Mac
Mac runbooks for macOS Tahoe
Operator-grade troubleshooting for the Mac as home infrastructure on macOS Tahoe (macOS 26): Time Machine to a NAS, Mac mini home servers, storage and System Data, displays and docks, Wi-Fi, and boot. Every page is source-backed, pinned to the exact macOS point release, and written to leave you with a fix — not a list of vague tips.
From backup to a real storage plan — the operator path
Treat the Mac as infrastructure: get a restorable backup, keep it fast, optionally run it as a server, and plan real storage when libraries outgrow it. Each step links a source-backed runbook.
1 · Back up
Get a real, restorable backup
Back up over the network with Time Machine to a NAS, and build a 3-2-1 plan for your Mac — Time Machine alone is not enough.
Back up your Mac2 · Reclaim & speed up
Fix slow and full
Reclaim space when System Data balloons, and fix a Mac that got slow after the Tahoe update.
Free up space3 · Run a server
Use a Mac mini as a home server
Keep a Mac mini from sleeping, set it up headless, and tune Plex/Jellyfin transcoding.
Mac mini server4 · Add storage
Thinking about a NAS?
If Time Machine and photo libraries are outgrowing the Mac, plan real storage — the home NAS pillar and the Synology vs UGREEN vs DIY buying guide.
Plan a NASBackups & Time Machine
Getting a real, restorable backup off a Mac — Time Machine to a NAS over SMB, sparsebundle repair, the 3-2-1 plan, and the iCloud storage trap.
Why Time Machine over SMB to a Synology, QNAP, TrueNAS, or Unraid NAS fails on macOS Tahoe (26) or macOS 27, and the exact fixes for the two separate Tahoe bugs.
Open runbookFix a Time Machine network backup whose sparsebundle is in use, couldn't be accessed, or is damaged — attach it with diskutil image, run fsck_apfs, and re-claim it.
Open runbookHow to build a real 3-2-1 backup for a Mac — three copies, two media, one offsite — using Time Machine, a NAS, and cloud, and where iCloud fits (and doesn't).
Open runbookWhy 'Optimize Mac Storage' can leave your Time Machine backup full of empty placeholders instead of real files — how iCloud dataless files work, and the fix.
Open runbookmacOS 27 removed AFP, so Time Machine to a Time Capsule, AirPort Disk, or AFP-only NAS share no longer works. Confirm it, keep your old history, and move to SMB.
Open runbookMac as a home server
Running a Mac mini 24/7 — stopping it from sleeping, Plex/Jellyfin transcoding, headless setup, auto power-on, and power cost.
Stop a Mac mini sleeping when you run it 24/7 as a Plex, Jellyfin, or file server on macOS Tahoe — the Energy setting most miss, plus pmset and caffeinate.
Open runbookHow to run a Mac mini headless as a 24/7 home server on macOS Tahoe (macOS 26) — never-sleep, auto-login, launchd for services, and the FileVault trade-off.
Open runbookTwo switches: the Tahoe 26.5 Energy setting (also on macOS 27) and pmset autorestart. Plus the FileVault catch that stops unattended login after power comes back.
Open runbookWhy an M4 Mac mini handles far more Plex/Jellyfin transcodes than the 'one stream' myth claims — VideoToolbox, why native beats Docker, and the AV1 caveat.
Open runbookSize a Mac mini for local LLMs (Ollama, LM Studio, MLX): M4, M4 Pro, or the new M6 / M5 Pro, 16 to 64GB, the macOS GPU memory ceiling, and the always-on settings.
Open runbookPerformance & system
A Mac that got slow after the Tahoe update — the memory leak, high-CPU processes (kernel_task, WindowServer, Spotlight), and beachballs.
Why your Mac feels slow, laggy, or runs out of memory after updating to macOS Tahoe (26) or macOS 27 — the two confirmed Tahoe bugs with exact fixes.
Open runbookFix "Your system has run out of application memory" on macOS Tahoe (26) or macOS 27 — the autofill bug, the Electron leak, and how to read Memory Pressure.
Open runbookStorage & disk space
Reclaiming space when 'System Data' or purgeable space balloons — APFS local snapshots, caches, and what's actually safe to delete.
What Time Machine local snapshots do, how macOS counts their space, and when to leave them alone or reclaim them after a real storage failure.
Open runbookSystem Data (formerly Other) is the macOS catch-all for caches, logs, VM files and app data. Find what is using space and clear it safely, without a cleaner app.
Open runbookmacOS 27 downloads Apple Intelligence models automatically. See the real size in Storage settings, why it isn't System Data, and safe ways to free space.
Open runbookDisplays & docks
External monitors and docks on Apple Silicon — displays not detected after an update, per-chip display limits, DisplayLink, and mirror-vs-extend.
Why an external monitor stopped working after a macOS Tahoe (26) or macOS 27 update — power-cycle the dock, force Detect Displays, and swap the cable.
Open runbookHow many external monitors each Apple Silicon chip supports (M1–M5, Pro, Max, Ultra) — the per-chip limits and why a dock can't add more without DisplayLink.
Open runbookWhy two monitors on a Mac dock mirror instead of extending — the mirror setting to uncheck, and why Apple Silicon's lack of DisplayPort MST is the real cause.
Open runbookAfter macOS 27, Mission Control stalls, windows land on the wrong Space, or a detected external display goes black. Collect evidence, try user-reported workarounds, file feedback.
Open runbookWi-Fi & networking
Mac networking — Wi-Fi that keeps dropping, 'connected but no internet', the Local Network permission that hides your NAS and printer, and Private Wi-Fi Address.
Why a Mac's Wi-Fi keeps disconnecting after updating to macOS Tahoe (26) or macOS 27 — read diagnostics with wdutil, reset the network config, and fix the router.
Open runbookMac shows Wi-Fi but pages or apps fail? Separate DNS and routing faults from an app-specific VPN or content-filter problem, then test the matching fix.
Open runbookCheck Local Network permission, Bonjour discovery, VPN routing, and direct reachability when a NAS or printer disappears after a macOS update.
Open runbookAn app can't find your NAS, printer, or media server on macOS 27 and never asks for Local Network access. Prove the device is reachable, then fix the permission safely.
Open runbookPrinter still shows up but macOS 27 says its software isn't compatible or a filter fails? Prove reachability, check the driver, add Rosetta, re-add the queue.
Open runbookBoot & security
When a Mac won't start or an app won't open — boot loops, stuck-at-login, the 'app is damaged' Gatekeeper message, Rosetta after macOS 27, and FileVault recovery.
What to do when an Apple Silicon Mac won't start, loops on restart, or hangs on the Apple logo — enter Recovery, use Safe Mode, and reinstall without erasing.
Open runbookFix a damaged-app warning safely: identify the exact macOS alert, re-download a verified build, check its signature and know when Open Anyway is appropriate.
Open runbookYour headless Mac won't accept Screen Sharing until someone logs in locally. macOS Tahoe 26 fixes this: unlock FileVault over SSH, then reconnect.
Open runbookmacOS 27 does not automatically restore Rosetta after upgrade. Check an Intel app, install Rosetta from Apple's prompt if needed, and plan for macOS 28.
Open runbookMac: common questions
What breaks on a Mac after updating to macOS 27?
macOS 27 Golden Gate (released 14 September 2026; the current stable build is 27.0.1, 26A434) installs only on Apple silicon. The common problems: Time Machine to a Time Capsule or AFP share stops because AFP was removed (Time Capsule and AFP on macOS 27); Intel apps won't open until Rosetta is reinstalled (Rosetta after macOS 27); an old printer says its software isn't compatible (printer after macOS 27); an app that can't see your NAS is usually missing its Local Network permission (no Local Network prompt); Mission Control stalls or a detected display goes black (Mission Control on macOS 27); and 20–30 GB of free space goes to Apple Intelligence models (Apple Intelligence storage).
How do I back up a Mac to a NAS?
Point Time Machine at an SMB share on the NAS, and keep an off-site copy too. If the backup stalls or the sparsebundle errors, the Time Machine to a NAS runbook and the Mac 3-2-1 plan cover the fixes.
Why is my Mac slow after the macOS Tahoe update?
Usually a post-update reindex, a memory pressure issue, or a high-CPU process settling in. The slow-after-Tahoe runbook walks through isolating kernel_task, WindowServer, and Spotlight before any drastic step.
What is 'System Data' and can I delete it?
It's a catch-all that includes APFS local snapshots and caches, which can balloon. The System Data runbook explains what's actually safe to clear and what to leave alone.
Can a Mac mini be a home server?
Yes — it's a capable, low-power option. Stop it sleeping, run it headless, and size transcoding to the chip: see the Mac mini home server setup. For bulk storage, pair it with a NAS (see the NAS buying guide).
28 Mac runbooks and growing. New macOS Tahoe operator pages are added as each theme is built out.