Linux Basic Commands

1. ls

ls

The ls command in Linux is used to list the contents of a directory (files and folders). It helps you see what's inside a folder.

Basic Syntax:

ls [options] [directory]

Common Examples:

1. List files in current directory

ls

👉 Shows names of files and folders in the current location.

2. List with details (-l for long format)

ls -l

👉 Shows detailed information like permissions, owner, size, and modified date.

Example output:

-rw-r--r-- 1 user user  2048 Jul 01 12:30 file.txt
drwxr-xr-x 2 user user  4096 Jul 01 12:15 folder

Include hidden files (-a for all)

ls -a

👉 Shows all files, including hidden files (those starting with . like .bashrc).

4. Combine options (-la)

ls -la

👉 Shows all files including hidden ones, in detailed format.

5. List files in a specific directory

ls /etc/sysconfig/network-scripts

👉 Lists contents inside the /etc/sysconfig/network-scripts folder.

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2. pwd

pwd

pwd Command in Linux

pwd stands for Print Working Directory.
It shows the full path of your current location in the filesystem.

🔹 Basic Syntax:

pwd

🔹 Example:

Let’s say you open a terminal and type:

pwd

Output:

/

👉 This means you're currently in the Documents folder, inside the ashwin user's home directory.

🔹 When to Use:

• To know where you are in the system.

• Useful while working with nested directories.

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3. cd

cd Command in Linux

cd stands for Change Directory.
It is used to navigate between folders in the Linux file system.

🔹 Basic Syntax:

cd [directory_path]
cd /etc/sysconfig

🔹 Common Examples:

1. Go to a specific directory

cd /etc/sysconfig/network-scripts

👉 Moves you to the Documents folder.

2. Go to your home directory

cd

or

cd ~

👉 Takes you to your user's home directory, like /home/ashwin.

3. Go back to the previous directory

cd ..

👉 Takes you to the previous directory you were in.

4. Navigate using relative path

cd /var/log

👉 Moves into /var/log from your current location.

🔹 Check Your Location:

Use pwd to confirm where you are after using cd.

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4. / (Root Directory)

/ (Root Directory) in Linux

In Linux, / is called the root directory.
It is the top-most directory in the Linux filesystem. All other files and folders are stored under this root.

🔹 Think of it like:

A tree 🌳 — / is the root and everything else (like /home, /etc, /bin, etc.) are branches.

🔹 Example:

Type this in terminal:

cd /
pwd

Output:

/

👉 This means you are now in the root directory.

🔹 Listing contents of /:

ls /

You may see folders like:

bin   boot  dev  etc  home  lib  media  mnt  opt  proc  root  run  sbin  tmp  usr  var

Each of these has a special purpose. For example:

• /home → User folders

• /etc → Configuration files

• /bin → Basic Linux commands

• /var → Logs and variable data

🔹 Visual Structure:

/
├── bin
├── etc
├── home
│   └── ashwin
├── var
├── usr
└── tmp

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5. mkdir

mkdir Command in Linux

mkdir stands for "make directory".
It is used to create a new folder (directory) in the Linux file system.

🔹 Basic Syntax:

mkdir [directory_name]

🔹 Examples:

✅ 1. Create a single directory

mkdir myfolder

👉 Creates a folder named myfolder in the current directory.

✅ 2. Create multiple directories at once

mkdir folder1 folder2 folder3

👉 Creates three folders in the current location.

✅ 3. Create nested directories (with -p option)

mkdir -p projects/linux/scripts

👉 Creates the full path, including parent folders if they don’t exist.

🔹 Verify the creation:

Use ls to list and confirm:

ls

🔹 Example in Practice:

cd ~
mkdir practice
cd practice
mkdir -p linux/directory1
ls -R

👉 This creates a structure like:

practice/
└── linux/
    └── directory1/

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6. rm

rm stands for remove.
It is used to delete files and directories in Linux.

⚠️ Be careful: Once deleted with rm, files cannot be recovered easily.

🔹 Basic Syntax:

rm [options] [file_or_directory]

🔹 Examples:

✅ 1. Remove a single file

rm file.txt

👉 Deletes file.txt from the current directory.

✅ 2. Remove multiple files

rm file1.txt file2.txt

👉 Deletes both files at once.

✅ 3. Remove an empty directory (use -d)

rm -d empty_folder

👉 Deletes an empty folder.

✅ 4. Remove a non-empty directory (use -r or -rf)

rm -r myfolder

👉 Recursively deletes the folder and everything inside it.

Use -f to force delete (no confirmation):

rm -rf myfolder

⚠️ Dangerous! This will delete everything inside without asking.

🔹 Practice Example:

mkdir testfolder
touch testfolder/file1.txt
rm -r testfolder

👉 This creates a folder, adds a file, and then deletes the whole folder.

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7. useradd

useradd Command in Linux

The useradd command is used to create a new user on a Linux system.
It’s a simple and user-friendly command (more interactive than useradd).

🔹 Basic Syntax:

useradd [username]

🔹 Example:

useradd ashwin

👉 This will start an interactive setup like:

Adding user `ashwin` ...
Adding new group `ashwin` (1001) ...
Adding new user `ashwin` (1001) with group `ashwin` ...
Creating home directory `/home/ashwin` ...
Copying files from `/etc/skel` ...
New password:
Retype new password:
Full Name []:
Room Number []:
Work Phone []:
Home Phone []:
Other []:
Is the information correct? [Y/n]

🔹 What this does:

• Creates a user account ashwin

• Creates a home directory: /home/ashwin

• Assigns a default group

• Sets up a password

• Adds user info (optional)

🔹 Verify the user was added:

id ashwin

or

cat /etc/passwd | grep ashwin

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8. userdel

userdel Command in Linux

The userdel command is used to delete a user account from the system.

⚠️ Requires root privileges, so use it with sudo.

🔹 Basic Syntax:

userdel [username]

🔹 Example:

userdel ashwin

👉 This command deletes the user account named ashwin.

🔸 Note: By default, this does not delete the user's home directory.

🔹 Delete user and their home directory:

userdel -r ashwin

👉 This removes:

• The user account ashwin

• Their home folder: /home/ashwin

• Their mail spool and personal files

🔹 How to confirm user is deleted:

cat /etc/passwd | grep ashwin

👉 If no output, the user is deleted.

🔹 Warning:

Don’t delete users while they are logged in.
It can cause system issues. First, check:

who
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9. vi

vi Command in Linux

vi is a text editor in Linux, used to view and edit files directly in the terminal.

It's one of the most powerful and widely available editors on Unix/Linux systems.

🔹 Basic Syntax:

vi filename

🔹 Example:

vi notes.txt

👉 This opens (or creates, if not exists) a file named notes.txt for editing.

🔹 Modes in vi:

1. Normal Mode (default when you open vi)
   – For navigation and commands

2. Insert Mode
   – For typing text
   – Press i to enter Insert mode

3. Command Mode
   – For saving, quitting, searching
   – Press : to enter command mode

🔹 Basic Commands:

🔹 Example Flow:

1. Open a file:

vi hello.txt

2. Press i → Enter Insert Mode

3. Type:

Hello, this is my first vi file!

4. Press Esc → Go back to Normal Mode

5. Type :wq! → Save and quit
   
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10. cat

cat Command in Linux

cat stands for "concatenate", but it’s commonly used to view the contents of a file.

🔹 Basic Syntax:

cat [options] filename

🔹 Most Common Uses & Examples:

✅ 1. View contents of a file

cat file.txt

👉 Displays the content of file.txt in the terminal.

✅ 2. Create a new file using cat

cat > newfile.txt

Then type your content:

Hello, this is a new file.

Press Ctrl + D to save and exit.

✅ 3. Append content to an existing file

cat >> file.txt

Type new content and press Ctrl + D.

✅ 4. Combine multiple files into one

cat file1.txt file2.txt > combined.txt

👉 Combines file1.txt and file2.txt into combined.txt.

✅ 5. Show line numbers

cat -n file.txt

👉 Displays the file with line numbers:

     1  This is line 1
     2  This is line 2

🔹 Summary Table:

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11. clear

clear Command in Linux

The clear command is used to clear the terminal screen.
It doesn’t delete files or commands — it just makes your terminal window look clean.

🔹 Syntax:

clear

🔹 Example:

Before:

$ ls
bin sbin root sys etc home
$ pwd
/home/ashwin
$ clear

After:
👉 All the previous output is cleared, and you’re left with a fresh terminal prompt.

🔹 Shortcut Alternative:

Instead of typing clear, you can also press:

Ctrl + L

👉 This also clears the screen (works in most terminals).

🔹 Important Note:

• It does not delete history. You can still scroll up with the mouse or scroll bar to see old commands/output.

• It’s purely for visual clarity.

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12. history

history Command in Linux

The history command shows a list of all previously run commands in the terminal.
It’s very useful to recall or repeat past commands.

🔹 Syntax:

history

🔹 Example:

history

👉 Output:

  1  ls
  2  pwd
  3  cd /home/ashwin
  4  mkdir test
  5  history

This shows:

• Line numbers for each command

• The exact command you typed earlier

🔹 Useful Options & Examples:

✅ 1. Run a previous command by number

!3

👉 Runs the 3rd command from the history (in this case: cd /home/ashwin)

✅ 2. Search your command history

history | grep mkdir

👉 Finds all mkdir commands you've used before.

✅ 3. Repeat the last command

!!

👉 Runs the most recent command again.

✅ 4. Clear your command history

history -c

👉 Clears all saved history for the current session.

✅ 5. Save history to a file

history > my_history.txt

👉 Saves your full command history into my_history.txt.

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13. touch

touch Command in Linux

The touch command is used to:

1. Create an empty file.

2. Update the timestamp of an existing file (access and modification time).

📌 Syntax:

touch filename

🔹 1. Create a New Empty File

touch myfile.txt

🟢 This creates an empty file named myfile.txt in the current directory.

🔹 2. Create Multiple Files at Once

touch file1.txt file2.txt file3.txt

🟢 This creates all three files in one command.

🔹 3. Update Timestamp of Existing File

touch existingfile.txt

🟢 If existingfile.txt already exists, touch will not delete it — it simply updates the last modified time to the current time.

🔹 4. Change Timestamp to Specific Time

touch -t 202507011200 myfile.txt

🟢 This sets the time to 1st July 2025, 12:00 PM.

🔹 5. Don’t Create New File (Only Update if Exists)

touch -c myfile.txt

🟢 If the file doesn’t exist, it does nothing.

✅ Summary Table

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