Satyam Arya

50 Most Important Linux Commands You Should Know

Satyam Arya

Linux is an open-source operating system that is based on the Unix operating system. Linux is known for its stability, security, and flexibility, and can be customized to suit the needs of the user. It is used in a wide range of applications, from servers and desktop computers to smartphones, embedded systems, and more. One of the key features of Linux is its open-source nature, which means that its source code is freely available for anyone to modify and distribute, subject to the terms of various open-source licenses.

Why Linux?

Linux Architecture

Linux Important Directories

50 important Linux commands:

1. cd

cd <directory path>

cd stands for “change directory”. It is used to change the current working directory.

2. ls

ls

ls stands for “list”. It is used to list the contents of a directory.

ls -a

The -a option is used to show all files and directories, including hidden files

ls -l

The -l option is used to display the results in a long format

ls -R

The -R option is used to display the results recursively, i.e., it will show the contents of all subdirectories as well.

3. pwd

pwd

pwd stands for “present working directory”. When you run the ‘pwd’ command, it will display the full path of the current directory in the terminal

4. mkdir

mkdir <folder name>

mkdir stands for “make directory”. When you run the ‘mkdir’ command, it will create a new directory with the name you specify.

mkdir -p example/example2

This command will create the “example” directory if it doesn’t already exist, and then create the “example2” directory inside it

5. rm

rm <file name>
rm -r <folder name>

rm stands for “remove”. It is a command used in the Linux terminal to remove files.

6. mv

mv <source> <destination>

mv stands for “move”. When you run the ‘mv’ command, it will move the specified file or directory to a new location, or rename the file or directory.

7. cp

cp <source> <destination>

cp stands for “copy”. When you run the ‘cp’ command, it will create a copy of the specified file or directory in a new location

To copy all data which starts from D alphabet

cp -rvf /root/D* /home

8. touch

touch <file name>

touch command is used to create a new empty file or update the timestamp of an existing file. 

stat hello.txt  
touch -a hello.txt    // to change access time
touch -m hello.txt    // to change modified time
touch hello.txt       // to change all
touch .file.txt

This command is used to create hidden file

touch test-{1..4}.txt

9. sudo

sudo <command you want to run>

sudo is a command that allows a user with administrative privileges (i.e., the “superuser”) to execute a command with elevated permissions.

Note: It’s important to note that you should only use ‘sudo’ when necessary, as it can be dangerous to run commands with elevated permissions if you’re not sure what the command will do

sudo su satyam

The command “sudo su satyam” is used to switch to the user satyam

sudo su

The command “sudo su” is used to switch to the root user

To exit type exit

10. rmdir

rmdir <folder name>

rmdir is used to remove an empty directory. If the directory contains files or other directories, the ‘rmdir’ command will fail

rm -rf

removes non-empty file and directory

11. cat

cat <file name>

cat command is used to display the contents of a file on the terminal.

cat > hello.txt

cat > file2.txt creates a new file named file2.txt and allows you to enter text into that file from the terminal

cat >> hello.txt
cat hello1.txt >> hello2.txt

This command is used to append the contents of one file to another file.

cat hello1.txt > hello2.txt

When this command is executed, the contents of hello1.txt are written to hello2.txt. If hello2.txt already exists, its contents are overwritten with the contents of hello1.txt. If hello2.txt does not exist, it is created and the contents of hello1.txt are written to it.

cat hello1.txt hello2.txt > hello3.txt

This command is used to concatenate the contents of two files and redirect the output to a third file

12. echo

echo "Hello, World"

echo command is used to display a string of text on the terminal.

13. clear

clear

clear command is used to clear the terminal screen. It will remove all the previous commands, outputs, and prompts from the terminal window, making it appear as if you have a fresh terminal window open.

14. history

history

history command is used to display a list of previously executed commands in the terminal.

15. wc

It is used to count the number of lines, words, and characters in a given text file

wc -l /etc/passwd
wc -w /etc/passwd
wc -c /etc/passwd

16. ping

ping hostname

ping command is used to test the connectivity between two networked devices, such as a local machine and a remote server. The ping command sends a small packet of data to the remote device and waits for a response. If a response is received, it indicates that the two devices are connected and able to communicate with each other

17. whoami

whoami

whoami command is used to display the username of the current user. When you log in to a Linux system, you are assigned a unique username that identifies you to the system.

18. hostname

hostname

hostname command is used to display the hostname of the current system. The hostname is the name given to a computer or device on a network

19. zip/unzip

zip <archive name> <file names separated by space>
unzip <archive name>

zip command is used to compress files and create zip archives, while the “unzip” command is used to extract files from zip archives

20. man

man [command_name]

man command is used to display the manual page for a particular command or topic

Press q to quit

21. alias

alias newcommand='originalcommand'

alias command is used to create a shortcut or alternate name for a command or group of commands.

22. diff

diff file1 file2

diff command is used to compare the contents of two files and highlight the differences between them. The diff command is often used in software development and system administration to compare different versions of files, or to identify changes made to a file over time.

23. head/tail

head -3 filename
tail -3 filename

head command displays the first few lines of a file.

tail command displays the last few lines of a file

24. cmp

cmp file1 file2

cmp command is used to compare two files byte by byte and display the differences between them. The cmp command is often used in software development and system administration to check for changes made to a file, or to verify that two files are identical.

25. passwd

passwd

passwd command is used to change a user’s password.

26. wget

wget [URL]

wget command is used to download files from the internet. By default, the file will be saved with the same name as it has on the web.

27. which 

which git

It allows you to locate the location of a specified executable file in the system’s path.

28. tr

tr set1 set2

tr command is used to translate or delete characters. It takes two sets of characters and replaces any occurrences of characters in the first set with the corresponding characters in the second set. If the second set is shorter than the first, any extra characters in the first set will be deleted.

29. 

sudo apt update
sudo apt upgrade
sudo apt install tree
sudo apt purge tree

30. find

find [expression]

find command is used to search for files and directories in a specified location. It is a powerful command that allows you to search for files based on various criteria such as name, size, type, modification date, and ownership

find *.txt
find /downloads -name key.pem

To search a file with less than 10MB in a folder

find /downloads -size -10M

To search a file with more than 10MB in a folder

find /downloads -size +10M

Using find command based on users

find / -user root

Using find command based on groups

find / -group groupname

31. locate

locate [expression]

locate command is used to search for files and directories in a database of the file system. This command is much faster than the find command because it searches a pre-built database instead of searching the entire file system

32. chmod

chmod mode <file_name>

chmod command is used to change the permissions of files and directories. It stands for “change mode” and is used to specify who can read, write, or execute a file

The mode argument specifies the new permissions to be set, and can be represented in two different formats:

To view file permissions

ls -l file_name

Example:

-rw-r--r-- 1 user group 1024 Jul 10 10:30 example.txt
  1. -rw-r--r--: This part represents the file permissions
  2. 1: This number indicates the number of hard links to the file.
  3. user: This is the username of the file’s owner.
  4. group: This is the group name to which the file belongs.
  5. 1024: This number indicates the file size in bytes.
  6. Jul 10 10:30: This is the date and time when the file was last modified.
  7. example.txt: This is the name of the file.

To view directory permissions

ls -ld <directory_path>

33. chown

chown new_owner <file_name>

chown command is used to change the ownership of a file or directory. It stands for “change owner” and is often used to transfer ownership from one user to another

For changing group owner

chown group_name <file_name>

34. chgrp

To change group of a file

sudo chgrp devops demofile.txt

35. grep

grep pattern [file(s)_name]

grep command is used to search for specific text patterns within one or more files. The name grep stands for “global regular expression print”

Some common options for the grep command include:

To search a word

grep root /etc/passwd

To search a word in multiple files

grep root /etc/passwd /etc/group

To search a string insensitive in file

grep -i Root /etc/passwd

To search a string in all files

grep -r root /

To inverts the search, i.e., returns all lines that do not match the pattern

grep -v root /etc/passwd

To display the file names that match the string

grep -l root /etc/passwd /etc/group

To display the file names that do not match the string

grep -L root /etc/passwd /etc/group

To display the string match total line number

grep -c root /etc/passwd

To display the string match line with number

grep -n root /etc/passwd

To display the lines that start with a string

grep ^root /etc/passwd

To display the lines that end with a string

grep root$ /etc/passwd

To search and redirect output into a new file

grep root /etc/passwd > demo.txt

36. top

top

top command is used to monitor the system’s processes and their resource utilization. It provides a real-time, dynamic view of the processes running on a system, showing which processes are using the most CPU time, memory, and other system resources

37. kill

kill PID(s)

kill command is used to terminate a process by sending it a signal. A signal is a software interrupt that can be used to communicate with a running process

38. uname

uname
uname -r

uname shows the name of the kernel (OS)

uname -r shows the version of the kernel

39. useradd

useradd username

useradd command is used in Linux to create a new user account

Note: When you create a new user account with useradd, you will need to set a password for the account using the passwd command before the account can be used.

passwd username

If we want to check all users

sudo cat /etc/passwd

To check user account properties

grep satyam /etc/passwd

To check user password properties

grep satyam /etc/shadow

groupadd command is used in Linux to create a new group

groupadd groupname
gpasswd -a satyam groupname             # To add single member in a group
gpasswd -M satyam,rahul groupname       # To add multiple member in a group

If we want to check all groups

sudo cat /etc/group

To check group account properties

grep groupname /etc/group

To check admin properties

grep groupname /etc/gshadow

40. userdel

userdel username

userdel command is used in Linux to delete a user account

Note: When you delete a user account with userdel, all files and directories associated with that user account will be removed. Be sure to back up any important data before deleting a user account

groupdel groupname

groupdel command is used in Linux to delete group

gpasswd -d satyam groupname        # To remove group member
gpasswd -A satyam groupname        # To make group admin

41. lscpu

lscpu

lscpu command is a Linux command that is used to display information about the CPU architecture of the system. It is useful for identifying the number of processors, cores, threads, and their respective speeds, as well as other details about the CPU architecture

42. ifconfig

ifconfig is used to display network interface configuration information on Unix-like systems. It displays information about all active network interfaces on your computer, such as their IP addresses, MAC addresses, and network-related statistics

43. tree

tree

displays the directory structure in a tree-like format

44. 

cat /etc/os-release
lsb_release -a

It is used to display information about the operating system installed on a Linux system. It typically shows details such as the operating system name, version, and other related information.

45. ln

  1. ln <source_file> <target_link>: This creates a hard link between the source_file and the target_link. Both the source file and the target link will point to the same underlying file data on the disk. If you make changes to either the source file or the target link, it will reflect in both.
  2. ln -s <source_file> <target_link>: This creates a symbolic link (also known as a soft link) between the source_file and the target_link. A symbolic link is a special type of file that acts as a pointer to the source file.

46. awk

It allows you to perform various text manipulation tasks.

awk 'pattern { action }' input_file
awk 'NR>=1 && NR<=20 && /TRACE/ {print NR,$1,$2,$5}' application.log > final.log

47. tar

tar stands for “tape archive” and is used to create, view, and extract files from an archive file or a collection of files compressed into a single file.

Create a new archive of files

tar -cvf archive.tar file1.txt file2.txt
tar -cvf /folder/archive.tar file1.txt file2.txt

Extract files from an existing archive

tar -xvf archive.tar

Create a compressed archive using gzip

tar -cvzf archive.tar.gz file1.txt file2.txt directory/

Extract files from a compressed archive using gzip

tar -xvzf archive.tar.gz

Create a compressed archive using bzip2

tar -cvjf archive.tar.gz /var

48. systemctl

It provides a convenient way to start, stop, enable, disable, and view the status of various services and daemons on the system

To view status

systemctl status <service_name>
systemctl status docker

To start a service

systemctl start docker

To stop the specified service

systemctl stop docker

To stop and then start the specified service

systemctl restart docker

This command configures the specified service to start automatically when the system boots up

systemctl enable <service_name>

This command prevents the specified service from starting automatically on system boot

systemctl disable <service_name>

Vim vs Nano editor

nano example.txt

This will open a new file named “example.txt” in Nano.

Start typing your text and when you are finished, press “Ctrl” + “O” to save your changes. To exit Nano, press “Ctrl” + “X”

vim example.txt

This will open a new file named “example.txt” in Vim.

Press the “i” key to enter insert mode and start typing your text. When you are finished, press the “Esc” key to exit insert mode. To save your changes, type :w and press Enter. To exit Vim, type :q and press Enter.

It has 3 modes:

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

base64

The base64 command is used to encode and decode data using the Base64 encoding scheme

To encode a string, use the following command:

echo "Hello, world" | base64

This command encodes the string “Hello, world!” and displays the encoded output on the terminal.

To decode a string, use the following command:

echo "SGVsbG8sIHdvcmxkIQ==" | base64 --decode

ssh

ssh command is used to securely connect to a remote server or device over a network. The ssh command uses the SSH (Secure Shell) protocol to establish a secure connection between the local and remote machines, allowing you to perform remote operations on the remote machine as if you were sitting in front of it

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