Firewall

Common Problems 115119

RHEL 8 – Cockpit Web Console Unavailable After Hardening Change

🟡 Medium   ⏱ 5–30 min  Last verified: 20 May 2026 📖 ~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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Common Problems 116123

Certbot Renewal Fails on Ubuntu 26.04 LTS

🟠 High   ⏱ 5–30 min  Last verified: 20 May 2026 Affected versions: 26.04 📖 ~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 […]

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Common Problems 115109

RHEL 8 – Postfix Mail Queue Stalls from DNS Resolver Problems

🟡 Medium   ⏱ 5–30 min  Last verified: 20 May 2026 📖 ~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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Common Problems 121681

Debian 9 – Fail2ban Not Banning with nftables Backend – Jail Action Fix

🟡 Medium   ⏱ 5–30 min  Last verified: 20 May 2026 Affected versions: Debian 9 📖 ~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 & […]

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Common Problems 120172

Debian 12 – Fail2ban Not Banning with nftables Backend – Jail Action Fix

🟡 Medium   ⏱ 5–30 min  Last verified: 20 May 2026 Affected versions: Debian 12 📖 ~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 & […]

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Common Problems 121181

Debian 10 – Fail2ban Not Banning with nftables Backend – Jail Action Fix

🟡 Medium   ⏱ 5–30 min  Last verified: 20 May 2026 Affected versions: Debian 10 📖 ~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 & […]

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Common Problems 117110

Ubuntu 22.04 LTS Fail2ban Not Banning Attackers Due to Journal Backend Misconfig

🟡 Medium   ⏱ 5–30 min  Last verified: 20 May 2026 📖 ~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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Common Problems 120682

Debian 11 – Fail2ban Not Banning with nftables Backend – Jail Action Fix

🟡 Medium   ⏱ 5–30 min  Last verified: 20 May 2026 Affected versions: Debian 11 📖 ~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 & […]

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Common Problems 115603

RHEL 7 – Postfix Service Starts but Mail Queue Never Drains

🟡 Medium   ⏱ 5–30 min  Last verified: 20 May 2026 📖 ~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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Common Problems 121671

Debian 9 – KVM Bridge Networking Stops Passing Traffic – Host Bridge Repair

🟠 High   ⏱ 5–30 min  Last verified: 20 May 2026 Affected versions: Debian 9 📖 ~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 & […]

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