File and Directory Navigation Commands

1. pwd (Print Working Directory)

Shows your current location in the file system.

pwd

# Output: /home/username

2. ls (List Directory Contents)

Displays files and folders in the current directory.

ls                    # Basic listing

ls -l                 # Long format with details

ls -la                # Include hidden files

ls -lh                # Human-readable file sizes

3. cd (Change Directory)

Navigate between directories.

cd /home/username     # Go to specific directory

cd ..                 # Go up one directory

cd ~                  # Go to home directory

cd -                  # Go to previous directory

4. mkdir (Make Directory)

Create new directories.

mkdir new_folder      # Create single directory

mkdir -p path/to/new/folder  # Create nested directories

5. rmdir (Remove Directory)

Delete empty directories.

rmdir empty_folder    # Remove empty directory

File Operations Commands

6. touch (Create Empty File)

Create new empty files or update timestamps.

touch newfile.txt     # Create new file

touch file1.txt file2.txt  # Create multiple files

7. cp (Copy Files)

Copy files and directories.

cp file1.txt file2.txt        # Copy file

cp -r folder1 folder2         # Copy directory recursively

cp file.txt /path/to/destination/  # Copy to specific location

8. mv (Move/Rename Files)

Move or rename files and directories.

mv oldname.txt newname.txt    # Rename file

mv file.txt /new/location/    # Move file

mv folder1 folder2            # Rename/move directory

9. rm (Remove Files)

Delete files and directories.

rm file.txt           # Delete file

rm -r folder          # Delete directory recursively

rm -f file.txt        # Force delete without confirmation

rm -rf folder         # Force delete directory (use carefully!)

File Content Commands

10. cat (Display File Content)

Show entire file contents.

cat filename.txt      # Display file content

cat file1.txt file2.txt  # Display multiple files

11. less (View File Content Page by Page)

View large files with scrolling capability.

less largefile.txt    # Navigate with arrow keys, q to quit

12. head (Show First Lines)

Display the beginning of a file.

head filename.txt     # Show first 10 lines

head -n 5 filename.txt  # Show first 5 lines

13. tail (Show Last Lines)

Display the end of a file.

tail filename.txt     # Show last 10 lines

tail -f logfile.txt   # Follow file updates in real-time

14. grep (Search Text)

Search for patterns in files.

grep "search_term" filename.txt     # Find text in file

grep -r "search_term" /directory/   # Search recursively

grep -i "search_term" filename.txt  # Case-insensitive search

File Permissions and Ownership

15. chmod (Change File Permissions)

Modify file and directory permissions.

chmod 755 filename    # Set specific permissions

chmod +x script.sh    # Make file executable

chmod -w filename     # Remove write permission

16. chown (Change File Ownership)

Change file and directory ownership.

sudo chown user:group filename     # Change owner and group

sudo chown -R user:group folder/   # Change recursively

System Information Commands

17. whoami (Current User)

Display current username.

whoami

# Output: your_username

18. id (User Information)

Show user and group IDs.

id                    # Current user info

id username           # Specific user info

19. uname (System Information)

Display system information.

uname -a              # All system information

uname -r              # Kernel version

20. df (Disk Space Usage)

Show disk space usage.

df -h                 # Human-readable disk usage

df -i                 # Show inode usage

21. du (Directory Usage)

Display directory size information.

du -sh folder/        # Show directory size

du -h --max-depth=1   # Show subdirectory sizes

22. free (Memory Usage)

Display memory usage information.

free -h               # Human-readable memory info

Process Management Commands

23. ps (Process Status)

Show running processes.

ps aux                # All running processes

ps -ef                # Full process information

24. top (Real-time Process Monitor)

Display real-time system processes.

top                   # Interactive process monitor

htop                  # Enhanced version (if installed)

25. kill (Terminate Processes)

Stop running processes.

kill PID              # Kill process by ID

killall firefox       # Kill all instances of program

kill -9 PID           # Force kill process

Network Commands

26. ping (Test Network Connectivity)

Test network connections.

ping google.com       # Test connection to website

ping -c 4 google.com  # Ping 4 times only

27. wget (Download Files)

Download files from the internet.

wget https://example.com/file.zip    # Download file

wget -c https://example.com/file.zip # Resume interrupted download

28. curl (Transfer Data)

Transfer data to/from servers.

curl https://api.example.com         # Get webpage/API data

curl -O https://example.com/file.zip # Download file

Package Management Commands

29. apt update (Update Package Lists)

Update the package repository information.

sudo apt update       # Update package lists

30. apt upgrade (Upgrade Packages)

Upgrade installed packages.

sudo apt upgrade      # Upgrade all packages

sudo apt upgrade package_name  # Upgrade specific package

31. apt install (Install Packages)

Install new software packages.

sudo apt install package_name        # Install package

sudo apt install package1 package2   # Install multiple packages

32. apt remove (Remove Packages)

Remove installed packages.

sudo apt remove package_name         # Remove package

sudo apt autoremove                  # Remove unnecessary packages

Text Processing Commands

33. sort (Sort Lines)

Sort lines in text files.

sort filename.txt     # Sort alphabetically

sort -n numbers.txt   # Sort numerically

sort -r filename.txt  # Reverse sort

34. wc (Word Count)

Count lines, words, and characters.

wc filename.txt       # Lines, words, characters

wc -l filename.txt    # Count lines only

wc -w filename.txt    # Count words only

35. cut (Extract Columns)

Extract specific columns from text.

cut -d',' -f1,3 data.csv    # Extract columns 1 and 3 from CSV

cut -c1-10 filename.txt     # Extract characters 1-10

Archive and Compression Commands

36. tar (Archive Files)

Create and extract tar archives.

tar -cvf archive.tar folder/         # Create tar archive

tar -xvf archive.tar                 # Extract tar archive

tar -czvf archive.tar.gz folder/     # Create compressed archive

tar -xzvf archive.tar.gz             # Extract compressed archive

37. zip (Create ZIP Archives)

Create ZIP compressed archives.

zip -r archive.zip folder/           # Create ZIP archive

zip archive.zip file1.txt file2.txt # Add specific files

38. unzip (Extract ZIP Archives)

Extract ZIP archives.

unzip archive.zip                    # Extract ZIP file

unzip -l archive.zip                 # List contents without extracting

System Control Commands

39. sudo (Run as Administrator)

Execute commands with administrative privileges.

sudo command          # Run command as root

sudo -u username command  # Run command as specific user

40. history (Command History)

Show previously executed commands.

history               # Show all command history

history 10            # Show last 10 commands

!123                  # Execute command number 123

Helpful Command Tips

Command Combinations

You can combine commands using pipes (|) and redirections:

ls -la | grep "txt"              # List only .txt files

cat file.txt | sort | uniq       # Sort file and remove duplicates

ps aux | grep firefox            # Find Firefox processes

Command Shortcuts

• Tab: Auto-complete commands and filenames
• Ctrl + C: Cancel current command
• Ctrl + L: Clear terminal screen
• Ctrl + R: Search command history
• !!: Repeat last command

Getting Help

Every Ubuntu command comes with built-in help:

man command_name      # Open manual page

command_name --help   # Show quick help

info command_name     # Show detailed information

Best Practices for Ubuntu Command Usage

1. Always backup important data before running destructive commands like rm -rf
2. Use tab completion to avoid typos and save time
3. Read command output carefully before proceeding with potentially harmful operations
4. Practice in a safe environment when learning new commands
5. Keep your system updated with regular apt update && apt upgrade

Common Ubuntu Command Mistakes to Avoid

• Running rm -rf / (deletes everything)
• Using sudo unnecessarily for regular file operations
• Not checking current directory before running commands
• Forgetting to backup before major system changes
• Ignoring error messages and warnings