🔧 General Troubleshooting

Practical fixes for common Linux, networking, and application problems.

• /usr/local/sbin Is a Symlink: The 'Duplicate' Script That Was One File
• \"Operation not permitted\" on macOS: Agent Sandbox vs TCC (They Look Identical)
• A Cowork MCP Tool Called Before Its Schema Loads Can Return an Empty Result Instead of an Error
• A GUI App's CLI May Not Share Its Name (Spark's CLI Is SparklyRemote)
• A WSL-Launched MCP Server on Windows Doesn't Inherit Claude Desktop's env Block Unless You Also Set WSLENV
• Adobe Creative Cloud Error 108: 'Another Installer Instance Is Running' (macOS)
• Alert Script Never Emails: set -e + && Short-Circuit Kills the Run That Matters
• An MCP Server Reporting \"Connected\" Can Still Be Broken — Verify It Over stdio
• Ansible Check Mode False Positives in Verify/Assert Tasks
• Ansible Fails with Permission Denied While ssh <alias> Works (Host Alias Bypass)
• Ansible Ignores ansible.cfg on WSL2 Windows Mounts
• Ansible Jinja {% include %} Glues the Partial's Last Line to the Next
• Ansible lookup('file', ...) Relative Paths Resolve Against playbook_dir, Not Your Shell's cwd
• Ansible reboot.yml: become Timeout on WSL2 Hosts (Exclude Them)
• Ansible regex_search Capture Groups in set_fact: the Backslash Escaping Is Context-Dependent, Not Broken
• Ansible SSH Timeout During dnf upgrade on Fedora Hosts
• ansible-lint in CI Without the Vault Password: 100+ internal-error Findings and Unlinted Playbooks
• Ansible: Ubuntu Reboot Detection Misses Kernel Upgrades
• Ansible: Vault Password File Not Found
• Auditing & Cleaning macOS Background App Activity (sfltool dumpbtm)
• Castopod 'Max size is 2MiB' — Stock PHP Upload Limits Resurface After a Server Rebuild
• Castopod Feed Empty-GUID Backfill: Natively-Uploaded Episodes Silently Collide in Strict RSS Clients
• Changing ansible_port Breaks Every Control Node's known_hosts (the ssh-askpass Red Herring)
• Claude Code Keychain Prompt Keeps Reappearing on macOS (ACL vs Partition List)
• Claude Code Won't Log In (Warp & iTerm2) — Corrupt Keychain Credential
• Claude Desktop MCP Mass-Disconnect After Blocking SSH Reboot
• Claude Desktop MCP: Four False Signals When Diagnosing a Dead Plugin
• Claude Desktop Skips Remote MCP Servers Defined With a Bare url Key
• claude-mem Silently Fails with Claude Code 2.1+ (Empty --setting-sources)
• Concurrent Claude Sessions Silently Clobber Vault Journal Writes
• Concurrent Sessions in One Git Checkout: Commits Land on the Wrong Branch
• Copying Nintendo Switch Captures to a Mac: MTP Is a Dead End, Use the microSD
• Cowork's Built-In Shell Is a Sandbox, Not the Local Machine
• Cron Heartbeat False Alarm: /var/run Cleared by Reboot
• do-release-upgrade Can Purge mysql-server-8.0 Without Installing a Replacement
• do-release-upgrade to 26.04 Crashes in _addSecuritySources() (ExplodedDeb822SourceEntry)
• Docker & Caddy Recovery After Reboot (Fedora + SELinux)
• Fantastical \"Couldn't communicate with a helper application\" After an App Store Update
• Fantastical Google Sync Error Flood — Phantom Calendars Fixed via syncselect
• Fantastical MCP Server: Permission Denied on Launch (macOS Quarantine)
• Fedora Networking & Kernel Troubleshooting
• Forgejo Actions: Jobs Finish, Then Are Marked Failed ~12 Minutes Later (Runner Too Old for the Server)
• Forgejo: Account Recovery & CLI Admin When Locked Out of the GUI
• Gemini CLI: Manual Update Guide
• Ghost EmailAnalytics Lag Warning — What It Means and When to Worry
• Gitea Actions Runner: Boot Race Condition Fix
• Grafana Says RESOLVED but Nothing Was Fixed: Stale Alerts After a DatasourceError
• iPhone Mirroring Hangs on 'Connecting…' — AWDL Data Stall (27.0 Beta)
• ISP SNI Filtering & Caddy Troubleshooting (RETRACTED)
• Keep Secrets Out of claude_desktop_config.json (No env Interpolation) — Wrapper + 0600 env File
• Logwatch Reports the Wrong Hostname (<host>-hetzner) After a Migration
• macOS Delivers No Notifications — Stuck Game Mode From a Zombie App
• macOS Repeating Alert Tone from Mirrored iPhone Notification
• MajorDocs Setup & Publishing Pipeline
• MCP Python SDK 2.0 Breaks Unpinned uv-run Servers
• Molly Stuck Loading: Expired Build from a Stale F-Droid Repo
• Mystery Device on Pi-hole: macOS Adopted a Thunderbolt Dock's Name as Its Hostname
• OBS Studio — \"Error opening file: (null)\" After Windows Profile Rename
• OBS Studio — Update Fails with \"Files in Use\" Even Though OBS Is Closed
• Obsidian Vault Recovery — Loading Cache Hang
• Ollama Drops Off Tailscale When Mac Sleeps
• Ollama: ollama run with Piped Stdin Bypasses Chat Template + SYSTEM Prompt
• Patching PHP 8.4 Implicit-Nullable Deprecations in Vendor Packages
• Postfix Starts Before Its Milters at Boot, Failing the First Inbound Message
• Python smtplib: Missing Date/Message-ID Headers Break Mail Clients
• Search Console Says 'Excluded by noindex' — Telling a Deliberate Archive Noindex From a Real Fault
• SELinux: Dovecot Sieve-Pipe Scripts Break After restorecon (Missing bin_t fcontext Rule)
• SELinux: Fixing Dovecot Mail Spool Context (/var/vmail)
• SELinux: Wrong /etc/localtime Label Silently Breaks Timezone Changes
• SSH to MajorMac Hangs Indefinitely Reading Inside ~/Documents (Full Disk Access)
• Thunderbird Running Slow or Beachballing — A Diagnostic Playbook
• Time Machine 'Unknown Error': Case-Sensitive APFS Destination (and Encrypting It Correctly)
• Time Machine: Orphaned APFS .previous Folder Blocks All Backups
• Ubuntu dist-upgrade Quarantines Third-Party Repos
• Uninstalling Docker Desktop Leaves Dangling Symlinks in /usr/local/bin
• Verify a Health/Alarm Matcher by Counting Bound Instances, Not by Reading Config
• Warp \"Silent\" CLI-Agent Notifications: Check warp.log for OSC 777 Before Blaming the Plugin
• wget/curl: URLs with Special Characters Fail in Bash
• WordPress 6.7 _load_textdomain_just_in_time Notice (Theme/Plugin Loads Translations Too Early)
• WordPress Auto-Updates Silently Fail for Months After a Root-Run Update (Root-Owned Files)
• wsl.exe Eats Your Shell Variables When the Script Is an Argument
• WSL2: PyTorch Training Deadlocks on Windows Filesystem Checkpoint Saves
• WSL2: screen/tmux Sessions Die When the Last Terminal Closes (Post-July-2026 Lifecycle Change)
• yt-dlp 'Requested format is not available' — Live Streams Serve an HLS-Only Ladder
• yt-dlp HTTP 403: Forbidden — the Subtitle and Unranged-GET Triggers
• yt-dlp HTTP 429: Too Many Requests (YouTube Rate Limiting)
• yt-dlp Merge Fails: 'Invalid data found when processing input' (Stale Cache)
• yt-dlp YouTube JS Challenge Fix (Fedora)

Boot & System

• VirtualBox Windows 11 VM: AHCI Freeze on Boot/Setup, and a Separate Unattend ProductKey Trap

Docker & Containers

• Docker Port Bind to a Tailscale IP Fails at Boot — Ordering Isn't Enough, Use ip_nonlocal_bind
• n8n Behind Reverse Proxy: X-Forwarded-For Trust Fix
• n8n Webhook Responds Slowly (or Times Out) Even Though the Real Work Is Fast
• Nextcloud AIO 'Upgrade to Latest Major': Benign Stream Error and the 33/34 Version Split
• Nextcloud AIO Container Unhealthy for 20 Hours After Nightly Update

GPU & Display

• LoRA adapter — GGUF conversion fails with 'config.json not found
• Qwen2.5-14B OOM on RTX 3080 Ti (12GB)

Networking

• A DNS Block That Looks Like a 503 (Blocked Subresources)
• A DNS Block That Looks Like a TLS Error (HTTPS-First vs Pi-hole)
• A Pi-hole Block Reaches an AI Agent as an SSRF-Guard Error, Not a DNS Error
• Ansible UNREACHABLE: Host Key Verification Failed After a Host Rebuild or Migration
• Apache Outage: Fail2ban Self-Ban + Missing iptables Rules
• Diagnosing Intermittent Connection Failures to a Home-Hosted Service (When Everything 'Looks' Fine)
• DNSSEC \"Enabled\" But Never Validates: The DS Record Has to Go to the Registrar, Not the DNS Host
• Dovecot IMAP Clients Fail to Sync: vsz_limit OOM from a Bloated Index Log
• Dovecot Phantom Mailboxes from .dovecot.lda-dupes (mail_home Overlapping the Maildir Root)
• Fail2ban & UFW Rule Bloat: 30k Rules Slowing Down a VPS
• firewalld: Mail Ports Wiped After Reload (IMAP + Webmail Outage)
• iOS Tailscale Clients Report HostName="localhost" — Breaks /etc/hosts Generators
• MagicDNS Names vs Pinned IPs for Tailscale SSH (After a Fleet Migration)
• Mail Client Stops Receiving: Fail2ban IMAP Self-Ban
• Migrating an Apex-CNAME Domain to deSEC: Rejected Records and the minimum_ttl Trap
• Namecheap DNS: Misfiled MX Records, No Null MX, and Apex CNAME Behaviour
• Pi-hole AI Blocklist Blocks Claude Desktop (ERR_CONNECTION_REFUSED)
• pihole allow list Hangs the CLI Instead of Listing the Allowlist
• Ping Latency Spikes That Are Really Collector Scheduling
• Postfix + SendGrid: TLS Handshake Failure (Port 465 vs 587)
• Postfix header_checks Can't Act on Milter-Added Headers (Use Sieve)
• rsync over Tailscale: Hung in TCP Teardown After Transfer Completes
• SSH Permission denied (publickey) After Rotating a Key — Backfill Every authorized_keys
• SSH Alias Fails on One Fleet Host — Service Account Squats the Standard User's UID
• SSH Alias Falls Through to MagicDNS — Host-Key Verification Failure (No Host Block)
• Steam Deck Wi-Fi Flapping: IWD Periodic Scan + rtw88 Power Save
• Tailscale Boot Race Conditions (SSH Unreachable After Reboot)
• tailscale cert Can Silently Return the Stale Cached Cert Instead of Renewing
• Tailscale SSH none-Auth Root Login Looks Like a Vulnerability — It Usually Isn't
• Tailscale SSH: Unexpected Re-Authentication Prompt
• Thunderbird Gmail IMAP: [TRYCREATE] No folder [Gmail]/All Mail (THROTTLED)
• Transient LAN Latency With No Root Cause: An Elimination Method
• Wi-Fi Game Streaming Stutter: 160 MHz Channel Width Saturating the 5 GHz Radio
• Windows OpenSSH + WSL: Large or Quoted Commands Fail Over SSH
• Windows OpenSSH + WSL: sftp Hangs Because Subsystems Launch Through the DefaultShell
• Windows OpenSSH Server (sshd) Stops After Reboot
• Windows OpenSSH: WSL as Default Shell Breaks Remote Commands

Performance

• Diagnosing Recurring CPU Spikes on a Small VPS with atop
• Game Crashes With Plenty of Free RAM: RADAR_PRE_LEAK and the Tiny System-Managed Pagefile

Security

• Castopod Posts Don't Appear on Mastodon — Diagnosing the Federation Path
• Castopod: Stale Federated Avatar URLs After Remote Profile Updates
• Certbot Renewal Fails With 'Account Does Not Exist': A Stale ACMEv1 Account ID After Migration
• ClamAV Safe Scheduling on Live Servers
• ClamAV Weekly Scan False Alerts: Exit-Code Pitfalls
• Custom Fail2ban Jail: Apache Directory Scanning & Junk Methods
• Fail2ban Misses Low-and-Slow Brute Force: Per-Connection Thresholds and Short findtime
• Fail2ban SMTP-Auth Jail, Notify-Only: Getting Emailed on Every Failed SMTP AUTH Without Actually Banning
• Fedora CA Bundle Missing Symlink — Postfix Relay Silently Stops
• Logwatch Falsely Reports 'No freshclam updates' in ClamAV Daemon Mode
• Mail Over ~500 KB Bypasses SpamAssassin Entirely: spamc's Silent Size Ceiling
• Mitigating Apache HTTP/2 CVE-2026-23918 by Disabling mod_http2 Before a Distro Patch Ships
• Netdata apps-group FD-utilisation false 100% (silenced fleet-wide)
• Secrets Leaking Through 'Harmless' Diagnostic Commands (ansible-inventory, SELECT *, --diff)
• SELinux Confined ClamAV: Your 'Passing' Scans May Never Have Read a File
• Tuning Netdata web_log_1m_successful for Redirect-Heavy WordPress Sites

Storage

• Diagnosing Disk Space Alerts
• mdadm RAID Recovery After USB Hub Disconnect
• Windows 11 CapabilityAccessManager 500GB Storage Bug — How to Verify

Systemd

• Systemd Session Scope Fails at Login (session-cN.scope)