If you already have a running Nagios-2.x environment, you can change over to Nagios 3.0 with little effort. The existing configuration will usually run unchanged.
Nagios 3.0 is very particular when testing, however. It is quite possible that a so far undiscovered error—one tolerated or ignored by Nagios 2.0—will prevent Nagios 3.0 from starting. It is therefore a good idea to test your configuration before upgrading. To do this, you run the installation as described in 1.2 Compiling Source Code in page 39 with
make all, but without running
make install. You will obtain an executable Nagios-3.0 binary in the
base subdirectory, which you can use to test the existing configuration from the source code ...