nmon
nmon (Nigel’s Monitor) is a lightweight performance monitoring tool for Linux that captures CPU, memory, network, disk, file system, and process data. Originally developed by IBM for AIX and later ported to Linux, nmon is famous for its compact single-screen display and its ability to generate detailed performance reports for capacity planning and bottleneck analysis.
Key Features
- Compact single-screen display — All key metrics visible at once without scrolling
- Data capture mode — Record metrics to CSV files for offline analysis in spreadsheets
- CPU utilisation — Per-processor and overall CPU usage with user/system/wait breakdowns
- Disk I/O — Per-disk read/write operations, transfer rates, and busy percentages
- Network stats — Per-interface packet and byte counts
- Memory management — Physical and virtual memory, swap, and page statistics
- Top processes — Most resource-intensive processes with CPU and memory usage
- Interactive mode — Toggle metric groups on/off with single keystrokes
Why Use It
nmon is extremely lightweight — it runs on minimal systems with very little overhead. Its CSV capture mode is invaluable for capacity planning, allowing you to record performance data over hours or days and analyse trends in Excel or LibreOffice Calc.
Use Cases
- Capacity planning — Capture performance data over time to understand utilisation trends
- Root cause analysis — Correlate CPU, disk, and network spikes to identify bottlenecks
- Benchmarking — Compare system performance before and after hardware or software changes
- Lightweight monitoring — Monitor resource-constrained systems like Raspberry Pi and embedded devices
Platform
Linux (x86_64, ARM, POWER), AIX
Licence
GNU General Public License v3.0