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Nmon simple.png
nmon showing the basics: CPU and memory
Developer(s) Nigel Griffiths
Operating system AIX, Linux
Type System monitor
License open source (since July 2009)
Website www.ibm.com/developerworks/aix/library/au-analyze_aix/

nmon (short hand for Nigel's Monitor) is a computer performance system monitor tool for the AIX and Linux operating systems developed by IBM employee Nigel Griffiths. The tool displays onscreen or saves to a data file the operating system statistics to aid the understanding of computer resource use, tuning options and bottlenecks.


The original nmon version was for the IBM AIX operating system (Release 4.3 and above) and was freely downloadable binary format only tool from the IBM AIX wiki.[1]

  • Later a version was written for the Linux operating system running on IA-32, x86-64, RS/6000 and Power processor, Mainframe. nmon for Linux was released by IBM to open source in July 2009. The code is available from the Sourceforge open source repository.[2]
  • The nmon for AIX code was later bundled in as part of the AIX operating systems. From AIX 5.3 TL09 and AIX 6.1 TL02 onward it was including in the default installation on AIX and fully supported by IBM. The nmon command [3] and the topas command [4] are the same binary but behave differently depending on the command name used. Users can switch between topas mode and nmon mode with the tilde (~) key.

The two editions (AIX and Linux) have completely different source code but offer many similar features, command line options and data - as much as the underlying operating system allow. nmon is used by AIX and Linux Systems Administrators and performance tuning specialists around the world.


  • There are two run time modes available:
  1. In Online Mode it uses curses for efficient screen handling, which updates the terminal frequently for real-time monitoring.
  2. 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 concentrates on performance information for the performance tuner and in a concise layout to aid understanding. This includes: CPU, memory, disks, adapters, networks, NFS, Kernel statistics, File-systems, Workload Manager (AIX), Workload Partitions (AIX) and Top Processes.
  • nmon includes support for older AIX releases, Linux running on x86, POWER and Mainframe platforms and other Linux supporting hardware.



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 commands allow saving data in a format suitable for a spreadsheet or simple further processing. Linux utility dstat can be used to produce text data, even in comma separated value format, which is quite suitable for spreadsheet programs.


External links[edit]