Linux Server Security Hardening Checklist

1. User Account and Authentication

Disable root login via SSH
Use strong passwords or passphrases
Implement SSH key-based authentication
Set up fail2ban to prevent brute-force attacks
Implement multi-factor authentication (MFA) where possible
Regularly audit user accounts and remove unnecessary ones

2. System Updates and Patch Management

Enable automatic security updates
Regularly check for and install system updates
(Debian/Ubuntu)sudo apt update && sudo apt upgrade (CentOS/RHEL)sudo yum update
Subscribe to security mailing lists for your distribution
Implement a patch management strategy for critical systems

3. Firewall Configuration

Enable and configure a firewall (e.g., UFW, firewalld, or iptables)
Allow only necessary incoming connections
Implement egress filtering to control outgoing traffic
Regularly review and update firewall rules

4. SSH Hardening

Change the default SSH port
Disable SSH protocol 1
Limit SSH access to specific IP addresses or ranges
Set idle timeout interval
Disable empty passwords
Use strong ciphers and MACs

5. File System Security

Use appropriate file permissions
Implement disk encryption for sensitive data
Use a separate partition for /home, /tmp, and /var
Enable and configure SELinux or AppArmor
Regularly scan for and remove unused or obsolete files

6. Network Security

Disable unnecessary network services
Use secure protocols (HTTPS, SFTP, etc.) instead of their insecure counterparts
Implement network segmentation for sensitive systems
Configure and use a VPN for remote access when possible
Implement intrusion detection/prevention systems (IDS/IPS)

7. Logging and Monitoring

Enable and configure system logging
Set up log rotation to manage log files
Implement centralized logging for multiple servers
Use log analysis tools to detect security incidents
Set up alerts for suspicious activities

8. Application Security

Keep all installed applications up-to-date
Remove or disable unnecessary applications and services
Use application sandboxing when possible
Implement web application firewalls (WAF) for web servers
Regularly audit installed packages and remove unused ones

9. Backup and Disaster Recovery

Implement a regular backup strategy
Store backups securely, preferably off-site
Regularly test backup restoration processes
Create and maintain an incident response plan
Document recovery procedures for critical systems

10. Regular Security Audits

Conduct regular vulnerability scans
Perform penetration testing periodically
Review and update security policies regularly
Stay informed about new security threats and vulnerabilities
Conduct security awareness training for system administrators

Note: This checklist provides a foundation for Linux server security.
However, security is an ongoing process, and you should continually assess and improve your security measures.
Always refer to the latest security best practices and your organization's specific security requirements.