiles.txt
Command:
cat hardF1
Description:
Check content of the hard link - hardF1
Command:
ln myfiles.txt softF1
Description:
Create Soft-link to myfiles.txt
Command:
cat softF1
Description:
Check content of the soft link - softF1
183

Foreground processes Background processes
Require a user to start them or to interact
with them.
Run independently of a user.
Command:
ps -p 13
Description:
Display information about the process with process ID – 13
Command:
ulimit -f 100
Description:
Set the file size limit to 51,200 bytes
Command:
lsmod
Description:
184

Find out what kernel modules are currently loaded
Absolute path Relative path
The path of a file or directory from the
root directory.
The path of a file or directory from the
present working directory.
Command:
sudo yum install php
Description:
Install php version 7.2
Command:
php -r 'echo "Hello Worldrn";'
Description:
Run a PHP statement from the command line without creating a file
Command:
php -a
Description:
Start a PHP interactive shell
185

man -a ls
# Display all man Pages of the ls command
man -k ls
# Allows users to search the short command descriptions and manual page names for ls command
man -w ls
# Displays the location of the manual page of the ls command
Command:
yum install man
Description:
Install man package in Centos
Command:
du -h -d 1 /
Description:
Display disk usage of all top-level directories
Command:
man -f ls
Description:
Display man Pages and Print Short Description of the ls command
186

cat /etc/redhat-release
# Display Linux distribution name and version
ls ~
# Display the contents of the home directory
ls ../
# Display the contents of the parent directory
Command:
ps -U root -u root
Description:
Display all process running under the root user account
Command:
cal -1
Description:
Display current month calendar
Command:
cal -j
Description:
Print the calendar in day numbers
187

ps r
# List only running processes on Linux
ps T
# List all processes on this current terminal
ps -f
# List processes along with the parent process ID associated with the current Terminal
Command:
nmcli connection show
Description:
Display what are the network connection connected in our system
Command:
su
Description:
Used to switch from one account to another
Command:
ps aux | grep 'telnet'
Description:
Searches for the id of the process 'telnet'
188

ps -x
# View all processes owned by you
ps -eo pid,ppid,cmd,%mem,%cpu --sort=-%mem
# Display the processes using highest memory
sudo yum list --installed | more
# Lists installed packages on CentOS
Command:
sudo rpm -qa
Description:
Get a list of all installed packages with rpm command
Command:
sudo rpm -q nginx
Description:
Check whether nginx package installed or not
sudo rpm -qa | more
189

Command:
sudo rpm -q bash
Description:
Check whether bash package installed or not
Command:
sudo yum history
Description:
List all installed packages with yum on CentOS history command
Command:
sudo yum history info 2
Description:
Examine history entries in detail using transaction ID [2]
Command:
file /etc/passwd
Description:
Displays the file type of a given file
[root@localhost manju]# file /etc/passwd
/etc/passwd: ASCII text
190

Command:
wc /etc/passwd
Output:
46 91 2373 /etc/passwd
The /etc/passwd file has 46 lines, 91 words and 2373 letters present in it
Command:
grep root: /etc/passwd
Description:
Display all lines from /etc/passwd containing the string "root"
Command:
grep -n root /etc/passwd
Description:
Display all lines from /etc/passwd containing the string "root" with line numbers
Command:
grep -c false /etc/passwd
Description:
Display the number of accounts that have /bin/false as their shell
191

lastb
# Display the last unsuccessful login attempts
du /etc/passwd
# Display the disk usage of a /etc/passwd file
killall proc
# Kill all the process named proc
wget https://repo.mysql.com/mysql80-community-release-el8-1.noarch.rpm
# Download the RPM file to install
sudo yum localinstall mysql80-community-release-el8-1.noarch.rpm
# Install the RPM file
Command:
grep ^root: /etc/passwd
Description:
Display all lines from /etc/passwd starting with the string "root" followed by colon
Command:
last | head
Description:
Displays information about the users who logged in and out of the system
(Display the top 10 lines only)
192

sudo yum localinstall https://repo.mysql.com/mysql80-community-release-el7-1.noarch.rpm
# Install the RPM package via URL
curl --version
# Display curl Version
curl -O http://website.com/myfiles.tar.gz
# Download the file (myfiles.tar.gz) from url "http://website.com/myfiles.tar.gz"
# Saved as myfiles.tar.gz
curl -o files.tar.gz http://website.com/myfiles.tar.gz
# Download the file (myfiles.tar.gz) from url "http://website.com/myfiles.tar.gz"
# Saved as files.tar.gz
echo 'https://repo.mysql.com/mysql80-community-release-el8-1.noarch.rpm' > urls.txt
xargs -n 1 curl -O < urls.txt
# Download files from a list of URLs in "urls.txt" file
exit 110
# Exit from the terminal window
sudo -l
# know which commands are permitted and not permitted on the current host
193

Disadvantages of Open Source Operating System:
Command:
Description:
Check all installed packages of ftp
Command:
Description:
Find files in the /home directory which were modified more than 120 days ago
Command:
echo -e "thellonworld"
 Difficulty to use
 Compatibility Issues
find /home -mtime +120
hello
world
history | grep cd | head -12
Searches history of first 12 commands which have cd word match
194
rpm -qa | grep ftp

 The /etc directory contains configuration files in Linux.
 The Network File System (NFS) is a mechanism for storing files on a network.
 "init" is the first process in linux which is started by the kernel and its process id is 1.
Samba enables Linux / UNIX machines to communicate with
Windows machines in a network.
egrep "Hello|Einstein" file.txt
Returns line with Hello or Einstein in the file.txt
date "+%s"
Prints the date in seconds
cat file.txt | uniq
Display duplicate record only once
195

Command:
cd ../../..
Command:
ps -ef | grep xlogo
Description:
List all the processes on the system containing the string 'xlogo'
echo -n "abc";echo "def"
echo "abc";echo "def"
Takes you three folders back
abcdef
abc
def
ls -ltr /etc List the files in /etc in order of last modification
196

cat /etc/passwd /etc/group
# Display the contents of multiple files (/etc/passwd and /etc/group)
find /tmp -name *.txt -exec rm -f {} ;
# Searches for all files in the /tmp directory named *.txt and deletes them
Command:
ls -Rlh /var | grep [0-9]M
Description:
List the files in /var larger than 1 megabyte but less than 1 gigabyte
Command:
ls -lhS
Description:
List files by size
echo "use" "of" "Linux"
use of Linux
197

watch -n 5 tail -n 3 /etc/passwd
# Display the end of the /etc/passwd file every 5 seconds
watch -n 1 'ls -l | wc -l'
# Monitor the number of files in a folder
watch -t -n 1 date
# Display the clock
find / -name "*.txt"
# Search all files with .txt extension
find . -name "*file*"
# Search all files containing "file" in the name
find /home -name "*file*"
# Search all files in /home containing "file" in the name
grep -nre "hello computer" ./*
# Search for files containing the string "hello computer" in the current directory
(echo In Linux; exit 0) && echo OK || echo exit
(echo In Linux; exit 4) && echo OK || echo exit
In Linux
OK
In Linux
exit
198

Command:
free -t -m
Command:
gnome-system-monitor
Description:
Displays what programs are running and how much processor time, memory and disk space are being used
lsblk -m
lsblk -S
Display free memory size in MB
Display device permissions and ownership
Display SCSI (Small Computer Systems Interface) devices
lsblk -n List devices without the header
199

ls -R
# List out all the contents of subdirectories
compgen -c
# Displays the list of all commands which we can use in the command-line interface
hostnamectl
# Display system information including operating system, kernel and release version
Command:
ls -l ~
Description:
Check the file and folder permissions
Command:
ls ./Documents
Description:
Display the list of files that reside in the Documents folder
 pwd -L → Prints a symbolic path
 pwd -P → Prints the actual full path
200

Command:
find . -type f
Command:
find . -type d
Description:
Find directories
find . -iname "*.jpg"
find . -type f -perm 777
Find files
Find files by case-insensitive extension (ex: .jpg, .JPG, .jpG)
Find files by octal permission
cd logs; ls -lt | head; du -sh ; df -h
Concatenating all of the above tasks in a
single line using the "; " operator
201

cal; { date; uptime; }; pwd
March 2022
1 2 3 4 5
6 7 8 9 10 11 12
13 14 15 16 17 18 19
20 21 22 23 24 25 26
27 28 29 30 31
Tue Mar 29 00:52:38 PDT 2022
00:52:38 up 54 min, 2 users, load average: 0.00, 0.01, 0.05
/home/manju
{ echo "Albert Einstein"; pwd; uptime; date; }
Albert Einstein
/home/manju
00:26:53 up 28 min, 2 users, load average: 0.00, 0.01, 0.05
Tue Mar 29 00:26:53 PDT 2022
shutdown -r
# Kicks off a reboot
shutdown +0
# Shuts down the system immediately
shutdown -r +5
# Begins a reboot of the system in five minutes
202

Command:
kill 12838
Command:
ss -t -r state established
Description:
List all the established ports
ss -t -r state listening
mtr google.com
Terminate the process with process ID 12838
List all sockets in listening state
Diagnose Network Issues
sudo tcpdump --list-interfaces
List all network interfaces
shutdown -Fr now
Force the file system check during
reboot
203

mpstat -P 0
# Print processor statistics and helps to monitor CPU utilization on the system
chmod 777 myfiles.txt
# Assign (read, write and execute) permission to everyone
chmod 766 myfiles.txt
# Assign full permission to the owner and read and write permission to group and others
chmod -x myfiles.txt
# Remove the execution permission of myfiles.txt file
history 30
# List the last 30 commands we have entered on the system
find ~ -empty
# Find all empty files in home directory
gzip -l *.gz
# Display compression ratio of the compressed file
ls -al --time-style=+%D | grep `date +%D`
List today's files only
204

Command:
ps -efH | more
Command:
df -T
Description:
Display what type of file system
mkdir ~/temp
ls *py
# List all Python files
# Display the list of all shells
# Display details about message queue, semaphore and shared memory
View current running processes in a tree structure
Creates a directory called temp under home directory
205
chsh -l
ipcs -a

ipcs -s
# List the accessible semaphores
ipcs -m
# List all the Shared Memory
quotastats
# Display the report of quota system statistics gathered from the kernel
rpcinfo
# Display all of the RPC (Remote Procedure Call) services of the local host
slabtop
# Display kernel slab cache information in real-time
tload
# Display a graph of the current system load average to the specified tty
ipcs -q
Lists only message queues for which the current process has read access
206

cat /proc/devices
# Display the device drivers configured for the currently running kernel
cat /proc/dma
# Display the DMA channels currently used
cat /proc/filesystems
# Display the file systems configured into the kernel
cat /proc/kmsg
# Display the messages generated by the kernel
cat /proc/loadavg
# Display the system load average
ls /proc/net
# List the network protocols
cat /proc/stat
# Display the system operating statistics
cat /proc/uptime
# Display the time the system has been up
ls /etc/udev
# List the contents of udev configuration directory

Command:
poweroff -i -f
[2 = 2 ] ; echo $?
# 0 (logically TRUE)
[ 2 = 6 ] ; echo $?
# 1 (logically FALSE)
type echo
# echo is a shell builtin
find /usr -print
# Find and print all files under "/usr"
systemctl list-units --type=target
# List all target unit configuration
systemctl list-units --type=service
# List all service unit configuration
systemctl list-sockets
# List all socket units in memory
Shutdown the system
systemctl list-timers
# List all timer units in memory
systemctl list-dependencies --all
# List dependency of all unit services
systemctl poweroff
# Shut down the system
207

systemctl reboot
# Shut down and reboot the system
systemctl suspend
# Suspend the system
systemctl hibernate
# Hibernate the system
loginctl user-status
# Display terse runtime status information of the user of the caller's session
loginctl session-status
# Display terse runtime status information of the caller's session
ip route show
# Display all the routing table in numerical addresses
ip neigh
# Display the current content of the ARP (Address Resolution Protocol) cache tables
netstat -l --inet
# Find listening ports
netstat -ln --tcp
# Find listening TCP ports (numeric)
208

Command:
atq
lsof | grep deleted
# Print all deleted files which are claiming disk space
echo $$
# Display the Process ID of the current process
echo $!
# Display the Process ID of most recently started background job
date --date="yesterday"
# Display yesterday 's date
date --date="10 days ago"
# Display date 10 days ago
ls / | wc -w
# List the number of directories in the root directory
sudo sfdisk -l -uM
# Display the size of each partition in MB
Lists the user's pending jobs
sudo parted -l
# Lists out the partition details
df -h | grep ^/dev
# Filter out real hard disk partitions/file systems
209

sudo blkid
# Displays information about available block devices
ls / > info.txt
cat info.txt
bin
boot
dev
etc
home
lib
lib64
media
mnt
opt
proc
root
run
sbin
srv
sys
tmp
usr
var
export NAME="Albert Einstein"
echo $NAME
Albert Einstein
TZ=US/Pacific date
# Display the current date/time in US/Pacific time zone
ls -l /etc/shadow
# Display the user password stored in an encrypted form and the password expiry data
sudo journalctl --since yesterday
# Display all the logs since yesterday
sudo journalctl --since "2019-12-10 13:00:00"
# Display all the logs since 2019-12-10 13:00:00
journalctl -disk-usage
# Display the total size of the journal logs
210

Command:
ls -m
ls -Q
# Add quotation marks to all directories and files
ss -f unix
# List Unix Sockets
ss --raw
# List Raw Sockets
tracepath www.google.com
# Traces a path to a network host (www.google.com) discovering MTU along the path
echo -e "123b4"
echo -e "123r456"
echo D*
# Lists all of the files and directories in the current directory whose name starts with letter D
Prints out directories and files separated by a comma
124 3 is over-written by 4
456
123 is overwritten by 456
echo *.desktop
# Lists all of the .desktop files in the current directory
211

echo $'I'm a Linux Learner.'
echo $USER
# Print the name of the currently logged in user
echo -e "033[0;32mGREEN"
GREEN
echo -e "033[0;31mRED"
RED
echo "This is the list of directories and files on this system: $(ls)"
This is the list of directories and files on this system: Desktop
Documents
Downloads
Music
Pictures
Public
Templates
Videos
I'm a Linux Learner.
echo -e 'Hello, vWorld!'
Hello,
World!
212

echo *s
# Print all files and folders that end by letter "s"
echo [[:upper:]]*
# Print all files and folders that start by upper case character
echo $((2 + 3))
→ 5
echo $(($((2**2)) * 3))
→ 12
echo Four divided by two equals $((4/2))
→ Four divided by two equals 2
echo Capital-{A,B,C}-Letter
→ Capital-A-Letter Capital-B-Letter Capital-C-Letter
echo {1..5}
→ 1 2 3 4 5
echo {A..Z}
→ A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
echo x{P{1,2},Q{3,4}}y
→ xP1y xP2y xQ3y xQ4y
213

echo The total price is $500.00
→ The total price is 00.00
echo "$USER $((3*2)) $(cal)"
manju 6 March 2022
1 2 3 4 5
6 7 8 9 10 11 12
13 14 15 16 17 18 19
20 21 22 23 24 25 26
27 28 29 30 31
echo $(cal)
echo "$(cal)"
echo The total price is $500.00
→The total price is $500.00
March 2022 Su Mo Tu We Th Fr Sa 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31
March 2022
1 2 3 4 5
6 7 8 9 10 11 12
13 14 15 16 17 18 19
20 21 22 23 24 25 26
27 28 29 30 31
echo -e "aMy Laptop shut "down"."
→My Laptop shut "down".
echo -e "C:WIK2NLINUX_OS.EXE"
→ C:WIK2NLINUX_OS.EXE
214

sudo lsof -i -P -n | grep LISTEN
sudo netstat -tulpn | grep LISTEN
sudo ss -tulw
# Check what ports are open
netstat -ap | grep ssh
# Find out on which port a program is running
[root@localhost manju]# ipcs -m -l
------ Shared Memory Limits --------
max number of segments = 4096
max seg size (kbytes) = 18014398509465599
max total shared memory (kbytes) = 18014398442373116
min seg size (bytes) = 1
[root@localhost manju]# ipcs -m -p
------ Shared Memory Creator/Last-op PIDs --------
shmid owner cpid lpid
131072 manju 2998 3135
163841 manju 2998 3135
327682 manju 3277 6920
360451 manju 2827 1406
Check ports in use
Lists the Limits for Inter-process
Communication facility
Display the process ids that accessed
Inter-process Communication facility
recently

[root@localhost manju]# ipcs -u
------ Messages Status --------
allocated queues = 0
used headers = 0
used space = 0 bytes
------ Shared Memory Status --------
segments allocated 4
pages allocated 2432
pages resident 319
pages swapped 0
Swap performance: 0 attempts 0 successes
------ Semaphore Status --------
used arrays = 0
allocated semaphores = 0
dmidecode -t baseboard
# Display all the system baseboard related information
dmidecode -t bios
# Display the BIOS information
Display the status of current usage
of Inter-process Communication facility
dmidecode -t 16
# Display the maximum RAM supported by the system

Command:
Description:
Display the information about the manufacturer, model and serial number of the system
dmidecode -t system
The Linux philosophy is 'Laugh in the face of danger'. Oops. Wrong One. 'Do it
yourself'. Yes, that's it.
Linus Torvalds

nmcli con show -a
# Display the active network connections
netstat -r
# Display the kernel routing table
yum install nmap
# Install nmap on CentOS
nmap google.com
# Scan a hostname
nmap 193.169.1.1
# Scan a ip address
nmap --iflist
# Display host interfaces and routes
echo [![:digit:]]*
# Print all files and folders that are not beginning with a numeral
echo *[[:lower:]123]
# Print all files and folders ending with a lowercase letter or the numeral
echo g*
# Print all files and folders beginning with "g"
215

echo b*.txt
# Print all files and folders beginning with "b" followed by any characters and ending with ".txt"
echo [abc]*
# Print all files and folders beginning with either "a", "b" or "c"
netstat -t
# Display the download status of active connections
netstat -x
# Display Information about all connections, listeners and shared endpoints for Network Direct
netstat -n
# Numerical display of addresses and port numbers
echo $LANG
# Display the language of a Linux system
echo "AAA" | grep AAA
→ AAA
echo "AAA" | grep BBB
→
echo "AAA" | grep -E 'AAA|BBB'
→ AAA
echo "BBB" | grep -E 'AAA|BBB'
→ BBB
216

echo "albert einstein" | tr a-z A-Z
→ ALBERT EINSTEIN
echo "albert einstein" | tr [:lower:] E
→ EEEEEE EEEEEEEE
echo " Albert Einstein was a German-born theoretical physicist." | fold -w 12
echo " Albert Einstein was a German-born theoretical physicist." | fold -w 12 -s
printf "English theoretical physicist: %sn" Hawking
→ English theoretical physicist: Hawking
Albert Eins
tein was a G
erman-born t
heoretical p
hysicist.
Albert
Einstein
was a
German-born
theoretical
physicist.
217

ls /usr/bin | pr -3 -w 65 | head
# Display a directory listing of /usr/bin in a paginated, three-column output format
for i in A B C D; do echo $i; done
for i in {A..D}; do echo $i; done
for i in file*.txt; do echo $i; done
echo ${!BASH*}
# List all the variables in the environment with names that begin with BASH
bc <<< "6+6"
A
B
C
D
A
B
C
D
file1.txt
file.txt
12
Scientists=("Einstein" "Hawking" "Darwin"); for i
in ${Scientists[*]}; do echo $i; done
Einstein
Hawking
Darwin
Scientists=("Einstein" "Hawking" "Darwin"); for i
in "${Scientists[*]}"; do echo $i; done
Einstein Hawking Darwin
218

df -k
# Check the file system space
ls -alh
# List all folders in directory with details
find /home -name file.txt
# Check all files in /home directory with the name file.txt
find /home -iname File.txt
# Search all files in /home directory irrespective to case sensitive
find / -ctime +90
# Search for the files which were modified more than 90 days back
find / -size 0c
# Search all empty files
find / -size +1G
# Search all files and folders which are more than 1GB
df -a
# Display the file system's complete disk usage
df -i
# Display used and free inodes
df -h
Display disk space in
human-readable format
219

du -ch *.png
# Display the size of each png file in the current directory
du -a /etc/ | sort -n -r | head -n 10
# List top 10 directories consuming disk space in /etc/
ac
# Display the total amount of time users are connected to the system
ac --individual-totals
# Display a report on login times for individual users
cancel
# Cancels print jobs
yum install finger
# Install finger tool (CentOS)
finger manju
# Display the details of a user "manju"
chfn
# Allows you to modify user's information
finger -s manju
# Display idle status and login details of a user "manju"
220

groups
# List all Groups the Current User is a Member of
id -nG
# List all Groups the Current User is a Member of
groupadd mygroup
# Create a new group named "mygroup"
groupdel mygroup
# Delete a group named "mygroup"
less /etc/group
# List all Groups
getent group
# List all Groups
usermod -a -G mygroup manju
# Add an existing user "manju" to a group "mygroup"
userdel manju
# Delete a user "manju"
chgrp mygroup test.txt
# Change the owning group of the file test.txt to the group named "mygroup"
221

sudo depmod -a
# Generates a list of all kernel module dependences and associated map files
dirname /usr/bin
→ /usr
dirname /Desktop/root
→ /Desktop
dmesg > kernel_messages.txt
# Read all messages from kernel ring buffer to a file "kernel_messages.txt"
dmesg | grep -i memory
# Display the kernel messages which relate to memory usage
egrep -c '^Hello|World$' myfiles.txt
# Count the number of lines in myfiles.txt which begin with the word 'Hello' or end with the word 'World'
ex myfiles.txt
# Edits the file myfiles.txt
expand myfiles.txt
# Expand the file myfiles.txt − changing tabs to spaces − and display on standard output
expand --tabs=10 myfiles.txt > myfiles0.txt
# Convert the tabs in the file myfiles.txt to 10 spaces each, and write the output to myfiles0.txt
222

expr 2 = 5
# 0
fc -l
# Lists the history of commands
!l
# Executes the most recently executed command that begins with the letter "l"
fc -e - l
# Executes the most recently executed command that begins with the letter "l"
fmt myfiles.txt
# Display a reformatted version of the file "myfiles.txt "
fmt < myfiles.txt > myfiles0.txt
# Reformat "myfiles.txt" and write the output to the file "myfiles0.txt"
finger -p manju
# Display information about the user "manju"
fold -w5 myfiles.txt > myfiles0.txt
# Wrap the lines of myfiles.txt to a width of 5 characters and writes the output to myfiles0.txt
for file in *.txt ; do wc -l $file ; done
# Performs a word count of all files in the current directory with the .txt extension
Returns 0 (false)
223

grep manju /etc/passwd
# Search /etc/passwd for user "manju"
groupmod -n group mygroup
# Change the group "mygroup" to "group"
head myfiles.txt
# Display the first 10 lines of "myfiles.txt"
head -15 myfiles.txt
# Display the first 15 lines of "myfiles.txt"
head myfiles.txt myfiles0.txt
# Display the first 10 lines of both myfiles.txt and myfiles0.txt − with a header before each that indicates the file name
head -n 5K myfiles.txt
# Display the first 5,000 lines of "myfiles.txt"
head -n 4 *.txt
# Display the first 4 lines of every file in the working directory whose file name ends with the .txt extension
iostat
# Display operating system storage input and output statistics
last reboot | less
# Display listing of last logged in users and system last reboot time and date
224

last -x | less
# Display last shutdown date and time
last shutdown
# Display last shutdown date and time
ldd /bin/bash
# Display the shared library dependencies of the program /bin/bash
less -N myfiles.txt
# View the file myfiles.txt − displaying a line number at the beginning of each line
ls *.{html,php,txt}
# List all files with .html, .php and .txt file extension
ls /
# List the contents of root directory
ls [aeiou]*
# List only files that begin with a vowel (a, e, i, o and u)
lsof -i -U
# List all open Internet, x.25 (HP-UX) and UNIX domain files
lsof -i 4 -a -p 555
# List all open IPv4 network files in use by the process whose Process ID is 555
lsof -i 6
List only open IPv6
network files
225

xz myfiles.txt
# Compress the file "myfiles.txt" into "myfiles.txt.xz"
xz -dk myfiles.txt.xz
# Decompress "myfiles.txt.xz" into "myfiles.txt"
mkdir -m a=rwx dir
# Create the directory "dir" and set its file mode so that all users may read, write and execute it
modinfo snd
# Display all available information about the "snd" Linux kernel module
more +3 myfiles.txt
# Display the contents of file "myfiles.txt" beginning at line 3
more +/"Hello" myfiles.txt
# Display the contents of file "myfiles.txt" beginning at the first line containing the string "Hello"
netstat -g
# Display multicast group membership information for both IPv4 and IPv6
netstat -c
# Print netstat information every few second
netstat -natp
# Display statistics about active Internet connections
226

netstat -rn
# Display the routing table for all IP addresses bound to the server
netstat -an
# Display information about all active connections to the server
od -b myfiles.txt
# Display the contents of "myfiles.txt" in octal format
od -Ax -c myfiles.txt
# Display the contents of "myfiles.txt" in ASCII character format − with byte offsets displayed as hexadecimal
trap -l
# Display a list of signal names and their corresponding numbers
trap
# Display a list of the currently-set signal traps
yum list openssh
# Search for a package with a name "OpenSSH"
yum grouplist
# List all available Group Packages
yum repolist
# List all enabled Yum repositories
227

yum repolist all
# List all Enabled and Disabled Yum Repositories
paste 1.txt 2.txt
# Display the contents of 1.txt and 2.txt side-by-side
ls -a | pr -n -h "Files in $(pwd)" > dc.txt
cat dc.txt
2022-04-02 01:10 Files in /home/manju Page 1
1 .
2 ..
3 1.txt
4 2.txt
5 .bash_history
6 .bash_logout
7 .bash_profile
8 .bashrc
9 bio.txt
10 .cache
11 .config
12 Data.txt
13 Desktop
14 dir
15 Documents
228

printf "Hi, I'm %s.n" $LOGNAME
→ Hi, I'm manju.
printf "%.*s" 6 "abcdefg"
→ abcdef
ps -eLf
# Get information about threads
ps axms
# Get information about threads
 ps -eo euser,ruser,suser,fuser,f,comm,label
 ps axZ
 ps -eM
Get security information
Command:
pstree -h
Description:
Display all processes as a tree, with the current process and its ancestors highlighted
rm -- 1.txt
# Delete "1.txt" file in the current directory
rm /home/manju/2.txt
# Delete "2.txt" file in the directory "/home/manju"
rm ./1.txt
229

ip route list
# List current routing table
route -n
# Display routing table for all IPs bound to the server
script -c 'echo "Hello, World!"' hello.txt
cat hello.txt
sfdisk -s
# List the sizes of all disks
ls -d ~/.ssh
# Check if the .ssh directory exists or not
sha224sum myfiles.txt
# Display the SHA224 checksum of the "myfiles.txt" file in the current directory
Script started, file is hello.txt
Hello, World!
Script done, file is hello.txt
Script started on Sat 02 Apr 2022 03:24:52 AM PDT
Hello, World!
Script done on Sat 02 Apr 2022 03:24:52 AM PDT
230

shutdown 8:00
# Schedule the system to shut down at 8 A.M
shutdown 20:00
# Schedule the system to shut down at 8 P.M
shutdown +15 "The system will be shutdown in 15 minutes."
# Schedule the system to shut down in 15 minutes with the normal message alerting users that the system is shutting down
shutdown -P now
# Power off the system immediately
sleep 10
# Delay for 10 seconds
startx -- -depth 16
# Start an X session at 16 bits color depth
231

time cal
# Reports how long it took for the "cal" command to complete
tr "[:lower:]" "[:upper:]" < myfiles.txt
# Translate the contents of "myfiles.txt" to uppercase
tr -cd "[:print:]" < myfiles.txt
# Remove all non-printable characters from "myfiles.txt"
cat myfiles.txt
tr -cs "[:alpha:]" "n" < myfiles.txt
uncompress myfiles.txt.xz
# Uncompress the file "myfiles.txt.xz"
w manju
# Display information for the user named "manju"
write albert
# Write a message to the user "albert"
Hello World
Hello
World
xlsfonts
# Lists all fonts available to the default X server and display
xset q
Display the values of all current X Window
System preferences
yes | rm -i *.txt
Remove all files with the extension .txt
from the current directory
232

233
What is Linux and why is it so popular?
Whether you know it or not you are already using Linux (the best-known and most-used open
source operating system) every day. From supercomputers to smartphones, the Linux operating
system is everywhere. As an operating system, Linux is a family of open source Unix-like
software based on the Linux kernel - that sits underneath all of the other software on a computer,
receiving requests from those programs and relaying these requests to the computer's hardware.
With regard to careers, it is becoming increasingly valuable to have Linux skills rather than just
knowing how to use Windows. In general, Linux is harder to manage than Windows, but offers
more flexibility and configuration options.
Every desktop computer uses an operating system. The most popular operating systems in use
today are: Windows, Mac OS, and LINUX. Linux is the best-known notoriously reliable and
highly secure open source portable operating system -- very much like UNIX -- that has become
very popular over the last several years -- created as a task done for pleasure by Linus Torvalds -
- computer science student at the University of Helsinki in Finland -- in the early 1990s and later
developed by more than a thousand people around the world.
Linux is fast, free and easy to use, that sits underneath all the other software on a computer −
runs your computer -- handling all interactions between you and the hardware i.e., whether
you're typing a letter, calculating a money budget, or managing your food recipes on your
computer, the Linux operating system (similar to other Operating Systems, such as Windows XP,
Windows 7, Windows 8, and Mac OS X) provides the essential air that your computer breathes.
Linux is the most important technology advancement of the twenty-first century and Licensed
under the General Public License (GPL) that Linux uses ensures that the software will always be
open to anyone and whose source code is open and available for any user to check, which makes
it easier to find and repair vulnerabilities and it power the laptops, development machines and

234
servers at Google, Facebook, Twitter, NASA, and New York Stock Exchange, just to name a
few. Linux has many more features to amaze its users such as: Live CD/USB, Graphical user
interface (X Window System) etc.
Why LINUX?
Although Microsoft Windows (which is the most likely the victim of viruses and malware) has
made great improvements in reliability in recent years, it considered less reliable than Linux.
Linux is notoriously reliable and secure and it is free from constant battling viruses and malware
(which may affect your desktops, laptops, and servers by corrupting files, causing slow downs,
crashes, costly repairs and taking over basic functions of your operating system) – and it keep
yourself free from licensing fees i.e., zero cost of entry ... as in free. You can install Linux on as
many reliable computer ecosystems on the planet as you like without paying a cent for software
or server licensing. While Microsoft Windows usually costs between $99.00 and $199.00 USD
for each licensed copy and fear of losing data.
Below are some examples of where Linux is being used today:
 Android phones and tablets
 Servers
 TV, Cameras, DVD players, etc.
 Amazon
 Google
 U.S. Postal service
 New York Stock Exchange
Linux Operating System has primarily three components:

235
 Kernel
Kernel is the core part of Linux Operating System and interacts directly with hardware. It is
responsible for all major activities of the Linux operating system.
 System Library
System libraries are special programs using which application programs accesses Kernel's
features.
 System Utility
System Utility programs are responsible to do specialized tasks.
Important features of Linux Operating System:
 Portable
 Open Source
 Multi-User
 Multiprogramming
 Hierarchical File System
 Security
Now Linux (successfully being used by several millions of users worldwide) has grown passed
the stage where it was almost exclusively an academic system, useful only to a handful of people
with a technical background. It provides more than the operating system: there is an entire
infrastructure supporting the chain of effort of creating an operating system, of making and
testing programs for it, of bringing everything to the users, of supplying maintenance, updates
and support and customizations, runs on different platforms including the Intel and Alpha
platform. Today, Linux is ready to accept the challenge of a fast-changing world to do various

types of operations, call application programs etc. Since the hiring focus is shifting more
and more toward DevOps type skills, a Linux skill set will be the types of things that will
make you very deployable.
[manju@localhost ~]$ echo al{an,bert,exander}
alan albert alexander
[manju@localhost ~]$ mkdir {txt,doc,pdf}files
txtfiles docfiles pdffiles
[manju@localhost ~]$ x=Albert; y="$x won $100.00"; echo $y
Albert won $100.00
[manju@localhost ~]$ x=5; test $x -eq 10; echo $?
1
[manju@localhost ~]$ x=5; test $x -eq 5; echo $?
0
exit status of the test command is 1
exit status of the test command is 0
cat /etc/profile
# Display System login initialization file
cat /etc/bashrc
# Display System BASH shell configuration file
cat .bash_profile
# Display Login initialization file
236

[manju@localhost ~]$ date
Wed Sep 28 08:14:17 PDT 2022
[manju@localhost ~]$ alias x=date
[manju@localhost ~]$ x
Wed Sep 28 08:14:27 PDT 2022
[manju@localhost ~]$ echo $BASH_VERSION
4.2.46(1)-release
[manju@localhost ~]$ echo $HISTCMD
290
[manju@localhost ~]$ echo $HOSTTYPE
x86_64
[manju@localhost ~]$ echo $OSTYPE
linux-gnu
[manju@localhost ~]$ echo $PPID
3563
[manju@localhost ~]$ echo $SHLVL
2
[manju@localhost ~]$ echo $TERM
xterm-256color
[manju@localhost ~]$ echo $EUID
1000
Display the current BASH version number
Display the number of the current command in the history list
Display the type of machine the host runs on
Display the operating system in use
Display the process ID for shell's parent shell
Display the current shell level
Display the terminal type
Display the Effective user ID
237

PS1="w" Display the full pathname of the current working directory
PS1="W" Display the name of the current working directory
[manju@localhost ~]$ PS1="d"
Sun Oct 02 # Display the Current date
[manju@localhost ~]$ PS1="h"
localhost # Display the Hostname
[manju@localhost ~]$ PS1="s"
bash # Display the Shell type currently active
[manju@localhost ~]$ PS1="t"
18:42:10 # Display the Time of day in hours, minutes, and seconds
[manju@localhost ~]$ PS1="u"
manju # Display the Username
[manju@localhost ~]$ PS1="v"
4.2 # Display the Shell version
[manju@localhost ~]$ PS1="Hellon World"
Hello
World
[manju@localhost ~]$ PS1="Hello World"
Hello World
238

Directory Function
/ The top-level directory of a Linux system that holds all files, device
information, and system information organized into directories
/home Holds users ' home directories
/bin Contains every essential command and utility program
/usr Contains the commands and files that the system uses
/usr/bin Include utility programs and user-friendly commands
/usr/sbin Holds commands for system administration
/usr/lib Contains programming language libraries
/usr/share/doc Contains documentation for Linux
/usr/share/man Contains the online "man" files
/var/spool Contains spooled files, such as those produced for network transfers and
printing operations
/sbin Contains commands for system administration used to boot the system
/var Holds a variety of files, including mailbox files
/dev Holds file interfaces for devices like printers and terminals
/etc Holds all system files, including configuration files
find myfiles -name '*.c' -ls
Using the -ls command, all files in the "myfiles" directory
with the .c extension are searched and displayed
239

find / -user manju -print
Finds every file in a user's home directory and every
file that user owns in other user directories
ls /usr/share/X11
# List the system X11 configuration and support files
ls /etc/X11
# List the configuration files
ls /etc/gdm
# Display the contents of GDM configuration directory
ls /usr/share/gdm
# Display the contents of GDM configuration directory for default settings and themes
ls /etc/gconf
# List the GConf configuration files
ls /usr/share/gnome
# List the Files used by GNOME applications
ls /usr/share/doc/gnome*
# Display the contents of Documentation for various GNOME packages, including libraries
240

ls /usr/share/icons
# List the Icons used in KDE desktop and applications
rpm -qa | more
# Displays a list of all installed packages
ls /etc/cron.d
# List the directory with numerous crontab files that is only accessible to the root user
ls /etc/cron.hourly
# List the directory for tasks performed hourly
ls /etc/cron.daily
# List the directory for tasks performed daily
ls /etc/cron.weekly
# List the directory for tasks performed weekly
ls /etc/cron.monthly
# List the directory for tasks performed monthly
ls /etc/mtab
# List the currently mounted file systems
ls /etc/services
# List the services run on the system and the ports they use
241

ls /etc/cups
# List the CUPS printer configuration files
ls /proc/net
# List the Directory for network devices
free -s 3
# Display the current usage status of Memory continuously after regular interval
ls -lhR /var | grep - | grep [1-9]*M
# List "/var" files larger than 1 MB but less than 1 GB
whereis -b ls
# Search only the binary file related to a command "ls"
whereis -m ls
# Searches only for man pages related to a command "ls"
whereis -s ls
# Searches only for source files related to a command "ls"
[manju@localhost ~]$ echo "Alan" "Mathison" "Turing"
Alan Mathison Turing
242

watch -t -n 1 date
# Display the date
[manju@localhost ~]$ echo "Albert" > 1.txt && cat 1.txt
Albert
du -sh * --time
# Check each file's size and the date and time it was last edited
dmidecode -s system-serial-number
# Display the serial number of Linux server
ls -aril
# Display all the files with sequence number
yum search mod_
# Display all the modules
du -sch *
# Display the sum of size of all files and folders in present directory
dmidecode | grep -A3 '^System Information'
# Display the server hardware name and model
dmesg | grep -i firmware
# Display all firmware error
243

cat /proc/cpuinfo | grep processor | wc -l
# Display the number of cores
netstat -ap | grep 80
# Display the process id which is using port number 80
dmidecode --type memory
# Display the physical memory attached to the Server
dirs
# Display the list of currently remembered directories
blkid -i /dev/sda
# Display information about available block devices
crontab -e
This command runs crontab
[manju@localhost ~]$ df -h /home
Filesystem Size Used Avail Use% Mounted on
/dev/sda3 18G 5.2G 13G 29% /
Look for free disk space using the df command within
the /home directory
244

[manju@localhost ~]$ hostname -I
192.168.6.131 192.168.122.1
badblocks -s /dev/sda
# Check for unreadable blocks on disk sda
tail -10 /var/log/messages
# Display the last 10 syslog messages
lsof -u manju
# List files opened by the user "manju"
sudo shutdown -r 2
# Shuts down and reboots the machine in 2 minutes
albert
[manju@localhost ~]$ cat 1.txt | tr a-z A-Z > 2.txt
ALBERT
cat /etc/passwd | column -t -s :
# Display the contents of "/etc/passwd" in column
Display all local IP addresses of the host
245

nmcli d
# Display the status of all network interfaces
grep "^[[:alnum:]]" myfiles.txt
# Search for a line which will start with alphanumeric characters in "myfiles.txt"
grep "^[[:alpha:]]" myfiles.txt
# Search for a line which will start with alpha characters in "myfiles.txt"
grep "^[[:blank:]]" myfiles.txt
# Search for a line which will start with blank characters in "myfiles.txt"
grep "^[[:digit:]]" myfiles.txt
# Search for a line which will start with digit characters in "myfiles.txt"
grep "^[[:lower:]]" myfiles.txt
# Search for a line which will start with lowercase letters in "myfiles.txt"
grep "^[[:punct:]]" myfiles.txt
# Search for a line which will start with punctuation characters in "myfiles.txt"
grep "^[[:graph:]]" myfiles.txt
# Search for a line which will start with graphical characters in "myfiles.txt"
grep "^[[:print:]]" myfiles.txt
# Search for a line which will start with printable characters in "myfiles.txt"
246

grep "^[[:space:]]" myfiles.txt
# Search for a line which will start with space characters in "myfiles.txt"
grep "^[[:upper:]]" myfiles.txt
# Search for a line which will start with uppercase letters in "myfiles.txt"
grep "^[[:xdigit:]]" myfiles.txt
# Search for a line which will start with hexadecimal digits in "myfiles.txt"
vmstat -a
# Display active and inactive system memory
vmstat -s
# Display memory and scheduling statistics
vmstat -f
# Display number of forks created since system boot
vmstat -D
# Display a quick summary statistic of all disk activity
vmstat -d
# Display a detailed statistic on each disk usage
vmstat 5 -S M
This command is used to update the statistics every five
seconds and change the display units to megabytes
247

[manju@localhost ~]$ free -h --total
total used free shared buff/cache available
Mem: 976M 566M 75M 8.7M 334M 209M
Swap: 2.0G 84K 2.0G
Total: 3.0G 566M 2.1G
 hostname -s
 hostname --short
Display the short version of the hostname
hostname --all-ip-addresses
# Display All Network Addresses
date -r /etc/hosts
# Display Last Modified Timestamp of a Date File
Albert Einstein
Elsa Einstein
[manju@localhost ~]$ cat 1.txt > 2.txt
Albert Einstein
248

Albert Einstein
Elsa Einstein
[manju@localhost ~]$ cat -n 12.txt
1 Albert Einstein
2 Elsa Einstein
Albert Einstein
[manju@localhost ~]$ cat -e 1.txt
Albert Einstein$
sudo shutdown 08:00
# Shutdown the system at 8 AM in the morning
grep 'but|is' phy.txt
# Search for the words "but" and "is" in the phy.txt file
grep 'is|but|of' phy.txt
# Search for the words "but", "is" and "of" in the phy.txt file
grep -e but -e is -e of phy.txt
249

echo "The system will be shutdown in 10 minutes." | wall
The message (The system will be shutdown in 10 minutes.) will
be broadcasted to all users that are currently logged in
[manju@localhost ~]$ echo -e 'Albert Einstein'
Albert Einstein
[manju@localhost ~]$ echo -e 'Albert c Einstein'
Albert [manju@localhost ~]$
ss --all
# List all listening and non-listening connections
ss --listen
# List only listening sockets
ss -t state listening
# Find all listening TCP connections
[manju@localhost ~]$ hostname -I | awk '{print $1}'
192.168.6.131
System's IP address
250

yum erase httpd
# Uninstall apache
chmod 644 1.txt
 User: 6 = 4 + 2 (read and write)
 Group: 4 = 4 + 0 + 0 (read)
 Others: 4 = 4 + 0 + 0 (read)
 read has the value of 4
 write has the value of 2
 execute has the value of 1
 no permission has the value of 0
 7 = 4 + 2 + 1 (read, write and execute)



rpm -qi httpd
# Display information about a particular package (apache)
sudo rpm -qa | wc -l
# Display the total number of packages installed
sudo repoquery -a --installed
# List all installed packages with the repoquery command
251
6 = 4 + 2 + 0 (read and write)
5 = 4 + 0 + 1 (read and execute)
4 = 4 + 0 + 0 (read)

cat /var/log/boot.log
# Display all information related to booting operations
cat /var/log/maillog
# Display all information related to mail servers and archiving emails
cat /var/log/yum.log
# Display Yum command logs
mkdir -m777 myfiles
# Create a directory "myfiles" with read, write and execute permissions
rpm -qa centos-release
# Display CentOS version
ps -AlFH
# Get information about threads (LWP and NLWP)
 ps -eM
 ps axZ
ps -auxf | sort -nr -k 4 | head -10
# Display the top 10 memory consuming process
Get Security Information of Linux Process
252

ps -auxf | sort -nr -k 3 | head -10
# Display the top 10 CPU consuming process
sar -n DEV | more
# Monitor, collect and report Linux system activity
# create or overwrite "1.txt" file
echo "Albert Einstein" > 1.txt
# create or append to "1.txt" file
echo "Albert Einstein" >> 1.txt
grep -i "is" phy.txt
# Search for a given string in a file "phy.txt"
grep -A 3 -i "is" phy.txt
# Print the matched line and the following three lines
grep -r "is" *
# Recursively look for a given string in all files
export | grep ORACLE
# Display oracle related environment variables
253

chkconfig --list | grep network
# View the startup configuration of Linux network service
shutdown -r 18:30
# Shutdown the system immediately and reboot at 18:30
find /home -size +1024 -print
# Find files above 1MB in home directory
find /home -size +1024 -size -4096 -print
# Find files above 1Mb and below 4MB in home directory
netstat -ain
# Display the Kernel Interface table
sar -n SOCK | more
# Display networking Statistics
find /home -size +10000k
# Find files greater than 10000k in the home directory
ls -ld /home
# List information about the home directory instead of its contents
254

chmod go=+r 1.txt
# Add read permission for the owner and the group
chown manju 1.txt
# Change ownership of a file "1.txt" to user "manju"
du -sh *
# Display the disk usages of the files in the current directory
du -sh .[!.]* *
# Display the disk usages of the files (including hidden files) in the current directory
du -sch .[!.]* *
Display the total disk usage of the files
(including hidden files) in the current directory
du --threshold=1G -sh .[!.]* *
Display only files with more than 1GB in size which
located under current directory
255

iostat -kx
# Display general information about the disk operations in real time
netstat -ntlp
# Display open TCP sockets
netstat -nulp
# Display open UDP sockets
netstat -nxlp
# Display open Unix sockets
dmidecode -q | less
# Display BIOS information
systemctl --failed
# List failed services
losetup
# Display information about all loop devices
sudo yum install parted
# Install parted
parted -v
# Check Parted version
parted -l
# Lists partition layout on all block devices
parted -m
# Displays machine parseable output
Parted is a well-known command line
tool that allows us to easily manage
hard disk partitions
quit
# Exit the parted shell
256

 getfacl --access 1.txt
 getfacl -a 1.txt
 getfacl -n 1.txt
 getfacl --numeric 1.txt
# Display the file access
control list of a file "1.txt"
List the numeric user and
group IDs w.r.t file "1.txt"
sudo tcpdump -D
# List of all available network interfaces in the system
[manju@localhost ~]$ xz myfiles.txt
[manju@localhost ~]$ ls | grep myfiles
myfiles
myfiles.txt.xz
Compress a file "myfiles.txt"
using xz command
[manju@localhost ~]$ free -t | awk 'NR == 2 {print $3/$2*100}'
61.852
[manju@localhost ~]$ free -t | awk 'FNR == 2 {print $3/$2*100}'
61.852
Display Memory Utilization
257

[manju@localhost ~]$ free -t | awk 'NR == 3 {print $3/$2*100}'
2.54155
[manju@localhost ~]$ free -t | awk 'FNR == 3 {print $3/$2*100}'
2.54155
Display Swap Utilization
[manju@localhost ~]$ free -t | awk 'FNR == 2 {printf("%.2f% n"), $3/$2*100}'
61.86%
[manju@localhost ~]$ free -t | awk 'NR == 2 {printf("%.2f% n"), $3/$2*100}'
61.86%
Display Memory Utilization with Percent Symbol and two decimal places
[manju@localhost ~]$ free -t | awk 'FNR == 3 {printf("%.2f% n"), $3/$2*100}'
2.65%
[manju@localhost ~]$ free -t | awk 'NR == 3 {printf("%.2f% n"), $3/$2*100}'
2.65%
Display Swap Utilization with Percent Symbol and two decimal places
258

[manju@localhost ~]$ top -b -n1 | grep ^%Cpu | awk '{cpu+=$9}END{print 100-cpu/NR}'
100
Display CPU Utilization
[manju@localhost ~]$ top -b -n1 | grep ^%Cpu | awk '{cpu+=$9}END{printf("%.2f% n"), 100-cpu/NR}'
100.00%
Display CPU Utilization with Percent Symbol and two decimal places
swapon -s
# Print swap usage summaries
swapon -a
# Activate all of swap space
swapoff -a
# Deactivate all of swap space
[manju@localhost ~]$ cat /etc/system-release
CentOS Linux release 7.3.1611 (Core)
Display the version of CentOS
alias -p
# List all Aliases
lsof -i :8080
# Check which process is running on port 8080
259

sudo netstat -anp | grep tcp | grep LISTEN
# Display the various in-use ports and the process using it
sudo netstat -anp | grep 8080
# Display the process listening on port 8080
printf "%sn" *
# Prints the files and directories that are in the current directory
printf "%sn" */
# Prints only the directories in the current directory
printf "%sn" *.{gif,jpg,png}
# Lists only some image files
[manju@localhost ~]$ alias x='date'
Fri Oct 7 03:51:39 PDT 2022
[manju@localhost ~]$ unalias x
bash: x: command not found...
# create an alias
# preview the alias
# remove the alias
260

[manju@localhost ~]$ x="alan"; printf '%sn' "${x^}"
Alan
[manju@localhost ~]$ x="alan"; printf '%sn' "${x^^}"
ALAN
[manju@localhost ~]$ x="alan"; declare -u name="$x"; echo "$name"
ALAN
find . -name "xyz[a-z][0-9]"
find . -mmin -120
# Search for files changed during the previous two hours
find . -mmin +120
# Search for files that haven't been updated in the past two hours
Find directories and files with names starting with "xyz" and
ending with an alpha character after a one-digit
find . -mtime -3
# Find files that have been modified within the last 3 days
find . -mtime +3
# Find files that have not been modified within the last 3 days
261

[manju@localhost ~]$ names="Albert Alan John Mary"; x=(${names// / }); echo ${x[0]}
Albert
[manju@localhost ~]$ names="Albert Alan John Mary"; x=(${names// / }); echo ${x[3]}
Mary
names="Albert+Alan+John+Mary";
x=(${names//+/ });
echo ${x[0]}
# Output: Albert
names="Albert+Alan+John+Mary";
x=(${names//+/ });
echo ${x[3]}
# Output: Mary
[manju@localhost ~]$ awk '{print $2}' <<< "Alan Mathison Turing"
Mathison
[manju@localhost ~]$ awk '{print $1}' <<< "Alan Mathison Turing"
Alan
x='4 * 2'; echo "$x"
# prints 4 * 2
x='4 * 2'; echo $x
# prints 4, the list of files in the current directory, and 2
x=(hello world); echo "${x[@]/#/A}"
# Output: Ahello Aworld
262

x='4 * 2'; echo "$(($x))"
# prints 8
[manju@localhost ~]$ x="ALAN"; printf '%sn' "${x,}"
aLAN
[manju@localhost ~]$ x="ALAN"; printf '%sn' "${x,,}"
alan
[manju@localhost ~]$ x="Alan"; echo "${x~~}"
aLAN
[manju@localhost ~]$ x="Alan"; echo "${x~}"
alan
[manju@localhost ~]$ x='You are a genius'; echo "${x/a/A}"
You Are a genius
[manju@localhost ~]$ x='You are a genius'; echo "${x//a/A}"
You Are A genius
[manju@localhost ~]$ x='You are a genius'; echo "${x/%s/N}"
You are a geniuN
[manju@localhost ~]$ x='You are a genius'; echo "${x/s/}"
You are a geniu
263

[manju@localhost ~]$ x='You are a genius'; echo "${x#*a}"
re a genius
[manju@localhost ~]$ x='You are a genius'; echo "${x#*g}"
enius
[manju@localhost ~]$ foo=25; i=foo; echo ${i}
foo
[manju@localhost ~]$ foo=25; i=foo; echo ${!i}
25
[manju@localhost ~]$ x='You are a genius'; echo "${x%a*}"
You are
[manju@localhost ~]$ x='You are a genius'; echo "${x%%a*}"
You
[manju@localhost ~]$ x=Bob-Dev-Fox; echo ${x%%-*}
Bob
[manju@localhost ~]$ x=Bob-Dev-Fox; echo ${x%-*}
Bob-Dev
[manju@localhost ~]$ x=Bob-Dev-Fox; echo ${x##*-}
Fox
[manju@localhost ~]$ x=Bob-Dev-Fox; echo ${x#*-}
Dev-Fox
264

find . -type f -path '*/Documents/*'
# Find only files within a folder called Documents
find . -type f -path '*/Documents/*' -o -path '*/ Downloads/*'
# Find only files within a folder called Documents or Downloads
find . -type f -not -path '*/Documents/*'
# Find all files except the ones contained in a folder called Documents
find . -type f -not -path '*log' -not -path '*/Documents/*'
# Find all files except the ones contained in a folder called Documents or log files
[manju@localhost ~]$ find /dev -type b
/dev/sr0
/dev/sda3
/dev/sda2
/dev/sda1
/dev/sda
find . -maxdepth 1 -type f -name "*.txt"
# Find every.txt file from the current directory alone
[manju@localhost ~]$ echo "$(printf "%04d" "${x}")"
0000
Block devices
[manju@localhost ~]$ echo '16 / 5' | bc
3
[manju@localhost ~]$ echo '16 / 5' | bc -l
3.20000000000000000000
265

[manju@localhost ~]$ echo "$(printf "%05d" "${x}")"
00000
[manju@localhost ~]$ echo ""'""
"'"
[manju@localhost ~]$ echo '3 5 + p' | dc
8
[manju@localhost ~]$ dc <<< '3 5 + p'
8
[manju@localhost ~]$ echo '3 5 * p' | dc
15
[manju@localhost ~]$ dc <<< '3 5 * p'
15
[manju@localhost ~]$ expr 'Alan Turing' : 'Ala(.*)ring'
n Tu
[manju@localhost ~]$ echo '12 == 12 && 18 > 12' | bc
1 (True)
[manju@localhost ~]$ echo '12 == 13 && 18 > 12' | bc
0 (False)
266

[manju@localhost ~]$ expr PQRSTUVWXYZ : PQRS
4
ls -ral
# Listing of all files in reverse alphabetical order
Display the number of matching characters
 ls -tl
 ls -trl
# List the files such that the one that was most recently edited is at the top of the list
find . -regex ".*(.sh|.txt)$"
# Find .sh or .txt files
[manju@localhost ~]$ find . -iregex ".*(.sh|.pdf)$"
./bc.pdf
./1.PDF
./data.sh
./1.sh
./2.SH
./1.pdf
./2.sh
find . -type f -print
# List only regular files
[manju@localhost ~]$ echo "alan+alan+alan+alan" | xargs -d +
alan alan alan alan
[manju@localhost ~]$ echo "alan+alan+alan+alan" | xargs -d + -n 2
alan alan
alan alan
267

[manju@localhost ~]$ echo -e "2nalbertn" > 1.txt
2
albert
 ps -eLf --sort -nlwp | head
 ps -eLf
Display information about process threads
"Linux is a superbly polished copy of an antique - shinier than the original,
perhaps, but still defined by it."
— Jaron Lanier, You Are Not a Gadget
268

Best Linux Books that Every Superuser Should Read:
 How Linux Works: What Every Superuser Should Know
Book by Brian Ward
 The Linux Programming Interface
Book by Michael Kerrisk
 Linux pocket guide
Book by Daniel J. Barrett
 Linux for Beginners
Book by Jason Cannon
 How Linux Works: What Every Superuser Should Know
Book by Brian Ward
 Linux Kernel Development
Book by Robert Love
 Linux: The Complete Reference
Book by Richard Petersen
 Linux in a Nutshell
Book by Ellen Siever and Robert Love
 Linux Basics for Hackers: Getting Started with Networking, Scripting, and Security
in Kali
Book by OccupyTheWeb

 Linux Command Line and Shell Scripting Bible
Book by Christine Bresnahan and Richard BLUM
 Linux Administration: The Linux Operating System and Command Line Guide for
Linux Administrators
 The Art of Unix Programming
Book by Eric S. Raymond
 The Linux Command Line, 2nd Edition: A Complete Introduction
Book by William Shotts
 Linux Bible
Book by Christopher Negus
 Linux System Programming: Talking Directly to the Kernel and C Library
Book by Robert Love
 A Practical Guide to Linux Commands, Editors, and Shell Programming
Book by Mark G. Sobell
 Linux for Beginners and Command Line Kung Fu
 Linux Device Drivers
Book by Alessandro Rubini, Greg Kroah-Hartman, and Jonathan Corbet
 Advanced Linux programming
Book by Alex Samuel, Jeffrey Oldham, and Mark Mitchell
 Understanding the Linux Kernel

Book by Daniel Pierre Bovet and Marco Cesati
 Learn Linux Quickly: A Beginner-friendly Guide to Getting Up and Running with
the World's Most Powerful Operating System
Book by Ahmed Alkabary
 Linux administration
Book by Wale Soyinka
 Linux For Dummies
Book by Richard Blum
 Linux Essentials
 The Linux Command Line Beginner's Guide
Book by Jonathan Moeller
 Linux All-in-One for Dummies
Book by Emmett Dulaney
 Learning the bash Shell
Book by Cameron Newham
 Linux for Developers: Jumpstart Your Linux Programming Skills
Book by William "Bo" Rothwell
 Lfm: Linux Field Manual
Book by Tim Bryant
 CompTIA Linux+ Study Guide: Exam XK0-005

 sed & awk
Book by Arnold Robbins and Dale Dougherty
 Linux From Scratch
Book by Gerard Beekmans
Linux is a complex example of the wisdom of crowds. It's a good
example in the sense that it shows you can set people to work in
a decentralized way - that is, without anyone really directing
their efforts in a particular direction - and still trust that they're
going to come up with good answers.
− James Surowiecki

One final thought:
If you feel that this information has been useful to you, please take a
moment to share it with your friends on LinkedIn, Facebook and
Twitter. Consider writing a brief review on Google Play Books if you
feel that this book has helped you in your Linux Admin career and you
have learned something worthwhile.
In the big view, I believe Linux to be incredibly amazing. This is a
fantastic platform that serves as a neutral, dependable hub for
developers and enterprise organizations to build, manage, and scale
open technology projects and ecosystems. I want to spread my passion
to as many individuals as I can. I also hope that this is not the end of
your learning.
Thank you!

Did I miss any commands? Let me know! Email me manjunath5496@gmail.com

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