Debian Terminal Basics

Introduction

The terminal is a powerful interface that allows users to interact with their Debian system through text commands. While graphical user interfaces (GUIs) make many tasks accessible, mastering the terminal unlocks the full potential of your Debian system, offering greater control, efficiency, and the ability to automate tasks.

In this guide, you'll learn the essential terminal concepts and commands that form the foundation of working with Debian Linux. Whether you're a complete beginner or looking to refresh your knowledge, this tutorial will equip you with the skills to navigate, manipulate, and control your Debian system effectively through the command line.

Opening the Terminal

In Debian, there are several ways to access the terminal:

1. Using the Application Menu: Click on Applications → System Tools → Terminal
2. Keyboard Shortcut: Press Ctrl + Alt + T (works in most Debian desktop environments)
3. Right-click on Desktop: Some desktop environments allow you to right-click and select "Open Terminal"

Once opened, you'll see a window with a prompt that typically looks like:

bash

username@hostname:~$

This prompt tells you:

• Your username
• The hostname of your computer
• Your current directory (~ represents your home directory)
• $ indicates you're a regular user (# would indicate root user)

Basic Navigation Commands

Checking Your Current Location

To find out which directory you're currently in:

bash

pwd

Output:

/home/username

The pwd command stands for "print working directory" and shows your current location in the filesystem.

Listing Directory Contents

To see the files and folders in your current directory:

bash

ls

Output:

Documents  Downloads  Music  Pictures  Videos

Add options to see more details:

bash

ls -l

Output:

drwxr-xr-x 2 username username 4096 Mar 10 09:23 Documents
drwxr-xr-x 2 username username 4096 Mar 12 15:42 Downloads
drwxr-xr-x 2 username username 4096 Feb 25 20:11 Music
drwxr-xr-x 2 username username 4096 Mar 01 11:33 Pictures
drwxr-xr-x 2 username username 4096 Feb 20 18:57 Videos

The -l option shows:

• File permissions
• Number of links
• Owner
• Group
• File size
• Last modified date
• File/directory name

To show hidden files (those starting with a dot):

bash

ls -a

Output:

.  ..  .bash_history  .bashrc  .config  Documents  Downloads  Music  Pictures  Videos

Combine options:

bash

ls -la

Changing Directories

To move to another directory:

bash

cd Documents

To move up one level to the parent directory:

bash

cd ..

To return to your home directory from anywhere:

bash

cd

or

bash

cd ~

To navigate to a specific path:

bash

cd /usr/share/doc

To return to the previous directory you were in:

bash

cd -

File and Directory Operations

Creating Directories

To create a new directory:

bash

mkdir projects

To create nested directories (including parent directories if they don't exist):

bash

mkdir -p projects/website/css

Creating Files

To create an empty file:

bash

touch myfile.txt

To create and edit a file in one step:

bash

nano myfile.txt

This opens the nano text editor where you can type content, save with Ctrl+O, and exit with Ctrl+X.

Copying Files and Directories

To copy a file:

bash

cp myfile.txt myfile_backup.txt

To copy a directory with all its contents:

bash

cp -r projects projects_backup

Moving or Renaming Files and Directories

The mv command is used for both moving and renaming:

bash

# To rename a file
mv myfile.txt newname.txt

# To move a file to another directory
mv newname.txt Documents/

# To move and rename at the same time
mv myfile_backup.txt Documents/archived_file.txt

Removing Files and Directories

To delete a file:

bash

rm unwanted_file.txt

To delete an empty directory:

bash

rmdir empty_folder

To delete a directory and all its contents (use with caution!):

bash

rm -r projects_backup

⚠️ Warning: Unlike graphical environments, the terminal doesn't have a trash bin or recycle folder. When you delete something with rm, it's permanently gone!

Viewing File Contents

Displaying Entire File Contents

To display the entire contents of a file:

bash

cat README.txt

Viewing Files Page by Page

For larger files, use less to view content one screen at a time:

bash

less large_logfile.log

Navigation in less:

• Space or Page Down: next page
• b or Page Up: previous page
• /pattern: search for "pattern"
• q: quit

Viewing the Beginning or End of a File

To see the first 10 lines of a file:

bash

head README.txt

To specify number of lines:

bash

head -n 5 README.txt

To see the last 10 lines of a file:

bash

tail README.txt

To continuously watch new content being added to a file (useful for log files):

bash

tail -f /var/log/syslog

Understanding File Permissions

In Debian and all Linux systems, every file and directory has permissions that control who can read, write, or execute them.

When you run ls -l, you'll see something like:

-rw-r--r-- 1 username groupname 2048 Mar 12 14:30 myfile.txt

The first block of characters represents permissions:

• First character: file type (- for regular file, d for directory)
• Next three characters: owner permissions
• Next three characters: group permissions
• Last three characters: other users' permissions

Each set of three characters represents:

• r: read permission
• w: write permission
• x: execute permission (for files) or access permission (for directories)
• -: permission not granted

Changing File Permissions

To modify permissions, use the chmod command:

bash

# Give the owner execute permission
chmod u+x script.sh

# Remove write permission for group and others
chmod go-w myfile.txt

# Set specific permissions (read/write for owner, read for group and others)
chmod 644 myfile.txt

The numeric format (like 644) represents:

• First digit: owner permissions
• Second digit: group permissions
• Third digit: other users' permissions

Each digit is calculated by: read (4) + write (2) + execute (1)

Common permission values:

• 755: rwxr-xr-x (directories, scripts)
• 644: rw-r--r-- (regular files)

Finding Files and Directories

Using the Find Command

To search for files by name:

bash

find /home/username -name "*.txt"

To search for directories:

bash

find /home/username -type d -name "project*"

To find files modified in the last 7 days:

bash

find /home/username -type f -mtime -7

Using grep to Search File Contents

To search for a pattern in a specific file:

bash

grep "error" logfile.txt

Output:

error: failed to connect to database
critical error: system shutdown initiated

To search recursively through all files in a directory:

bash

grep -r "function" /home/username/projects/

To ignore case sensitivity:

bash

grep -i "ERROR" logfile.txt

Command History and Shortcuts

Command History

To view previously executed commands:

bash

history

Output:

1  ls
2  cd Documents
3  pwd
4  ls -la
5  cd ..

To run a command from history by its number:

bash

!3

This would execute pwd from the example above.

To search through command history:

• Press Ctrl+R
• Type part of the command
• Press Enter to execute it or arrows to edit

Useful Keyboard Shortcuts

• Ctrl+C: Interrupt/stop the current command
• Ctrl+Z: Suspend the current command
• Ctrl+D: Exit the current shell
• Ctrl+L: Clear the screen
• Ctrl+A: Move cursor to beginning of line
• Ctrl+E: Move cursor to end of line
• Ctrl+W: Delete the word before the cursor
• Tab: Auto-complete commands, filenames, or directories

Redirecting Input and Output

The terminal allows you to redirect command output to files or use files as input.

Redirecting Output to a File

To save command output to a file (overwrites existing content):

bash

ls -la > directory_listing.txt

To append command output to a file:

bash

echo "New line" >> notes.txt

Redirecting Input from a File

To use a file as input for a command:

bash

sort < unsorted_list.txt

Piping Commands

Pipes (|) connect the output of one command to the input of another:

bash

ls -la | grep "Jan"

This filters the directory listing to show only entries containing "Jan".

Output:

-rw-r--r-- 1 username groupname 1024 Jan 15 10:23 january_report.txt
drwxr-xr-x 2 username username 4096 Jan 30 18:43 January_Photos

Multiple pipes can be chained together:

bash

cat log.txt | grep "error" | sort | uniq

This sequence:

1. Shows the contents of log.txt
2. Filters for lines containing "error"
3. Sorts these lines
4. Removes duplicate lines

Package Management Basics

Debian uses the APT (Advanced Package Tool) system for installing, updating, and removing software.

Updating Package Lists

Before installing new packages, update the package lists:

bash

sudo apt update

Upgrading Installed Packages

To upgrade all installed packages to their latest versions:

bash

sudo apt upgrade

Installing Software

To install a new package:

bash

sudo apt install package_name

Example:

bash

sudo apt install htop

Removing Software

To remove an installed package:

bash

sudo apt remove package_name

To remove the package along with its configuration files:

bash

sudo apt purge package_name

Searching for Packages

To search for available packages:

bash

apt search keyword

Example:

bash

apt search text-editor

System Information Commands

Checking System Resources

To see a dynamic view of system processes:

bash

top

A more user-friendly alternative:

bash

htop

To check disk space usage:

bash

df -h

Output:

Filesystem      Size  Used Avail Use% Mounted on
/dev/sda1        20G   12G  6.8G  64% /
/dev/sda2       100G   23G   77G  24% /home

To check memory usage:

bash

free -h

Output:

              total        used        free      shared  buff/cache   available
Mem:           7.7G        2.1G        3.8G        287M        1.8G        5.1G
Swap:          2.0G          0B        2.0G

Checking System and Kernel Information

To see kernel and OS information:

bash

uname -a

Output:

Linux hostname 5.10.0-21-amd64 #1 SMP Debian 5.10.162-1 (2023-01-21) x86_64 GNU/Linux

To see Debian version information:

bash

lsb_release -a

Output:

No LSB modules are available.
Distributor ID: Debian
Description:    Debian GNU/Linux 11 (bullseye)
Release:        11
Codename:       bullseye

Process Management

Viewing Running Processes

To list all running processes:

bash

ps aux

To filter for specific processes:

bash

ps aux | grep firefox

Killing Processes

To terminate a process by its ID:

bash

kill 1234

To forcefully terminate a stubborn process:

bash

kill -9 1234

To kill a process by name:

bash

killall firefox

Terminal Customization

Bash Configuration Files

The main configuration files for the Bash shell are:

• ~/.bashrc: Contains user-specific Bash settings
• ~/.bash_profile: Executed for login shells
• ~/.bash_history: Contains your command history
• ~/.bash_logout: Executed when exiting a login shell

To apply changes from .bashrc without logging out:

bash

source ~/.bashrc

Creating Aliases

Aliases are shorthand commands you can create for convenience.

Add these to your ~/.bashrc file:

bash

# List aliases
alias ll='ls -la'
alias la='ls -a'

# Navigation aliases
alias documents='cd ~/Documents'
alias downloads='cd ~/Downloads'

# System aliases
alias update='sudo apt update && sudo apt upgrade'

Working with Archives

Creating Archives

To create a tar archive:

bash

tar -cvf archive.tar directory/

To create a compressed archive with gzip:

bash

tar -czvf archive.tar.gz directory/

Extracting Archives

To extract a tar archive:

bash

tar -xvf archive.tar

To extract a compressed archive:

bash

tar -xzvf archive.tar.gz

Connecting to Remote Systems

SSH Remote Login

To connect to a remote Debian server:

bash

ssh username@remote_host

Example:

bash

ssh [email protected]

File Transfer with SCP

To copy a file to a remote system:

bash

scp localfile.txt username@remote_host:/path/to/destination/

To copy a file from a remote system:

bash

scp username@remote_host:/path/to/remotefile.txt local_directory/

Common Terminal Tasks

Network Troubleshooting

To check if a server is reachable:

bash

ping google.com

To trace the route to a server:

bash

traceroute google.com

To view network interfaces and IP addresses:

bash

ip addr

Scheduling Tasks with Cron

To edit your crontab file:

bash

crontab -e

Example entry (run a backup script every day at 2 AM):

0 2 * * * /home/username/scripts/backup.sh

Checking Logs

Most system logs are located in /var/log/. To view the system log:

bash

sudo less /var/log/syslog

To view authentication attempts:

bash

sudo less /var/log/auth.log

Terminal Workflow Diagram

Here's a visual representation of a typical terminal workflow:

Summary

In this guide, you've learned the essential terminal commands and concepts for working with Debian Linux:

• Navigating the file system with commands like pwd, ls, and cd
• Managing files and directories with mkdir, touch, cp, mv, and rm
• Viewing and manipulating file contents using cat, less, head, and tail
• Understanding and changing file permissions with chmod
• Finding files and text patterns using find and grep
• Redirecting input and output with >, >>, and pipes (|)
• Managing packages with APT
• Checking system information and resources
• Managing processes
• Customizing your terminal environment
• Working with archives and remote systems

Mastering these basics will provide a solid foundation for more advanced terminal usage and will make your Debian experience more productive.

Exercises

1. Create a directory structure for a hypothetical web project with folders for HTML, CSS, and JavaScript files.
2. Write a shell command that finds all PNG images in your home directory and copies them to a new "Images" folder.
3. Create a bash alias that shows system information using multiple commands.
4. Write a command to find all text files in your Documents folder containing the word "important".
5. Create a tar.gz archive of your home directory's configuration files (all hidden files).

Additional Resources

• The Debian Administrator's Handbook: Available in the package debian-handbook
• Manual pages: Access with man [command]
• Info pages: More detailed than man pages, access with info [command]
• Built-in help: Most commands support the --help option

Remember, the best way to learn the terminal is through regular practice. Start incorporating these commands into your daily work, and you'll quickly become proficient with the Debian terminal.