Nmon is wonderful, if you need to monitor you server resources in realtime it’s your tool, if you need to monitor resources statistics over time and save them it’s your tool, if you need to check what’s the status of your server’s resources in a precise moment it’s your tool.
I can’t imagine a scenario where you don’t need nmon, more useful and flexible than sar, simpler and more straightforward than any other web based tool, imho it’s the perfect companion for collectd.

Sadly during on my last server setup I noticed that the latest nmon package distributed by Epel repository lacks of all the cron scripts you need to automate nmon startup and data collection, which imho are very useful also if you get nmon directly from the official GNU/Linux project site.

Here’s some hints from the old packages, first of all create the /var/log/nmon directory with nobody user as owner.

Create a new script in cron for example /etc/cron.d/nmon-script.
This cron will launch /usr/bin/nmon-script every day (for example at midnight).

Now you have to create the /usr/bin/nmon-script file (remember to give execution permission) which has:

• some configuration parameters in /etc/sysconfig/nmon-script
• commands to kill, cleanup old files (disabled in the example, note the leading # at line 15)

Create the /etc/sysconfig/nmon-script which contains some useful varibles (the directory where to save nmon archive files, retention and nmon options).

That’s enough, at the next midnight nmon will start to save your resources statistics in /var/log/nmon/<hostname>_AAMMDD_0000.nmon files.

You can download all the scripts and files to quickly setup the nmon-script:
nmon-script.tar.gz (656B)
SHA256 hash: 953667d8e2806e4858426fb000d7f3cfc898c53e26ffc7694bf2722442668aa8

[EDIT]

Nmon is not distributed by Epel but from RPMForge!!
Although RPMForge version is quite old it has nmon-script cron, I suggest to move to the latest version from the official GNU/Linux project site which do not have nmon-script.