Linux Most Commonly Used Commands

This page provides a comprehensive overview of the most commonly used commands in Linux. It covers a wide range of commands that are essential for navigating the Linux operating system, managing files and directories, working with users and permissions, networking, process management, system information, and more.

The article is structured into sections, making it easy to locate commands based on their respective categories. Each command is presented with a brief description of its functionality and usage. The commands are accompanied by examples and explanations, enabling readers to understand how they can be applied in practical scenarios.

File and Directory Operations

File and directory operations involve various commands that allow you to interact with files and directories in Linux. Here is a brief description of some common file and directory operations:

Command	Description
ls	Lists all files and directories in the present working directory
ls -R	Lists files in sub-directories as well
ls -a	Lists hidden files as well
ls -al	Lists files and directories with detailed information like permissions, size, owner, etc.
cd or cd ~	Navigate to HOME directory
cd ..	Move one level up
cd	To change to a particular directory
cd /	Move to the root directory
cat > filename	Creates a new file and then allow you to add on the file. Ctrl D to get out of it.
cat filename	Displays the file content
cat file1 file2 > file3	Joins two files (file1, file2) and stores the output in a new file (file3)
mv file "new file path"	Moves the files to the new location
mv filename new_file_name	Renames the file to a new filename
rm filename	Deletes a file
mkdir directoryname	Creates a new directory in the present working directory or at the specified path
rmdir	Deletes an empty directory
mv	Renames or moves a file or directory

User and Permissions Management

User and permissions management commands help you manage users and control access to files and directories. Some common commands in this category include chown for changing ownership of files and directories, chmod for modifying file permissions, adduser for adding new users, passwd for changing user passwords, and userdel for removing users.

Command	Description
chown user filename	Changes the ownership of a file/directory
chown user:group filename	Changes the user and group for a file or directory
sudo adduser username	Adds a new user
sudo passwd -l 'username'	Changes the password of a user
sudo userdel -r 'username'	Removes a user and their home directory
sudo usermod -a -G GROUPNAME USERNAME	Adds a user to a group
sudo deluser USER GROUPNAME	Removes a user from a group
chmod	Changes the permissions of a file or directory
chmod +x filename	Grants execute permission to a file
chmod u+rwx filename	Grants read, write, and execute permissions to the owner

Text Editing

Text editing commands are used to create, modify, and view text files in Linux. The most commonly used text editor in Linux is vi or vim. Commands like i, a, and o are used to insert text in vi, while dd and dw are used to delete text. Other commands like y, p, and :wq are used for copying, pasting, and saving changes, respectively.

Command	Description
vi	Opens the vi text editor
i	Inserts at the cursor position (goes into insert mode)
a	Writes after the cursor (goes into insert mode)
A	Writes at the end of the line (goes into insert mode)
ESC	Terminates insert mode
u	Undoes the last change
U	Undoes all changes to the entire line
o	Opens a new line (goes into insert mode)
dd	Deletes a line
3dd	Deletes 3 lines
D	Deletes contents of the line after the cursor
C	Deletes contents of a line after the cursor and inserts new text
dw	Deletes a word
4dw	Deletes 4 words
cw	Changes a word
x	Deletes a character at the cursor
r	Replaces a character
R	Overwrites characters from the cursor onward
s	Substitutes one character under the cursor and continues to insert
S	Substitutes the entire line and begins to insert at the beginning of the line
~	Changes the case of an individual character

Networking

Networking commands in Linux help you manage network connections and troubleshoot network-related issues. Commands like ping are used to check network connectivity, ifconfig displays network interface configuration, ssh allows remote login to another machine, and scp is used for secure file transfer between hosts.

Command	Description
ssh username@ip-address or hostname	Logs into a remote Linux machine using SSH
ping hostname	Pings and analyzes network and host connections
scp file username@hostname:destination	Copies a file securely to a remote server
ssh-keygen	Generates SSH key pairs
ifconfig	Displays network interface configuration
netstat	Displays network connections and statistics

Process Management

Process management commands are used to monitor and control running processes in Linux. ps displays information about running processes, kill terminates processes, top provides real-time monitoring of processes, and bg and fg are used to manage processes in the background and foreground, respectively.

Command	Description
ps	Gives the status of processes running for a user
ps PID	Gives the status of a particular process
pidof	Gives the Process ID (PID) of a process
kill PID	Terminates a process
top	Details on all active processes
bg	Sends a process to the background
fg	Runs a stopped process in the foreground

System Information

System information commands provide information about the system's hardware and software. Commands like date display the current date and time, uptime shows system uptime, who lists the currently logged-in users, and df provides information about disk space usage.

Command	Description
date	Displays the current date and time
cal	Displays a calendar
uptime	Displays system uptime
who	Lists users currently logged in
df	Gives free hard disk space on your system
free	Gives free RAM on your system

Other Useful Commands

There are various other useful commands in Linux that perform different tasks. Some examples include history for displaying command history, clear for clearing the terminal screen, and exit for exiting the current shell or terminal session. These commands help enhance productivity and perform routine tasks efficiently.

Command	Description
history	Displays a list of previously executed commands
clear	Clears the terminal screen
exit	Exits the current shell or terminal session

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