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@@ -7,6 +7,7 @@ Practical fixes for common Linux, networking, and application problems.
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## 🌐 Networking & Web
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- [Apache Outage: Fail2ban Self-Ban + Missing iptables Rules](networking/fail2ban-self-ban-apache-outage.md)
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- [Mail Client Stops Receiving: Fail2ban IMAP Self-Ban](networking/fail2ban-imap-self-ban-mail-client.md)
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- [ISP SNI Filtering & Caddy](isp-sni-filtering-caddy.md)
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- [yt-dlp YouTube JS Challenge Fix](yt-dlp-fedora-js-challenge.md)
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@@ -0,0 +1,119 @@
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# Mail Client Stops Receiving: Fail2ban IMAP Self-Ban
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## 🛑 Problem
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A mail client stops receiving new email on one device while other devices (e.g., phone on cellular) continue to work normally. The mail server is healthy — Postfix is delivering to maildir and Dovecot is running — but the affected device receives no new messages and is never prompted for credentials.
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---
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## 🔍 Diagnosis
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### Step 1 — Confirm the mail server is delivering
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```bash
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ssh root@<mailserver> "tail -20 /var/log/maillog | grep 'status=sent'"
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```
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If you see `status=sent (delivered to maildir)`, the server is working. The issue is on the client side.
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---
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### Step 2 — Check if the client is connecting at all
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```bash
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ssh root@<mailserver> "grep '<client_ip>' /var/log/maillog | tail -10"
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```
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If there are **zero results**, the client is not reaching the server at all — not a credentials or sync issue.
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---
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### Step 3 — Get the client's current public IP
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Run this on the affected machine:
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```bash
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curl -s https://api.ipify.org
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```
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---
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### Step 4 — Check if that IP is banned by Fail2ban
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```bash
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ssh root@<mailserver> "fail2ban-client status postfix-sasl"
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ssh root@<mailserver> "fail2ban-client status dovecot-invalid"
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```
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Look for the IP in the `Banned IP list`. If it's there, that's your problem.
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---
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### Step 5 — Find when the ban was applied
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```bash
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ssh root@<mailserver> "grep '<client_ip>' /var/log/fail2ban.log | tail -20"
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```
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This shows the exact timestamps of auth failures and the ban event.
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---
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## ✅ Fix
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Unban the IP from all relevant jails:
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```bash
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fail2ban-client set postfix-sasl unbanip <IP>
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fail2ban-client set dovecot-invalid unbanip <IP>
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```
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Mail should resume immediately without restarting any services.
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---
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## 🔁 Why This Happens
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| Symptom | Cause |
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|---|---|
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| One device stops getting mail, others don't | Each device has a different public IP. Only the banned IP is blocked. |
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| No auth prompt in the mail client | Fail2ban issues a TCP `REJECT` — the client sees a connection error, not an auth failure, so it doesn't prompt for new credentials. It silently retries on a timer. |
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| Multiple failed attempts before ban | The mail client retried with a previously valid session token or stale auth state, triggering the `maxretry` threshold. |
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| Ban on `postfix-sasl` blocks IMAP (port 993) | The `postfix-sasl` jail monitors ports 25, 465, 587, 143, 993, 110, and 995 — not just SMTP. A failed SMTP auth attempt can ban access to IMAP as well. |
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---
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## ⚠️ Key Notes
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- **Fail2ban `postfix-sasl` covers all mail ports** — a single jail can lock out SMTP *and* IMAP simultaneously.
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- **The affected device's IP is never logged in Dovecot** once banned — the rejection happens at the iptables/Fail2ban layer before Dovecot sees the connection.
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- **Tailscale doesn't help** if the mail client connects via the public interface — the ban applies to the public IP, not the Tailscale IP.
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- Check when the ban happened: `grep '<IP>' /var/log/fail2ban.log` shows exact timestamps.
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---
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## 🔎 Quick Diagnostic Commands
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```bash
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# Get your current public IP (run on affected machine)
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curl -s https://api.ipify.org
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# Check all Fail2ban jail statuses
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fail2ban-client status
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# Check a specific jail for a banned IP
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fail2ban-client status postfix-sasl
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fail2ban-client status dovecot-invalid
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# Unban from a specific jail
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fail2ban-client set postfix-sasl unbanip <IP>
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fail2ban-client set dovecot-invalid unbanip <IP>
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# Unban from all jails at once
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for jail in $(fail2ban-client status | grep "Jail list" | sed 's/.*://;s/,/ /g'); do
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fail2ban-client set $jail unbanip <IP> 2>/dev/null && echo "Unbanned from $jail"
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done
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# Find when a specific IP was banned
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grep '<IP>' /var/log/fail2ban.log | tail -20
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```
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@@ -31,7 +31,7 @@ DNS record and Caddy entry have been removed.
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## Content
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- 36 articles across 5 domains
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- 37 articles across 5 domains
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- Source of truth: `MajorVault/20-Projects/MajorTwin/08-Wiki/`
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- Deployed via Gitea webhook (push from MajorAir → auto-pull on majorlab)
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@@ -63,7 +63,7 @@ rsync -av --include="*.md" --include="*/" --exclude="*" \
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---
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*Updated 2026-03-13*
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*Updated 2026-03-14*
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## Canonical Update Workflow
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@@ -91,3 +91,14 @@ Every time a new article is added, the following **MUST** be updated to maintain
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4. **Root `README.md`**: Sync with the main `index.md` (Article count, domain lists, and Recently Updated).
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> [!note] The rsync one-liner in the Update Workflow section above was a one-off during initial setup. It is no longer the canonical method.
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---
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## Related
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- [[majorlab|majorlab]] — deploy host (port 8092, Caddy reverse proxy, Gitea webhook)
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- [[01-Phases|Implementation Phases]] — Phase 9 (wiki & knowledge base)
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- [[09-Lessons-Learned-v5|Lessons Learned v5]] — ISP SNI filtering on wiki.majorshouse.com (why it's notes.majorshouse.com)
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- [[MajorAir|MajorAir]] — push host for git workflow
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- [[MajorRig|MajorRig]] — alternative git push host (WSL2 path documented)
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- [[03-11-2026|Status Update 2026-03-11]] — deployment date journal entry
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- [[03-13-2026|Status Update 2026-03-13]] — content expansion and SUMMARY.md sync
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15
README.md
15
README.md
@@ -2,8 +2,8 @@
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> A growing reference of Linux, self-hosting, open source, streaming, and troubleshooting guides. Written by MajorLinux. Used by MajorTwin.
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>
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**Last updated:** 2026-03-13
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**Article count:** 36
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**Last updated:** 2026-03-14
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**Article count:** 37
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## Domains
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@@ -13,7 +13,7 @@
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| 🏠 Self-Hosting & Homelab | `02-selfhosting/` | 8 |
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| 🔓 Open Source Tools | `03-opensource/` | 9 |
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| 🎙️ Streaming & Podcasting | `04-streaming/` | 1 |
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| 🔧 General Troubleshooting | `05-troubleshooting/` | 9 |
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| 🔧 General Troubleshooting | `05-troubleshooting/` | 10 |
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---
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@@ -101,6 +101,7 @@
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## 🔧 General Troubleshooting
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- [Apache Outage: Fail2ban Self-Ban + Missing iptables Rules](05-troubleshooting/networking/fail2ban-self-ban-apache-outage.md) — diagnosing and fixing Apache outages caused by missing firewall rules and Fail2ban self-bans
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- [Mail Client Stops Receiving: Fail2ban IMAP Self-Ban](05-troubleshooting/networking/fail2ban-imap-self-ban-mail-client.md) — diagnosing why one device stops receiving email when the mail server is healthy
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- [Docker & Caddy Recovery After Reboot (Fedora + SELinux)](05-troubleshooting/docker-caddy-selinux-post-reboot-recovery.md) — fixing docker.socket, SELinux port blocks, and httpd_can_network_connect after reboot
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- [ISP SNI Filtering with Caddy](05-troubleshooting/isp-sni-filtering-caddy.md) — troubleshooting why wiki.majorshouse.com was blocked by Google Fiber
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- [Obsidian Cache Hang Recovery](05-troubleshooting/obsidian-cache-hang-recovery.md) — resolving "Loading cache" hang in Obsidian by cleaning Electron app data and ML artifacts
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@@ -115,6 +116,7 @@
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| Date | Article | Domain |
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| 2026-03-14 | [Mail Client Stops Receiving: Fail2ban IMAP Self-Ban](05-troubleshooting/networking/fail2ban-imap-self-ban-mail-client.md) | Troubleshooting |
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| 2026-03-14 | [SearXNG: Private Self-Hosted Search](03-opensource/alternatives/searxng.md) | Open Source |
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| 2026-03-14 | [FreshRSS: Self-Hosted RSS Reader](03-opensource/alternatives/freshrss.md) | Open Source |
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| 2026-03-14 | [Gitea: Self-Hosted Git](03-opensource/alternatives/gitea.md) | Open Source |
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@@ -136,3 +138,10 @@
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| Pi-hole setup and local DNS | Self-Hosting | Medium | No |
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| OBS audio routing on Linux (PipeWire) | Streaming | Medium | No |
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| Nextcloud setup with Docker | Self-Hosting | Medium | No |
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---
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## Related
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- [[MajorWiki-Deploy-Status|MajorWiki Deploy Status]] — deployment status and git workflow
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- [[01-Phases|Implementation Phases]] — Phase 9 (wiki & knowledge base)
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- [[majorlab|majorlab]] — hosting server
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@@ -32,6 +32,7 @@
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* [OBS Studio Setup & Encoding](04-streaming/obs/obs-studio-setup-encoding.md)
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* [Troubleshooting](05-troubleshooting/index.md)
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* [Apache Outage: Fail2ban Self-Ban + Missing iptables Rules](05-troubleshooting/networking/fail2ban-self-ban-apache-outage.md)
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* [Mail Client Stops Receiving: Fail2ban IMAP Self-Ban](05-troubleshooting/networking/fail2ban-imap-self-ban-mail-client.md)
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* [Docker & Caddy Recovery After Reboot (Fedora + SELinux)](05-troubleshooting/docker-caddy-selinux-post-reboot-recovery.md)
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* [ISP SNI Filtering with Caddy](05-troubleshooting/isp-sni-filtering-caddy.md)
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* [Obsidian Vault Recovery — Loading Cache Hang](05-troubleshooting/obsidian-cache-hang-recovery.md)
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15
index.md
15
index.md
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> A growing reference of Linux, self-hosting, open source, streaming, and troubleshooting guides. Written by MajorLinux. Used by MajorTwin.
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>
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> **Last updated:** 2026-03-13
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> **Article count:** 36
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> **Last updated:** 2026-03-14
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> **Article count:** 37
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## Domains
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@@ -13,7 +13,7 @@
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| 🏠 Self-Hosting & Homelab | `02-selfhosting/` | 8 |
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| 🔓 Open Source Tools | `03-opensource/` | 9 |
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| 🎙️ Streaming & Podcasting | `04-streaming/` | 1 |
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| 🔧 General Troubleshooting | `05-troubleshooting/` | 9 |
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| 🔧 General Troubleshooting | `05-troubleshooting/` | 10 |
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---
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@@ -101,6 +101,7 @@
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## 🔧 General Troubleshooting
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- [Apache Outage: Fail2ban Self-Ban + Missing iptables Rules](05-troubleshooting/networking/fail2ban-self-ban-apache-outage.md) — diagnosing and fixing Apache outages caused by missing firewall rules and Fail2ban self-bans
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- [Mail Client Stops Receiving: Fail2ban IMAP Self-Ban](05-troubleshooting/networking/fail2ban-imap-self-ban-mail-client.md) — diagnosing why one device stops receiving email when the mail server is healthy
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- [Docker & Caddy Recovery After Reboot (Fedora + SELinux)](05-troubleshooting/docker-caddy-selinux-post-reboot-recovery.md) — fixing docker.socket, SELinux port blocks, and httpd_can_network_connect after reboot
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- [ISP SNI Filtering with Caddy](05-troubleshooting/isp-sni-filtering-caddy.md) — troubleshooting why wiki.majorshouse.com was blocked by Google Fiber
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- [Obsidian Cache Hang Recovery](05-troubleshooting/obsidian-cache-hang-recovery.md) — resolving "Loading cache" hang in Obsidian by cleaning Electron app data and ML artifacts
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@@ -115,6 +116,7 @@
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| Date | Article | Domain |
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|---|---|---|
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| 2026-03-14 | [Mail Client Stops Receiving: Fail2ban IMAP Self-Ban](05-troubleshooting/networking/fail2ban-imap-self-ban-mail-client.md) | Troubleshooting |
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| 2026-03-14 | [SearXNG: Private Self-Hosted Search](03-opensource/alternatives/searxng.md) | Open Source |
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| 2026-03-14 | [FreshRSS: Self-Hosted RSS Reader](03-opensource/alternatives/freshrss.md) | Open Source |
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| 2026-03-14 | [Gitea: Self-Hosted Git](03-opensource/alternatives/gitea.md) | Open Source |
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@@ -135,3 +137,10 @@
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| Troubleshooting NVIDIA on Linux | Troubleshooting | Medium | No |
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| Pi-hole setup and local DNS | Self-Hosting | Medium | No |
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| Nextcloud setup with Docker | Self-Hosting | Medium | No |
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---
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## Related
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- [[MajorWiki-Deploy-Status|MajorWiki Deploy Status]] — deployment status and update workflow
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- [[01-Phases|Implementation Phases]] — Phase 9 (wiki & knowledge base)
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- [[majorlab|majorlab]] — hosting server (notes.majorshouse.com)
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