MacOS_Process_Monitor

A tiny macOS menu bar app that shows the number of processes owned by the current user and notifies when the count climbs past 85% of kern.maxprocperuid — the limit that, once hit, causes fork() to start returning EAGAIN and breaks terminals, browsers, and most apps.

Mirrors ps -u $USER | wc -l exactly so the menu bar number matches what you see in a shell.

What the menu bar shows

The status item shows your per-UID process count against the cap. The default is text — <count>/<limit> (<pct>%) in monospaced digits — but the Display submenu offers seven configurations: three text and four custom-drawn icons.

Mode	displayMode	Menu bar
Count / limit / pct (default)	countTotalPct
Count / limit	countTotal
Percent	percent
Gauge (needle)	gauge
Arc	arc
Pie	pie
Wedge	wedge

Severity is colour-coded on the icon modes — green < 50%, orange < 85%, red ≥ 85% — and the text modes turn red at/above the 85% threshold:

30% (green)	70% (orange)	90% (red)	text ≥ 85%

The threshold notification has a 5pt hysteresis so a single bounce around the limit doesn't spam alerts.

Click the icon for:

• Sparkline of the recent count history.
• Crash-looping submenu — names caught by the respawn-loop detector (shown only when there's something to report).
• Top spawners submenu — the processes spawning the most children; click an entry to open a floating detail window for it.
• Open Activity Monitor (⌘A).
• Start at Login toggle.
• Quit (⌘Q).

The detail window auto-refreshes every 2s while open and has a manual Refresh button. There is no "Refresh now" in the main menu — the 5s polling loop makes it redundant.

Build

Requires Xcode command line tools (Swift 5.9+, macOS 13+).

./scripts/build-app.sh

Produces build/ProcessMonitor.app. The script wraps the Swift Package Manager binary in a .app bundle and ad-hoc codesigns it — the signature is required, because UNUserNotificationCenter silently drops notification requests from unsigned bundles and threshold alerts won't fire.

Run

open ~/Applications/ProcessMonitor.app

~/Applications/ProcessMonitor.app is a symlink to build/ProcessMonitor.app, so rebuilds propagate without re-copying. The icon appears in the menu bar (no Dock icon — LSUIElement is set).

On first launch macOS will ask for notification permission. Approve it, otherwise the threshold alert can't fire.

Configuration

Tunables live at the top of Sources/ProcessMonitor/main.swift:

• warnPct — threshold in percent (default 85)
• pollSeconds — refresh interval in seconds (default 5)

Rebuild after changing.

Start at login (optional)

Use the Start at Login toggle in the menu. It registers the app via SMAppService.mainApp (bundle-ID based) rather than a LaunchAgent — macOS manages the lifecycle, and the app must live in /Applications or ~/Applications for registration to be accepted (which is what the ~/Applications symlink above provides).