Kevin's Docs

Appearance

Ubuntu — Configuration and Hardening Guide ​

Complete guide to configure, secure and administer an Ubuntu server.

Overview ​

Ubuntu is one of the most popular Linux distributions for servers. This documentation covers essential configurations to deploy and harden an Ubuntu server for production.

Whether you deploy on a VPS, a dedicated server, or in the cloud, the first hours after provisioning are critical to establish a secure baseline.

Prerequisites ​

  • Root or sudo access to an Ubuntu server (22.04 LTS or later)
  • Working SSH connection
  • Basic Linux command-line knowledge

System Configuration ​

Keyboard Layout ​

bash
# Launch the keyboard configuration wizard
sudo dpkg-reconfigure keyboard-configuration

# Restart the service
sudo service keyboard-setup restart

# Configure system locales
sudo dpkg-reconfigure locales

System Update ​

bash
# Update available package lists
sudo apt update

# Upgrade all installed packages
sudo apt upgrade -y

# Clean up obsolete packages
sudo apt autoremove -y

For a full upgrade including new kernels:

bash
sudo apt update
sudo apt full-upgrade -y
sudo apt autoremove -y
sudo apt autoclean
sudo reboot

Warning: A reboot can temporarily interrupt services. Plan this during a maintenance window.

Password Management ​

bash
# Change the current account password
passwd

# Change another user's password (root required)
sudo passwd username

User Management ​

Principle of Least Privilege ​

Using root directly is dangerous. Create a user with limited sudo privileges instead.

Create a New User ​

bash
# Create a user with a home directory
sudo adduser username

# Alternative with full options
sudo useradd -m -s /bin/bash -G sudo username

Grant Sudo Privileges ​

bash
# Add the user to the sudo group
sudo usermod -aG sudo username

# Verify group membership
groups username

Disable Root SSH Login ​

Once the sudo user is created and tested:

bash
# Edit SSH configuration
sudo nano /etc/ssh/sshd_config

# Add or modify this line
# PermitRootLogin no

# Restart SSH
sudo systemctl restart ssh

SSH Hardening ​

SSH is the main access vector to your server. Hardening it is critical to prevent intrusions.

Changing the SSH Port ​

Benefits:

  • Reduces automated scan noise (bots)
  • Limits attack surface
  • Cleaner logs (fewer intrusion attempts)

Important: Changing the SSH port is not sufficient protection by itself. It's an additional defense layer, not a replacement for strong authentication (SSH keys) and a firewall.

Configuration for Ubuntu 23.04+ ​

Ubuntu 23.04+ uses systemd socket activation for SSH:

bash
# Check if ssh.socket is used
systemctl status ssh.socket

# Open the socket configuration
sudo nano /lib/systemd/system/ssh.socket
ini
# /lib/systemd/system/ssh.socket
[Socket]
ListenStream=49152
Accept=no

Port choice: Ports 49152–65535 are dynamic/private ports rarely used by other services.

bash
# Reload systemd
sudo systemctl daemon-reload
sudo systemctl restart ssh.service
sudo systemctl status ssh.service

# Verify the new listening port
sudo ss -tlnp | grep ssh

Configure the Firewall ​

Before closing your current session, allow the new port:

bash
sudo ufw allow 49152/tcp
sudo ufw delete allow 22/tcp
sudo ufw enable
sudo ufw status numbered

CRITICAL: Never close your current SSH session before verifying you can connect on the new port in a second session.

Test Connection ​

bash
# In a NEW terminal
ssh username@server_ip -p 49152

Additional SSH Configuration ​

bash
# /etc/ssh/sshd_config

# Disable root login
PermitRootLogin no

# Key-based authentication only
PubkeyAuthentication yes
PasswordAuthentication no
PermitEmptyPasswords no

# Disable challenge-response authentication
ChallengeResponseAuthentication no

# Restrict allowed users
AllowUsers username other_user

# Connection timeouts
LoginGraceTime 30
ClientAliveInterval 300
ClientAliveCountMax 2

# Disable X11 forwarding
X11Forwarding no

# Enforce SSH protocol version 2
Protocol 2

# Limit authentication attempts
MaxAuthTries 3
MaxSessions 10
bash
# Test configuration before restarting
sudo sshd -t

# If no errors, restart
sudo systemctl restart ssh

Security Best Practices ​

  • Update regularly: sudo apt update && sudo apt upgrade at least weekly
  • Use a firewall: UFW or iptables to control inbound/outbound traffic
  • Install Fail2Ban: Automatically ban IPs with repeated failed attempts
  • Enable unattended upgrades: For security patches
  • Monitor logs: /var/log/auth.log for login attempts
  • Back up regularly: Automate backups with cron and rsync

Install Fail2Ban ​

bash
sudo apt install fail2ban -y
sudo cp /etc/fail2ban/jail.conf /etc/fail2ban/jail.local
sudo nano /etc/fail2ban/jail.local
ini
# /etc/fail2ban/jail.local
[sshd]
enabled = true
port = 49152
filter = sshd
logpath = /var/log/auth.log
maxretry = 3
bantime = 3600
findtime = 600
bash
sudo systemctl restart fail2ban
sudo fail2ban-client status sshd

Monitoring and Maintenance ​

Monitor SSH Connections ​

bash
# Show recent successful logins
last -a

# Show recent failed login attempts
sudo grep "Failed password" /var/log/auth.log | tail -n 20

# Active SSH sessions
who

# Real-time SSH log monitoring
sudo tail -f /var/log/auth.log

Automatic Updates ​

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

Post-Installation Checklist ​

  • System updated (apt update && apt upgrade)
  • Keyboard and locales configured
  • Sudo user created and tested
  • Root SSH login disabled
  • SSH port changed and tested
  • SSH key-based authentication configured
  • Password authentication for SSH disabled
  • UFW firewall configured and active
  • Fail2Ban installed and configured
  • Unattended upgrades enabled
  • Backups configured

Resources ​