Suricata is a high-performance, open-source network intrusion detection and prevention system (IDS/IPS) that inspects traffic in real time against a rule set to identify threats, policy violations, and malicious activity. On RHEL 9, Suricata integrates cleanly with systemd and can run in passive IDS mode (logging alerts without blocking) or active IPS mode (dropping malicious […]
Port knocking is a security technique that hides your SSH port from network scanners by keeping it firewalled until a specific sequence of connection attempts is made. On RHEL 9, combining knockd with nftables lets you expose SSH only to clients who know the secret knock sequence, dramatically reducing brute-force exposure. This tutorial walks through […]
The Linux kernel exposes hundreds of tunable parameters through the sysctl interface that control network behavior, memory protection, and file system security. Many of these defaults prioritize compatibility over security. By writing a hardening configuration to /etc/sysctl.d/, you can reduce the kernel attack surface, enable mitigations against common network attacks, and enforce memory safety features […]
PAM (Pluggable Authentication Modules) is the framework that sits between Linux applications and the underlying authentication mechanisms. Almost every program that authenticates users on RHEL 9 — SSH, su, sudo, login, and graphical sessions — goes through PAM. By configuring PAM you can enforce password complexity requirements, lock accounts after failed login attempts, set resource […]
AIDE (Advanced Intrusion Detection Environment) is an open-source file integrity monitoring tool that detects unauthorized changes to files on a Linux system. It creates a cryptographic baseline database of your file system and compares the current state against that baseline on every check, alerting you to any additions, deletions, or modifications. AIDE is recommended by […]
Login banners and warning messages are a simple but legally important security control on Linux systems. Before users authenticate, a visible warning that unauthorized access is prohibited can be critical for legal enforcement action if a system is breached. After login, a message of the day can display system status information relevant to administrators. Many […]
OpenSSL is the most widely used toolkit for working with SSL/TLS certificates on Linux systems. On RHEL 9, it provides everything you need to generate private keys, create certificate signing requests (CSRs), sign certificates using your own certificate authority, and convert between certificate formats. Understanding OpenSSL is essential for any sysadmin managing secure services. This […]
Rootkits are among the most dangerous forms of malware — they conceal themselves and other malicious software deep within the operating system, often modifying system binaries and kernel modules to hide their presence from standard tools. Detecting rootkits requires specialised scanners that check for known signatures, hidden files, suspicious processes, and tampered system binaries. This […]
nftables is the modern successor to iptables and is the default firewall framework in RHEL 9. It replaces iptables, ip6tables, arptables, and ebtables with a single unified tool, offering better performance through an improved kernel path, atomic rule replacement, and a cleaner, more readable configuration syntax. This tutorial covers everything you need to know to […]
iptables has been the standard Linux packet-filtering firewall for over two decades, and while RHEL 9 ships with nftables and firewalld as the preferred tools, iptables remains available and is widely understood by seasoned administrators. Learning iptables gives you deep insight into how Linux netfilter works and is valuable for managing legacy systems or containers […]
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