Linux Server Security Hardening: 5 Essential Tasks for Beginners

This article addresses Linux server security issues and summarizes 5 simple hardening steps for beginners: 1. **System Update and Patch Management**: Regularly update system packages (use `apt update` + `upgrade` + `autoremove` for Ubuntu/Debian, and `yum`/`dnf update` for CentOS) to fix known vulnerabilities. 2. **Strengthen User Permissions and Authentication**: Disable direct root login, create regular users with sudo privileges, and recommend SSH key-based login (generate key pairs locally and upload public keys to the server). 3. **Configure Firewall**: Only open necessary ports (e.g., SSH, HTTP/HTTPS). For Ubuntu, use `ufw` (enable and allow specified services); for CentOS, use `firewalld` (reload after opening ports), with default rejection of other connections. 4. **Close Unnecessary Services and Ports**: Disable insecure services like FTP and Telnet. Check open ports with `ss -tuln` and remove non-business-essential ports/services. 5. **Log Auditing and Monitoring**: Monitor critical logs such as `/var/log/auth.log` and use `tail -f` for real-time login attempt tracking. Install `fail2ban` to automatically ban repeatedly failed IPs.