Monitoring tools: nmon

by gorthx

Next up in my occasional monitoring tools review series: another oldie-but-goodie, readily available tool, nmon.

What: nmon
What it monitors: system stats
Where to get it: it’s probably pre-installed on your system. If not, get it from sourceforge.
Why you’d want (or not) to use it: Pretty much the same reasons you’d want to use sar, as I discussed previously.

I’ve (casually) used the interactive interface, and until a few weeks ago, thought that’s all that there was to this tool. Not so. There’s an option (-f) you can use to save a single data poll to a file, in “spreadsheet format”. You can also specify an interval and a number of polls to take:

nmon -f -s 60 -c 60
= poll once a minute for an hour.

nmon will create a file for you, with a default name of [server]-timestamp.nmon, or you can specify your own filename with -F.

To generate graphs, there are two Excel spreadsheets you can download from the wiki. I tried the nmon Analyzer Spreadsheet (the newer of the two). The docs recommend “keep the number of snapshots to around 300”. I agree. The graphs look a lot nicer with fewer data points in them. However, Excel graphs just aren’t as pretty as rrdtool graphs.

There’s an nmon2rrd tool, but it was compiled for AIX so I didn’t try it out.

Of the two, if I’m looking for on-the-spot visualization of system performance, nmon wins it. For storage and later review of the data, I’d go with sar + over nmon + the Excel spreadsheet. The graphs are prettier and easier to read with sar.

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