A lightweight system monitor daemon for macOS on Apple Silicon (M-series). Written in C11, it continuously polls thermal pressure and CPU load using native macOS APIs, logs timestamped stats to a file, and fires a system notification when pressure thresholds are exceeded.

• Polls vm.pressure_level via sysctlbyname for real-time thermal pressure
• Calculates total CPU usage across all cores using mach_host_self() and host_processor_info
• Appends timestamped entries to ~/Library/Logs/m4_sentinel.log
• Triggers a native macOS notification when thermal pressure exceeds the threshold
• Runs silently in the background with --daemon mode (uses fork() + setsid())
• Proper error handling for all Mach service calls
• Built with CoreFoundation and IOKit via a simple Makefile

• macOS 13+ on Apple Silicon (M1/M2/M3/M4)
• Xcode Command Line Tools (xcode-select --install)

git clone https://github.com/chakri192/m4-sentinel.git
cd m4-sentinel
make

This compiles sentinel.c and links CoreFoundation + IOKit, producing a sentinel binary.

./sentinel

Useful for testing — logs and alerts print to stdout alongside the log file.

./sentinel --daemon

The process detaches from the terminal using fork() and setsid(). Logs continue writing to:

~/Library/Logs/m4_sentinel.log

pkill sentinel

Or find the PID and kill it manually:

pgrep sentinel
kill <PID>

Each log entry looks like:

[2025-07-01 08:42:31]  thermal_pressure=0  cpu_load=34.7%
[2025-07-01 08:42:41]  thermal_pressure=1  cpu_load=78.2%  ⚠ ALERT SENT

Logs are appended — they persist across runs. Rotate manually if needed:

: > ~/Library/Logs/m4_sentinel.log   # clear the log

m4-sentinel/
├── sentinel.c     # Core monitor logic
├── Makefile       # Build and link instructions
├── .gitignore
└── README.md

Documentation assisted by local LLMs via Ollama: