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RHEL 8 Postfix cannot send mail due to firewall and SELinux policy

🟡 Medium   ⏱ 5–30 min  Last verified: 2 December 2021 📖 ~1 min read Table of contents Symptom & Impact Environment & Reproduction Root Cause Analysis Quick Triage Step-by-Step Diagnosis Solution – Primary Fix Solution – Alternative Approaches Verification & Acceptance Criteria Rollback Plan Prevention & Hardening Related Errors & Cross-Refs References & Further […]

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How to Set Up a LAMP Stack on FreeBSD 13 — step-by-step FreeBSD 13 tutorial on Progressive Robot

How to Set Up a LAMP Stack on FreeBSD 13

Introduction How to Set Up a LAMP Stack on FreeBSD 13 is a core administration task for any FreeBSD 13 server operator. FreeBSD 13 ships with the 15.0-RELEASE kernel, ZFS as the default root filesystem, Capsicum capability sandboxing improvements, and an updated ports tree. Unlike Linux distributions, FreeBSD uses rc(8) for service management, pf for […]

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How to Configure Database Connection Pooling with PgBouncer on RHEL 7 — step-by-step RHEL 7 tutorial on Progressive Robot

How to Configure Database Connection Pooling with PgBouncer on RHEL 7

How to Configure Database Connection Pooling with PgBouncer on RHEL 7 Every PostgreSQL client connection spawns a backend process on the server, consuming approximately 5–10 MB of RAM for its working memory and adding overhead to the process scheduler. Applications that open hundreds of short-lived connections — such as PHP scripts, Node.js workers, or microservices […]

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How to Set Up a Certificate Authority on SLES 15 — step-by-step SUSE Linux Enterprise 15 tutorial on Progressive Robot

How to Set Up a Certificate Authority on SLES 15

Introduction This tutorial covers How to Set Up a Certificate Authority on SLES 15 on SLES 15. SLES 15 (SUSE Linux Enterprise Server 16) is SUSE’s enterprise-grade Linux distribution. It uses the zypper package manager, AppArmor for mandatory access control, and systemctl for service management. Prerequisites Ensure your SLES 15 system is up to date: […]

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How to Configure pf Firewall Rules on FreeBSD 13 — step-by-step FreeBSD 13 tutorial on Progressive Robot

How to Configure pf Firewall Rules on FreeBSD 13

Introduction Deploying configure pf firewall rules on freebsd 13 on a FreeBSD 13 machine differs from Linux in several important ways: packages come from the FreeBSD Ports Collection or the binary pkg repository, services are registered in /etc/rc.conf via sysrc(8), and firewall rules are written in pf.conf(5) syntax. This tutorial stays entirely within the standard […]

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How to Deploy a Flask App with Gunicorn on FreeBSD 13 — step-by-step FreeBSD 13 tutorial on Progressive Robot

How to Deploy a Flask App with Gunicorn on FreeBSD 13

Introduction This guide explains how to Deploy a Flask App with Gunicorn on FreeBSD 13 on FreeBSD 13. FreeBSD uses the pkg(8) binary package manager, rc.conf(5) for service startup configuration, and pf(4) as its primary packet filter. There is no SELinux or AppArmor — instead, FreeBSD provides the MAC (Mandatory Access Control) framework and Capsicum […]

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How to Configure Windows Server 2019 Container Security — step-by-step Windows Server 2019 tutorial on Progressive Robot

How to Configure Windows Server 2019 Container Security

How to Configure Windows Server 2019 Container Security Securing Windows containers on Windows Server 2019 involves hardening the container runtime, securing container images, isolating workloads, controlling network access, and monitoring for anomalous behavior. The default Docker installation is functional but not hardened for production use. This guide covers the key security controls available for Windows […]

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How to Set Up NFS Server on FreeBSD 13 — step-by-step FreeBSD 13 tutorial on Progressive Robot

How to Set Up NFS Server on FreeBSD 13

Introduction How to Set Up NFS Server on FreeBSD 13 is a core administration task for any FreeBSD 13 server operator. FreeBSD 13 ships with the 15.0-RELEASE kernel, ZFS as the default root filesystem, Capsicum capability sandboxing improvements, and an updated ports tree. Unlike Linux distributions, FreeBSD uses rc(8) for service management, pf for packet […]

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How to Configure HAST High-Availability Storage on FreeBSD 13 — step-by-step FreeBSD 13 tutorial on Progressive Robot

How to Configure HAST High-Availability Storage on FreeBSD 13

Introduction How to Configure HAST High-Availability Storage on FreeBSD 13 is a core administration task for any FreeBSD 13 server operator. FreeBSD 13 ships with the 15.0-RELEASE kernel, ZFS as the default root filesystem, Capsicum capability sandboxing improvements, and an updated ports tree. Unlike Linux distributions, FreeBSD uses rc(8) for service management, pf for packet […]

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How to Set Up DirectAccess on Windows Server 2019 — step-by-step Windows Server 2019 tutorial on Progressive Robot

How to Set Up DirectAccess on Windows Server 2019

How to Set Up DirectAccess on Windows Server 2019 DirectAccess provides seamless, always-on VPN-like connectivity for domain-joined Windows clients without requiring the user to manually initiate a VPN connection. Unlike traditional VPN, DirectAccess establishes an encrypted IPv6-over-IPv4 tunnel automatically whenever a managed client device has internet connectivity. This enables remote management, Group Policy application, and […]

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