macOS Watchdog
Select event or periodic triggers for the problem being observed, then apply the quiet-watchdog contract before remediation.
Bind a watchdog's lifecycle to its premise state. When it cannot repair the
condition (broken WiFi, user quit the target app, prerequisite state gone),
stand down without waiting for a human to disable it.
Entry decision tree
| The situation is… | Go to |
|---|
| Installing a NEW watchdog from scratch | Select the trigger through references/event-driven-observers.md, then § Deploy and § The quiet-watchdog contract |
| An existing watchdog misbehaves (spam, re-launches apps, hammers) | § The quiet-watchdog contract, diagnose which clause it violates |
| Stopping / disabling / restarting a job | § Stop semantics |
| plist key details (KeepAlive forms, domains, logging, resource limits) | references/launchd-plist-reference.md |
| Choosing between event-driven and periodic for a source of truth | references/event-driven-observers.md § Select event vs periodic |
| Deploying / accepting an event-driven observer (WatchPaths, FSEvents, inotify-style) | references/event-driven-observers.md § Deployment SOP and § Acceptance SOP |
| Checking whether a plist edit is active, or comparing job argv / explicit ENV / configured paths / scheduling keys | Run scripts/inspect_native_job.py with the exact expected plist; read references/native-job-readback.md for result, scheduling-flag and source-selection rules |
| Setting up or recovering an already-authorized persistent calendar job with delivery deadlines | references/launchd-plist-reference.md § Calendar deadlines and recovery; check overdue work and actual delivery separately |
| Cooldown/backoff/notification-throttle patterns + sanitized war stories | references/quiet-watchdog-patterns.md |
| SRE alert layering (page vs ticket, fatigue numbers) | references/alert-discipline.md |
| A watchdog alert appears under Script Editor or its sender is unclear | references/alert-discipline.md § Message content; inspect the delivered card |
The quiet-watchdog contract
Before shipping or blessing any watchdog, every clause below must hold. Each clause exists because a real watchdog violated it.
1. Premise-state self-check — it knows when it has no job
The script's first act on every run: verify the state that justifies its existence still holds. If not, exit silently — no remediation, no notification, no side effects.
- A proxy-repair watchdog checks the proxy app is running first; user quit it → skip the cycle.
- A "did the config switch back" watcher checks the config state it watches; already switched → self-stop, not another round of misleading notifications. (Real case: a recovery watcher kept firing for 2h after its premise resolved, sending 3 spurious notices, because nothing told it to stop.)
2. Remediate first, page only on sustained failure
Detection stays honest on every cycle, but the disruptive action defers until the failure persists across N consecutive cycles (patient mode). Rationale: oscillating chains self-recover in minutes; a force-reconnect on a self-limiting blip is net-harmful. Measure your system's real self-recovery window before choosing N (one chain's 94-min observatory run showed ≤3 min self-recovery → N=2 cycles at 5-min interval).
When the trigger aggregates several independent sources into one verdict (not a single health check), the cross-source agreement fraction is a second, separate parameter from N — don't default to "all sources must agree." An all-or-nothing gate produces a false negative on exactly the correlated-but-partial incident the watchdog exists to catch, because real failures rarely take every source down at once (real case: a 9-source collection-health gate required 9/9 failing and missed a live incident sitting at 6/9; recalibrating against the actual incident data to a ≥60%-of-sources threshold caught it while three-fixture testing at 0%/11%/100% confirmed it still tolerated a single-source blip). Calibrate breadth (what fraction must agree) against real historical failure data the same way you calibrate depth (N) — a threshold picked from what "sounds strict enough" is a guess, not a calibration.
Escalation ladder (cheap → disruptive): refresh state → restart connection → remote repair. Each rung verifies before climbing.
3. Escalating auto-cooldown — an unfixable environment means silence
When the full repair ladder fails, the environment is unfixable by the watchdog (broken WiFi, captive portal, dead upstream). The naive behavior — re-run the entire ladder + notification every interval forever — is exactly "the watchdog keeps re-launching the app every 10 minutes."
ThrottleInterval does not fix this: it throttles process respawn, is a fixed delay with no backoff, and does nothing for a job that exits 0 after spamming. Cool-down must live in the application layer:
- Record consecutive exhausted rounds in a state file.
- After each exhausted round, stand down for an escalating tier (e.g. 30 min → 2 h → 6 h, last tier repeats).
- One notification when entering cool-down; zero during it. On tier expiry, retry one round; any real heal clears the counter and the cool-down state.
- A manual
pause [duration] command with a TTL state file is the fallback — but the auto path must work with no human command at all. A disable mechanism that requires the user to remember a command is not a mechanism.
Reusable implementation: scripts/watchdog-cooldown.sh (source it; provides paused_any, record_exhausted, clear_exhausted, cmd_pause/cmd_resume).
4. Never resurrect what the user explicitly quit
On macOS, open <url-scheme> launches the app when it isn't running, and open without -g steals foreground. A watchdog whose remediation uses URL schemes (or open -a, or restarting a GUI app) will read to the user as "I quit it and it came back."
Gate every such action: check the target process is alive before invoking its scheme, and pass -g so a legitimate action never pops a window. If the user quit the app mid-remediation, abort the ladder — cleanup traps must honor the same gate, or the "ensure connected on exit" fallback becomes the resurrector.
Deploy (mechanics that bite)
Before deploying or integrating an existing periodic observer, apply
references/probe-cost.md. Require bounded observation work and a completed native
launchd round; importing an existing script does not certify its cost or verdict.
Before declaring configuration active, use the native readback helper through
references/native-job-readback.md. Read explicit ENV from the job's own block;
do not take the first matching key from default or inherited environment sections.
Verify the completed business round separately from registration or process state.
- Location: user agent →
~/Library/LaunchAgents/ (GUI session context: can open apps, show notifications); system daemon → /Library/LaunchDaemons/ (root, no GUI access). Choose by whether the job needs the user's GUI session, not by habit.
- plist: for periodic jobs start from
assets/launchagent.template.plist; for event jobs follow references/event-driven-observers.md and its plist reference. Validate with plutil -lint. ProgramArguments element 0 = absolute path; never rely on shell PATH inheritance.
- Load/reload: before replacing or stopping an existing job, apply the ownership, active-work and pending-intent checks in
references/event-driven-observers.md § Deployment SOP. For an authorized idle job, load with launchctl bootstrap gui/$(id -u) <plist>; after a plist edit, bootout then bootstrap. Request one run of an idle owned job with launchctl kickstart gui/$(id -u)/<label>; -k terminates an existing instance and is not a routine test.
- Logs:
StandardOutPath/StandardErrorPath are non-negotiable (without them failures vanish), plus in-script log rotation (cap ~1 MB).
- Idempotency guard: re-running your deploy must not double-install. For periodic jobs only, use
scripts/new-launchagent.sh <label> <script> <interval> after the replacement checks above; it can boot out a loaded job. For event jobs use the event SOP. In both cases, verify loaded configuration through the native helper and completed work separately.
- TCC / Full Disk Access: a LaunchAgent reading protected files needs a working grant for its effective permission subject. Use
macos-permissions to inspect TCC attribution and verify a protected read from the actual job; the shell's interpreter path alone does not decide this.
- Batch throttling by default: any watchdog loop that spawns work (replays, fuzz, batch scans, parallel API calls) needs an explicit rate cap as a default parameter, not a later optimization. To the machine, an unthrottled loop and a runaway process are indistinguishable (real case: an unthrottled test replay forked 1,041 processes/sec for 7 minutes and pushed the die to 83 °C).
- Browser side-effect acceptance: a successful data fetch alone does not prove a browser-backed watchdog is ready. The deploying operator must declare a budget for task-owned spaces and pages, then independently inventory them across multiple rounds, including injected initialization and cleanup failures. Counts must stay within that lifecycle budget; protect user-owned and unknown-origin pages throughout. If the task requires no focus stealing, independently observe the foreground app and visible windows during those rounds; CDP success is not focus evidence. For ego lite lifecycle, locking, ownership conflicts and cleanup readback, load the named Skill
ego-lite-use when installed. Otherwise use the owning browser tool's documented lifecycle while meeting the same budget and readback requirements. Missing resource observations, or missing focus observations when no focus stealing is required, leave acceptance incomplete.
Stop semantics (the deprecated trap)
Before stopping or replacing a job, apply the ownership and active-work checks
in § Deploy and the current task's authorization boundary.
| Intent | Command |
|---|
| Stop now, allow re-bootstrap later | launchctl bootout gui/$(id -u)/<label> (daemon: sudo launchctl bootout system/<label>) |
| Prevent later loads across login (stop a loaded job separately) | launchctl disable user/$(id -u)/<label> (reverse: enable) |
| Edit then reload | bootout → edit plist → bootstrap |
Use bootstrap/bootout instead of deprecated load/unload. When a job
must remain disabled across later loads, apply disable; stopping an instance
alone does not establish that persistent override.
Troubleshooting quick map
| Symptom | First check |
|---|
| "It re-launches the app I quit" | URL-scheme/open calls missing the process-alive gate (clause 4) |
| "It spams the same repair every few minutes" | No exhausted-round cool-down (clause 3); also check the ladder's failure path doesn't reset its dead-counter |
| "It reports healthy through a real outage" | Health check certifies only the path it probes — one green probe ≠ all planes healthy (add the second plane's probe) |
| "bootout didn't stick / it came back" | Confirm the exact domain/service target and who bootstrapped it again; for a persistent stop follow § Stop semantics |
| Silent no-runs | StandardErrorPath missing → failures invisible; then log show --predicate 'process == "launchd"' --last 15m |
| "log mtime is fresh" but the job is actually failing | out.log all-green is not health — a failed pass may write nothing (set -e + prints-verified-only-on-success), so the last-success timestamp stays fresh forever. Judge the failure path (err.log / last-exit status), not success-side freshness (Pattern 7) |
| Works interactively, fails under launchd | TCC/FDA on the wrong interpreter; PATH assumptions in ProgramArguments |
| Observation becomes slower as history grows | Audit cold, warm and delta work using references/probe-cost.md; caching bytes does not bound parsing or queries |
Details and the sanitized war stories behind each clause: references/quiet-watchdog-patterns.md.