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File:Nmon simple.png
nmon showing the basics: CPU and memory
Developer(s) Nigel Griffiths
Operating system AIX, Linux
Type System monitor
Website nmon for AIX and Linux Performance Monitoring

nmon (short for Nigel's Monitor) is a popular system monitor tool for the AIX and Linux Operating Systems.



nmon is the bundled AIX tool and freely available Linux tool. Is used by Systems Administrators and performance tuning specialists around the world.

The prime features that make nmon unique are:

  • It is free and available for download from the IBM AIX Wiki website.
  • It is a single binary (one for each OS release), so installation is very simple.
  • There are two modes available:
    • In Online Mode it uses curses for efficient screen handling, which updates the terminal frequently for real-time monitoring.
    • In Capture Mode, the data is saved to a file in CSV format for later processing and graphing. The file also includes important configuration details that are useful for recommending tuning.
  • nmon takes very little CPU time to run but captures the key performance numbers.
  • Has been in development for 10 years and include many features requested by performance monitoring and systems administrator users.
  • nmon concentrates on useful performance information for the performance tuner and in a concise layout to aim understanding. This includes: CPU, memory, disks, adapters, networks, NFS, Kernel statistics, File-systems, Workload Manger (AIX), Workload Partitions (AIX) and Top Processes.
  • There are three main post processing tools, which are all available for free:
    • nmon Analyser is an Excel spreadsheet for graphing the collected data.
    • nmon2rrd creates Round-Robin Database (RRD) files via the Open Source RRDtool and then generates graphs and html files to display the data and graphs on a website.
    • nmon2web is similar to nmon2rrd but based on Perl.
  • These tools make it simple to produce reports with the key performance graphs or to automate the collection of performance data and create a website to aid tuning.
  • As it includes support for older AIX releases and Linux running on x86, POWER or Mainframe platforms this can be the one common tool used to monitor them all.
  • Although the author (Nigel Griffiths) works for IBM, it is a personal project, not an IBM product.
  • Discussion, hints and tips etc. are hosted on a IBM Performance tools Forum
  • nmon has been presented at many IT conferences including the UK UNIX User Group 2006 and IBM Power Systems Technical Universities held in the USA, European and Asia.

nmon for Linux

This was released by IBM to open source in July 2009.

Screen Shots


On AIX there is the topas command that can output reports to a file but this is not in a format that can be used easily as a source for a spread sheet or web tools like rrdtool.

On Linux there is the top command which is good for CPU and processes but does not cover disks and networks. For disk I/O, the iostat command can give you the details. But neither of these command allows for saving data in a format suitable for e spread sheet or simple further processing.

For monitoring many systems at a higher level the Ganglia open source tool is a good addition to lower detailed level nmon and Ganglia supports UNIX (including AIX) and Linux systems.

External links

Personal tools

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