Master Linux Performance Monitoring with nmon: Real‑Time & Scheduled Insights

nmon is a Linux performance data collection and analysis tool that is simple to use.

What nmon Can Do

It provides monitoring and analysis of various system performance data, including:

CPU usage

Memory usage

Kernel statistics and run‑queue information

Disk I/O speed, transfer rates, and read/write ratios

Available space in file systems

Network I/O speed, transfer rates, and read/write ratios

Processes consuming the most resources

How to Use nmon

Real‑time Monitoring

Run nmon interactively and use shortcut keys to display the metrics you care about, for example:

Press C – view CPU information

Press D – view disk information

Press T – view process information

Press M – view memory information

Press N – view network information

Press H for help on all shortcuts. This mode updates continuously, giving an at‑a‑glance view of system load, CPU utilization, memory consumption, network traffic, and disk activity.

Background Monitoring

To record resource usage over time for later analysis, run nmon in background mode, for example: ./nmon -f -s 10 -c 360 Options: -f: output file name in standard format _YYYYMMDD_HHMM.nmon -s: sampling interval in seconds -c: number of samples to collect

In the example, data is collected every 10 seconds for 360 samples, resulting in a one‑hour monitoring period.

Combined with a cron job, you can schedule regular monitoring, e.g.: 0 8 * * * /nmon -f -s 30 -c 1200 This runs every day at 08:00, sampling every 30 seconds for 1,200 samples (approximately 10 hours).

Analyzing nmon Results

Background or scheduled monitoring produces .nmon files that record system resource data. These files can be processed with the dedicated analysis tool nmon_analyser, which converts them to Excel spreadsheets and generates charts for visual interpretation of system performance.