Linux Server Security Best Practices

1. User Management and Authentication

Use strong passwords and implement password policies
Disable root login and use sudo for administrative tasks
Implement SSH key-based authentication
Use PAM (Pluggable Authentication Modules) for advanced authentication
Regularly audit user accounts and remove unnecessary ones

2. Network Security

Configure and enable a firewall (e.g., UFW or firewalld)
Close unused ports and limit open ports to necessary services
Use fail2ban to prevent brute-force attacks
Implement intrusion detection/prevention systems (IDS/IPS)
Use VPN for remote access when possible

3. SSH Hardening

Change the default SSH port
Disable password authentication (use key-based authentication)
Limit SSH access to specific IP addresses or ranges
Use SSH protocol version 2
Configure SSH idle timeout

Important: Always keep a backup method of access when making SSH changes!

4. System Updates and Patch Management

Regularly update the system and installed packages
Enable automatic security updates
Monitor security announcements for your distribution
Implement a patch management strategy for critical systems

5. File System Security

Use appropriate file permissions and ownership
Implement disk encryption for sensitive data
Use access control lists (ACLs) for fine-grained permissions
Regularly scan for and remove unused or outdated files
Disable unnecessary SUID/SGID binaries

6. Service Hardening

Disable or remove unnecessary services
Configure services to run with least privileges
Use chroot jails or containers to isolate services
Implement proper logging for all critical services

7. Monitoring and Logging

Configure centralized logging
Regularly review system and application logs
Use log analysis tools (e.g., logwatch, fail2ban)
Implement integrity checking tools (e.g., AIDE)
Set up alerts for suspicious activities

8. Backup and Disaster Recovery

Implement regular backups of critical data
Test backup restoration processes
Store backups securely, preferably off-site
Develop and maintain a disaster recovery plan

9. Application Security

Keep all installed applications up-to-date
Use application firewalls when appropriate
Implement proper input validation in custom applications
Use secure protocols (HTTPS, SFTP) instead of their insecure counterparts

10. Security Auditing and Compliance

Regularly perform security audits
Use security scanning tools (e.g., Nmap, OpenVAS)
Implement and follow security policies and procedures
Stay informed about relevant compliance requirements (e.g., GDPR, HIPAA)

Remember: Security is an ongoing process. Regularly review and update your security measures to protect against new threats and vulnerabilities.