Why Linux Server Security Matters

A Linux server is powerful and flexible, but without proper security measures, it can be vulnerable to cyberattacks, data breaches, and unauthorized access.

With 2025 approaching, new security threats require updated best practices to protect your server.

1. Firewall Configuration: Your First Line of Defense

A firewall controls incoming and outgoing traffic, blocking unauthorized connections.

✅ Set Up UFW (Ubuntu/Debian)

sudo apt install ufw -y
sudo ufw default deny incoming
sudo ufw default allow outgoing
sudo ufw allow 22/tcp   # SSH
sudo ufw allow 80/tcp   # HTTP
sudo ufw allow 443/tcp  # HTTPS
sudo ufw enable
        

✅ Set Up firewalld (CentOS/RHEL)

sudo yum install firewalld -y
sudo systemctl enable --now firewalld
sudo firewall-cmd --permanent --add-service=ssh
sudo firewall-cmd --permanent --add-service=http
sudo firewall-cmd --permanent --add-service=https
sudo firewall-cmd --reload
        

2. Secure SSH: Prevent Unauthorized Access

✅ Change the Default SSH Port

sudo nano /etc/ssh/sshd_config
# Change from:
Port 22
# To a custom port:
Port 2222
sudo systemctl restart sshd
        

✅ Disable Root Login

sudo nano /etc/ssh/sshd_config
# Change:
PermitRootLogin no
sudo systemctl restart sshd
        

✅ Use SSH Key Authentication

ssh-keygen -t rsa -b 4096
ssh-copy-id user@your_server_ip
sudo nano /etc/ssh/sshd_config
PasswordAuthentication no
sudo systemctl restart sshd
        

3. File Permissions & Access Control

Restrict who can access files to minimize risks.

✅ Set Correct File & Directory Permissions

sudo find /var/www -type f -exec chmod 644 {} ;
sudo find /var/www -type d -exec chmod 755 {} ;
        

✅ Restrict Access to Sensitive Files

chmod 600 /etc/ssh/sshd_config
chmod 600 ~/.ssh/authorized_keys
        

4. Prevent Brute-Force Attacks with Fail2Ban

Fail2Ban blocks IPs after multiple failed login attempts.

✅ Install & Configure Fail2Ban

# Ubuntu/Debian
sudo apt install fail2ban -y
# CentOS/RHEL
sudo yum install fail2ban -y
        

✅ Enable SSH Protection

sudo nano /etc/fail2ban/jail.local
# Add:
[sshd]
enabled = true
port = 2222
bantime = 86400
findtime = 600
maxretry = 3
sudo systemctl restart fail2ban
        

️ 5. Enforce Mandatory Security Policies with SELinux & AppArmor

✅ Enable SELinux (CentOS/RHEL)

sudo setenforce 1
sestatus
# To enable permanently:
sudo nano /etc/selinux/config
SELINUX=enforcing
sudo reboot
        

✅ Enable AppArmor (Ubuntu/Debian)

sudo apt install apparmor apparmor-profiles -y
sudo systemctl enable --now apparmor
        

Additional Security Tips

✅ Disable Unused Services

sudo systemctl list-units --type=service
sudo systemctl disable cups
        

✅ Enable Automatic Security Updates

# Ubuntu/Debian
sudo apt install unattended-upgrades -y
sudo dpkg-reconfigure unattended-upgrades
# CentOS/RHEL
sudo yum install yum-cron -y
sudo systemctl enable --now yum-cron
        

✅ Monitor Your Server Logs

sudo journalctl -xe
sudo tail -f /var/log/auth.log  # (Debian/Ubuntu)
sudo tail -f /var/log/secure    # (CentOS/RHEL)
        

Conclusion: Keep Your Linux Server Secure in 2025

By following these best practices, you can significantly improve your Linux server’s security.

Key Takeaways:

• ✅ Set up a firewall (UFW, firewalld)
• ✅ Secure SSH (disable root login, use key-based authentication)
• ✅ Restrict file permissions (600 for sensitive files, 755 for directories)
• ✅ Use Fail2Ban (prevent brute-force attacks)
• ✅ Enforce security policies (SELinux/AppArmor)

By staying proactive, you can ensure your Linux server remains safe and resilient against cyber threats in 2025!