Nmon – Monitor Linux System and Network Performance

If you are looking for a very easy-to-use performance monitoring tool for Linux, I highly recommend installing and using the Nmon command-line utility.

Nmon short for (Ngel’s Monitor), is a fully interactive Linux system performance monitoring command-line utility that was originally developed by IBM for the AIX systems and later ported to the Linux platform.

The important benefit of the nmon tool is that it allows you to monitor the performance of your Linux system aspects such as CPU utilization, memory usage, disk space, network utilization, top processes, virtual machine stats, file systems, resources, power micro-partition and more, in a single, concise view.

In addition to monitoring your Linux system interactively, nmon can also be used in batch mode to gather and save performance data for later analysis.

Nmon Linux Performance Monitoring Tool
Nmon Linux Performance Monitoring Tool

A very nice thing I really like about this tool is the fact that it is fully interactive and helps the Linux user or the system administrator with the necessary command to get the most out of it.

Installing Nmon Monitoring Tool in Linux

If you are using a Debian/Ubuntu-based Linux distribution you can easily install the Nmon command-line utility by grabbing it from the default repositories.

To install, Open a new terminal (CTRL+ALT+T) and use the following command.

$ sudo apt-get install nmon

Are you a Fedora user? To install it on your machine open a new terminal and run the following command.

# dnf install nmon

On RHEL-based distributions such as Rocky Linux and AlmaLinux, users can install it by installing the EPEL repository as shown:

------------- On RHEL, Rocky & AlmaLinux 9 ------------- 
# dnf install https://dl.fedoraproject.org/pub/epel/epel-release-latest-9.noarch.rpm
# yum install nmon

------------- On RHEL, Rocky & AlmaLinux 8 -------------
# dnf install https://dl.fedoraproject.org/pub/epel/epel-release-latest-8.noarch.rpm
# yum install nmon

On other Linux distributions, you can install nmon via the default package manager as shown.

$ sudo emerge -a sys-process/nmon  [On Gentoo Linux]
$ sudo apk add nmon                [On Alpine Linux]
$ sudo pacman -S nmon              [On Arch Linux]
$ sudo zypper install nmon         [On OpenSUSE] 

How to use Nmon to Monitor Linux Performance

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
Nmon Linux Performance Monitoring Tool
Nmon Linux Performance Monitoring Tool

As you guys can see from the above screenshot, the nmon command-line utility runs completely in interactive mode and it presents the user with the keys to toggle statistics.

Monitor Linux CPU Utilisation

For example, if you would like to collect some statistics on CPU performance you should hit the ‘c‘ key on the keyboard of the system you are using. After hitting the ‘c‘ key on my keyboard I get a very nice output that gives me information on my CPU usage.

Nmon - Monitor Linux CPU Usage
Nmon – Monitor Linux CPU Usage

The following are the keys you can use with the utility to get information on other system resources present in your machine.

  • m – Memory
  • j – Filesystems
  • d – Disks
  • n – Network
  • V – Virtual Memory
  • r – Resource
  • N – NFS
  • k – kernel
  • t – Top-processes
  • . – only busy disks/procs
  • U – Utilisation

Monitor Linux Top Processes Statistics

To get stats on top processes that are running on your Linux system press the key ‘t‘ on your keyboard and wait for the information to show up.

Nmon - Monitor Linux Top Processes Usage
Nmon – Monitor Linux Top Processes Usage

Those familiar with the top utility will understand and be able to interpret the above information very easily. If you are new to Linux system administering and have never used the top utility before, run the following command in your terminal and try to compare the produced output with the above one. Do they look similar, or is it the same output?

# top
Top - Monitor Linux Processes Usage
Top – Monitor Linux Processes Usage

It looks like I am running the top process monitoring utility when I use the key ‘t‘ with the Nmon tool to me.

Monitor Linux Network Statistics

How about some network stats? Just press ‘n‘ on your keyboard.

Nmon - Monitor Linux Network Statistics
Nmon – Monitor Linux Network Statistics

Monitor Linux Disk I/O Graphs

Use the ‘d‘ key to get information on disks.

Nmon - Monitor Linux Disk Statistics
Nmon – Monitor Linux Disk Statistics

Check Linux Kernel Information

A very important key to use with this tool is ‘k‘, it is used to display some brief information on the kernel of your system.

Nmon - Check Linux Kernel Information
Nmon – Check Linux Kernel Information

Check Linux System Information

A very useful key for me is the key ‘r‘ which is used to give information on different resources such as machine architecture, operating system version, Linux version, and CPU. You can get an idea of the importance of the key ‘r‘ by looking at the following screenshot.

Nmon - Check Linux System Information
Nmon – Check Linux System Information

Monitor Linux File System Statistics

To get stats on the file systems press ‘j‘ on your keyboard.

Nmon - Check File System Statistics
Nmon – Check File System Statistics

As you can see from the above screenshot, we get information on the size of the file system, used space, free space, type of file system, and the mount point.

Check NFS Data

The key ‘N‘ can help to collect and display data on NFS.

Monitor NFS
NFS Data

So far it has been very easy to work with the Nmon utility. There are many other things you need to know about the utility and one of them is the fact that you can use it in data capture mode.

If you don’t like the data to be displayed on the screen you can easily capture a small sample file with the following command.

# nmon -f -s13 -c 30

After running the above command you will get a file with the ‘.nmon‘ extension in the directory where you were while working with the tool. What is the ‘-f‘ option? The following is a simple and short explanation of the options used in the above command.

  • The -f means you want the data saved to a file and not displayed on the screen.
  • The -s13 means you want to capture data every 13 seconds.
  • The -c 30 means you want thirty data points or snapshots.

There are many tools that can do the job of the Nmon utility, but none of them is so easy to use and friendly to a Linux beginner. Unfortunately, the tool does not have as many features as other tools such as collectl and it can not provide in-depth stats to the user.

In the end, I can say it is a very nice utility for a Linux system administrator, especially for someone that is not familiar with command-line options and commands.

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Oltjano Terpollari
Hi guys, I am a computer Geek and I go by the name Ambition. I do security stuff and I am studying computer engineering. I love programming and Linux.

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Leave a Reply
  1. Hi Friends,

    Can anyone please share how to capture the data during the load test or any duration?

    Please share the steps.

    Thanks in advance!

  2. I have generated script using jmeter, but i want to analyse the results using nmon but don’t know how to do that. Please help me out.

    • @Morteza,

      Thanks for updating us about Repoforge, as per you suggestion, we’ve updated the article and added instructions to install Nmon using Epel repository under CentOS and RHEL distributions..


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