How to Use the Command 'nmon' (with Examples)

Nmon, short for Nigel’s Monitor, is a valuable tool for system administrators and performance tuners. It provides insights into system performance and is particularly useful for capturing system data for analysis and benchmarking. It was initially developed for AIX systems but has since been ported to various Linux distributions. Nmon allows users to view real-time performance statistics and save performance data records, making it a versatile tool for monitoring the health of computer systems.

Use case 1: Start nmon

Code:

nmon

Motivation:
Starting nmon without any additional arguments is the simplest way to begin monitoring your system in real-time. This is ideal for users who want to quickly check the current performance metrics without saving the data for later analysis. It provides an immediate snapshot of the current system state, which can be especially helpful for debugging and troubleshooting on-the-fly.

Explanation:
The nmon command, when executed on its own, launches the interactive mode, showcasing live performance statistics across a variety of sections, including CPU usage, memory usage, disk I/O, network performance, and more. This mode is ideal for hands-on monitoring when you want to see the impact of changes in real-time, such as starting a heavy process or deploying an application.

Example Output:
Upon starting nmon, a console interface opens, displaying real-time statistics. Users can navigate through options using keyboard shortcuts like pressing ‘c’ for CPU, ’m’ for memory, etc. You will see a dynamic display of graphs, numbers, and other figures that update in real-time as the system runs.

Use case 2: Save records to file ("-s 300 -c 288" by default)

Code:

nmon -f

Motivation:
Saving performance data to a file is particularly beneficial for historical analysis, reporting, or when needing to share performance data with other team members for collaborative diagnostics. By default, nmon will log data every 300 seconds (5 minutes), taking a total of 288 measurements, which covers a full 24-hour period.

Explanation:

• -f: This option tells nmon to capture performance data and store it in a file. The resulting file can be opened and analyzed later, using other tools capable of interpreting nmon log files, such as built-in spreadsheet tools or third-party applications.

Example Output:
Executing nmon -f creates a file with a name in the format hostname_YYMMDD_HHMM.nmon. This file grows as nmon takes performance metrics snapshots. The data stored in the file includes detailed statistics about the system’s operations across the specified period, which is crucial for trend analysis or capacity planning.

Use case 3: Save records to file with specified measurement frequency and count

Code:

nmon -f -s 30 -c 240

Motivation:
There are scenarios where users require more granular data or a shorter overall monitoring period. For instance, if you’re testing new software and want to capture detailed performance data over a two-hour window with updates every 30 seconds, this use case is ideal. This could be invaluable when troubleshooting performance spikes or evaluating the behavior of new applications under load.

Explanation:

• -f: As in the previous use case, this option saves the performance data to a file.
• -s 30: Configures nmon to take performance measurements every 30 seconds. This increased granularity is useful for detecting quick, transient issues that might be missed at longer intervals.
• -c 240: Directs nmon to take a total of 240 measurements. At 30-second intervals, this results in capturing data for a total of 7,200 seconds, or two hours.

Example Output:
This command generates a file similar to the previous use case but with timestamps that are 30 seconds apart. The higher frequency of data capture results in a more detailed dataset, allowing for a finer-grained analysis of system performance over the specified period.

Conclusion:

Nmon is a powerful tool for monitoring and analyzing system performance metrics in Linux and AIX environments. Whether you need real-time data for instant troubleshooting or detailed logs for in-depth analysis, nmon provides a flexible interface and a plethora of options to cater to various administrative needs. By tailoring its use with specific command-line arguments, users can optimize their monitoring tasks to align perfectly with their operational and diagnostic requirements.