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Linux | Nmon - GeeksforGeeks

Last Updated : 11 Jul, 2025

Nmon is a fully interactive performance monitoring command-line utility tool for Linux. It is a benchmark tool that displays performance about the CPU, MEMORY, NETWORK, DISKS, FILE SYSTEM, NFS, TOP PROCESSES, RESOURCES, AND POWER MICRO-PARTITION.

Nmon, or Nigel's Monitor, is a very lightweight, command-line system-performance monitoring tool on Linux platforms. It assists sysadmins and devs in monitoring and analyzing important system resources in real time or off a recorded timeline.

Nmon is an open-source performance-monitoring tool for checking:

• CPU load – assist in monitoring usage of processors and spotting bottlenecks.
• Usage of memory – indicate how much RAM is taken or available.
• Disk I/O – tracks disk reading/writing data.
• Network bandwidth – reports data transfer throughput on the network.
• Processes – displays running processes and their memory consumption.
• Kernel stats and more – contains information about the operating system such as interrupts, context switches, and load averages.

On Ubuntu/Debian :

$ sudo apt-get install nmon

On Fedora:

# yum install nmon

CentOS/RHEL:

# yum install epel-release
# yum install nmon

Once the installation of Nmon has been finished and you launch it from the terminal by typing the ‘nmon‘ command you will be presented with the following output.

$ nmon

Check CPU by processor

In order to get the CPU performance, you should hit the ‘c‘ key on the keyboard of the system you are using.

Top Process Details

In order to get the top processes that are running currently, you should hit the ‘t‘ key on the keyboard of the system you are using.

Check Network Statistics

In order to check network statistics, you should hit the ‘n‘ key on the keyboard of the system you are using.

Disk I/O Graphs

In order to get informations of disks, you should hit the ‘d‘ key on the keyboard of the system you are using.

Check Kernel Information

In order to check kernel information, you should hit the ‘k‘ key on the keyboard of the system you are using.

Get System Information

In order to get system information on different resources such as operating system version, Linux Version, Machine architecture, you should hit the ‘r‘ key on the keyboard of the system you are using.

Check File System Statistics

In order to check File System Statistics, you should hit the ‘j‘ key on the keyboard of the system you are using. You can get information on the size of the file system, used space, free space, type of the file system and the mount point.

Virtual Memory Statistics

In order to check Virtual Memory Statistics, you should hit the ‘V‘ key on the keyboard of the system you are using.

CPU Long Term

In order to check CPU Long Term Statistics, you should hit the ‘l‘ key on the keyboard of the system you are using.

Nmon generates performance data that can be opened and examined by multiple tools. System administrators and developers are able to use this to track resource consumption, debug the bottlenecks, and maximize Linux system performance.

You can open .nmon files using:

• Excel or LibreOffice Calc – Great for sorting and filtering system performance metrics like CPU, memory, and disk use.
• nmonchart – Enables the conversion of Nmon files to easy-to-read HTML graphs to support web-based performance monitoring and reporting.
• nmon_analyzer – An Excel plugin for creating graphs and graphs showing data as charts and detecting trends in performance.

Example Command to Generate Graphs:

nmonchart yourfile.nmon      # This command will create interactive HTML performance charts from the .nmon file

Also Read: How use Nmon and “Java Nmon Analyzer” for Monitor Linux Performance

There are many tools we can use for different purpose like:

If you're on Linux—be it Ubuntu, Debian, CentOS, Fedora, or RHEL—Nmon is one of the most potent and lightweight tools you can use to monitor the performance of your system. It gives you live details about vital metrics like CPU usage, memory usage, disk I/O, network usage, top processes, kernel stats, etc., all from your command prompt.

Unlike basic tools such as top or htop, Nmon not only monitors real-time performance but also records history for detailed analysis. With nmonchart and nmon_analyzer support for visual reporting, you can effortlessly transform performance logs into readable graphs and charts to identify bottlenecks and streamline Linux systems with ease.

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