Even simple things are hard when you have never done them.
There is a pretty good How-to at http://nagios.sourceforge.net/docs/3_0/quickstart-ubuntu.html for installing Nagios, and plugins, generally. I use Debian, so there may be a few minor differences between an Ubuntu install and my installation on Debian. Mostly I wanted to add a few notes about issues I run into when adding a remote server to the nagios family. You have to do a few things that are not in the instructions.
Before you begin, make sure you have a C-language compiler installed as well as ‘make.’
# aptitude install gcc make
also, your ssl_version in Nagios-Plugins will fail if you do not have libssl-dev installed.
# aptitude install libssl-dev
Your make will continue to fail in an unhelpful manner if you do not now re-run your configure command.
[nagios-plugins-src-dir]$ ./configure --with-nagios-user=nagios --with-nagios-group=nagios
Then run make and it will run properly.
Run make install as root.
[nagios-plugins-src-dir]# make install
Change ownership of the nagios-installation directory to nagios.
# chown -R nagios:nagios /usr/local/nagios
The plugins live in the /usr/local/nagios/libexec folder.
Make sure your nagios@nagiosserver can shell into the nagios@remote-server without a pass-phrase or it will not be able to run "command_over_ssl." I am not yet running the NRE as I understand ssl well enough to use it.
Thanks to Dave Bonnell for the libssl-dev suggestion http://sourceforge.net/mailarchive/message.php?msg_id=29576799
Make sure you ssh into each remote server as nagios@nagiosserver to get past the "Add this server to known hosts" dialog, otherwise nagios will not be able to send test requests automatically.