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System Performance Monitoring

The following article is provided on an advice basis only. This article references 3rd party software that may require licensing. When experiencing performance issues with a Diffusion server, we recommend using Nmon. Nmon is an easy to use performance monitoring tool for Linux.

What is Nmon?

Nmon is a system tuner and benchmark tool that can be used to display performance data about the following:

  • CPU
  • Memory
  • Network
  • Disks
  • File Systems
  • NFS
  • Top processes

Installing Nmon in Linux

Debian / Ubuntu Use the following command:

  • sudo apt-get install nmon

Fedora Use the following command:

  • sudo yum install nmon

CentOS/RHEL Download from the following link.

Using Nmon

Once installed, Nmon can be stated with the following command.


You will then see the following output. 


You can then use the following keyboard shortcuts.

  • q – exit nmon
  • h – to see quick help screen (press again to hide)
  • c – CPU stats
  • m – memory stats
  • d – disk stats
  • k – kernel stats
  • n – network stats
  • N – see NFS stats
  • j – see file system stats
  • t – see top processes
  • V – see virtual memory stats
  • . – see only busy disks/processes.
  • v – verbose mode

For example, pressing c will show the CPU statistics in real-time.


Capturing Nmon Output

You can capture the data to a file for later analysis and graphing. Use the following command

nmon -f -s 2 -c 30

Nmon will run in the background. Once the data capture has been completed it will save it in a .nmon file. The arguments which can be supplied when capturing data are as follows:

  • -f : Start data collection.
  • -s 2 : Wait 2 seconds before refreshing the screen.
  • -c 30 : Total number of refreshes.
  • -t : Include top processes.

Viewing Nmon Output

We recommend using nmon Analyser (external site) to create an Excel spreadsheet containing the data and some graphs to aid in analysis and reporting. This will only run on Windows.