A private Certificate Authority (CA) lets you issue and manage TLS certificates for internal services without paying a public CA for every certificate. On RHEL 9, OpenSSL provides all the tools needed to build a two-tier CA hierarchy: a root CA (kept offline and highly protected) and an intermediate CA (used for day-to-day signing). This […]
SELinux (Security-Enhanced Linux) enforces Mandatory Access Control (MAC) on RHEL 9, confining processes to only the resources they are explicitly permitted to access regardless of traditional Unix file permissions. While RHEL ships with comprehensive base policies, custom applications often generate AVC (Access Vector Cache) denials because their access patterns are not covered by existing policy […]
HashiCorp Vault is an open-source secrets management platform that provides secure storage, access control, and auditing for sensitive data such as API keys, passwords, certificates, and encryption keys. Instead of hardcoding secrets in application configs or environment variables, applications request them from Vault at runtime using short-lived tokens or AppRole credentials. This tutorial covers installing […]
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 […]
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