Suricata is a high-performance, open-source network threat detection engine that can operate as an Intrusion Detection System (IDS) to alert on suspicious traffic, or as an Intrusion Prevention System (IPS) to actively block it. On RHEL 8, Suricata integrates naturally with firewalld‘s NFQUEUE target for inline packet inspection, and its Lua scripting and Eve JSON […]
Port knocking is a stealthy technique that keeps SSH’s port 22 invisible to network scanners until a client sends a precise sequence of connection attempts to predetermined ports. On RHEL 8, combining knockd with firewalld creates a powerful two-layer defense: the firewall silently drops all traffic on port 22 by default, and only the knock […]
The Linux kernel exposes hundreds of tunable parameters through the /proc/sys virtual filesystem, and sysctl is the tool used to read and write these values persistently. Many default kernel settings prioritize compatibility and functionality over security, leaving attack surface that can be closed with targeted configuration. On RHEL 8, persistent sysctl settings are stored in […]
Pluggable Authentication Modules (PAM) is the authentication framework at the heart of every RHEL 8 login, password change, and session management operation. PAM allows system administrators to configure authentication policies without modifying individual applications — by editing stack files in /etc/pam.d/, you can enforce account lockout after failed attempts, require strong passwords, limit resource usage, […]
AIDE (Advanced Intrusion Detection Environment) is a host-based intrusion detection tool that detects unauthorized changes to files and directories by comparing a live system snapshot against a baseline database. On RHEL 8, AIDE is available directly from the standard repositories and integrates cleanly with systemd for scheduled integrity checks. Detecting modified binaries, configuration files, or […]
Login banners are a critical security control that display legal warnings before and after users authenticate to a system. On RHEL 8, three separate mechanisms control banner messages: /etc/issue for local console pre-login text, /etc/issue.net for SSH pre-login banners, and /etc/motd for the message of the day shown after login. Properly configured banners inform authorized […]
SSL/TLS certificates are the foundation of encrypted communications on the internet, authenticating servers and encrypting data in transit. On RHEL 8, OpenSSL provides a full-featured toolkit for creating your own Certificate Authority, generating server certificates, and managing the entire certificate lifecycle. Understanding this process is essential for securing internal services without relying on external providers. […]
Rootkits are malicious software packages designed to gain persistent, hidden root-level access to a system by replacing or patching critical binaries, kernel modules, or configuration files. Two widely used open-source tools — rkhunter (Rootkit Hunter) and chkrootkit — complement each other by using different detection techniques: signature databases, hash comparisons, and behavioural checks. On RHEL […]
nftables is the modern replacement for iptables, ip6tables, arptables, and ebtables, and it ships in the RHEL 8 kernel by default. It uses a single unified rule language, supports atomic rule set replacement, and performs better at scale due to its netlink-based architecture. While firewalld can use nftables as its backend, many system administrators prefer […]
Although firewalld ships as the default firewall manager on RHEL 8, some administrators prefer the well-known iptables command syntax for its long history, broad documentation, and deterministic rule ordering. RHEL 8 supports running iptables as a standalone service through the iptables-services package, which must be installed after disabling firewalld to avoid conflicts. This tutorial covers […]
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