Interactive Linux CLI Tutorial

1

What is the Command Line?

Understanding terminals and shells

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A Brief History

Back in the 1970s, computers were massive mainframes shared by many users. There were no mice or graphical interfaces - just text terminals connected to the central computer. Users typed commands and received text responses.

Even though we now have beautiful graphical interfaces, the command line remains incredibly powerful. In cybersecurity especially, you'll use it constantly!

Terminal vs Shell

Terminal - The window/program that displays text and accepts your keyboard input
Shell - The program that interprets your commands and runs them (Ubuntu uses "bash" by default)

Opening the Terminal in Ubuntu (on your Mac)

Since you're running Ubuntu in VirtualBox on your Mac, here's how to open the terminal:

Click Activities in the top-left corner of Ubuntu
Type Terminal in the search box
Click the Terminal icon to open it

Pro Tip for Mac Users: You can right-click on the Terminal icon in the dock and select "Add to Favorites" so it's always easy to find!

Important - Mac Keyboard in Ubuntu: Inside the Ubuntu terminal, you'll use the Control key (not Command ⌘). So shortcuts like cancel command are Control+C, not ⌘+C.

Quick Check

What is the shell?

The window where you type commands The program that interprets and runs your commands A type of Linux distribution

2

Your First Commands: pwd and ls

Finding out where you are and what's around you

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Where Am I? (pwd)

When you open a terminal, you're always "in" a directory (folder). To find out which one, use:

pwd

pwd stands for "Print Working Directory". It shows your current location in the file system.

You'll likely see something like:

/home/amy

This is your "home directory" - your personal space on the computer.

What's Here? (ls)

To see what files and folders are in your current location:

ls

ls stands for "list". It shows the contents of the current directory.

Useful ls Options

Command	What it does
`ls -l`	Long format - shows details like size, date, permissions
`ls -a`	Shows ALL files, including hidden ones (starting with .)
`ls -la`	Combines both - detailed list of all files

Try It Yourself!

Open your terminal (Activities → search "Terminal")
Type pwd and press Enter - note where you are
Type ls to see your files
Type ls -la to see hidden files too

Quick Check

What does the -a option do with ls?

Shows files alphabetically Shows only large files Shows ALL files including hidden ones

3

Moving Around: cd

Navigating between directories

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Changing Directories

cd stands for "Change Directory". It's how you move around the file system.

cd Documents

This moves you into the Documents folder (if it exists).

Special Shortcuts

Command	What it does
`cd ~`	Go to your home directory
`cd ..`	Go up one level (to parent folder)
`cd /`	Go to the root of the file system
`cd -`	Go back to the previous directory
`cd`	Go home (same as cd ~)

Absolute vs Relative Paths

Absolute path - Starts with / and gives the full location: /home/amy/Documents
Relative path - Relative to where you are now: Documents or ../Downloads

Pro Tip: Press TAB to auto-complete folder and file names! Type the first few letters and press TAB.

Try It Yourself!

Type pwd to see where you are
Type cd / to go to the root
Type ls to see system folders
Type cd ~ to return home
Try cd Documents then cd .. to go back

Quick Check

What does cd .. do?

Goes to your home directory Goes up one level to the parent folder Shows the current directory

4

Creating Directories: mkdir

Making new folders

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Making Directories

mkdir stands for "Make Directory". It creates new folders.

mkdir my_folder

Creating Nested Directories

Use the -p flag to create parent directories as needed:

mkdir -p projects/python/scripts

This creates all three folders at once, even if projects doesn't exist yet.

Naming Best Practices:

Avoid spaces - use underscores or hyphens: my_folder or my-folder
Linux is case-sensitive: "Folder" and "folder" are different!
Stick to letters, numbers, underscores, and hyphens

Try It Yourself!

Go to your home directory: cd ~
Create a practice folder: mkdir practice
Check it exists: ls
Create nested folders: mkdir -p practice/level1/level2
Navigate in: cd practice/level1/level2
Check where you are: pwd

Quick Check

What does the -p flag do with mkdir?

Creates parent directories as needed Makes the folder password protected Prints the path of the new folder

5

Creating Files: touch and echo

Making new files and adding content

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Creating Empty Files with touch

touch creates an empty file (or updates a file's timestamp if it exists).

touch myfile.txt

Creating Files with Content using echo

echo prints text. Combined with >, it writes to a file:

echo "Hello, World!" > greeting.txt

Redirection Operators

Operator	What it does
`>`	Writes to file (overwrites existing content!)
`>>`	Appends to file (adds to the end)

Warning! Using > will overwrite the entire file without asking! Use >> to add to existing content safely.

Try It Yourself!

Go to your practice folder: cd ~/practice
Create an empty file: touch notes.txt
Create a file with text: echo "My first line" > notes.txt
Add another line: echo "My second line" >> notes.txt
Check your files: ls

Quick Check

What's the difference between > and >> ?

> appends, >> overwrites > overwrites, >> appends They do the same thing

6

Viewing Files: cat, less, and head

Reading file contents

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cat - Display File Contents

cat (concatenate) displays the entire contents of a file:

cat notes.txt

less - Paginated Viewing

For longer files, less lets you scroll through page by page:

less /var/log/syslog

Press q to quit, Space for next page, b for previous page.

head and tail - Partial Views

Command	What it does
`head file.txt`	Shows first 10 lines
`head -n 5 file.txt`	Shows first 5 lines
`tail file.txt`	Shows last 10 lines
`tail -n 20 file.txt`	Shows last 20 lines

Try It Yourself!

View your notes file: cat ~/practice/notes.txt
Try viewing a system log: less /var/log/syslog
Press q to exit less
View just the first 5 lines: head -n 5 /var/log/syslog

Quick Check

Which command is best for viewing a very long file?

cat - it shows everything at once head - it shows just the beginning less - it lets you scroll through pages

7

Copying and Moving: cp and mv

Duplicating and relocating files

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cp - Copy Files

The syntax is: cp source destination

cp notes.txt notes_backup.txt

Copying Directories

Use -r (recursive) to copy folders and their contents:

cp -r practice practice_backup

mv - Move or Rename Files

mv moves files. It's also how you rename things!

mv oldname.txt newname.txt

Move to a different location:

mv notes.txt ~/Documents/

Remember:

cp creates a duplicate (original stays)
mv relocates (original is gone from old location)

Try It Yourself!

Go to practice: cd ~/practice
Copy your notes: cp notes.txt notes_copy.txt
Verify: ls
Rename the copy: mv notes_copy.txt backup.txt
Verify again: ls

Quick Check

How do you rename a file using the command line?

Use the rename command Use mv oldname newname Use cp with special flags

8

Deleting Files: rm and rmdir

Removing files and directories (carefully!)

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rm - Remove Files

rm unwanted_file.txt

CRITICAL WARNING! Unlike dragging to the Trash, rm permanently deletes files! There is NO undo, NO recycle bin, NO recovery. The file is GONE forever. Always double-check before pressing Enter!

rmdir - Remove Empty Directories

rmdir only works on empty directories:

rmdir empty_folder

rm -r - Remove Directories with Contents

To delete a folder AND everything inside:

rm -r folder_with_stuff

Safety Options

Command	What it does
`rm -i file.txt`	Interactive - asks for confirmation
`rm -ri folder`	Asks before each file in folder

Never run: rm -rf / or rm -rf ~
These will destroy your entire system or home directory!

Try It Yourself!

Go to practice: cd ~/practice
Create a test file: touch deleteme.txt
Verify: ls
Delete safely: rm -i deleteme.txt (type 'y' to confirm)
Verify it's gone: ls

Quick Check

Why is rm dangerous?

It permanently deletes with no recovery option It's slow and can crash the system It sends files to an insecure location

9

Piping and Chaining Commands

Combining commands for power

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Pipes (|)

The pipe | sends the output of one command as input to another:

ls -la | less

This takes the directory listing and lets you scroll through it.

Useful Text Commands to Pipe

Command	What it does
`wc -l`	Counts lines
`sort`	Sorts alphabetically
`uniq`	Removes duplicate adjacent lines
`grep "text"`	Filters lines containing "text"

Chaining Example

Count unique sorted lines:

cat file.txt | sort | uniq | wc -l

Command Chaining with && and ;

Operator	What it does
`cmd1 && cmd2`	Run cmd2 only if cmd1 succeeds
`cmd1 ; cmd2`	Run cmd2 regardless of cmd1's result

mkdir newproject && cd newproject

Try It Yourself!

Count files in home: ls ~ | wc -l
Find .txt files: ls ~ | grep ".txt"
Chain commands: cd ~/practice && ls

Quick Check

What does the pipe | do?

Runs two commands at the same time Sends output of one command as input to another Creates a new file

10

Superuser Powers: sudo

Running commands as administrator

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What is sudo?

sudo stands for "Superuser Do". It runs a command with administrator privileges.

sudo apt update

This updates the list of available software packages (requires admin rights).

When Do You Need sudo?

Installing or removing software
Modifying system configuration files
Managing services
Accessing protected directories

Installing Software Example

sudo apt install tree

This installs "tree" - a useful program that shows directories as a tree structure.

Security Warning!

Only use sudo when necessary
Never run sudo su (creates unrestricted shell)
Always understand what a command does before running it with sudo
If a website tells you to run a sudo command, verify it's legitimate first!

Getting Help: man

The man command shows the manual for any command:

man ls

Press q to quit the manual.

Try It Yourself!

Update package list: sudo apt update
Enter your password when prompted
Install tree: sudo apt install tree
Use your new command: tree ~/practice
Read a manual: man pwd (press q to exit)

Quick Check

When should you use sudo?

Always, it makes commands run faster Never, it's dangerous Only when necessary, like installing software

What is the Command Line?

A Brief History

Terminal vs Shell

Opening the Terminal in Ubuntu (on your Mac)

Quick Check

Your First Commands: pwd and ls

Where Am I? (pwd)

What's Here? (ls)

Useful ls Options

Try It Yourself!

Quick Check

Moving Around: cd

Changing Directories

Special Shortcuts

Absolute vs Relative Paths

Try It Yourself!

Quick Check

Creating Directories: mkdir

Making Directories

Creating Nested Directories

Try It Yourself!

Quick Check

Creating Files: touch and echo

Creating Empty Files with touch

Creating Files with Content using echo

Redirection Operators

Try It Yourself!

Quick Check

Viewing Files: cat, less, and head

cat - Display File Contents

less - Paginated Viewing

head and tail - Partial Views

Try It Yourself!

Quick Check

Copying and Moving: cp and mv

cp - Copy Files

Copying Directories

mv - Move or Rename Files

Try It Yourself!

Quick Check

Deleting Files: rm and rmdir

rm - Remove Files

rmdir - Remove Empty Directories

rm -r - Remove Directories with Contents

Safety Options

Try It Yourself!

Quick Check

Piping and Chaining Commands

Pipes (|)

Useful Text Commands to Pipe

Chaining Example

Command Chaining with && and ;

Try It Yourself!

Quick Check

Superuser Powers: sudo

What is sudo?

When Do You Need sudo?

Installing Software Example

Getting Help: man

Try It Yourself!

Quick Check

Congratulations!