Debian Server Introduction

What is Debian?

Debian is one of the oldest and most respected Linux distributions available. First released in 1993, it has built a strong reputation for stability, security, and an extensive software ecosystem. Debian serves as the foundation for many other popular distributions, including Ubuntu.

When we talk about a "Debian server," we're referring to a computer running the Debian operating system that's configured to provide services to other computers or users over a network.

Why Choose Debian for Servers?

Debian offers several advantages that make it an excellent choice for server environments:

• Stability: Debian's "stable" release undergoes extensive testing before release, resulting in a highly reliable system.
• Security: The Debian security team provides timely updates for security vulnerabilities.
• Package Management: The APT (Advanced Package Tool) system makes software installation and updates straightforward.
• Longevity: Each stable release is supported for approximately 5 years.
• Community Support: Being one of the oldest Linux distributions, Debian has a vast community and extensive documentation.
• Free and Open Source: Debian is committed to free software principles.

Debian Release Cycles

Debian uses a tiered release system with three main branches:

• Stable: Recommended for production servers (currently "Bookworm" or Debian 12)
• Testing: The next version being prepared for stable release
• Unstable: Cutting-edge packages, not recommended for servers

For servers, you should always use the Stable branch to ensure reliability and security.

Getting Started with Debian Server

System Requirements

Debian has modest hardware requirements, making it suitable for various server applications:

• Minimum: 512MB RAM, 10GB disk space, 1GHz processor
• Recommended: 1GB+ RAM, 20GB+ disk space, dual-core processor

Requirements will vary based on the services you plan to run.

Installation Basics

The Debian installation process is straightforward:

1. Download the Debian installer from debian.org
2. Create a bootable USB drive or DVD
3. Boot from the installation media
4. Follow the step-by-step installer

For servers, the "netinst" (network installer) image is recommended as it downloads the latest packages during installation.

Here's what the basic installation process looks like:

First Steps After Installation

Once you've installed Debian, there are several important steps to take:

1. Update your system

bash

sudo apt update
sudo apt upgrade

2. Secure SSH access (if using remote access)

bash

sudo nano /etc/ssh/sshd_config

Change the default SSH port, disable root login, and use key-based authentication:

Port 2222
PermitRootLogin no
PasswordAuthentication no

After editing, restart the SSH service:

bash

sudo systemctl restart sshd

3. Install a firewall

bash

sudo apt install ufw
sudo ufw allow 2222/tcp  # Allow your custom SSH port
sudo ufw enable

4. Set up automatic security updates

bash

sudo apt install unattended-upgrades
sudo dpkg-reconfigure unattended-upgrades

Basic Server Administration

Package Management

Debian's package management system is one of its strongest features:

• apt: The recommended command-line tool for package management
• apt-get: A more traditional alternative
• dpkg: The underlying package management system

Common package commands:

bash

# Search for a package
apt search apache2

# Install a package
sudo apt install apache2

# Remove a package
sudo apt remove apache2

# Update package lists
sudo apt update

# Upgrade installed packages
sudo apt upgrade

# Show package information
apt show apache2

Service Management with systemd

Debian uses systemd to manage services. Here are the basic commands:

bash

# Start a service
sudo systemctl start apache2

# Stop a service
sudo systemctl stop apache2

# Restart a service
sudo systemctl restart apache2

# Enable a service to start at boot
sudo systemctl enable apache2

# Disable a service from starting at boot
sudo systemctl disable apache2

# Check service status
sudo systemctl status apache2

Example output of a status command:

● apache2.service - The Apache HTTP Server
     Loaded: loaded (/lib/systemd/system/apache2.service; enabled; vendor preset: enabled)
     Active: active (running) since Mon 2023-09-25 15:30:42 UTC; 2h 12min ago
       Docs: https://httpd.apache.org/docs/2.4/
   Main PID: 1234 (apache2)
      Tasks: 55 (limit: 1132)
     Memory: 26.9M
        CPU: 652ms
     CGroup: /system.slice/apache2.service
             ├─1234 /usr/sbin/apache2 -k start
             ├─1235 /usr/sbin/apache2 -k start
             └─1236 /usr/sbin/apache2 -k start

User Management

Managing users is a fundamental aspect of server administration:

bash

# Add a new user
sudo adduser username

# Add user to a group
sudo usermod -aG sudo username

# Change user password
sudo passwd username

# Delete a user
sudo deluser username

# List all users
cut -d: -f1 /etc/passwd

File Permissions

Understanding file permissions is crucial for server security:

bash

# Change file owner
sudo chown username:groupname file.txt

# Change file permissions
sudo chmod 755 file.txt

# Set permissions recursively
sudo chmod -R 755 directory/

Permission bits explained:

• 4: Read permission
• 2: Write permission
• 1: Execute permission
• Common combinations:
  • 755 (rwxr-xr-x): Owner can read, write, execute; group and others can read and execute
  • 644 (rw-r--r--): Owner can read and write; group and others can only read
  • 700 (rwx------): Owner can read, write, execute; no access for group and others

Common Server Configurations

Web Server (Apache)

bash

# Install Apache
sudo apt install apache2

# Check status
sudo systemctl status apache2

# Basic configuration file
sudo nano /etc/apache2/apache2.conf

# Site-specific configuration
sudo nano /etc/apache2/sites-available/000-default.conf

# Enable a site
sudo a2ensite site-name

# Enable a module
sudo a2enmod rewrite

# Test configuration
sudo apache2ctl configtest

# Restart after changes
sudo systemctl restart apache2

Database Server (MariaDB/MySQL)

bash

# Install MariaDB
sudo apt install mariadb-server

# Secure the installation
sudo mysql_secure_installation

# Access MySQL shell
sudo mysql

Basic MySQL commands:

sql

-- Create a database
CREATE DATABASE mywebsite;

-- Create a user
CREATE USER 'webuser'@'localhost' IDENTIFIED BY 'password';

-- Grant privileges
GRANT ALL PRIVILEGES ON mywebsite.* TO 'webuser'@'localhost';

-- Apply privileges
FLUSH PRIVILEGES;

-- Exit
EXIT;

SSH Server

bash

# Install SSH server if not already installed
sudo apt install openssh-server

# Secure configuration
sudo nano /etc/ssh/sshd_config

# Restart SSH after configuration changes
sudo systemctl restart sshd

Monitoring and Maintenance

Regular maintenance is essential for a healthy server:

bash

# Check disk usage
df -h

# Check memory usage
free -m

# Check running processes
top

# View system logs
sudo journalctl -xe

# Check load average
uptime

# Update and upgrade
sudo apt update && sudo apt upgrade -y

Basic Backup Strategy

Implement a simple backup strategy:

bash

# Install rsync
sudo apt install rsync

# Create a backup script
sudo nano /usr/local/bin/backup.sh

Example backup script:

bash

#!/bin/bash
# Simple backup script

# Set variables
BACKUP_DIR="/backup"
SOURCE_DIR="/var/www"
DATE=$(date +%Y-%m-%d)

# Create backup directory if it doesn't exist
mkdir -p $BACKUP_DIR

# Create the backup using rsync
rsync -avh --delete $SOURCE_DIR $BACKUP_DIR/www-$DATE

# Keep only the last 7 backups
find $BACKUP_DIR -type d -name "www-*" | sort | head -n -7 | xargs rm -rf

Make the script executable:

bash

sudo chmod +x /usr/local/bin/backup.sh

Schedule with cron:

bash

sudo crontab -e

Add this line to run the backup daily at 2 AM:

0 2 * * * /usr/local/bin/backup.sh

Troubleshooting Common Issues

Service Won't Start

Check these common issues:

1. Configuration errors:

bash

sudo systemctl status service-name

2. Log files:

bash

sudo journalctl -u service-name

3. File permission problems:

bash

sudo ls -la /path/to/service/directory

System Running Slowly

Investigate with these tools:

bash

# Check CPU and memory usage
htop

# Check disk I/O
sudo apt install iotop
sudo iotop

# Find large files
sudo find / -type f -size +100M -exec ls -lh {} \;

# Check for running processes consuming resources
ps aux | sort -rk 3,3 | head -n 10

Summary

Debian serves as an excellent platform for servers due to its stability, security, and extensive package ecosystem. In this introduction, we've covered:

• Why Debian is ideal for server environments
• Basic installation and initial setup
• Essential administration tasks including package, service, and user management
• Common server applications like web and database servers
• Monitoring, maintenance, and basic troubleshooting

As you continue your journey with Debian servers, you'll discover its flexibility and power for handling a wide range of server applications.

Exercises

1. Install Debian in a virtual machine using the netinst installer.
2. Configure SSH for secure remote access with key-based authentication.
3. Set up a basic web server using Apache and create a simple HTML page.
4. Install and secure MariaDB, creating a database and user.
5. Create a backup script that archives a specific directory and schedule it with cron.

Additional Resources

• Debian Administrator's Handbook
• Debian Wiki
• Linux Command Library
• Debian Security Information
• The Debian Reference