Every time you modify your configuration files, you also have to restart Icinga. It is important to run a sanity check on your configuration files because in case of an error Icinga will not be (re)started.
In order to verify your configuration, run Icinga using the -v command line option:
#> /usr/local/icinga/bin/icinga -v /usr/local/icinga/etc/icinga.cfg
If you've forgotten to enter some critical data or misconfigured things, Icinga will show a warning or error message that should point you to the location of the problem.
Error messages generally print out the line in the configuration file that seems to be the source of the problem.
On errors, Icinga will often exit the pre-flight check and return to the command prompt after printing only the first error that it has encountered.
This is done because one error might lead to consecutive errors as the remainder of the configuration data is verified.
If you get any error messages you'll need to go and edit your configuration files to remedy the problem. Warning messages can generally be safely ignored, since they are only recommendations and not requirements.
Instead of specifying the paths to binary and config file you can issue
#> /etc/init.d/icinga checkconfig
which results in just a non-zero return code if your config contains any errors. This might be useful if you want to restart Icinga automatically.
#> /etc/init.d/icinga show-errors
the command will create a file containing the errors found. If there are any the contents of the file is shown ("show-errors" starting with Icinga 1.0.2).
Once you've verified your configuration files and fixed possible errors you can go ahead with Section 4.2, “Starting and Stopping Icinga”.
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